What have i done wrong now?

tom_babbs · Oct 20, 2012

1989 3l s2 in 1983 car.
Recently i have changed my head gasket, during the disassembly process i managed to break the inlet camshaft. Which rather mucked up my plan to reassemble with all of the timing points marked carefully with tipex.
Anyway i purchased a replacement camshaft and gasket set and re built the engine last weekend.
Got it started monday night but the timing sounded a bit out.
Went for a little drive on tuesday and it had a massive flat spot in the power.
Today re set the timing and i have slightly improved it but i still have terrible power from 3000rpm up. It sounds alright but when driven it just wont pull.
I have checked for vacuum leaks as that is what it feels like but nothing obvious.
Also it turns over very slowly when cranked.
Is this all pointing towards the camshaft timing?

Thanks for any suggestions Tom

bmnelsc · Oct 20, 2012

Firstly lets hope you were supplied with the correct cam - that would just be plain awful.

You don't say if you went through the complicated camshaft timing process as described in the Porsche manual so I would suspect a timing issue. I haven't had mine off so this is NOT from direct experience and there may be shortcuts to the Porsche procedures.

There are a couple of things they talk about - e.g. how to orient the cams so the slack is out of the chain (when at 10 before TDC on no.4 IIRC) which gives the appropriate slack in the chain for the tensioner to take up while ensuring the cams are the correct number of links apart on the drive gears - I believe this is the only point where ALL the valves are nearest to closed. Then once you have the cams back on you need to set the cam timing with a dial indicator on the exhaust cam which correctly orients the timing belt drive gear to the cam.

I'd read through those sections - it might give you an idea of where you may of gone wrong. Good luck....

robdimond · Oct 21, 2012

Tom.

Sounds like you need to follow the factory procedure. It's difficult to understand what the manual is on about, but this video series for the 32-valve 928 makes it clear:

http://www.youtube.com/watch?v=0qoZTKL8rU8

Would be difficult to be accurate enough anyway I think with Tipex marks.

Looked back at your earlier thread and now I remember it... did you find the missing chunk of camshaft or did the PO just put in a broken one!

Rob

tom_babbs · Oct 21, 2012

I found the missing piece, must have broken it whilst stripping it, doh!
Had another fiddle with it this morning and i have now got it running nearly right, got good power low down but really comes alive at 3500rpm, feels like my old fto that had variable valve timing.
Might try and get hold of a dial indicator and measure the dwell(?), or i might just tweak it and try it until i get it right!
Either way it is very close now and the car is at least driveable. Yay

tom_babbs · Oct 23, 2012

Think i have it sorted now, final little tweak tonight and i seem to have nice smooth power throughout, yay!
All the reading i have done about timing etc might have inspired me to try and improve on the existing system, i think replacing the afm with a maf and installing a tuneable chip (like the setup in the link at the bottom) might be the way forward, but i should propably do some work on the handling first!

http://www.roguetuning.com/free_944_tuning_tools