Let he/she amongst us who has never commited a brain dead act upon their 928 cast the first flame .....
Ah .... not going to be me.
With rad cap on, the max boil over point is ~110C/232F: To cook a TB to even a 'rare' state would take more than that - that is just a parboil.
If the pump were 'dead headed', or discharge passages blocked, it would not take long to overheat and spurt coolant out the relief valve/cap: the rad would not get up to temp, hoses would stay cold, etc.
If the pump suction were plugged, much of the same except there would be no cooling of the pump bearing/seal, and the pump would cavitate, bearing get hot - maybe even moan - but the engine would still overheat and puke coolant!
Would the alleged hypothetical DIY person referred to have left nappies in place after the 1st new pump, or the 2nd? (If it were both, I'd be thinking of a CAT scan for brain stem injury ).
In any event, draining coolant should show something were any foreign material present, unless the paper were as strong as cloth - but if normal temps were achieved with firm hoses and a warm rad, things would seem to be OK!

 

You know, at least that one would make sense. It has to be something IMHO that is linked with the work performed. I would really like to hear about the IR temp. on the pulleys etc.

Regards,

 

Goliver wrote:
I'll finish the pinch collar adjustment / readings tonight, and read the temps on the T-Belt pulleys this weekend with the Laser Thermometer.

Garth wrote:
What if the discharge passages passed the towels on through the holes into areas elsewhere (block?) Also the temp looks great on the dash gauge, no overheating, no spurting of coolant out of relief valve, etc.

Garth wrote:
Phew! No cat scan needed. My .01 percent chance of leaving paper in was during the 1st original WP replacement, definitely not after the 2nd WP installation. I made an effort to inspect the coolant, WP, and passages. What I could see was no paper traces on the WP impeller, passages, coolant was clean as a whistle.

Garth wrote:
Paper seemed to be really strong when I tested a piece in a bucket of drained coolant (insert ad / plug for Brawny Towels here). Definitely normal temps, firm hoses, fan and T-Stat cycling. If towels were in there, me wonders what kind of flush it would take to remove the evidence? Not that I did it or anything...

 

Rob, just out of curiosity, where are you checking T belt tension with the Kempf tool, and have you had anyone drop by yet to verify proper tensioning yet?

 

Bill Swift wrote:
Checking tension halfway between the cam gear 1-4, and the idler roller (right before the center T-Belt cover). Yes it's the Kempf tool. No second set of eyes yet have dropped by, but the invitation is definitely open (and welcome).

Thanks

 

Been reading this thread (sorry for your trouble) and as it turns out, just had the t-belt in my 78 replaced today and guess what... Is the moaning in your car constant or just at idle? Certainly not intending to highjack this thread but, there is a moan, ever so soft when idling but the instant you touch the gas pedal it stops.

 

Chuck - Looking at the pics of your GTS makes me want to trade up - really bad! Guess I should fix what I have in the meantime. I want to diagnose more today. Once I have done that, I'll pass along more detail on the moaning characteristics. Thanks

Guys - What if the coolant softened up the towels enough to allow them to pass through the WP passages down into the block area? You think it would still create enough backpressure to fry water pumps? Not that I did it (left paper towel in there) or anything....

 

Rob, you're scarin' me...

 

Sharkskin wrote:
Hell I'm scared too! In 7 or 8 Motorcycles, and probably 15 or so cars over the years, never has a DIY project been so scary / stressful, especially since it is the beloved Shark!

I just did the pinch collar adjustment minutes ago. The collar moved back 0.9 millimeters. That is within spec - correct?

 

Correct, in that 0.9mm is a small amount - and that is a very good indicator: the critical measure, while you are there is the crank end float.

 

I'm going to try and assimilate all of the data I have gathered yesterday on the T-Belt job, and in a nutshell wrap this thing up in a post later today or tonight. There is some very interesting data indeed.

Things are also looking very positive at this point.

In the meantime, can somebody pop their air intake tubes, and point a thermometer in the cam cover breather holes and see what kind of T-Belt temps they record? It would be nice to have some data to compare to.

Chuck Z and Garth, you have PM's.

Thanks

 

Plugging the water passages would not cause enough back pressure to cause pump problems.
In fact, on older cars, and maybe the 928 as well, when the thermostat closes, it blocks all flow of water.

 

Let the driving begin!

It appears all was fixed way back when the bad Genuine Porsche new rebuilt Water Pump was replaced. And since then have I been chasing down a problem that wasn’t there (can you say “over-analyze”).

A little background:
After the T-Belt, Genuine PCNA rebuilt WP, rollers were replaced, and tensioner rebuilt, a rather pronounced moaning noise was emanating from the front center of the engine.

After inspection, the T-Belt was getting way too hot, and the belt was wobbling fore and aft on the cam gears. Hence too much stress on the belt, and the much-exaggerated moaning sound apparently from the belt itself.

Second go around: Replaced tensioner and belt again – no difference. Drats….

Third go around: Replaced WP once again – moaning apparently softer in volume, and no more hunting of the belt. Impression still being left on the back side of Tbelt though after stopping motor, and belt parking on the tensioner roller and WP pulley. Double drats….

Here’s where more research (and help from you guys – much thanks!) wrapped up the project as completed:

Take a brand new T-Belt that is cold, park it on the cold Tensioner Roller for a few minutes (in my case I gave it about 15 minutes). Roll the belt off the roller, that section will have a definite impression (who would have thunk it?)! The impression is so pronounced that you can feel the ridge where the Tbelt was over the center groove on the tensioner roller, and is very visible. Do the same thing with a hot belt and roller, and the only difference is a sheen appearance added also. Since a used T-Belt has this same sheen, one can only conclude from this that: 1) The back side Tbelt rubber is semi-soft enough to actually compress a small amount when new, and when parked against the WP Pulley or Tensioner Roller. 2) The sheen is normal, since a used Tbelt has this and is much shinier than a new belt (flat black appearance).

At first I was petrified to see the impression and the shiny spot on the TBelt, but once I realized it also occurs when cold, then you could conclude that this is just a normal characteristic of the new Tbelt. And yes, the tension setting was perfect.

So if you’re doing a TB job, and see a groove made on the belt when manually turning it, this may not necessarily be bad. One for the knowledge base…

Also since the moaning is still there but much softer, one could conclude that the reduction in noise was a direct result of a Water Pump that was going bad. A lot of posts mention a little moan is normal when the Tbelt is replaced. This has to be the case, since less stress on the Tbelt occurred after the bad WP was replaced, and a subsequent reduction in the moaning occurred at the same time. This proves that the problem is not a bearing, or other such issue, since the noise dropped in intensity some, when the bad WP was replaced. Another one for the knowledge base…

I also took temps with the IR Thermometer with Center TB cover removed (very cool to watch the belt do it’s thing). WP pulley was warmer at the pulley belt surface area, than at the impeller shaft, thus bearings not heating up, and the new pump is fine. Pulley was at 170 degrees Fahrenheit. Oil pump was an almost identical 173 or so degrees. Crank gear was the hottest about 178. The belts hottest spot was 174 right after passing over the crank gear. I’m guessing these numbers / readings are ok.

What I thought was really interesting and amazing here, is how fast the Tbelt changes temperature from one area to another, in just a matter of nanoseconds! The belt is 174 over the tensioner roller, then cools to 168 over the pass side cam gear, rises to 170 at the WP, drops to 165 at drivers side cam gear, rises to 168 after the oil pump gear, then repeats all over again on the next revolution. The temperature spread is basically 10 degrees in one revolution of the belt over a split-second’s time. Cool…

Anyway I’m posting the summary in hopes of helping another 928 DIY’er in the future, so he / she doesn’t have to go through the same dilemmas I just went through, and to hopefully add a couple of things to the “Knowledge Base” for our beloved Sharks.

BTW – No paper towels left in the motor behind the WP, sorry I was just grasping at straws at that point! Phew!!

HTH…

Rob (Can now do a TB / WP job with eyes wide shut, and the wallet really wide open).

 

Congrats!

 

Awesome Rob! glad to hear it's all good now.