924Board.org

Min

Well, I figured I should probably post this eventually, I need some thoughts on what’s happened to my engine, a few months ago (December, maybe November) I had my camshaft reground back to stock by a reputable place, and I had a group of cam followers Surfaced and polished. Installed those into my head, had them all adjusted to spec. Drove the car for awhile, it was great, the best I had ever had the car running in the time that i had owned it. Over time it slowly got worse again, started sounding weird (tappet noise). Opened the oil filler cap and looked at the first lobe on the cam, to my surprise it looked pitted. because of this I got suspicious and took off the whole cover again, to my amazement, my newly reground cam had 3-4 lobes extremely worn, one of them almost ROUND!!! .... Now this surprised me a lot, This pitting on the tips of the lobes has been described to me as 2 hardened surfaces hitting each other, My first thoughts were perhaps the place that reground the cam didn't know what they where doing, but I trust this place, and would like to think of other things that could have caused this kind of damage. I figured perhaps a oil starvation problem, but the oil tube is clear, and when the car is running, when I take off the oil filler cap their is plenty of oil coming out, not to mention the worn lobes seem random, the worst one is the intake lobe on number 3 cylinder, one of the other bad ones is the intake on Cylinder 1 (which I definitely know is getting plenty of oil) ... The only other thing I can think of (which I've never replaced in this car) is that the valve springs might be weak, and some of them are floating and impacting the tips of the lobes as they are spinning, What do you guys think? ... I don't want to replace my cam and have this just happen again.

Min

Min · Posted: Fri May 20, 2005 5:28 pm Post subject:

Note, I've also rechecked the adjustment of my followers, and its as I had it set when we installed the cam, all the adjustment screws have at least 3 threads of adjustment. (we installed the cam with the head off, and spent alot of time making sure the adjustment was good).

Min

Ozzie · Posted: Fri May 20, 2005 5:31 pm Post subject:

Unless the case hardening on the lobes wasn't done properly you have pretty well answered your own question.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Paul · Posted: Fri May 20, 2005 10:56 pm Post subject:

I'd go show it to the place that ground the cam.

D Hook · Joined: 02 Nov 2002 Posts: 3158 Location: Omaha, NE

I read on Rennlist on the 928 page about guys having the same problems on 928's when they'd get their cams redone. Something about the way they do them doesn't create the same hardened surface as the billet (?) cam from the factory. IIRC, the cam is built up with a weld and reground from that. The weld doesn't have the same strength maybe? I'm not sure of the process myself but I remember reading about the same problem over there.
I'll try to find the thread. Or you might want to go over and post it on the 928 board and see if anyone can help you find a good place to have it done.

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

I've never heard of anyone having success in cam followers Surfaced and polished.
They usually go first then your cam.
I bet the followers were bad not the cam.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Paul · Posted: Sat May 21, 2005 3:04 pm Post subject:

It's most likely a soft cam since there's no sign of the lack of oil.

If we accept that lubrication is not the problem, it doesn't matter which one is harder, both the cam and followers should last for years and many miles.

As stated before, take it back and insist on another one.

Min · Posted: Sun May 22, 2005 10:05 am Post subject:

so you guys don't think weak valve springs could have caused this problem?

Min

Gram · Posted: Sun May 22, 2005 10:35 am Post subject:

Can't see how weak springs have anything to do with it.
_________________
'82 924 NA Euro (hers)
'98 Audi A4 TDI (ours)

Min · Posted: Sun May 22, 2005 10:56 am Post subject:

reving to 6k rpm, valves floating and smashing the followers into the tip of the cam. ... or no?

Min

Gram · Posted: Sun May 22, 2005 11:03 am Post subject:

Oh..umm..dunno.
_________________
'82 924 NA Euro (hers)
'98 Audi A4 TDI (ours)

Lizard · Posted: Sun May 22, 2005 11:40 am Post subject:

no, either caps or cam.
_________________
3 928s,

leadfoot · Posted: Sun May 22, 2005 7:45 pm Post subject:

Sounds like they didn't do a very good job at hardening the cam after they ground it.
Mine was ground and hardened and has been in the car for over two years now and has no signs of wear in it.
What process did they do to harden it??
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...