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Help me understand what I am seeing with my timing belt...

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Old 02-15-2017, 10:08 PM   #61
skpyle
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Hi Stan! As far as I can tell, the snap ring is not there, and the shaft has been pulled to the back of the bore in the arm. However, the roller turns just fine, and has no marks on the back edge from scraping the arm.

I am going to disassemble it shortly (I hope) and will get back here with the results.


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Old 02-15-2017, 10:52 PM   #62
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Got the tensioner roller arm disassembled.
The roller shaft came out just fine after a couple of taps with a hammer and brass drift.

Definitely no snap ring in the groove. That let the bolt pull the shaft all the way into the bore in the tensioner arm. I will order a snap ring.

I removed the tensioner pivot bolt bushings. They look a little janky for being new. I am not saying they are not new, just rough looking. There is the obvious broken flange on the outer bushing. The crud you see resisted cleaning with denatured alcohol and a toothbrush and a rifle bore brush. I am going to order new bushings.

I did see some crud in the bore for the bushings in the arm. I am going to run some red scotchbrite in there to clean it up.





I I would say this explains why the belt was tracking so far out on the roller. No circlip.











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Old 02-15-2017, 11:03 PM   #63
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well that a new one on me,
I have test fit these parts and with no snapring the shaft will pass through till the edge of the roller hits the arm.

Good news a snapring will put the bearing in the right spot .

As for the water pump I would remove the bolts one at a time ,
and put PTFE sealant on them , then install.
no need to pull the pump
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Old 02-15-2017, 11:20 PM   #64
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Quote:
Originally Posted by Mrmerlin View Post
well that a new one on me,
I have test fit these parts and with no snapring the shaft will pass through till the edge of the roller hits the arm.
I have a handful of those snap rings on my shelf. I bought a bunch after the second or forth time I found a main roller with no snap ring. Maybe those rollers were all previously done by the same doofus, I don't know. But, I got tired of not having a replacement on hand.

Quote:
Good news a snapring will put the bearing in the right spot .
True. But, _only_ a missing snap ring doesn't account for 100% of the main roller tracking error, me thinks.

skpyle, put something on that pivot bolt and triple-check that it's straight, or not. A few degrees of bend isn't visible without some sort of 'aid.'
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Old 02-15-2017, 11:36 PM   #65
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Stan, on this one, the shaft gets tight right before the end of the bore. I am guessing the bolt, nut, and washer pulled it tight, but not through.

Should I be concerned about the uneven wear pattern on the outer surface of the main roller? Or, will it even out in running.

With all due respect, I am still very concerned at the play in the water pump shaft. I would think there should be no play at all. Especially for only having 2000 miles on it.
I have seen in the past your recommendation for PTFE sealant on the water pump bolts, and had planned on following it this time.

Thanks!



worf928: I am definitely going to test spin the tensioner bolt with a die at the end of the threaded portion.
Regardless, I am replacing the bolt and bushings, then carefully installing the bolt as per your experience.
And I am definitely getting a new snap ring.

Thanks!



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Old 02-16-2017, 02:04 AM   #66
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Quote:
Originally Posted by Mrmerlin View Post
As for the water pump I would remove the bolts one at a time ,
and put PTFE sealant on them , then install.
no need to pull the pump
I am guessing that Stan did not see the post where Seth has measurable play in the water pump shaft.
If Stan did see the post, I will have to disagree with him just this one time.
I would replace that water pump at this point.
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Old 02-16-2017, 03:28 AM   #67
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Alright guys, silly question: Since I have to replace the water pump, tensioner pivot bolt, etc..., should I upgrade to the 87+ system with the double shear mount for the pivot bolt?

Just a thought...

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Old 02-16-2017, 07:17 AM   #68
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Quote:
Originally Posted by skpyle View Post
Alright guys, silly question: Since I have to replace the water pump, tensioner pivot bolt, etc..., should I upgrade to the 87+ system with the double shear mount for the pivot bolt?
In an ideal world with a fat wallet, yes.

Keep in mind, though, that there are thousands of pre-87.5 928s running around with the stock setup and not throwing timing belts.
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Old 02-16-2017, 10:16 AM   #69
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Oh did I miss the point that the shaft of the WP has play?

If so then a replacement WP should be procured.
NOTE a good pump will spin by hand a few revs till the shaft stops
there should be no play in the shaft side to side

Your original tensioner system will work fine.
the roller will even out its surface after the belt runs on it
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Old 02-16-2017, 10:40 AM   #70
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worf928: Good point. I got a little carried away there. (Me? No...)
Thanks for the reality check.



Mrmerlin: Yep, water pump is bad. Hmmm...this one turns smoothly, but stiffly. As soon as I stop turning, it stops turning.
Please see post #43 on page 3 for details of the play in the water pump pulley.
Thanks for the advice!


I disassembled the tensioner last night. No surprises, at least to me. The boot is new and pliable. I counted 35 Bellville washers in 4 distinct stacks. All of them appear to be copper coated. I found no major crud in the tensioner bore. The O-ring on the rear piston appears new, but I may change it just because. I did find a little damage to the back side of a few of the teeth on the crank sprocket. I'll bet its from a puller. I will dress the damage with a small fine file.
No photos of the above as I was pressed for time. I will try to get some Friday.

Question: what is the purpose of the tiny valve/piston that moves back and forth inside the rear piston at the back of the tensioner Bellville washer stack?


Thanks again!

Seth K. Pyle
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Old 02-16-2017, 11:12 AM   #71
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This is how a new pump should feel, the bearing offers resistance to the shaft spinning,

Hmmm...this one turns smoothly, but stiffly. As soon as I stop turning, it stops turning.
This is good.


After rereading your post in 43.

But most pumps will exhibit a very small amount of play that will increase slightly as the bearing wears into its new home.
I am going to go with your pump is in good condition and fit for use.

The valve in the piston is like a shock absorber they added this to act as a dampener force to the shim stack
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Old 02-16-2017, 11:16 AM   #72
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Excellent, thanks for the info, Stan!

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Old 02-16-2017, 09:56 PM   #73
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Seth. Bad Water Pump. Really? Are you sure? What brand was used?
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Old 02-16-2017, 10:11 PM   #74
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Hello Mike, Yes, the water pump outer bearing has failed, as far as I can tell. I can feel noticeable play in the water pump pulley. Please refer to post #43 on page 3 for details of me measuring the play at the water pump pulley.

As far as I can tell, it is a Laso composite impeller water pump. I don't necessarily think the water pump failed on its own. I am leaning towards it is collateral damage from what was going on with the timing belt.

Seth K. Pyle
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Old 02-16-2017, 10:14 PM   #75
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If the water pump has some extra axial play it's due to the belt being pulled forward. I've seen it many times in the past. Had one shop doing a job on a car I maintained a month or so back that I couldn't get it in quick enough for the owner and he sent me pictures of the job as they were doing it. Same thing, circlip missing. Told the guy exactly what was going to happen if they did not pull it apart and redo the job. Owner was not happy and wished he'd just waited a couple of weeks as this place kept his car for 5 weeks.

Missing that one small 20 cent part can cause a lot of expense for someone. As shown here.
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