Joekaistoe

I'm hoping someone out there can help me with diagnosing my issue.

I recently swapped my 30 lb OEM flywheel for an OEM 23 lb flywheel on my 1979-ish 12A(as well as working on a number of other things listed in this post). Once I was able to test drive it, I found I have a shake that's most noticeable at my shifter. The shake is at its worst when I have it high idling at 2000 rpm when cold, but it varies with rpm (less noticeable at 3000, a bit more at 5000, etc.). The shake occurs clutch in and out, in gear and in neutral, moving or stationary. It wasn't present with the 30lb flywheel.

So far I've checked my motor mounts (no cracking or separation present) and ran it with the belt removed to check if it was caused by the fan, water pump, or alternator (no change). Transmission mount looked fine when I pulled the transmission for the flywheel work, so I left it.

I know the logical conclusion is that the flywheel is causing the issue, but I've read in multiple places that the 23 lb 81-82 flywheel can be swapped in for the 30 lb 79-80 flywheel without a problem. There's a few things that might complicate this, though:

• My engine is a 1979-ish, which means I know the housings are 79, the middle iron is 81+, the front and rear housings are a mystery, and so are the rotors. However, there was no vibration when I had the 30# flywheel.
• I did not swap the likely 79 front counterweight for the 81-82 counterweight
• The engine I pulled the 81-82 flywheel from appears to be a 81-82, but had the beehive oil cooler and came from a 1985 car (which may be the reason for the beehive, so they didn't have to install a front mount oil cooler). I weighed one of the rotors and it came in at 4621g (10.2lb), which matches 81-82 rotor weights according to Mazdatrix.
• The flywheel, while having all other indicators of being from an 81-82, including weight, has a "2" where the "21" should be according to the Mazdatrix site for identifying flywheels.

Has anyone else done a SA flywheel swap to an 81-82 flywheel? Did you have more shaking/vibration in the shifter afterward? Did swapping in the matching front counterweight fix the problem?

Is there some weird Canadian half-breed 12A motor that I could have gotten from the 85 car, or is it more likely someone just swapped an 81-82 in?

Maxwedge

iTrader: (1)

The front and rear weights are matched to prevent this.

t_g_farrell

iTrader: (1)

I swapped on an 82 flywheel on my 80 SA and no real shakiness. I mean it doesn't dampen the engine movement as much as a 30lb flywheel but its minor. So there is some extra vibration but its not "shaky". I would recheck the rubber engine and tranny mounts first, could be that simple. Use a pry bar on the mounted tranny and see if it moves around. Same on the engine. It could be your engine is a bastard and has different counter weight and rotors in them based on your description. I assume you didn't build the motor.

Joekaistoe

I didn't build the motor, I've just been fixing their "mistakes". I know the person who built the motor had this 1981 and a 1979(and liked his 79 better) so my best guess is that rotating assembly should be either 1979 or 1981, whichever was worse. That's why I'm 95% certain the front counterweight is a 1979, since it's heavier. Since the 79 and 81 rotors are similar weights, it shouldn't matter too much which ones he chose as long as they were a matched set.

It was built by a former member here, ColinR.

Part of my issue is that the vibration/shaking in the shifter is not a huge amount; to the point I'm not sure if the flywheel is out of balance, or if the lighter flywheel is just not covering up roughness that already existed. That and many sources say an out of balance motor should shake worse at higher rpms, but mine is the worst at 2000rpm. If it was a V8 with a mild cam I wouldn't even question it. On top of that, installing an unbroken shifter return spring has stiffened up the shifter, so some of the vibration may have already existed but went unnoticed.

I'll try prying at my mounts to see if they're part of the culprit. I'm also going to burn off a bit more gas and fill it back up to see if the 5 month old stabilized fuel sitting in it is a contributing factor, too.

How much vibration do you feel in your flywheel-swapped car (lets say 1 is smooth as butter, 5 is washboard dirt road)? Can you feel it in the chassis at any rpm?

mustanghammer

iTrader: (3)

Mismatch between front counter weight and flywheel gets my vote

Banzai

iTrader: (13)

Maybe you could post a short video of the vibration for others to see. I will say that it makes sense to me that if it's an actual out of rotational balance situation, more rpm would only exaggerate the problem. I'd say that generally, vibrations that exist at certain speeds and go away at slower or higher speeds usually have something to do with worn or failing parts. Does the whole engine shake at 2000 rpm?

LongDuck

Just a note; a lightweight flywheel will allow more vibration to come through the transmission and shift tower, because there's literally less mass there to dampen the impulses of the rotating mass. You may just be feeling this. If the mismatched front and rear counterweight were the problem, the vibration would be bad at 2k and worse are 4k and shake the engine apart at 7k. It's a shame you don't know what front counterweight is in there, though.

Also, you should check the condition of your THREE rubber boots that surround the shifter. If these have been cut to facilitate faster dropping of the trans, then the shifter will shake like crazy and that's nothing to do with the engine balance. It comes down to replacing all 3 of those rubber boots and trying a heavier shift **** if it bugs you that much. Changing the momentum of the shifter may help.

The side benefit is that the cabin noise will be significantly reduced with new boots in place. A tremendous amount of noise is reflected off the road and up into the trans tunnel.

mustanghammer

iTrader: (3)

So was changing the flywheel (and clutch/pressure plate) the only change you made before the vibrations started?

Joekaistoe

Thanks for all the help!

I'll take a video next time I have a chance to go out and run the car. At 2000 rpm, the vibration can be felt in the chassis, but it's only to the degree of lightly rattling loose plastic parts, not rattling fillings.

All the boots are now in good shape; the bottom rubber boot was destroyed, so I replaced it.

I did a fair bit of other work over the winter. Quoting my "What did you do on your RX7" post:
The ones relevant to the engine and drivetrain are the flywheel, clutch and pressure plate, shifter return spring and boot, clutch free play, fixing the exhaust leak, and cleaning up the grounds.

LongDuck

Uhhh,... The way you just described the chassis vibration makes me think you have mismatched front- and rear- counterbalances. It should not be shaking that much, and if you continue to suffer through it, your trans and engine mounts will fail shortly, followed by engine bearings.

We need somebody in here who has installed mismatched counterbalances who can confirm what you're feeling. Rotary engines are renowned for their smoothness,

Joekaistoe

I don't particularly want to have to crack open the front cover if I don't have to, but I will if need be.

I was under the impression that the 79/80 flywheel was balanced the same as the 81/82, since you can use the same automatic counterweight from 79-82.

I've attached a link to a couple videos on google drive showing the shifter vibration; the first while driving, and the second while in neutral. The metallic rattle at low rpm is from a broken weld on the muffler surround heat shield, and the rattle at upper rpms is the center console (it's loud because it's next to the phone microphone).

https://drive.google.com/drive/folde...S2?usp=sharing

Benjamin4456

My apologies for the incoming brief thread-jack, but is a 2k rpm engine vibration common for 12A's? My current engine creates a fair amount of vibration at right about 2k rpm, but above and below there it's smooth as silk. I only really noticed this after swapping to a competition Mazda trans mount a few years ago, just curious if it's a common thing or perhaps a sign that the engine is a fair bit out of balance. For context, I hate crossing that "rpm line" because it makes everything in my interior start buzzing.

Once again, my apologies for the thread-jack.

Joekaistoe

Took my distributor out and stuck a borescope in the front cover to see what front counterweight I have. It appears to be a 1979/1980 front counterweight based on the squared edges and size of it. Here's a link to the borescope video:
I also uploaded the video of the shifter vibration in neutral to Youtube in case anyone cared to check it out:

Joekaistoe

Everybody place your bets now on if the shaking is due to a counterweight mismatch! I have the 81-82 front counterweight on the engine and it's ready to be cleaned up and reassembled.

New counterweight

Old counterweight

Toruki

I'm going glass half full and say you've nailed it.

Joekaistoe

Well, I have to admit, I was about 75% certain that changing the front counterweight would not help because the auto transmission counterweight is the same across 79-82. But lo and behold, I finished putting everything back together today, started the car, and the shaking is gone!

​I did also replace the distributor cap, as the center button was broken off, but that would only effect the trailing plugs since I have the leading is set up as direct fire.

TL;DR: Change the front counterweight to the 81-82 counterweight if you swap a 81-82 flywheel into a 79-80 engine to prevent excess vibration.

j_tso

iTrader: (2)

What was the spoon for?

Joekaistoe

I was actually wondering if anyone would notice that. The oil pump key fell out of the keyway and found its way under the oil pickup. I used the spoon to push it out from under the pickup to get it out of the oil pan.

t_g_farrell

iTrader: (1)

So what was the counterweight you pulled out? Like I said, I did this swap and the shaking was not that noticeable. My engine was for sure a stock OEM from new which, other than flywheel/clutch work has never been out of the car or opened.
Glad you have it sorted!

LongDuck

Would now be the wrong time to tell you that a broken center button electrode on your Distributor Cap will cause a vibration at certain RPMs?

Just kidding, dude. Glad you got it changed, as your bearings and rotors will thank you for it.

Joekaistoe

As best as I can tell, it's a 79/80 counterweight. I've read that the factory doesn't balance these all that precisely, so it could just be that my combination of flywheel, rotors and front counterweight all added up to cause extra vibration.