Guy's I have been reading as many posts about 20B's as I can sponging up info as I have my own conversion ready to start in a few months. I have a good running engine but plan to strip and rebuild it to be safe. I have read a lot of people talking about dowelling the housings to make them more rigid. Can someone explain further what this process involves and costs? I assume like the 13B the 20B has 4" or so dowels between the housings and plates? If so I am not sure I understand the mod? Some pics would be good if possible.

Cheers
Lee

 

Lots of people run thicker engine studs from front to back. The 18 that hold the whole engine together. Various tuners do their own kits. It invovles milling ALL the plates and rotor housings to suite the larger diameter studs.

For example

http://www.mazdatrix.com/studkit.htm

 

dowel pinning or pinning is the process of adding those "4" or so dowels between the housings and plates" to other thru bolts in the motor

there are a ton of threads about pinning motors. it would be best to read the various threads as they will probably answer questions you haven't even thought about yet.

https://www.rx7club.com/search.php?searchid=9283557

 

Thanks for some info guys.. I have done some more searching and found a few more answers.. Well arguements on the subject! At least I know the basic points and how the process is done. I am only thinking at this stage to just topping 600bhp flywheel power It is going to be a street car after all so need to be driveable. Sounds like I may not need to worry at this level. But then there is always the thought of future proofing. I have a B code block for the record. Can you not swap the housing for a 13B with a bit of machining. I am sure I read most housing and plates interchange with a tickle?? I suppose that said solving the twist to begin with is the answer. I was thinking about making a brace plate to bolt to the bottom of the engine where the sump fits? I am sure this must have been done?

McCarthy. I was reading your build thread last night. Some nice work.. I need to get up-to-date with where you are though. I am currently planning how best to situate the motor without having to move too much or cut the bulkhead or inlet manifolds. I will have single turbo so gather that gives a bit more room. When I get the engine near the engine bay I am sure I will be posting plenty more! Just trying to find out as much as possible to avoid surprises before then.

Cheers
Lee

 

a picture is worth a thousand words.

from my album:

 

---^ some how i dont think thats going to be accurate "milling" for the dowels...hehe

 

Thank you for the pics guys'..

From what I gather the stud kit is the safer option as it requires less material to be removed from the plates and housings. That said it sounds like this will be over kill for what I am aiming for power wise and some kind of brace plating could be more than ample. I had a few ideas on how to do this just need to look at practicalities and space.. My mind says to me some well made plates positioned in suitable places should make the engine more rigid that just thicker bolts?

 

Love the DIY approach. The plates look hand laped as well. Have you done numerious engines this way?


I've come to find out that when you drill an existing metal hole, the drill bit tends to center itself.

 

so all it pretty much is, is just drilling bigger holes to fit bigger dowel pins and studs?

 

No! It's drilling more holes to fit MORE dowel pins (not bigger dowels). All the dowels are the same size. Your just installing more dowels to make the block stronger.

 

Thanks for clearing that up for me

 

Lol, and I'd say your less accurate for doing it that way.. we all do it differently. Mine are all done in a milltronics milling centre with very tight tolerances this assures that I can replace any piece with another and it will fit exactly the same. Running it on a open machine works but isn't as accurate especially when doing all 16 holes, I won't dowel plates though.

~S~

 

how is that less accurate than a drill press? or how is it less accurate than a VMC? 1982 bridgeport, .0015 backlash X, .0005 backlash Z, with dro its plenty accurate....

 

To be fair he has a point. If you know how to use your equipment properly then there should be no problem either route you go. And it is each to there own. I know some very skilled machinist and they can turn out better work on basic machinery than I have seen from people with full 5 axis machine centres with all the bells and whistles!

 

not to get off topic a bit, but how is a drill press going to be more precise at reaming holes than a REAL mill? there is no weight or rigidity to them at all....you should give it a try...drill and ream some holes on a mill and a drillpress..then measure the hole and tell me what the micrometer says

 

t-von is right and so is Zero R.

Using the drill press method the parts will be unique to the motor. One would float the drill and then reamer through the middle plate and into the housing and end plate. Then use the previously reamed hole in the middle plate as a guide to ream the other housing and end plate.

Us machinist call it it "transferring". Most definitely not as accurate, but most importantly, not as repeatable, as CNC'ing the holes. It works though.

 

Thanks Tony, we don't use a drill bit we use a end mill so it's more accurate. We do one plate/housing at a time it is very accurate as well as repeatable, drill bits tend to follow, end mills don't. We do this so if we build your engine and you have need for a replacement it will fit exactly like the one you had prior. Not only will it fit your engine, but I could fit any housing or plate to anyone else's engine. Not to sound pissy but maybe that is why we don't crack plates with our setups while others say they do.

~S~

 

Hey cool...one of my pics is floating around. Here are some others.

I agree, and so does my machinist, mill > drill press.

 

note that on the 20B large center iron, there is very little material around the tension bolts in some areas, which makes doweling harder and is one reason why many people use studs instead. I dowelled mine and had to turn the ends of the dowels down in some areas so that there would be enough material left.

 

Another option is to use one piece solid dowel pins to replace the OEM pin..
Goopy Performance has them for the 20B.. i have seen them used in 20Bs motors that they drag race with great results.
there is a post of rotary car club..

*******************************/rotary_forum/showthread.php?p=162489

 

this is a great example of why i wonder why i bother trying to help people, as all the nitpickers come in and crap on you.

know how many shops in california or on the west coast do rotary engine pinning? only mazdatrix and i had no plans to ship all the motors out to be pinned. i contracted a milling shop to attempt it 2 times and i wasn't greatly pleased with the work performed that cost $450, so i started doing it myself, with patience it can be done to the standard that it requires by using the center iron as a basis and working out from there with smaller bits and then reaming the final holes.

do the pins need to be less than .005 within spec? no they do not. nor do i plan on purchasing a $5000 piece of machinery to do a few $300 jobs.

the point is having the pins rigidify the engine and allow the tension bolts to still pass through them and torque down the engine properly. again, does that require an expensive 6 axis electronic mill? newp.


and yeah i hand lapped the irons too, i slid them on the driveway until it took the mirror finish off...

anyways, back to work and ignoring this forum again.

dicks.

 

Calm down Karack, I cant speak for everyone but I wasnt trying to crap on anything you do. But we can both agree that the mill is more accurate than a drill press, correct? Take it with a grain of salt buddy.

 

guess it's just the stress getting to me and i'm misreading things. i only put up that picture to show how dowelling actually works, not to sell anything as i only do it very rarely.

yes a table reamer works best but you can be pretty accurate with various other methods as well was my point, so long as you take measurements and use mild pressure.

 

LOL.

The rotary is a sloppy motor. Karak's method will work fine.