dprantl

Fixed. Cams were one chain tooth too far apart. Don't ask me how that made the car run so crappy. The OP may want to change the image that I used as a comparison in one of my previous posts. I don't know if it's an optical illusion or what, but that pic the exhaust cam marker looks like it is pointing to the middle of a chain link. That's exactly how I set mine and it was off.

Dan
'91 928GT S/C 475hp/460lb.ft

FRporscheman

While reading your posts I was thinking you might have had a cam timed wrong. I'm glad you got it fixed, and I'm glad it didn't hurt anything!

I think the pic is fine, the arrows point directly to the tooth that goes into the middle of the blue chain link. Maybe it moved or skipped while you were handling or installing?

RajDatta

Dan, consider yourself lucky you got out without any damage. If I remember correctly, there are 18 teeth to each cam which would equate to approx 20 degrees per tooth. You could have easily bent valves if you were a full link off. The fact that you were 1 chain tooth apart would mean only 10 degrees approx. One more chain tooth and BANG!
It's important to make sure you are 7 links apart on the two cam marks/casting lugs. The cam marks have to be in the middle of the marked links, in or out and you could be a full chain link off. Consider yourself very lucky.
This picture is a good example of that.


Regards.
Raj

dprantl

Raj, the picture above is perfect. I was referring to the one I attached before. I marked it now, check it out. Doesn't it look like the exhaust cam is pointing to the middle of a link? On the bottom part of the image which shows my engine, I thought I got it precisely the same as top part of the image that was taken from the beginning of this thread. I'm not sure why I used that image rather than the one you just linked, maybe because the VarioCam tensioner is collapsed in that pic and I wanted to see one of the VarioCam in the same position as mine was...

Dan
'91 928GT S/C 475hp/460lb.ft

RajDatta

Dan, I see what you mean, probably not the best picture to use for this job. The one I posted above is an excellent example. Also, looking at your pictures more carefully, I can see that you were 1/2 a link off on the exhaust side. You were not between the 7th link but instead between 7th and 8th link. Fortunately, you were only out on one side which saved your valves.
If you look carefully, the top picture has the cam turned a bit but the cam mark does point to the middle of the link, unlike the picture on the bottom.
Raj

grey ghost

Great write up, I will use it when I get my 94 back together.

Went to do a timing belt this past weekend and pulled the valve cover for inspection and found that i am missing quite a few teeth on my camshaft sprockets. Thinking I might as well do a head job while I have the car down.

will do a leak down this weekend. to see if the rings are any good. current mileage is a little over 200k on it.

FRporscheman

My '95 had about 180k on it when I rebuilt it, and it actually did benefit from new rings. I could feel the difference. Especially compared to my '93 with 240k miles which has about half the power .

grey ghost

did my leak down test this weekend this is what we found.

Cyl #1 leak down at 6 %
Cyl #2 leak down at 15% with oil in cylinder it was 12%
Cyl #3 leak down at 22% with oil in cylinder it was 11%
Cyl #4 leak down at 14% with oil in cylinder it was 9 %

the current plan is to get the head done. the question is do I do just new rings? or pistons and rings
will put new rods and mains either way.

thanks for input.

FRporscheman

Of course it depends on the condition of your pistons... but in general you could reuse the pistons, no problem.

The following is from http://www.lovehorsepower.com/MR2_Do...wn_testing.htm

"Listen for leakage at the following places:

* Adjacent cylinders sparkplug hole. Use a piece of small rubber vacuum hose, stick one end near the spark plug hole and the other end in your ear. Leakage, air hiss, heard here may be a blown head gasket between cylinders or it may be leakage heard through an open valve.
* Exhaust pipe. May indicate a burnt or stuck exhaust valve.
* Carburetor or throttle body. May indicate a bent or stuck intake valve.
* Oil filler or dipstick hole. May indicate broken rings or a damaged piston.
* Radiator filler cap. Bubbles here will indicate a leaking head gasket or cracked head.
"

C5Driver951

This DIY is a great write and was invaluable in making the job go a lot smoother... Thanks Arash!

The only thing that should be corrected on the original write-up is the 12mm cheese head is actually a 10mm. I have an 8,10, and 12 now, but the 12 was not used.

Great parts list too.

I would HIGHLY recommend timing the cams when doing this job. It made my car run smoother and stronger when I was done.

If you're in the Central Jersey area and you need any of the 944/968 specific tools, I'd be happy to loan them out or help. Oh, and dial gauges are cool. This was actually an interesting project, seeing how the whole VarioCam system worked when putting pressure on it and removing it.

Thanks again,
Joel

odurandina

FRPorscheman, Raj, killer thread...


Porscheman, are you kidding about your '93 and epic power loss ?


can you talk briefly about what's been done with this car to get it that far as a daily driver ?


i'm fortunate to have the owner of a certain white 968 Turbo S doing this chain, front seals, H20 pump and belts !


i'd be lost.

FRporscheman

I'm glad it worked out for you Joel. I'll go fix the mistake! A properly timed cam is easy to accomplish, it's not magic like some people think!

Being completely frank, my '93 has about 165-170 psi compression. Before 3000 rpm, the car barely has enough power to accelerate uphill. Past 3000 rpm it feels like my 944, maybe slower. After 4200 when the intake resonates, it feels slightly better. The cams are timed right, the head is rebuilt, the head was shaved a couple of thousandths, and I used a 1.4mm (or 1.6mm?) headgasket. It's slow. It has koni yellows, 250# springs, 245/255 pirellis, and it's still more fun to drive my factory-stock 944.

odurandina

sounds like it was driven hard but well-maintained.

why chance damaging the block or the crank ?

i realize it's a lot of $$$ but why not just do a rebuild ?

potent951turbo

Are the pictures down or is it just me?

ernie9468

They are down.