blown 87

Thanks man, I will fill that out.

PorKen

You can, and I didn't?

You must do a Kempf check quickly, or the T/D will begin compensating for the twisting of the belt.

The measurements at installation are to check for mininum or maximum piston travel requirements. The actual piston extension will vary with the age of the belt, and the temperature of the engine.

SteveG

I must have misunderstood or misremembered your email to Rick Sobek; he queried you in November on this issue, after taking possession of the car.

vbatla

Before I mark the cams at 45 degree and remove the bottom cover, i noticed that (at TDC) the drivers side cam gear notch lines up but the passenger side is about 1/2 tooth off. Is this as close as it can get? Seems like one notch over would put it too far the other way.

Also, of what I can see of the tensioner, the boot is gone and there appears to be a wire/spring sticking out of the top. The belt service was last done approx 45,000 miles ago. The person who performed the service disabled the warning light.

Thanks for all the help!!!!

dprantl

The latest belt pictures posted by vbatla is exactly the kind of disaster waiting to happen with a stock tensioner system. The plastic bushings are worn causing the arm to tilt away from the engine and the belt is rubbing itself away on something. Run that car just a little longer and it's time for some valve replacements. This can never happen with a Porkensioner.

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

dprantl

vbatla, that is not good. The mechanic had no business disabling the belt warning, the stock system pretty much relies on it to ensure proper belt tension. I am also willing to bet that he did not replace the plastic bushings on the tensioner arm, which is causing this problem.

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

James Bailey

Blame that one on a bad design ??? operator error !

BC

With all respect to all opinions, you should be sure to include that the disaster is the dereliction in duty to maintenance, whatever tensioner is used - in that example. It doesn't matter is god himself did the work and replaced the parts - if they wear out, problems happen.

dprantl

Yes of course, I agree with you 100%. My point is that it is a bad design (apart from other reasons I've already mentioned) to have to replace all those failure parts, especially when there is another design that does not require any of it. Maybe it was good in the '70's, but not today.

You could say the same thing about Lucas. If you take apart every wiring harness every 10k miles and replace the wire insulation on every wire, the car will never have any electrical problems.

Or, how about a pure 928 example? The design of the water pump is bad. There is so little space for the impeller shaft that it is common for the bearing housing to fail and the impeller comes loose, causing all manner of serious problems. On other engine designs, this could never ever happen (well, maybe if you ran the same pump for 500k miles) because the design has a much larger impeller/bearing area. So to compensate for this bad design, the manufacturers state the maintenance interval for changing the pump is 60k miles, 50% less than others. Of course, if you follow this interval your car will be fine, but that does not mean it's a good design.

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

Landseer

There should be more people willing to argue, debate and redesign.

Keep the faith. Celebrate the differences. Good engineers often disagree. With passion.

Wish I was worthy of having a strong opinion, quite frankly. Let's remember protect all the creatives.

vbatla

Yes, it appears that the tensioner was in need of attention during the last belt change. I still haven't decided on the OEM tensioner of Porken's. Lots of debate in this thread. Pros & Cons for both.


I rotated the crank to 45 degree and marked the cams. You pros out there; do the rotors appear positioned correctly?


Also, notice the amount of belt play. (Last 2 pics) I could easily slide the belt off the passenger cam gear the way it sits. The tensioner roller is spinning freely. Talk about living on borrowed time!


One last thing: Is James Bailey the "Jim Bailey" that used to work at 928 Intl? If so, "Hello", I met you in Aneheim (928 Intl) back in the 90's. I was working on an issue with the cruise control. Thanks for all of the help with parts/diagnostics over the years!

Mrmerlin

you need to rotate the cams another 180 degrees from the pictures you posted.
The rotors will be at the 3 O clock position when the crank is at TDC for #1( this is viewed while looking at the front of the engine or said another way the rotors should face the left fender of the car.
The belt is most likely rubbing on the back side of the crank damper due to a bent pivot bolt or worn bushings or both, plus the tensioner roller is probably loose on its bearings

Mrmerlin

when the engine is at the 45 degree mark BTDC the cuts in the cam pulleys will be about 5 teeth before the cuts on the cam housings

jacal128

I an looking to redo the timing belt and water pump, the PO said he already did it but has no documents. All the other work he did was half *** at best, so I feel might as well do it while I am doing the top end. My question is is it worth rebuilding the OE tensioner or going with the PK tensioner. I can see good on both sides, I do have a budget and a lot of item I would like to do. Thanks Jack

Stromius

It's worth closely inspecting those cams gears. The teeth look cupped and definatley the annodizing is gone. Once they coating is gone, the cams wear down. Best to consider replacing them along with the oil and crank gear.

The 32V'r cam timing tool would make setting the new cams easy at 45' (www.liftbars.com).