My 1980 RX7 has a light wieght steel fly wheel (don't know what brand) installed by the previous owner. I decided I was going to install the fly wheel in my new1983 street port. I know that the fly wheel has to match the rotors so I was going to measure the counter balance (http://www.mazdatrix.com/faq/Rcounterweights.htm) on 1980 to see what year the engine was.

I removed the flywheel from the 1980 only to find that the counter wieght was from a 1986 to 1988 13B (my measurement was .531"). I have reved this engine to 8000 rpm on track days before and it has always been smooth as silk.

So I decided to reinstall the fly wheel on the 1980 as I was worried that it may unbalance the 1983 engine. Now the 1980 runs like crap, it it noticably rough from idle and as revs approach 6000rpm it feels like the driveline is going to shake right out of the car! I have taken it all apart again and reistalled, but it still runs like it is out of balance.

Two things that I think might be the problem.

1. When I removed the fly wheel/counter balance I put a pry bar behind the flywheel/counter balanace and hit the bottom of the bar with a sledge to break the fw/cb loose. I now know this is incorrect. Could this have damaged the e-shaft or a bearing or something?

2. Does the flywheel orientation on the counter balance mater? There is a mark on the flywheel, but I did not know how or what it should be lined up with.

Any other thoughts or comments on why the 13b counter balance might have been used and why this is out of balance now? I drove this car for 2 years and it was always smooth...

Thanks

 

you may have bent the fw/cb out of shape so when you rev it, it doesnt spin as smoothly as it did b4 you tried to pry it out... it may have messed up the e-shaft but i dont think so

 

Flywheels don't bend that easily, unless you wailed on it with a 20# sledge. And the year of the car makes no difference, it's the year of the engine that's important. I still haven't understood what you did with what parts, lol.

If you're putting the same parts back on the same engine, did you check the pilot bearing? The flywheel is keyed so it can only go on one way, the cw is indexed by the bolt holes, so it can only go one way also.

Also recheck/retorque everything including the driveshaft and tranny mount.

 

It sounds like maybe the flywheel isn't completely seated or is skewed. Make sure its seated on the shaft correctly before you torque it down. As trochiod mentioned, check the pilot bearing and make sure you haven't buggered it somehow. Another thought, when you removed the tranny and dropped the drive shaft, did you modify the shaft so that it's not balanced anymore and is it bolted up good to the flange on the diff?

 

I know on my toyota pickup there is a Right way to hook up the drivling to the rear end and if you dont line it up right it will vibrate dont know about RX7's but you might look into that

 

I will clearify a few things

I re installed the light wieght fly wheel on the 1980.

The vibaration is in the engine or flywheel/clutch/pressure plate it vibrates with the car in neutral or with the clutch disengaged (pedal down) so it is not in the transmission or driveshaft.

I used a 5lb sledge to hit the breaker bar.

When I installed the fly wheel on the counter balance, i was able to finger tighten all the bolts on, so the orientation must have been correct.

 

What is the condition of the transmission mount?

 

Bent flywheel or not properly installed flywheel is about all it could be possably tranny mounts but not likley if it still does it with the clutch depressed you said you were banging on it might have warped it a lil wouldnt take much....one way to find out is to take it back out and inspect it. look for warpidge etc. then get more info on how it all goes together with the counterballance and slap her back in.......and cross your fingers hahaha your gunna have to take it out again anyways unless you dont care about the vibration. maby the flywheel you got was already out of balance??? that sucks tho... more work less driving. good luck

 

What is acceptable for run out in a flywheel?

I had a apprentice mechanic freind (he works in heavy equipment like backhoe) suggest pulling the starter and using a dial indicator to measure the run out on the fly wheel. We tried that and measured run out of 6 thou. Does nto sound like much, but could that be the culpret?
Thanks

 

I believe specs are .0016-.0028 with a max of .0035.

Did you inspect the transmission mount?

Also have you replaced the water pump or had the fan clutch off recently?

 

u-joints?

 

Sounds like the rear counterweight is wrong for the engine.

As was stated before,it doesnt matter what year the car is,rotary engines of all vintages can find their way into just about any year RX-7.With their age,engine rebuilds and multiple owners,it can be tough to say exactly what year engine rotors you have.Clearly,its something ahead of the transmission,and if the only thing that has changed is the counterweight/flywheel,then its likely to be the counterweight/flywheel.
Youd have to wail on the flywheel badly to get it to warp,and itd be pretty obvious when your cranking the engine over,as the ring gear is gonna be out of whack.Itd likely sound really bad when the starter is doing its thing.Bending the E-shaft is highly unlikely,its a very small diameter,stout little stub.

 

What was the condition of the pilot bearing when you pulled the tranny/clutch? Assuming you reinstalled all of the same parts correctly, the vibration may come down to the pilot bearing.

Here's my reasoning why. I replaced the clutch on my 2nd gen, once I began driving it, I had a vibration that I never had before. I have since has another clutch and 2 more trannys installed to try and eliminate the vibration with no success. Even repaired the tranny mount.

A couple of years before the clutch change, I heard this terrible grinding noise like someone had put large sand grains in the tranny. At the time I had no idea what it was, but I was on a long road trip and the grinding quickly went away. What I found when I replaced the clutch is that the pilot bearing had ground itself to dust.

I installed a new pilot bearing with the new clutch and the vibrations began. Thinking that perhaps the lack of a pilot bearing had cause uneven wear on the bearing of the trannys input shaft, I changed out the tranny, no change and the 2nd tranny had bad 2nd gear synchros, so i installed a 3rd tranny, still no change.

At that point I was at a loss as to what was causing the vibration and still am to this day. Fwiw, the original tranny I first removed had perfect shifts and syncros. Once I changed the clutch, none of the 3 different trannys will shift smoothly into 2nd. I finally gave up and decided to live with it.

As a side note, anytime the driveshaft is removed, mark the rear of the shaft and the pinion flange so when the shaft is reinstalled it will be clocked the same way it came out.