Does the flywheel have locating pins for the pressure plate? Perhaps one of them (or all of them) aren't in place and the flywheel has shifted a bit, causing the vibration at higher RPMs.

This would show up more when driving since the pressure plate would have more pressure causing a pronounced out of balance feel. Just my 2 cent's worth.

Bob

2 test to do
 

Mick You didn't say what bell housing is in the car?? Also was it trued to the back of the motor before installing. If it's a Lakewood, Start there and center bell housing, replace pilot bushing. and retry for road test. If this fails the next thing is to locate vibration source. This would mean removing the clutch assembly from the fly wheel and run the motor at the rpm you have the problem with. You will need a block of wood to support the back of the motor. If the vibration is gone, bad clutch assembly or wrong balance on pressure plate or cracked disc. It may be as easy as installing a new clutch. Again make sure that the bell is centered on flywheel, new bushing and reinstall.
What dampener is on the motor?? I had some issues with an ATI one. Until the fluid warmed up I got a bad vibration for the balancer. There is a company that will come for about 1K and custom balance the balancer to the rotating assembly. I think this ius more for Nascar motors.
I am going with a bad clutch if the motor was smooth to start. The other possibility you don't want to know. Are you sure the motor has not downed a cylinder??? Bad MSD ignition cap or rotor??? Oil pressure is good when hot??
Pull the chutch and retest would be first step. Rick L. Mick you can also take the flywheel and clutch asembly to a place that will balance cranks and have this checked. I have done flywheels on tire balancer and found only 1 flywheel out of balance by .75 of an oz. Any one have a good tire machine??

We have some good brain power working here thanks guys. Bell is a QT and was absolutely spot on when indicated. I want to dive right in and check pilot bearing and flywheel bolts but I don't want to go right by the problem on the way in. I was thinking about running it with the flywheel off once I have it back apart. If the motor is adequately supported that seems feasible? I also have other flywheels to try on it. I will check what breed damper it is. That would be an easy change/test also wouldn't it?

It should be fine to just support it under the rear of the engine and run it without a flywheel.

The damper is an easy swap....doesn't take that long at all if you have a good puller.

How would you start it with the F/W off? The other F/W check makes sense though.

Steve

I balance a lot of engines and sort out some of these problems after someone has rebuilt, repaired cars---

An area that hasn't been mentioned----if you lose part of the clutch disc facing you will have an severe out of balance issue----and thats even if everything was balanced correctly.

Now---an item of interest that all of you can tuck away----about the 428 being externally balanced----it doesn't matter if its a 428 engine---when you change the stroke it is no longer a 428---a 428 block, yes--- however from that point on--- balance is balance no matter how you arrive at it .

ROFL, good point Steve.......kinda hard to pull the flywheel off with the engine running.....ROFL

It's too early in the morning. That's my excuse anyway.

i vote for the clutch/flywheel assy oob, rpm related and it was dynoed and didn't show up there. take the assy off and have it balanced and see what it shows.

That is the plan to pull the clutch/flywheel. I will spin it on the tire balancing machine before taking it to the engine shop. I tried it with the clutch in and out and there seems to be no difference. Other than price/quality what's the diff in dampers and anyone recommending a certain breed http://www.summitracing.com/search/?...balancer&RC=25 better yet anyone have one I could borrow and try?

I just changed out my POS balancer (that came apart) to a Romac brand and I must say that it's a beauty. It's an under two hour job if you have the puller that actually fits (I spent some time fabbing mine to work, then it took all of five minutes to remove it). But if your timing marks are on and appear to advance properly with increasing RPM, I doubt it's going to be the balancer. Here's my detailed thread on the change out: http://www.clubcobra.com/forums/fe-talk/105025-crankshaft-dampner-separated-arghh.html

Ive seen cases where a crank with a crack in the web will vibrate like that under load, but still drive etc due to the shape of the crack, even the oil pressure still seems normal until the crack really gets bad, not likely & hope thats not the case here, but worth keeping in mind..

I believe that a balancer on an internal-neutral balanced engine is there only to minimize harmonic type forces in the crankshaft. So, unless it is coming apart or the ring has shifter substantially, it's pretty unlikely it's causing an engine vibration problem. I think I would be looking at a problem in the original balance work, the flywheel/clutch assembly or a bad cylinder from a plug or wire.

Had it up on stands today and while going over the car nutting and bolting it and looking it over I had a pretty good "aha". The drivers side motor mount has two bolts in the block side. One was missing and the other was loose! I thought OK good find take my public humiliation at leaving critical fasteners loose and get on with it. While replacing one and tightening them both I clearly remebered doing them up. You guys know what I mean as they are a trick to get to, esp the drivers side. Anyway got it back down to test and it does the same thing at the same RPM. Not as badly now it's tightened down again but definetely there very noticeable and consistent. I've come to the conclusion I'm commited to going in as the vibration is so bad it's shaking fasteners loose. Thanks for your ideas, I'll check back on your suggestions and keep you posted.

When the engine came over from the builder, presumably it had the flywheel on it, but no block plate, right? Who pulled the flywheel off to put the plate on? Any chance that the flywheel bolts were "snugged" and to-be-torqued later?

Good question Patrick the motor came with nothing on the back of crank. I installed and checked the QT bell, Fidanza flywheel, ARP bolts, pilot and Mcleod dual friction clutch (not necessarily in that order). It may be a little anal but I'll be noting which bolt was where and position of pressure plate to flywheel before checking assembly balance.

The F/W should only bolt up one way. It's not like you can bolt it to the crank a hole off or something like that. At least not without something big wrong.

Assuming when the clutch was pushed you had the trans in gear, this means the clutch and transmission were not turning. I think this rules out from the Pilot bearing to the wheels. That leaves the flywheel, pressure plate, damper, and engine. I would focus my search on those parts.

I would still check everything that I could before reassembly.

Maybe I'm missing something here.Seems like it would be easy to remove certain systems from the equation.

Am I correct in assuming:

Vibration present revving engine up or down whether car is moving or standing still. (rules out the driveshaft and rear end.)
Vibration present while revving the engine with the clutch in or out while moving or standing still. (Kind of rules out the tranny, maybe not if pilot bushing is really bad, but probably does.)

So, if it were me, I would just remove the trans and then run the motor with the clutch assembly attached. If the vibration is still there, you've eliminated the tranny. Then remove the clutch assembly and then rev the motor. If still there, it's inside the motor. If the vibration is gone, it's the clutch assembly.

My bet is on the clutch.

Yep, pretty much. I think once he pulls the tunnel and starts taking stuff apart he's going to spot something that has come loose, be it pressure plate, flywheel, or what have you. We had a thread a year or two ago about aluminum flywheels and bolts backing out of them. You can check the torque on your pressure plate bolts through the fork hole -- I know because I took some shots of me doing just that for that thread. But if he disconnects the trans and revs it and it vibrates, and it still vibrates with the pressure plate and driven disk sitting on the shop floor (and the flywheel bolts are nice and tight), then it's engine related.

Just thought of something. Reving it with the bell housing off and back of engine setting on a block of wood might be a bit risky. I would hate to hear if flopped up off the wood block and knocked it out from under the engine.

Give it some thought and make sure it is supported well.