^^^ if everything else has been inspected and looks good,

then I think Constantine has a good point about an engine running issue

 

Short story report follows. It's been a busy, busy weekend.

Brian and I (mostly Brian) went over, double-checked, reviewed a number of things and actually did a couple of things. We managed to *change* the vibration a bit. It's less noticeable at ~1200 rpms, a bit stronger at 2400 and slightly less strong at 3600 (IIRC.)

Stan, as far as the various bolts and nuts are concerned, we had a 'torque list' that we went through. It was double-checked and I have no lack of light. Brian's pretty **** about using my torque wrenches and I don't think there's more than one or two bolts on the entire car that were tightened to feel. And I do mean the entire car - at least as far as the bolts that we've touched are concerned.

At this point we have decided that the vibration is most-likely due to a low-frequency but very consistent misfire. I suspect that this non-02-loop Euro is tuned too rich and that due to the vagaries of cylinder-to-cylinder A/F ratio control on a batch-fire injection system, that one cylinder is rich enough to quench one of out 10 or 20 firing attempts. It may also be spark related.

With the new torque tube (thanks, again, Constantine) with a non-bent drive shaft and all the other work we've done to it, the characteristic vibrations of the whole system have been changed. So, it is possible - even likely - that this vibration has been present for a while but was masked by or cancelled out by other vibrations.

At least, that's the story we're sticking to for now since we are 99% certain that the source of vibration is on the engine-side of the flywheel. We tested for the vibration, engine running, with no pressure plate, discs, or intermediate shaft. (And the fact that that is only possible with the dual-mass clutch is about the only thing I like about the DD clutch. However, Brian is now the master of the DD clutch and with a snap of his fingers it will drop out )

 

Thanks Stan and Constantine for your comments.

After 2 days of double and tripple checking everything, including dropping the clutch, measuring runout on the flywheel and IP, and running the car without the PP, the vibration remains. The clutch is back in and works perfedtly. We feel confident at this point that the issue is forward of the flywheel.

A few things to note:

• While the car was down for this recent work, I replaced a leaking tensioner adjustment bolt and re-tensioned the TB. This entailed removing the air pump and AC compressor belts and moving the units out of the way.
  
• There is a new harmonic "noise" that appears to be coming from the front of the engine, at idle and up through the rev range. We were unable to pinpoint it with a stethascope. To my untrained ear, I would say it sounds like a bearing in an accessory unit (AC compressor, alternator, PS pump, air pump, fan). More investigation on this to come.
  
• There is a random miss that can be heard off idle in the 1200 RPM range - this is not a steady miss, more of a random "stumble". This has been present, more or less, since I have owned the car and before the engine out refresh, and before the vibraton became apparent. This might relate to an unusual plug reading for #7 that was taken before the engine out refresh. The plug had greyish ash deposits. I pulled 6, 7, and 8 plugs at about 2k miles after the engine out refresh, and attached pictures below. Will be taking a current reading.
  
• I need to check the CO to see if the MAF is dialed in. There are not cats, no O2 senser, no feedback loop - stock Euro LH config with full stock Euro exhast.

Keep in mind that during the engine out refresh last year, it got new wires, caps, rotors, plugs, temp II, cleaned/tested injectors, rebuilt MAF, TB, WP, tensioner rebuild, valve stem seals - the vibration was not present after this work/before the transmission RR and TT rebuild.

Despite this vibration, which crescendos in approx. 1200 rpm intervals, the engine is running very strong and is making good power.

Dave may have additional commentary to add....as I am sure I have forgotten something.

Anything else to check, based on work done recently? Thanks.

 

Thanks Dave, our posts crossed in cyberspace. And yes, I have done more bench pressing this weekend than I ever have. And dropping the clutch is easy; lifting it back into position is the gruntwork.

And I should add, I agree - this vibraton through the rev range as we feel it while stopped, clutch in, could very well have always been there. It is so slight that you may not notice it unless looking for it. However, now it is significanly amplified under load, and I suppose it is possible that the work done (tight TT bearings, driveshaft without wobble) has allowed this to be transmitted to the seat of the pants more apparently.

 

... motor mounts, oil pan gasket, fuel lines. CPS was ... a year old? That was not replaced (again.)

 

can you do a compression test?

Have you checked that the coil wires are not rubbing on any part of their run.
Look for abraded insulation from rubbing on a metal surface,
run the engine in the dark with the intake tubes removed look for fireflies

Have you inspected the caps and rotors for cracks or other damage?
verified the timing of both dizzys with the caps off.

Is it possible one of the coils is going bad?
Look for a corroded end on the coil wire connection

 

Correct. So much was done, I can't remember it all

CPS was a year old, so we didn't change it during the refresh.

 

You'll note that I made no mention of the clutch jumping back IN at the snap of your fingers...

 

Oh have the injectors been sent out for cleaning?

 

Yes, Witchunter, last Winter. Came back with a clean bill of health.

 

Sure can.

We have. However, that check is worth doing again.

That is actually not easy to do. There is no dark in my garage unless it is dark outside also.

New caps, new rotors. They can be removed and checked.

Absolutely. Or one of the coil amplifiers could be exhibiting an uncommon failure mode.

It might be worthwhile to swap coils side-to-side. But, only after we've localized the cylinder that is not doing its job consistently.

Brian's Euro is remarkably free of corrosion. It is one of the most-corrosion free 928s I've ever seen.

Nevertheless, checking all contact points throughout the spark system must be the next order of business. Caps, plug ends, rotors, coil connections and coil body grounds. Amplifier plugs and pins. Grounds for amps. And probably a few others.

Actually, the next order of business is a beer and Game of Thrones on TiVo.

'night folks.

 

hey ifn yer turning out the lights then start the engine and look for bugs,
whilst yer drinkin a cold brewski

 

i'm disappointed there aren't any suggestions to check for loose con-rod nuts rolling around in the oil pan

seriously though - I used to align and balance industrial motors in a past life and I definitely hope it's just an ignition problem and not a crank bearing, flywheel unbalance or worse - crankshaft problem.

a small weight variance can become an engine destroying situation at 3000rpm

 

I caught Dave tonight before he started drinking , and we checked for fireflies - nothing. Dave says he can smell unburned fuel out the exhaust - I just know it is a bit stinky with no cats. I brought the car home since I won't have any time to work on it for the next few weeks.

Me too.

So, has there ever been an instance where someone has damaged the thrust bearing or flywheel by hammering out/in the clutch centering pins? We did verify there is no runout on the flywheel.

 

How about the end of this story?