GregBBRD

I just read your thread. You had a very loose belt, for it to be hitting the cover. Tough to imagine the belt light not coming on...I'd be "testing" that circuit, when the car is back together.

If you had a piece of almost anything (except perhaps rubber) come loose, you should be able to see "witness" marks on one of the gears, since that piece would be run between the belt and that gear. Perhaps the damage is simply from the belt jumping over the crank gear.

Any mechanical overrev that caused damage would cause "instant" results....immediate feedback, as the engine quits.

How many total miles are on your car?

Charley B

66,000 total miles. Quite a few miles after over rev. incident with no indication of power loss.

mark kibort

As GB says, all very very rare failures if any. tensioner arm bushing? nah
pulley bearing? naha, makes a lot of noise first.
shoulder bolt fails? nah, not if the owner tightens it right or doesnt strip it out to leave it to fall out later.
water pump failure? nah, makes noise first (usually)
camshaft failure? sure, if the numbnut tensions the belt too much.
OIL LEAKS OUT? not a factor by any stretch! oil just gets the heat to the wasters quicker to change tension for block expansion. eventually this happens without the oil too.
belt juumps when cold? unlikely.

kempf tool is new!
kempf gauge is reading WAY high but ive proved why this is happening with the old belt vs new belt differences.
I can get that high reading anywhere on the span, but the place im checking it is correct. just before the center cover side area. just above the air pump bracket.

lets just calll the torque vs force measurement, really work! (force x Distance)



again, a solution looking for a problem. however, it seems that the PKtensioner is a maintenance free set up. I just dont know how it works under race conditions with frequenet fast blip engine rpm changes.

bliping throttle was my cause for skipped two teeth, and High revs period. tension was fine, but it still happened once in 13 years of racing. fluke? who knows. we retimed it and the car peformed fine at that point further for years!

I forgot my 4 years of German. what does this say. twist the belt 90 degrees by using force as much as you can?

mark kibort

ok, back to the situation.

what would all you folks do. Greg? what would you do?

use the tool, on clearly something that makes the effective tension well beyond that of the S4 and early, but not OB cars?

again, the 3.0 on the tensioning gauge is a full window past the normal tension setting. i dont dare set it to 4.0 as the spec shows, as it will have near double the tension of the S4 or pre S4 with HTD belts.

what would you do? use the porsche tool? use the kempf tool? go middle of the road for both?

Black Sea RD

Porsche stopped using the simpler version of the timing belt tool and adopted the more expensive and more precise 9201 tension tool for setting the timing belt tension early in the 928's history.

This tool also comes with a testing gauge that you use to test the accuracy of the tool before using.

The older style tool which was replicated by respected long time 928 owner and guru, Jay Kempf, was adopted by many since it's easier to use and cheaper than the 9201 tool.

However one has to respect the fact that Porsche stopped using the old tool for a reason and started to use the 9201 tool exclusively.

We always used the 9201 tool to set our timing belts in both our 1989 928 daily driver and our 1986.5 track car, both of which we had for years. Never a problem noted with our timing belts.

Mark K., just a remnder that not all water pump failures start with a noisy water pump. Mr. Veningers track car had a water pump fail by the pulley coming off the shaft with no forewarning.

Best regards,

mark kibort

Yes, porsche changed to the newer, more elaborate tension checker, BUT, i wonder and have reservations about the coorelation of the old belt tensioner and the new one. 4.5 is the setting on the old belt according to the WSM, and 5.0 is for the newer 928s (HTD belts).
as you clearly see by setting the belt to 3.0 with the new gauge, that correlates with almost off the chart on the Kempf tool, which when used on the HTD belt, is almost a direct converson for its window and 5.0

im very temped to do a quick change to the round belt as an experiement to see the difference in tension.

Also you can see from my tests that the actual tension of the belt is much higher with the old belt at 4.5, or even 4 based on the size of the teeth difference on the belt itself. the belt difference alone is worth 1.5 points on the meter scale. So do we think that the old belts need more tension than the newer belts?? the fact is, barring that gauge of mine being WAY off, this is what seems to be the situation.

as far as calibration. I have the 4.0 bar insert to calibrate the gauge. its dead on. All i really need to do is test my S4 , whch is due for a check (though i always check with my peak hole method which is pretty close to know if there is a major probem without removing a cover) and then i can correlate the gauge and the kempf too. if i test an they are both coorelated with each other, what would you do???use the kempf tool, that is not effected by belt rib thickness? or use the guage, that clearly will give a much lower , up to 1.5 points, on the gauge with use of a the OB, old style square tooth belt.

as far as the water pump losing an impeller and grenading an engine.... that is very rare and has nothing to do with the tensioner.

Charley B

Mark, why would you torture yourself beyond this conclusion?

Black Sea RD

Mark,

I would defer my comments as to what you should do to what Greg B. has already explained and offered to you in this thread.

Best regards,

mark kibort

Greg, as respected as he is, may have not thought of digging deeper to see what the tool actually does with tension. after all, there are few people that haved horibly worn gears or belts that slip. Im sure greg knows that their could be differences that are overlooked by many.

will the belt on the old buggers be over tensioned with the tool? certainly seems so. is it a problem. i guess it depends on some other factors, but if you have seen the tension on a stock HTD car, with the tool vs the 9201, and saw what ive seen with the OB belt tension using the 9201 and then comparing it to the kempf tool, you to would wonder what to do. Im sure Greg is wondering as well. I lean to the kempf tool, once I verify it is the same at 4.5 to 5.0 on the porsche gauge on my S4 or scots euro with HTD pulleys.

I have a pulley that looks like it was run by a belt made of acid. i want to say the carve out area is about 1/4" deep. i cant help wonder if the old buggers that are adjusted by shops that use the porsche 9201 tool, are not grossly overtensioned.

im beating myself up on this, because this is petty's motor, and i dont want to take any chances. i like the kempf tool, but also like the 9201. However, ive never seen this disparity in readings, SO, why wouldnt i question it. has no one else questioned it? anyone else know that the OB belts vs HTD are 1mm differnce on the roller that fits into it on the 9201? that the difference would account for about 1.5 to 2 on the meter? pretty simple! you can check this on the meter itself.

has anyone seen a pulley that has been subject to over tension??? maybe all the coating problems have been due to over tension.... HMmmm

GregBBRD

Truthfully, if I was assembling any kind of a high performance engine, I'd use all the pieces from the newer design and use the later belt. The advantage in more stable cam timing and igniton timing would be worth the extra expense.

That being said, I've tensioned many, many early cam belts with my 9201 tool and have had no problems....ever. I tensioned Jim Bailey's early cam belt just last week, using the 9201 tool and had no issues. The "factory" specification for the 2 valve engines is 4.5 "belt units". I've always used this number.

mark kibort

Greg, i get this. Sure, you are building the best stuff and will use the best stuff available to avoid any possiblity of issue.

however, just because you have trusted porsche with the conversion, doesnt make it correct for the older bugger. after all, we are talking about a pretty good design here to start. Im just concerned, and rightfully so, that the tool will over tension the belt. 4.5 units creates an OFF THE SCALE tension on the tool, for the OB design. well off the scale! Now, have you seen any issues with the "Brown car" of Jim Bailey?? probably not. after all, we are talking a pretty soft belt and metal pulleys. BUT, what would it cost to just investigate a little further as I did. reverse engineering of this type of mechanisim is not rocket science. AFTER ALL, didnt you and I agree that the porsche engineers are "CEMENTHEADS" when they designed the piston offsets for the 2 valve engines???? that seemed brain dead simple to me, and we corrected it and made a much better engine rebuild doing it the "Right way".

So, again, i just measured the set up im buildig at 4.0. its so far off the kempf scale it isnt even funny. So im going to back it off a bit or pretend i didnt even have the porsche tool. (of course after I calibrate it with my S4 using both tools to make sure they are equal on my car as far as values)

I dont want petty's engine to have cam pulleys that look like this!!!
(off a euro set of cams i got when i built my first euro /US 4.7) notice the deep grooves!! maybe that CementHead used the tool on that car too!

Mk

mark kibort

Greg, let me also ask you about the proper techique and reading of the 9201

Do you press on the body of the 9201 and then when you click the vertical slide into place, measuring belt tension, so you read the value that the max needle will read, or the final resting value that the measuring needle reads as you let go of the device???

in other words, when measuring the tension, there are two needles, one max and one actual. when you click in the measurment, and release the max value is higher than the final resting value and they are about 1 full point off each other.

Anyone can chime in here too!

as a side note, the pulleys from the euro that i showed were aluminum. the pulleys on the Petty motor here, are steel. both are OB style, non-HTD belt design. when did they change to steel?? or visa versa?

andy-gts

I used the Kempf tool twice and the tension belt kept coming on....brought it to mechanic with 9201 tool and was way low. he verified the kempf was way off.. that was mo in wichita and I sold the tool promptly....may be the kempf spring needs to be stronger for the proper calibration..I dont know but it didnt work well at all

mark kibort

well that certainly wasnt a good endorcement for the kempf tool. ive always been a litle suspicous of it, but like I said, i calibrated it to be at 5.0 at near max window, so mine was pretty close.
there needs to be a force or torque value for it so we can check it. i.e. get a weight tie it to the gauge like a spring scale and provide a calibrated value . Ill do this when i corelate it to the 9201.

Vilhuer

AFAIK Porsche invented 9201 for 944 cam and balance shaft belts and only aplied it to 928 as it was available. Other simpler tool was never replaced in a way that it could not be used anymore. Porsche just expected every shop to have 9201 so they did not bother to update other tool when later MY 928 had HTD and 32V changes.