engine and drivetrain engine vibration above ~4k.... after aggressive driving

[2joejoe2]

Hey guys and gals I need your help! 

 

I took my car for 30 mile  joy ride on some of my favorite curvy roads here in WI. After a shift at ~6500rpm my engine developed a vibration. I was a bout 5 miles from home so, I drove home slowly and when I got home I pulled of the valve cover but noticed nothing wrong. I was expecting to see a broken spring or a cracked rocker arm....but nothing... any ideas? .... please don't say spun bearing!!!

also the engine now shakes pretty bad when Idling.

the vibration feels like some think is terribly out of balance. 

 

Be for this the motor was running great. and it still is... its just vibrating. It doesn't even seem like its lacking power...........however, I didn't push it hard after the vibration developed 

 

Motor was rebuilt about 10k miles ago at which point whole rotating assembly was balanced. 

-9.5:1 pistons

-Ireland 292 cam

-dual mikuni 40s

 

 

 

 

 

 

 

[TobyB]

Check your carb sync.

 

Many (most?) linkages can be tweaked when the engine flops around while your foot's on the floor.

 

Then the usual- plugs, wires, float level, junk in the carbs, loose carb iso mount, blah de blah. 

Burnt plug wire will do it, even a slightly loose boot.

I usually start one of these with a compression test, just so I stop thinking the worst, then work backwards.

It's usually something minor.

 

t

 

[2joejoe2]

Thanks for the reply Toby, I check everything you mentioned and I did find a couple lose ish plug wires. I "fixed" those and took the car for a spin

Unfortunately I think I was on the wrong trail

What I failed to realize be for is that the vibration is only there when I press the clutch pedal in ( yeah the motor shakes at idle but an adjustment of the mixture screws fixed that)...................would that be the throw out bearing?  It sounds and feels pretty gnarly  ............I can feel it through both the clutch pedal and the shift lever

 

 

[JerryC]

I had a centering link in a pressure plate break once, long ago, different make of car. It vibrated a little, but more noticeable was the clutch would not fully disengage. New clutch and all was well again. Something may have come loose inside the bell housing and rubs when you press the clutch pedal. Loosened slave cylinder pushing release arm to the side? Who knows, it could be that simple.

[TobyB]

Yeah, the strap that holds the pressure plate itself to the outer housing can break, and that causes a very definite vibration, usually when the pedal's in.

Like Jerry,  after a while the clutch would engage itself when you tached up the engine.  A really wierd feeling.

The lateral straps do it a lot more than the longitudinal ones.

 

There are those who say that it's caused by poor heel- toe technique, but I'm not convinced of that, since the longituninal straps seem to hold fine.

Also, I'd never admit that my own shifting was anything other than perfect, of course.

 

fwiw

 

t

 

[2joejoe2]

That must be it........... and I will admit my heal to toe is not the best. 

I am running a 215mm clutch  which I hear is more susceptible to this failure......do you guys think I would benefit by switching to a 228mm clutch and flywheel set up? 

[TobyB]

Bingo, we have a winner- the stock Sachs p-p has the radial straps that break, the 228 has 'em the other way.  I found an aftermarket 215 that had 'em the correct way, and

never had a problem again.  Raced that clutch for 5 years after that, no problems.

 

So yes, the 228 would fix it one way, finding the other kind of pressure plate for 215 would do it the other.

 

Assuming that's the problem, of course...

 

t

 

[2joejoe2]

Toby, Do you recall which 215 pressure plate brand you got? 

 

I haven't had time to tear into my car but Im pretty certain that is the problem 

[TobyB]

I wish I did- I know I saved the box, but when they tear down your shop, twice, you tend to lose track of things.

It was really generic, came from Shucks at the time (now O'Really's) and I THINK was a reboxed Valeo.  But I won't swear to that.

All the details are written on the (buried somewhere) box lid.

 

Do you have a bit more vibration at all engine speeds than you used to?  When I lost one, I felt it go-

it was just a subtle increase in the engine vibration at all rpms above about 3500, because the friction

plate of the clutch assembly moved a bit off- center.  If you're running a stock clutch, I'd bet you could

get an inspection camera (or even a mirror) in there and look at the straps.  They usually break right

where they're rivetted to the cover....

 

t

 

[Adamha]

Torn or worn out engine mount? May explain if everything else is solid.

[TobyB]

Luk, not Valeo- Rockauto has 'em for $115, for a 320.  They make decent parts. 

 

The Sachs with the tabs are the ones I broke, and the Rabbit Racers hate.

 

t

 

[2joejoe2]

Sweet Thanks!! thats super affordable too.... Should every thing in the 320i clutch kit work if I am running a five speed? (245) 

[2joejoe2]

The engine does seem to vibrate a tad more even when the clutch isn't pressed in. but as soon as i press the clutch in it gets a lot worse. Also the clutch isnt engaging all the way. when driving its hard to shift...... 

 

I had a bore scope down there through the timing hole but I couldn't see much. because the bore scope was too big to move around in there 

[TobyB]

Yep, those were my exact symptoms, too.  The hard shifting was a real puzzler at first.

  If you're running the 320 5 speed with 215 flywheel, that's the kit you want.

 

Luk has made decent stuff, in my experience with them...

 

t

 

[2joejoe2]

4 hours ago, TobyB said:

Yep, those were my exact symptoms, too.  The hard shifting was a real puzzler at first.

  If you're running the 320 5 speed with 215 flywheel, that's the kit you want.

 

Luk has made decent stuff, in my experience with them...

 

t

 

Toby wins! pulled the car apart this afternoon and at first the pp looked Ok however when  looked at the straps with a mirror I saw that each strap had one of the corners broken off at the rivet. See photo