Well guys, it's rebuild time! Before having the motor yanked, I had a second compression test done. See attached pics. It's amazing that the thing even started up and idled at all. Look at the front rotor.... less than 1/2 of the specified compression. Also note the jagged pulses. The rear rotor is consistent but still FUBARR.

Some of you may remember my other engine issues a while back: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/possible-blown-engine-%7C-bad-idle-%7C-serious-oil-leak-%7C-hard-starting-468370/ The engine's health has definitely deteriorated since then
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A few notes on the latest:

1. Engine will NOT start when hot
2. Engine has difficulty starting when cold
3. Engine has terrible low end power (duh)
4. Under boost power delivery feels great
5. Engine has a tendancy to overheat in idle/city driving conditions
6. Results are in kgf/cm^2 (psi)
Compression test #1: (10-03-05, 103103 miles)
rotor #1: 4.9, 4.2, 7.8 (70, 60, 111)
rotor #2: 7.2, 7.0, 7.2 (103, 100, 103)

Compression test #2: (03-18-06, 104096 miles)
rotor #1: 1.0, 2.0, 3.0 (14.3, 28.6, 42.9)
rotor #2: 5.0, 5.0, 5.0 (71.4, 71.4, 71.4)
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I did beat on the thing pretty recently (2nd, 3rd gear pulls to redline), since I was in a destructive mood. However, the hard hot starting symptoms were present maybe 100 miles/1 month after my first compression test, and I was being nice to the car then.

The engine is coming out this Monday (03-21-06). I'm replacing most of the "soft stuff" under the hood (coolant/heater hoses, fuel lines, OMP lines). Replacing fuel pulsation damper and fuel pressure regulator with new units. Also have a BRAND NEW ENGINE WIRING HARNESS I have a set of used, low-milage twins that are going non-sequential. Also have a PFC/commander for engine management. Running a stock IC, downpipe, high flow cat, and M2 exhuast. Also have an ACT street/strip clutch and Koyo radiator going in. Car will be 100% street driven (for now). Initial tune will be on the street. Shooting for 300 rwhp. Dyno runs to follow after break-in and street tune.

I can't wait to have my new motor

 

wish I culd blow my motor and be happy about it......unfortunately I'd be pretty pissed because I don't have the money right now to just order a new motor.

 

good luck and at least you know what your in for.

 

Good luck with it. While you're in there, consider S/S Oil Metering Lines, Urethane Motor Mounts and an oil pan brace. Also, clean and flow test the injectors.

P.S. I am slapping on that midpipe this weekend. Flameage shall ensue

 

Haha, thanks Rich. I had mixed feelings about the SS OM lines. I decided to use the OEM (read: brittle) ones for the time being. Inectors will be worked over as you have suggested. The urethane MM are a great idea, but the ones I have right now are in reallly good shape (believe it or not). This business with the oil pan brace.... I haven't looked into it.

Try not to shoot too many flames (at me or your out of your exhuast) with your MP

 

Sounds like your doing it right. Good luck with the new engine. I will be in the same boat as you in the future. 81K original engine. I am stocking up on new parts to go in when it happens, but man this stuff can get expensive.

 

I'd suggest a downpipe also. I imagine your factory precat is pretty trashed after 100,000 miles.

-s-

 

If you want some good conditioned OMP lines, let me know. I have ones that I took off for S/S lines.

 

gl on the rebuild

 

Its interesting to see how your 2nd rotor lost that much compression in about a thousand miles.

 

I wasn't clear in my original post. I'm currently running an aftermarket DP, and plan on keeping it

 

I completely agree. The numbers are too even. I'm willing to bet he has more of a carbon sticking problem than anything. Look at the 1st rotors compression back in Oct. I stuck apex seal could cause that exact reading giving you an indication it's blown.


mdpalmer did your car sit up over the winter? 1000 miles over a 5 1/2 month period. It's not a good idea to let high mileage rotary's sit up a long time when they are carbon infested.

 

Let let you guys know what happened when the engine comes apart. It turns out that I live five miles from work ( 10 mi/day x 30 day/mo x 5 mo ~ 1500 mi), and I gingerly drove the car about three or four times a week. Part of the reason I did that was because of what you said I find the compression loss interesting too. BTW, cranking speeds for both tests were at 250 rpm.

 

Please find my old quote then? I know for a fact I never told anyone to granny drive there car for short trips (huge difference there)). I granny drive my car a lot, but you still have to get on it every now and them. Plus I'll put about 6k on my car in that time period. I never implied people granny drive their car 24/7. Plus I also do carbon cleanings which you may not have done. Granny driving has it's benefits if you keep the carbon build-up away.

 

My bad for not being clear. I AGREE with what you said. I actually spent tiem warming the car up prior to driving it (say, 5 minutes of idle time) and a minute or two after the OE temp gauge was at the usual "warmed up" position, I would give it a redline burst in 1st and 2nd gear. Had no real issues with the motor unless I was idling forever...

You will find this interesting: I had a look at my rotors/housings today... the rear rotor (especially) was COVERED with carbon!!! ****, I picked off a few flakes with my fingernails. Guess you were right

EDIT: what I meant to say was that I "tried to keep the engine from sitting for extended periods" because of yours and others' advice. Sorry for the confusion.

 

Letting any rotary idle for extended periods of time just causes even more carbon to build up. Our engines aren't that thermally efficient in fully combusting the fuel/air mixture. I get in my car, let the AWS do it's thing, then drive off.



Well it's not about me being right. I'm just trying to help the best I can based on my ownership experience with these engines. I've been driving rotarys for 15 yrs so I have a ton of ownership experience, however I'm always experimenting with ways to make them last longer. The mileage and reliability of my Fd is a prime example of all the years experience I have with taking care of these engines. Your going to find carbon flakes within the engine. The key difference if it the carbon is making the seals stick in place. Did you notice stuck seals as you pulled the engine apart? Old carbon is really hard to break down. Once it's built up, it's going to stay there and really no amount of reving is going to really remove it. Sometimes you need to help the engine out with chemicals and other techniques (which is what I do to keep mine from being carbon infested). My Fd was more slugish when it had 65k (when I bought it) compared to now with over 103k.

 

Yeah, it seems that there are a few schools of thought on the "warm-up" procedure with rotary engines. The consensus seems to be, "start the car, and DRIVE it, easily" at least until it warms up. The other school says "let it warm up before you put it under any load". I tried to go somewhere in the middle... but I'm not anyone to argue with someone who has more experience.

Unfortunatley, I wans't the person who yanked themotor out and disassembled it. I have a local shop doing the work. Believe me, I very much want to DIY, but facilities, tools, and experience work against me. I'll do the next motor myself.

About the "sticking"... I'll take some photos of the parts and play around with them to give you a better sense of what happened. All I can say is that the rear rotor had some serious carbon flakes, and the front housing was SERIOUSLY scored (by the exhaust ports.... apex seal looks to have cracked). Pics will make sense out of this. Thanks again for your input.

 

I perfectly understand what you tried to do by bridging the gap. It's just that people on this forum don't stress enough of an importance of carbon build-up removal. Your warm up and driving habits would have actually worked fine had you known other ways to remove the past carbon build-up. When the infestation gets out of had, carbon flakes can and will start to break away jamming apex seals and even breaking them (especially with the 3 piece seals). The thin top piece can't take that kind of hit when they have high miles on them. There too thin and brittle!

Just passing on more (hopefully) helpful info to you guys. Piece!

Edit: Oh yea! Make sure you get your fuel injectors cleaned and flow tested. I consider it a must for any rotary rebuild (especially turbo ones). One bad flowing injector can completely change your A/F ratio and turn a perfect tune into a deadly tune.