Engine Vibration

[Zack S.]

Well, I overreved the 2.0L at the track a while back, and now have a strange vibration. Happened right after the overrev, idles fine, just does it when I rev it up or under power. Have taken the engine apart- heads, cylinders and pistons at the shop today, a cursory inspection hasn't revealed much, #6 piston has a mark where the valve barely grazed it, all the cylinders look good, as do the rings. Going to have the heads/valves tested to see if anything bent. I also heard over the weekend that I might have tweaked the clutch somehow? Any advice would be awesome!

[moneymanager]

Have you checked the rocker arms? Often overreving bends them.

[Zack S.]

They all looked ok, would it be obvious? Or more subtle?

[moneymanager]

I'm no expert but have seen both... one with a hairline crack, the other just bent.

[Zack S.]

Thanks- I'll re- look

[Walt Fricke]

Expert or no, someone is always adding to the stock of knowledge. Bent or cracked rockers I have never seen. Mine have all just broken - they are castings. Once broke all 12 in one go (aluminum IS gear shed its teeth). But if Jim has seen them, they were real. I once found I had cracked a forged chain idler holder, which explained why it was up so close to the top of the chain housing, but no other symptoms.

But it is vibration that is the immediate issue, not increased valve lash (noise, usually, and not just when reved). The #6 valve (exhaust?) may well be bent, but I don't associate that with vibration. I bent all 6 of those once, and drove for a year or so before pulling the heads when a shop said the car felt down on power. No vibrations.

I am not up on the early flywheel clutches. When I have broken the drive straps on my later ones the problems were in clutch disengagement, but since you have things apart you should be able to check yours, as the pressure plate is part of the engine's balance. A missed shift does put a lot of "backward" pressure on the pressure plate - way more than in normal driving.

Walt Fricke

[racing97]

clutch drive straps out of wack, check the pressure plate look at the straps that hold the pressure ring to the cover. They must be symmetrical

regards

[al lkosmal]

This does not necessarily line up with your over-rev incident, but check the fan pulley/fan interface. My pulley wore into the mating surface (belt too tight), to the point of causing it to go off-center and create an imbalance that could be easily felt as an engine vibration. It drove me nuts, I checked everything three times, ran great...except for that vibration. One day I noticed the fan belt was vibrating......I mention it, because it is very easy to check......and you never know, you could get lucky and it's that easy.

Regards,

Al

[kodioneill]

Are the flywheel bolts ok ? Ring gear straight? Rear pulley key way ok? Alternator and fan ?

[Eagledriver]

I had a funny vibration for several races and then my clutch disc broke. I replaced the clutch disc and the vibration was gone. By the way don't use the cheap QSC clutch discs.

-Andy