zogster

After head gasket, inlet valves, timing and balance belt, plus water pump, and a few other trivial things, I have the engine back together and running - started first time, and things are mostly good I think. But it doesn't sound quite the same as before, and I really don't have enough knowledge to pin down quite what's wrong/different.

I'd say it generally sounds, from the driver's seat, a little 'boomier' perhaps (though nothing exhaust-related has changed), and mixed in there somewhere is a sound that I hear under acceleration only that I find hard to describe - a flutter of some kind, vaguely like the rapid beating of wings.

There's also a bit more vibration than before, especially between 2-3000 revs, more so closer to 3000.

I've tried recording what I hear, and whilst the audio from the cabin isn't so clear –*too much rattling and other non-engine noise, tough I may have another go - maybe these two audio files can help a sharp-eared expert diagnose the problem. One is at the exhaust, and one with the (stereo) mic held above the engine with the hood open. In both cases the car is not moving, and the engine is at idle and then revved just a little.

I'd appreciate any insights that anyone can give here.

https://dl.dropbox.com/u/41386204/Exhaust01.wav
https://dl.dropbox.com/u/41386204/EngineBay01.wav

John_AZ

You might look at this post:
https://rennlist.com/forums/7944059-post9.html

GL
John

MAGK944

I am going to bet that your lower balance belt roller is 180deg out. Common problem, people swear they have it correctly installed until I point out where they went wrong.

divil

Are you still having that idle problem you mentioned before when the engine's hot? John_AZ's link mentions a throttle position sensor problem that was heat dependent - definitely worth a look given your symptoms. Luckily it's easy to test the throttle position sensor with a multimeter - look it up on Clark's Garage.

F18Rep

True enough and my first guess as well. Also maybe a broken motor mount. Just guesses though...Bruce

spanky

I wld start with the balance shafts rotors. Remove the belt and remove both rotors frm the shafts . Chk that the narrow cover window on the lower rotor is blank/ empty. By hand rotate the balance shaft until the key is at the 12 noon position and then slide the rotor onto the shaft. BOTH Balance Shafts KEYS MUST be at the 12 noon position BEFORE you install the rotor on it.. Now go to the upper rotor position the rotor cover so that you see a 0 in the narrow cover window, rotate this upper balance balance shaft until its key is into the 12 noon position also and then slide the rotor onto the upper shaft. Check to ensure that the car is in fact @ TDC.!!! If it is not put it at TDC using the crank bolt and a 24 mm socket! Tighten/ torque bolts both to spec! Next position the belt and rotate the rotors/ sprockets into their set up position, Line up the notches on the sprockets with thre marks on the black engine cover. with the lower sprocket at the (raised line on the black cover (@ 7 oclock position and the upper sprocket at the ( notch @ 1 o clock position. After you tension the belt recheck that the sprockets have NOT moved on you as they are prone to do. It takes a few times to get this right. Go slow, check and then recheck your work always!! Good luck with this. I just remebered that Porsche changed/ updated the marks that we should see inside the narrow sprocket cover window and Im not sure what yr your car is. Can someone help us with that info ?? What I gave you is what works on my 87, 88 cars. Thanks to all.

zogster

THanks fellas - I'll look in to the balance shaft issue as a first step. But I suspect the motor mounts have never been replaced so they have to be worth checking.

And yes divil, I do still have the idle problem though it's improved a bit since I tightened up a loose connection on the j boot. Still wanders/hunts a bit when hot though, so I'll look at that TPS as you suggest.

Will keep you posted...

zogster

And ps, it's a '87 UK model 951, apologies for ommitting that info spanky. I definitely paid attention to upper vs. lower balance shaft differences, and followed instructions from clark's garage and, I think, arnnworx - but that's not to say I managed to do it right, so I'll follow your procedure and see what that turns up

StoogeMoe

Never mind the description. A picture is worth a thousand words. This is what your balance shafts should look like. Note the "O" in the opening of the cover plate. (This assumes your tabs aren't broken on the cover plates).

John_AZ

JIK your rollers do not look like the above picture and you changed them in the last decade...

The small black mark on the top of the balance shafts is the keyway.



GL
John

f1rocks

Have you put the engine under load for a little while? You may be hearing some lifter noise. On my rebuilds I get a little lifter noise until I run it under load in medium rpms for a few minutes.

xsbank

Exhaust gasket leak?

zogster

So after a couple of hours tinkering and fiddling... points and prizes go to anyone who guessed lower balance shaft out of alignment! I must have put the sprocket on 180° out of whack when I did the big re-assembly.

I checked the TPS also, as per the Clark's Garage procedure, and it seems to be behaving as it should - so if the idle issue persists (I only had time for a very brief test drive today) I'll look harder for vacuum leaks, or maybe just replace all the larger bore vacuum lines (and perhaps do the venturi delete thing).

The beating noise is still there under acceleration, and I can hear it a good deal more clearly now. The lifter noise explanation sounds plausible, especially as I'm not 100% sure I put them all back in the same locations in the cam tower (after a couple of weeks sitting in engine oil, the Sharpie numbers I'd scribbled on them had mysteriously disappeared). I may try and post a recording of it if I can get a clear one.

The boominess/throatiness that I thought was more prominent before has definitely eased off, but I think there's still a little there. I did re-use the exhaust gaskets so I guess it's worth checking those...

Thanks to everyone for their advice and input.

spanky

Grt news and good work!!

MAGK944

So what's my prize

Glad you got it sorted.