Aatos

Prelude:

I swapped in a 'new' engine and had it's heads worked (new valve guides).
After completing the job, the car has been running poorly, noticeable roughness and poor performance. I immediately checked the cam timing with porkens 32V'er, and everything seemed to be in order.

I've finally had time to look a more into this and checked plugs and compression:

Passenger side bank - all plugs look good and consistent 14k compression.
Drivers side bank - all plug oily and consistent 8-9k compression.

Well that explains the roughness, it's running on mostly 4 eh

I also removed cam cover and everything looks nice and clean inside. Some theories I have:

1) Blown rings on drivers side pistons
2) Weird problem on drivers side head gasket, installation error?
3) Too worn valve seats on the head, causing the cam to press valves open too early.

Anyone got ideas? I'm gonna obviously remove the head, but I guess I should atleast verify cam timing again before doing that.

Mrmerlin

did you measure the cam timing in relation to each cam IIRC there should 7 links between the two index points on each cam. If they replaced the guides then they would have had to cut the valves to the seats

WallyP

I agree with Mr Merlin - it almost has to be a cam timing error or clearance error.

Jim bailey - 928 International

The Porken tool measures two of the 4 cams I also recall that some FACTORY cams were missmarked and when you install according to the casting marks to time the cams on the chains it comes up wrong. Try using the dial indicator method to check the cam timing. Also a leakdown test would confirm that the pistons and cylinders are OK . Best to KNOW that before you start tearing it apart.

Aatos

I counted the links, seem to be ok. I shall try to lure vilhuer to come do the timing measurement with a dial before I proceed with the teardown.

Aatos

Do you know if there's more information about this somewhere? I tried searching bulletins and campaigns on Jim's CD's but no luck

RyanPerrella

Jim,

Never heard this before. Do you know what years would have been effected?

Jim bailey - 928 International

One of the TSBs as I recall and early S-4 cams ..... I have been doing this too long ....hard to remember what you read after 10 years or so I still see the photo in my head just not the details.

docmirror

Low compression on all jugs in one bank can only be cam timing. I would say ignition, but that's rather unlikely. Use a dial indicator to degree the intake cam. The WSM has some bizarre wording to finding the right plunge measurement. Search on my name a few months back for the definitive answer to the correct way. I think it was Mark K that finally explained it clearly for me. The pre-load method sucks, just do the total plunge method to find the right setting, starting at the heel of the cam.

Mrmerlin

as prelude to remoing the cam covers look into the fact that the timing belt is on the correct way and all of the timing marks line up, is it possible that one of the cams is cracked? and thus has moved?? .The driverside drive cam is know for cracking in the snout area

GregBBRD

Jim Bailey...as usual....is correct. There was a batch of cams that had the timing marks either miss marked or completely missing. I can find the bulletin, if you are interested.

Just find the lobe centers of the intake cams and compare it to the book specifications....the odds of having rings bad on one side of the engine, and all bad by the same amount is.....very, very low. If the valves did not get bent on the installation...you should be able to solve it with the cams.

Aatos

Greg, it would be great if you could find the bulletin!

Aatos

Someone kindly sent me the bulletin, it's number 9008 and concerns '89/'90 928 GT camshafts. I doubt that I have GT cams but is there a way to visually distinguish GT/S4 cams?

edit: link to docs timing method

Aatos

I finally had the opportunity to measure timing with a dial today. I did the measurement twice, and in both times cylinder 6 intake lift was 1.6mm ± 0.05. WSM gives 2.0mm ± 0.1 for the 5-8 cylinder bank so it's way off.

I'll re-measure exhaust timing tomorrow with 32V'r, but for now this is kind of puzzling as the cam gear marks are spot on now at TDC and I did measure timing twice with 32V'r when I assembled the thing. Is there a way to measure the exhaust cam timing with a dial?

Aatos

I checked exhaust timing with 32V'r and it was spot on in the middle. I also re-checked that the marked links in chain are on correct spots and that there's 7 links between the markings.

Very puzzling. Ideas I have:

- Stretched chain
- Incorrect cam or cams
- Alien intervention