michaeldean

Guys:
After changing my 951's rod bearings, head gasket etc, I now have a misfire and harsh clattering noise at about 4000 rpms. The idle seemed perfect - nice and smooth and the car runs well up to 4000. When you hit 4000 and the misfire develops, I can let it return to idle and the misfire vanishes quickly.
Compression is approx 110-120psi on all cylinders.
So, I removed the cam tower tonight and found 2 lifters were soft.
Is it possible that these symptoms can be caused by bad lifters?

Cheers,
Michael

triscadek

I've never had this happen with my 944,but I had a 70's V-8 that ran very low on oil, the lifters constantly clicked and would backfire through the intake when I accelerated.

This only happened once, but that was how it went then. FWIW.

michaeldean

Thanks for the info - in essence, I'm trying to decide whether I should replace one (or all the lifters) and test again, or remove the head (without testing the new lifters) to see if I screwed something up during reinstallation ... or the machine shop messed the head up in some way.

It seems very unlikely to me that these symptoms could be caused by a soft lifter…

Cheers,
Michael

M758

The clacking can be caused by bad lifters. Not so sure about misfires though.

SoCal Driver

You did get all the lifters back into the same bores they came out of???

Bryan

Is the misfire rhythmic? I would think a bad lifter would cause a rhythmic misfire.

Bryan

"At Porsche, we only make sports cars"

M758

[quote]Originally posted by SoCal Driver:
<strong>You did get all the lifters back into the same bores they came out of???</strong><hr></blockquote>

I talked to my father about this issues of liftera in the same bores. As I am doing full rebuild I was careful when removing my cam housing to ensure all the lifters stayed in the same bores. After this I asked him his opinion of this and he said there is no reason do worry about which hole they came from.

Now most people may think "well what does he know" I trust him not just because he is my father, but because he was a Mercedes Benz Master technician for over 30 years at local dealerships with the last 14 years at the same one. I am pretty certain he knows his stuff. Maybe not everything about Porsches and the 944, but about general German engine design he does.

My point don't worry about which hole the lifters came from. I did not when I did valve stem seals on my 944 Turbo 2 years ago to no ill effects. It does not mean that the two collapsed ones are not bad or that the went bad for any reason onther than normal wear.

SoCal Driver

Well who can argue with those credentials!

However I will.

Each cam follower, "lifter", can be adjusted in height separately.

Each cam follower, "lifter", will take on a different wear pattern than the one next to it.

Each cam follower, "lifter", will wear inside, where the spring and seals are, differently.

Randomly exchanging lifters may more so than may not cause future problems.

My basis is working on all sorts of cars since the early 1960's and owning and working on my 944 since 1985.

But you did take precautions to keep them in their same bores so it's possible that the oil pressure to the lifters may be restricted or bypassing or the lifters may have given up.

Your oil pressure can read ok on the block as it comes out of the oil pump but not be sufficient at the cam galley. Think there is a rubber seal or two that has to mate the cam galley with the head besides the flat gasket. Kind of like the old VW oil cooler seals.

You can try one of the after market lifter cleaners. The one you put in and drive for a few miles before changing the oil. Even the first change of oil after a rebuild can quite the lifters.

michaeldean

For the record, yes, all the lifters went back into the same bores they came out of.

SoCal Driver

Good.

How about the timing belt? Are you one tooth off?

Could do what you report.

Gerald Allgire

When I got my 84 it clattered and missed intermittently. That turned out to be two bad lifters. I was pretty sure which ones they were with the old screwdriver to the ear trick. When I took it apart those were the only two lifters that I could collapse. That was 2 1/2 years ago. I only replaced those two with the intention of replacing the cam with something bigger when the others died, but as luck would have it that hasn't happened. For the record it can matter which lifters are placed on which lobes. I say "can" because if all the lifters and lobes wear evenly then you can usually get away with mixing up the lifters. I don't recommend mixing them up, but I've built some pretty cool stuff from what's left in the motor pile. I even had one motor that had lifters from three different motors and a cam from another. That motor ran for several years. Sometimes it's fun to see just how far you can go before "it" goes.

michaeldean

Having the timing one tooth off was actually the first thing I suspected and double-checked. I'm quite certain that both belts are correctly aligned.
I'll try replacing the two collapsed lifters and see if that solves this.
Cheers,
Michael

SoCal Driver

Another cam related item that causes noise is the cam gear comes loose. The almost blown engine I pulled from my 83 had a loose cam gear. Wasn't my problem; just found it.

michaeldean

That is a possibility ... when I was working on the head, I wanted to change the cam sprocket oil seal. I took out the small bolt on the side of the shaft, extracted the end bit where the rotor is fixed. I put so much force on the cheese head bolt trying to get it out that the (new) torx bit sheared right off - the cheesehead bolt appeared undamaged.

Since my cam oil seal was not leaking, I decided to leave it alone. Perhaps it loosened just enough to allow the cam to turn independent on the sprocket?
Is there not a keyway in there, which would prevent one turning independent of the other?

Cheers
Michael