What's up everybody, hope everyone is running smoothly heading into winter.. I have a small problem that I'm hoping you can shed some light on.

Over the past year I have started the rebuilding process on my '86 2.8. I pulled the engine and sent the long block off for the 3.1 stroker rebuild. I lucked out having a local shop near Spokane (Sunwest Automotive) that did a solid job on the engine. While that was done I replaced almost everything I could get my hands on.. I almost nailed it first try.

After about 100 miles I've noticed while in park or drive and at lower speeds I have a vibration in the cab. It's not horrible, but noticeable. The vibration lessens while in gear and disappears while cruising above 20 mph, I thought I had read things correctly on here but I'm assuming I'm mistaken about using my old flywheel from the stock 2.8

I'm not horribly mad at this mistake, as I have to pull the cradle again to adjust the valves at 1000 miles. Plus I suspect I have just the slightest lower intake leak (where the bead of rtv is on the passenger side, this disappears once warm) my question to you fine fiero owners is how much this could potentially damage my engine driving through winter strictly to and from work? I'm almost to 200 miles now and live ten miles round trip from work, so I can make it to spring.

The car overall is driving really well other than the low rpm vibration. Good power, shifts smooth, running a bit rich due to an exhaust leak where the y pipe meets the cat pipe (cat removed), that's messing with the O2 sensor (also is a Bosch, will be putting the AC Delco and fixing leak soon). I didn't think I needed to re balance or replace my flywheel with such a minor performance rebuild.. but I was mistaken

The 86 2.8 is indeed external balanced with a counterweight cast into the flywheel. The 88 and later 2.8, 3.1 and 3.4 engines are all internally balanced which means the flywheel has a neutral balance.

Typically when the flywheel imbalance is wrong, you will feel it through the entire rpm range and the vibration will get faster and more intensive with RPM. The common failure mode for improper imbalance would be premature wear on the rear main crankshaft bearing, but most damage would be from WOT above 4000 rpm. Keep the rpms low and drive it as a commuter car and it should be fine until summer.

I acquired a Lumina APV 3.1 that already had an externally balanced flywheel on it. The builder had experienced undiagnosed vibration so it was removed in favor of a bigger build. He said he only had about 500 miles on the engine, so probably little if any damage was done. I purchased a flywheel for a 91 Beretta 3.1 from Rock Auto and have noticed no vibrations whatsoever.
https://www.rockauto.com/en...manual,flywheel,5348

Thanks for the replies guys, I will definitely be putting it around until I get it swapped. Like I said, the vibration is really only noticable in park and low rpm's in drive, I've eliminated everything else as a possibility and know I just threw the old flywheel on (inspected for cracks and such)

So I guess I'll just drive it like a granny for a few months, that way when I do have to pull the cradle I can adjust the valves while I'm at it. Much rather pull it one more time vs twice..

Just buy any 3.1L flywheel - they were all neutrally balanced.

https://www.rockauto.com/en...manual,flywheel,5348

Usually, this type of post goes the other way where a neutral balance 88 flywheel causes vibration with an 87 and lower V6. Go for an 88 V6 flywheel on RockAuto or someplace similar. Neutral balance flywheels are easy to come by. You can put your original in the Mall, could be someone out there is looking for one.

Will do, luckily the vibration isn't too bad. When cruising in 2nd at 40 the car is perfect. While idling it'll just doesn't seem right, plus I can fix a few things I overlooked. Thanks for the help! I'll keep her in put put mode

quote Originally posted by fieroguru: Just buy any 3.1L flywheel - they were all neutrally balanced. https://www.rockauto.com/en...manual,flywheel,5348

Vibrations of this type are more easily felt at low to medium rpm. They are still there at higher rpm but the pulses are so rapid that they seem like one, so we don't feel them.

I had a '54 Oldsmobile in which I bent the driveshaft while drag racing. Vibration was pretty rough in the lower gears but disappeared at road speed. I made a trip from Atlanta to Myrtle Beach. Though I couldn't feel it the vibration cracked the case on the transmission. Cost me a bundle stopping regularly on the way back to fill the trans with gear lube.

I think what happened was I had mis read something about the flywheel, then got distracted by the balancer.. I had to replace mine due to the seal bulging out. Got one from West Coast Fiero which is the same balancer just different timing marks. I made the correct ones and set timing and I know I'm pretty dead on.

Flash forward to mating up day and I just threw the damn flywheel on.. so close!