DaleClark

iTrader: (55)

Hi everyone -

This is something I've typed bits and pieces of but wanted to put together in one post.

So, something is wrong with your engine. What to do?

First, find out FOR SURE that you have an engine problem. Typical failures will be low compression from wear or a broken apex seal or a failed water seal. There's numerous resources for diagnosing a bad engine, this isn't about that.

OK, you know it's bad for sure. If this is your first time, give it a little time, it was a HUGE disappointment to me when I blew my first engine on my 88 Turbo back in the day. At that time it was my daily driver and I was a broke college student which didn't help things. But that was also why I decided to do it myself because I couldn't afford another way to do it.

Before we go down the rabbit hole, here are the options for a blown engine -

- Take it to a shop and have them do it. It's the most money but hopefully if the shop does a good job you write a check and pick up a running car in a month or two.
- Pull the engine, strip it to a short block, ship that to a shop to have rebuilt. Less money but really IMHO the stuff bolted to the engine is just as difficult as the engine itself.
- Buy a Mazda new engine. Last I saw they were $4500-5000 for an all brand new short block. This is a helluva deal. I think availability is a little tricky right now with shipping delays, but that is an option.
- Buy a known-good used engine. This is a crapshoot, though. But, worthwhile if you can get a good deal and know the story behind the engine and the mileage.

OK, so either those options aren't good for your budget or you just want to learn how to do it yourself. Let's talk about that.

DaleClark

iTrader: (55)

Reasons to rebuild yourself

- Less expensive than paying a shop to do it
- You can have pride in knowing you did it
- You can know everything that's going on inside that engine as it went together
- It's actually kind of fun . I enjoy the heck out of building engines.

Reasons not to do it yourself

- You don't have space/tools/know-how.
- You don't want to clean engine parts
- You will be distracted or rushed on the job. This takes time to do right.

One thing I tell everyone about doing a rebuild yourself - first thing is you have to accept that you could screw something up. You have to be willing to take that L, pull the engine, and go back through it. I've rebuilt probably 50-60 engines at this point, I'm not a pro shop but an advanced hobbyist. The first engine I did I screwed a lot of stuff up with the front cover stack. I have had 2 others that had problems - one had a pinched water seal (remedied by never using aftermarket seals again) and one had a stuck side seal. You just have to suck it up and start over.

OK, so all that said, some more thoughts on the matter....

DaleClark

iTrader: (55)

Cost

This is a crapshoot. It really depends on how bad the engine is. The big thing is how many "hard parts" you need - that's irons, rotor housings, and rotors.

I also believe that if engine parts are worn but are *still within spec* you can re-use them. When in doubt, throw it out, but there's a lot that's re-useable. Big shops may not re-use things because they don't want a customer thinking "man they just put old used junk in it" and sometimes it's less labor time for them to get a new, clean part and install instead of spending time to clean and inspect parts.

Biggest fixed expense is apex seals, you're looking at $400-ish for a set of 6. Apex seals are the #1 wear item in an engine, I've seen them worn down to 2/3rds the height of a new seal, they wear THAT much.

Expect to drop about $1000 on seals and such. That will also be the gaskets, O-rings, seal springs, etc. Of course you will probably need external (non-shortblock) parts as well.

DaleClark

iTrader: (55)

Time

This really depends on your skill and how many friends you can drag in to help . Here's how I break down an engine project -

Weekend 1 - pull engine and break down. I usually get 2 friends to come over and help. Get the engine out of the car and on an engine stand and break it all the way down to the rotors. This takes me 2.5 to 3 hours. I then (after lunch ) do a "first pass" of cleaning on the hard parts to look at things, see if there are any "red flags" like shot rotor housings, failed coolant seal walls, etc. that mean I need to find some hard parts. I also get a list of everything I need and order it that weekend.

Weekend 2 - CLEAN. You will clean like CRAZY doing an engine rebuild. There's always something more to clean. By the end of this weekend I have the engine bay clean and pressure washed, all the internal and external parts totally clean and inspected.

Weekend 3 - Build the engine. About half a day to assemble the rotors and fit all the side seals. I get EVERYTHING in place and ready then stack the short block up. At the end of the day I've got a complete short block that makes nice compression whooshes. I will typically this weekend also go over the external parts and tend to them - re-wrap a wiring harness, replace vacuum lines, clean more stuff.

Weekend 4 - assemble long block and drop it back in the car. By the end of the weekend I want to have a running driving car that had the first oil change and is ready for break-in miles.

The big thing with the timeline is you have to be prepared to see something wrong and STOP. Don't try and half-*** something, make a gasket out of a cereal box, JB weld a water pump back together etc. just to "hurry up and get it done". That's how you have big problems down the road.

DaleClark

iTrader: (55)

OK more on this tomorrow. Post up your thoughts - have you built an engine? Would you if you had the opportunity?

Dale

nmoffatt

iTrader: (15)

Thanks Dale!

I'm gradually getting myself mentally prepared to build 2 engines. I have an RX8 that needs a rebuild along with my FD. Both are perfectly drivable and have no starting issues so I've been procrastinating but with my luck they will go at the same time.

Which would you do first? I was thinking to practice on the 8 then move to the FD but from what I have read the 8 is more difficult to pull the engine so it might not be a good confidence builder.

cloud9

iTrader: (4)

Dale - have you ever considered doing a GoFundMe (or similar) to crowdfund/produce a video tutorial on engine rebuilds? I would 100% pay for a modern, ultra-thorough start to finish take on the procedure. Additional little segments scattered throughout digressing on component and modification options would be a nice bonus.

Jatt

iTrader: (2)

I'd support something like this for sure.
Eventually in the long haul want to setup a small shop in the garage where I can work on everything myself, minus fabrication and machining work. Look forward to learning a lot on this thread, have been reading quite a bit already and I'm glad you made this so we can close some of the learning curve and really gauge whether or not we should dive into this when we need to rebuild an engine.

SwappedNA

iTrader: (1)

Basically a Bob Ross of engine rebuilding? Except I wouldn't consider myself making a mistake a "Happy little accident" by any means.

driverx

iTrader: (7)

Hi Dale,

I've read and appreciated many of your posts--and couldn't agree more with the points you make here.

I built the short block in my '93 RX-7 a few years back, and I get a kick out of it every time I look at the car. I enjoyed building it, and I enjoy driving it even more.

I'd recommend taking it on to anyone with enough space/tools/know-how to be tempted.

In fact, I don't want my engine to die, but I'm looking forward to having the need/opportunity to do it again someday!

Subscribed.

zli944

iTrader: (2)

Completed a DIY rebuild a few years ago with minimal prior mechanical skills, started with a $100 Husky tool set and space was limited to an apartment car port and a single bedroom.
I think it's entirely doable, and while the car hasn't always run perfectly (turbo controls, idle issues, etc.), the actual block has held up beautifully through multiple track days now. My last compression check was at mid 90's on both rotors which I think is more than acceptable given I reused all major components, except sourcing one used rotor housing from a forum member. Original motor had around 80k miles with some major bearing wear and chattering on one of the rotors.

I think all FD owners should do it at least once, especially if the platform is new to you or the car itself is new to you.
It's an incredible learning experience and you really do understand ALL aspects of the car once that engine is out and back in. Every component, every hose, every hardline, it becomes an investment in yourself and your own ability to maintain the car in the future. There are also a bunch of things you'll find that need to be done as the process is underway. This is both a curse and a blessing, as, if you continually expand the scope of the project, it'll never get completed in time but some stuff you'll definitely want to do, like below:

-Properly sealing the oil pan
-Replacing motor mounts
-Redoing the turbo control solenoids and vacuum lines
-Replacing all coolant hoses
-Running wires for gauge sensors
-Installing gauge sensors
-Refreshing the wiring harness and checking for continuity from every connector pin to ECU plug

Again, while cars always interested me, before the FD, my most involved mechanical experience was changing the timing belt on a '83 944. There are NO special skills needed other than maybe the ability to google and sift through bullshit on the forums
It's also a matter of time. If you have kids, if you have a significant other, if your job is extremely demanding, a DIY rebuild may be out of the question. But if you have the patience to throw a few hours at it over a very long time, I think it's totally worth it and given the surge in FD pricing, slowly restoring one as a hobby is more than justifiable as a monetary investment.

Red94fd

iTrader: (5)

I rebuilt mine after getting ripped off. I found it amazing learning experience.
I had prior mechanic experience and to add that up experimented on my long gone rx8.
Just the fact that I can tell anybody whats inside my engine and I did it the best as i could and has worked out very well, is the most rewarding feeling.

DaleClark

iTrader: (55)

First off, I'm flattered by the comments in this thread, Thanks guys! I've toyed with the idea of doing Youtube or something like that, I may need to re-visit that some.

The good thing is there are a TON of good resources out there now on rebuilding engines, a lot of good stuff on Youtube in particular. There are also the older DVD's, like Bruce Turrentine's stuff from Rotary Aviation and the Australian rotary engine overhaul video (which isn't that great though ).

OK, let's continue this topic -

Tools

This is a biggie, a lot of people naturally assume you need a ton of expensive gear to do the job. You don't. Let's go over the "need to have's" and "nice to have's"

Engine Hoist

You have to have one to do this job to get the engine out of the car. Don't try some half-*** backyard thing to do this, you need a hoist. The good thing is they are cheap. This is what I have -

https://www.harborfreight.com/1-ton-...ane-61858.html

$229 from Harbor Freight. You don't need the more expensive 2-ton version, you are pulling a 300 pound rotary engine not a diesel from an 18-wheeler.

You DO NOT need a load leveler, they just get in the way and don't help at all. It makes more sense on long engines (like a straight six). You do need a good chain and shackles, I got about 3-4 feet of plastic coated chain from Lowe's ages ago and 2 shackles. The plastic coated helps prevent the chain from scratching stuff up.

You may be able to find an engine hoist for borrow from a friend or for rent from a tool rental place too. I borrowed one for YEARS before I finally got one. Really if you think you may do it more than once in your lifetime and you have the room for it get one, if you don't have the room or don't anticipate using it multiple times just borrow one.

Engine Stand

IMHO this is a key tool, first time I finally used one it was amazing. Not only does it safely and securely support the engine it makes it SUPER easy to work on, flip the engine upside-down, and roll the engine around as you are working on it. Again, the Harbor Freight stand is just fine -

https://www.harborfreight.com/1000-l...and-69886.html

I actually have the 3-wheel version of the stand that works great. For $75 you are in good shape there. Again, borrow or rent if you are saving money or don't have space. You could probably sell this on FB Marketplace after you are done to recoup some cost if you don't think you will be using it again.

If you are getting an engine stand, you HAVE TO HAVE a rotary engine adapter. The go-to has been Pineapple Racing's adapter -
https://www.pineappleracing.com/rota...adaptor-1.aspx

Other companies have had similar products. The nice thing with this is it puts the center of mass of the engine at the pivot point so you can easily rotate the engine upside-down and back up. Very sturdy and it will hold the engine secure even when torquing bolts.

There are cheap ways to do this, for YEARS my "engine stand" was a sheet of plywood and 2 saw horses. I drilled holes in the plywood so I could put an engine face-down onto it (hole for the e-shaft and water pump studs). It worked but it wasn't fun. Also you couldn't really build the long block on this setup, you ended up having to hang it from the engine hoist to do a lot of the work. But if $200 in adapter/engine stand is a deal breaker this can work.

Flywheel Socket

You will need a 54mm or 2 1/8" socket to remove the flywheel nut. For ages Sears was the go-to, they had the 2 1/8" socket in stock and you just went and got it. Here's one on Amazon -


That one is impact-rated, the socket I've used COUNTLESS times is my old Sears non-impact with a 3/4" drive to 1/2" drive adapter, never had a problem with it. But the big thing to keep in mind is you may not be able to find one locally, prepare ahead of time to order it.

You will also need a dead-blow hammer that's plastic. This is for removing the flywheel and separating the layers of the engine. Again HF to the rescue -

https://www.harborfreight.com/3-lb-n...mer-69002.html

Get the flywheel nut off (which is actually not that hard), thread it back on a bit, then get a pry bar behind the flywheel and whack around the perimeter of the flywheel to get it to break loose from the taper. Usually when you start getting mad at it it will come off.

It helps to have a tool to hold the flywheel so it doesn't turn, Mazdatrix has one and some other places do too, it bolts to the rear iron and has teeth that engage the flywheel to keep it from turning. You can also use 2 bolts and a chain - bolt one end to the rear iron and one to the flywheel. You want to use bolts you don't mind messing up, many times this will damage the bolts.

Feeler Gauges/Torque Wrench/Dial Indicator

This is the "precision" part of this. Again you can get this at H-F or borrow.

Torque wrench: https://www.harborfreight.com/hand-t...nch-63882.html

Feeler gauge: https://www.harborfreight.com/feeler...-pc-63665.html

Dial indicator with magnetic base: https://www.harborfreight.com/1-in-t...tor-63521.html

These 3 tools are the ones I've had for ages and they've been great. You need the torque wrench for the tension bolts and some other "mission critical" fasteners. For the flywheel nut, just tighten it until it can't move any more and you're done. I just hit it with my air impact gun until it won't tighten any more. Done this hundreds of times, never had a problem.

You need the dial indicator to check the end play of the engine. The feeler gauges are mainly for clearancing side seals, that's a whole topic we'll get to.

Nice-to-Have Tools

There are some things that make the job easier, go an extra level of detail, or are more "quality" than the cheap options.

Bench grinder with wire wheel - I use this a lot on an engine build project. The good folks at H-F are where I got mine from. You'll need the bench grinder, a stand, and I like having a wire wheel on one side and the grinding "stone" on the other. You can use this to clean rotors, threads on tension bolts, remove old gasket and RTV, tons of stuff.

Pressure washer - I have a nicer "large" electric pressure washer that does 90% of what a gas-powered one will do. Makes cleaning parts SUPER easy. Spray with degreaser, scrub a bit, blast it off. I clean EVERYTHING with the pressure washer, even the wiring harness, rat's nest, etc. But for years I just used degreaser, a brass brush, and a garden hose - takes more time, doesn't get it as clean, but it works.

Safety - it's worth having good safety stuff for the job. Safety glasses, ear protection, nitrile gloves for working with degreasers and heavier gloves when using the wire wheel. Some of this is a "must have" but having better quality stuff (like 3M safety glasses) is worthwhile.

Air compressor - they aren't as popular as they once were with the rise of powerful electric impact tools but they are still great. Big thing is being able to blow off dirt and water from parts while cleaning. Of course you can also use it for an impact gun, die grinder, etc.

Dremel - I use mine a LOT doing an engine rebuild. Wire wheel to clean, sanding flap wheel to clean and remove gaskets, you can also use the orange stone to port an engine.

There are tons more tools, probably some that I use that I've forgotten, but this is the main stuff.

To be continued.....

DaleClark

iTrader: (55)

Maybe do the RX-8 first. The stuff outside the engine on the RX-8 is a lot simpler, there are only 4 vacuum solenoids. It's a little harder to get the RX-8 engine out of the engine bay, though. Rotary Resurrection has some good how-to's on their website and also on the RX-8 forum about pulling the engine. The AC compressor gets in the way BIG TIME, it's almost worth just disconnecting the lines and pulling the compressor with the engine then re-charging the system.

Also the RX-8 has marks on the rotors for side seal length. So you just look at the rotors, see you need 1 "A" seal, 3 "B" seals, etc. and order the sizes. Pop them into the slot and done. You can hand fit the side seals but IMHO I don't think you gain much in doing so, it is slightly cheaper than the pre-cut side seals but the hours of work aren't worth it.

I did my daily driver RX-8 and was actually able to re-use all the hard parts - rotors, housings, everything. One rotor housing was a little "meh" but I decided to go for it, my compression numbers are excellent and the car starts great hot or cold so I'm happy.

The RX-8 engine is also slightly cheaper to rebuild, I think the WHOLE gasket kit is like $96 which is insanely cheap. This even includes the exhaust manifold gasket, the multi layer steel LIM gasket, etc.

Dale

Pete_89T2

iTrader: (4)

Great thread Dale, I'm enjoying this! One point to add on "must have" tools:

For the engine hoist, the 1 ton HF unit Dale linked will be perfectly fine for an FD, but if you also do work on FC's & FB's or other cars with the longer hoods, you should consider getting a hoist with a longer reach. I actually purchased the same type of HF 1 ton unit Dale linked years ago to work on my FC and found its lifting beam wasn't quite long enough to reach into the engine bay far enough to pluck the engine out of my FC. Brought it back to HF and spent a little more for the equivalent folding 2-ton hoist they sell, which has a roughly 12" longer lifting beam to do the job.

DaleClark

iTrader: (55)

^Good point, Pete, I remember pulling FC engines and the engine hoist would be hard up against the front bumper.

One thing you can do (that's a pain but we did it back then) is to pull the bumper off. Gives a little extra room and if the hoist bumps something it's just the bumper reinforcement.

Dale

j9fd3s

iTrader: (3)

on that subject, the hood does not need to come off to change the engine. leaving it on helps, as you skip the part where you damage it in storage, also you skip the part where its not aligned right (more of an FB/FC problem) when you put it back.

DaleClark

iTrader: (55)

^Yep. Zero reason to pull the hood on an FD when doing the engine. RX-8 you will need to do it but it's a piece of cake to line back up.

On that topic, my philosophy on pulling the engine -

You want to do as little work as possible to get the engine out of the car and on the stand. It is SO MUCH EASIER to work on the engine on the stand as opposed to in the car.

Start inside, then out, top, then bottom. I'll explain -

- Get in the car and unplug the ECU and pull the harness through the firewall. Do that now while you are still clean.
- Start removing things in the engine bay that are in the way - airbox, IC, battery and tray, battery cross member, etc.
- Unbolt engine from trans and release the throwout bearing. There are tons of posts and videos on how to release the pull-type bearing, it's not hard once you understand it, but you're gonna be stuck if you don't do it then start yanking the engine.
- Also get the motor mounts, downpipe, other stuff from below the car removed. This includes removing the oil cooler line clips. They will leak some so be prepared when you detach them.
- Once you've done a lot of the under the car stuff then start draining oil and coolant. This way when the coolant makes a big mess (which it normally does) you don't have to go lay in a puddle of coolant under the car. Don't forget the block drain at the left side bottom of the center iron.
- Unbolt starting/charging harness and remove that with the engine.
- The PS pump has 2 hoses going to it, one high pressure with a banjo bolt and a low pressure with a hose clamp. Remove those and pull the pump with the engine. Siphon fluid out of the PS tank so it doesn't go everywhere.
- Unbolt AC compressor and leave it in the car with lines attached. 4 12mm bolts, a ratcheting wrench helps here.
- Get a buddy on the engine hoist and start coming up. You will raise up some, pull forward some, and repeat. It helps having a jack and a block of wood on the trans so it stays up while you are removing. Go slow and check to make sure you didn't forget some wire or hose.

With it out you just have to remove the PS pump bracket (leave the PS pump on it, I usually never take them off the bracket in the process), remove the oil cooler lines, and you should be able to bolt up the engine stand adapter and get it on the stand. Then you can comfortably remove everything from the long block.

When removing parts, some key things to remember -

- TAKE PICTURES. Lots of them. Video too. You will be shocked how you forget in a month how it all goes together.
- Get a bunch of ziplock baggies and a sharpie. Put like items together with their bolts in a bag and label.
- Label everything. Tape and a sharpie is your best friend. Label wiring connections, hoses, etc. if you aren't 100% sure.
- Remove things in large components. For example, the wiring harness, fuel rails, and rat's nest can all come out as one giant component. It's literally 6 bolts that hold that whole assembly onto the engine. Remove it as a unit and if you need to work on it (replacing solenoids, doing vacuum hose, fixing the harness) it's easier to do.
- Put all bolts somewhere appropriate. Either bag and label or screw them back into the hole they go into. For example, the upper intake manifold is held to the LIM with 4 nuts and a bolt. After you remove it, thread. those 5 fasteners back on.
- DON'T GET IN A HURRY. Yeah, you want to see inside the engine and your friends are bored. Tough. Take your time and document, bag, and label. If you do that going back together will be SO much easier. If you start tossing bolts in a bucket and cutting wires and hoses you will regret it later.
- DON'T CUT STUFF. Those short fuel lines from the firewall to the engine? They are like $60 each or something dumb from Mazda. Take your time and remove the properly.
- Nothing is trash until it's trash. Have an old ratty hose, think you'll just throw it out and get a new one? Nope. Keep it until the new one is on the engine and you are happy with it. It's too easy to throw out some dumb little part that is no longer available or crazy expensive.

Really, putting the long block back together right is the hardest part. I've seen countless people do a fine job rebuilding the engine and the short block is great but the car won't start because they hooked up fuel lines backwards, forgot to attach a ground, spark plug wires on wrong, connectors swapped, hoses swapped, etc. If you take the time to document the process, label, and organize everything you will be SO much more likely to have a good result. I would say the majority of the engines I've done have fired right up and idled smooth on initial start because I took the time to check EVERYTHING.

By the same token, putting it all back together on an engine stand is SO SO much easier than in the car. You can sit on a stool with plenty of light and access. If you drop a bolt down somewhere, flip the engine upside-down and it will fall to the ground. Bolting the turbos on is a BREEZE on a stand.

OK, I'm trying not to get too off the mark talking about the external stuff, this is really more about the short block. More to come!

SwappedNA

iTrader: (1)

This raises an interesting question, though possibly slightly off topic, I'm mentioning it for the sake of what differentiating factors can cause a fresh engine to be different in compression than another fresh engine. I've had two FC engines over the past four years rebuilt (separate cars) by two very well known shops. I'll leave the names anonymous. Engine A was a S5 Turbo II jspec, it was virtually junk so it needed a new rotor, housings, and iron at the minimum, in addition to all new seals, springs, etc. Mazda OEM parts.

Engine B was a Series 4 Turbo II USDM engine. This one also had all new OEM seals, springs, new housings front and rear, and a new S5 center iron.

Engine A (which also had a streetport done with the builders other basic included services) tested in the 100's (PSI) when warm, all of the compression numbers were close enough to one another.

Engine B tested in the 90's, with one rotor face being 100 or 101 I believe. The highest rating of them all, and a good 11-14 PSI difference from the other rotor faces in that housing.

What could cause two very fresh engines to have such a drastic difference in compression readings?

DaleClark

iTrader: (55)

There are a few things that affect compression.

- Apex seals. Nice healthy new ones that seal up tight to the rotor housing. As they wear, they get shorter and you lose some of the force of the spring pressure at low RPM. Remember, compression tests are done at 250 RPM. Rotaries by their nature increase compression with RPM - the inertia of the spinning rotors pushes the apex seals outwards, tightening the seal to the rotor housing. I had a TurboII that I drove for probably 6 months with a blown engine - tip of an apex seal was broken off. With a fuel pump switch I could get it to start, and it idled rough, but at higher RPM it was smooth and made good power.

- Rotor housings. Scores, chatter, chrome flaking, etc. affect compression. If you have a spot or a groove where the pressure in one combustion chamber can leak back to the previous chamber, that will result in lower compression.

- Side seals/corner seals. The big thing here is the clearance and the springs. Weak springs mean worse low-RPM sealing. Also the bottoms of the corner seals and side seals typically wear, I've seen fairly deep wear into the bottom of the corner seal where the spring hits it. Also the side seal over time will wear its trailing edge into the corner seal, making a gap. That and how well the side seals are clearanced by the engine builder all come into play. I typically carefully file and sand the side seals until they are .003" (three thousands of an inch) gap between the side seal and corner seal.

Some other factors as well - carbon build up over time on the rotor faces, carbon keeping seals from moving properly, scoring on the irons, etc.

Another big one is porting. With a big porting job, when you are sucking air in to compress you don't get as much volume since some of that volume goes out the exhaust port at low RPM and you also have some left over exhaust gas that may dilute that air/fuel mix (exhaust gas is inert, it has no oxygen or fuel) so that will reduce compression at idle/low RPM. They do well at higher RPM since again you have inertia on your side and also it's moving fast enough that there's not enough time for exhaust dilution or leak down to occur.

Remember, we are talking around 100 psi in general. That's a LOT of pressure. The tiniest imperfection gives a way for that compression stroke to leak out a bit.

All that said, let's bring this back around to the discussion at hand.

So you're going to build your new motor, and you want the best compression possible. What should you do to ensure that?

#1 - new apex seals. Hands down, this is the BIGGIE in good compression. If you have a "tired motor and simply would replace the apex seals you'd have a remarkable difference.

#2 - clearancing side seals. This takes time to do right and it isn't a fun job. It can take me an easy 2 hours to do this, you have to hand-fit 12 side seals. The fun part is when you go too far on one and have to junk that side seal. Each slot on the rotor is different when you are talking about this fine amount of clearance - as stated, I do .003". This is also why sometimes Mazda motors and factory motors don't have the absolute best compression, there is a pretty good range of "acceptable" from the factory so some faces may have looser clearance which will drop compression for that face.

#3 - good corner seals. If they have a line worn into them on the side from the side seal and they have the corner seal spring worn into the bottom that will drop compression a good bit. I have actually re-used corner seals in the past that were still good and in-spec and had a happy engine. Yes, new is better, but sometimes affording an engine build that makes your car run again is even better.

#4 - rotor housing condition. If they are smooth and don't have chatter, grooves, too much flaking chrome, and haven't been gouged up by a broken apex seal you are good here. New is always better but I've built tons of engines with used housings with great results. The big thing is to find housings that are in decent shape. New housings are EXPENSIVE - like $1000 each.

If you address those points smartly you will have a motor that will make good compression, good power, and start every time. Those are the biggies, there are other things that affect it but you have to ask is it worth the cost? If I have a rotor housing that's smooth, looks good, clean cooling passages, etc. would paying $1000 for a new housing to replace it get me bang for the buck? Probably not. That's $1000 I can put into something the car needs more - maybe it needs new tires, a new wiring harness, or some paint work.

There's no sense in spending money just to spend money if you don't get a result out of it.

Also to go back to the original question - there is a difference in S4 and S5 rotors, S5's have higher compression (9.0:1 versus 8.5:1 in the 87-88) - that will change compression numbers as well.

Dale

SwappedNA

iTrader: (1)

That has me wondering if I would have been better off sourcing a good set of used housings that had no chattering or chrome flaking. In terms of going for the best possible compression on a new engine, approximately how much of a difference do new housings make (assuming they are used with new oem seals, etc?)

DaleClark

iTrader: (55)

Honestly I don't know. This would require a scientific approach to the topic - build a motor, compression test, take apart and swap housings, repeat.

In my opinion, I don't think you gain that much with a new housing over a good used one. I think you may not have the same amount of life - if you have a used housing with 80,000 miles on it I don't know how it would look in another 80,000 miles. But would that next 80,000 miles be better spent if you had put that money towards something the car REALLY needs?

For what it's worth, my RX-8 came to me with 135,000 miles. From everything I can tell about the car it's the original engine. I had about 4-5 broken corner seals, 2-3 broken side seals, side seal springs that were literally melted, and apex seals worn to a nub. One rotor housing had some chatter on the bottom, but the irons and rotors looked good. Cleaned it all up, put in new apex seals and springs, corner seals and springs, side seals and springs and all side seals hand-clearanced (that SUCKS even harder on an RX-8). Last I checked the motor was doing great - front rotor 8.1 8.3 7.7, rear rotor 8.3 8.4 8.6 (that's in kg/cm2, so 109 psi to 122 psi range). It wasn't worth dropping $2k on new rotor housings. This was also after about 10,000 miles on the engine.

Dale

SwappedNA

iTrader: (1)

I don't understand why people knock the Renesis. My S1 RX-8 had 164,000 on the original engine when I sold it. Still ran fine, took a second or two longer to hot start in hot weather, though. I'd still build a turbocharged Renesis if I ever owned another RX-8.

But back on topic, I'd like to see this video if you ever did decide to do one.

Howard Coleman

iTrader: (6)

"I don't think you gain that much with a new housing over a good used one"

i recently sold my personal motor that had been in my car for 3 years and had been run up to approx 575 on occasion. prior to selling it i did a comp check on it, somewhere just over 100. it does have a bit more overlap due to my ports. i sold it to buy a new Mazda motor and have since put around 500 miles on it and made about 600 with it. ( the new motor was disassembled and rebuilt so it had the same ports and internal pieces as the sold motor). it has, as i expected, gained compression (about 10%) with miles. my point is that it has about the same compression as the motor i had sold... good condition used rotor housings can be just as good as new rotor housings.

what makes them "good" in my opinion?

they need to be measured for parallel. Mazda says they must be discarded if they are out of parallel .0024 or more. this is the first thing i do before evaluating a used housing. unusual heat around the sparkplug area is often the culprit. an out of parallel housing will tend to lose the outer coolant seal when making power. you need a 3-4 inch micrometer to make the check. (i think you need 4 digital micrometers to properly evaluate and rebuild a motor)

after the housings pass parallel, have been examined for cracking around the spark plug boss, don't have lost chrome around the edges they need to be honed.

numerous shops offer honing but there is a big diff as to quality of work. my number one vendor as to honing is Rotary Specialties in Calgary Alberta. the housings get soda blasted so as to remove the calcium carbonate in the coolant passages and exterior grime. of course the main event is the diamond honing of the frictional surface.

a virtually like new set of rotor housings for a bargain price. a perfect match for your new set of straight apex seals. if the housing is not properly honed it will present an uneven surface to a straight apex seal.

i do have a lengthy engine build section on my website which may be of help.





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F1blueRx7

iTrader: (5)

Or just call Dale and bring him the engine. Twice. Vapor honing service in this area would be a major time saver to cut down on time spent cleaning, rent it out when not building engines, it'll pay for itself after a bit.