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jimbauman's Avatar
 
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Angry Tensioner failure on intial startup after rebuild

Well... my '86 3.2 engine is back together after a top end rebuild - I went through the first-time startup procedure, and it started right up. It sounded very good for the first 5 minutes, then the clacking sound of a right side tensioner failure appeared. Subtle at first, only at 2K RPM. Then gradually at lower RPMs as well.

I removed the chain cover and noticed I could compress the tensioner with hand pressure - and there were small marks inside the housing where the chain had made contact.

On startup, the oil pressure was excellent. And, if there was just air trapped, it should have been a problem from the very start.

FYI, on assembly, I did prime the tensioner - and also did the Jerry Woods anti-total-collpase upgrade (good thing too!).

Any ideas on what to check, or should I just get it over with and buy a new tensioner?

Thanks,

JB
Old 03-27-2005, 04:18 PM
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People, please send in ideas on this....I don't want it to happen to my 3.2 now closing in on the turning point of the rebuild. I helped Jim the day before.... reading out of the book for the initial cranking/etc. I wonder if waiting a day from initial cranking to startup had anything to do with this event. Also, what do you think about the "anti-collapse" upgrade in the tensioners? If this saved Jim from piston and valve contact then it seems like a thing to consider.

-henry
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1989 3.2 coupe, DIY top end at 77k, now 112k
Old 03-27-2005, 07:37 PM
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Remove the piston and verify that the cage for the one way check valve has not been damaged or come loose from the bottom of the tensioner piston bore.
Old 03-27-2005, 07:41 PM
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I had a new pressurized tensioner fail to tension as well. I applied some pressurized shop air into the intake port and managed to get a click. Apparently, the check valve was stuck. Worked fine after that. Knock on wood after 17k miiles.

Sherwood
Old 03-27-2005, 11:16 PM
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Is there a cross sectional diagram of the tensioner internals anywhere?

JB
Old 03-28-2005, 06:26 AM
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I see one on page 100-7 in Bentley. Not too clear where the slug would go or exaclty how the check valves work.
-h
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1989 3.2 coupe, DIY top end at 77k, now 112k
Old 03-28-2005, 06:35 AM
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I'm going to offer a guess as to how this works. Somebody chime in to correct me.

The ball check valve allows pressurized oil to enter the chamber and push the piston upward to apply tension against the idler arm/sprocket and chain. The piston OD/cylinder ID is sized to provide a controlled bleed-off when pressurized (or perhaps through internal orifices). During operation, the chamber is constantly refilled with oil.

When engine is OFF, oil pressure drops to zero. The internal spring provides some tension to prevent piston collapse. In addition, the check valve closes to prevent oil from bleeding back through the intake.

WAG,
Sherwood
Old 03-28-2005, 08:54 AM
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From the looks of things....I would say with 98% accuracy that's exactly how it works.

Why would the tensioner "collapse" during the run in, I guess sitting at the constant 2000 rpm? There is the spring and there is oil pressure and maybe not a lot of radical rpm changes. Even if the check valve got something caught in it, the tensioner should be keeping at least moderate tension. ???

BTW - The Woods slug goes just underneath the piston, above the check valve, to allow a max. of 1/8" travel. Jim had these in.

-h
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Old 03-28-2005, 10:20 AM
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The check valve is there to prevent collapse even when the engine is running.

The oil pressure fills the cylinder when the tension is low and the checkvalve, oil and slow bleed keep the chain tensioned during short moments of extreme tension against the tensioner.
Old 03-28-2005, 02:05 PM
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So, when a pressure fed tensioner fails, what *exactly* fails? Is a new tensioner the only solution, or are these simple enough th take apart, and put back together in working order?

JB
Old 03-28-2005, 02:18 PM
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Its both simple and expensive enough to where I would at least take it apart and see why its not holding.

My educated guess is that the check valve under the piston either has a piece of junk caught in it or is damaged.

If its just junk thats something you can fix with some solvent and compressed air.
Old 03-28-2005, 02:51 PM
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Jim,
I don't know if too tight of a fit of the arm on the idler arm shaft could be a contributing factor but it was way out of spec. on my engine. I made a lapping tool to bring the bore up to 15.000mm...it is still tight but feels much better. Since you are in there you may want to check this.
-Henry
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Old 03-29-2005, 05:07 AM
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Jim,
Have you found the root cause yet? Sure would like to get more info. on the exact failure modes of the cam chain systems.
-h
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Old 03-30-2005, 06:07 PM
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No - and I couldn't disassemble the old tensioner - I think the hard parts are pressed in. But, I have the new tensioner - I'll put it in tomorrow, and see what happens..... sigh...

JB
Old 03-30-2005, 06:17 PM
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Many of these "tensioner failures" are actually something else (like a clogged oil line) - did you break loose the oil line while the engine was running to check the pressure?

-Wayne
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Old 04-01-2005, 12:04 AM
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Jim,
I was waiting for Wayne (or others) to chime in with more root cause info....he has probably talked to or heard from a lot of people on tensioner failures.
Please....check the oil lines and pressure. I don't want to read about this happening again on your engine.

I am now considering opening up the oil lines at the end of initial cranking just to see if I have oil for sure. I also wonder what Wayne thinks of the Woods slugs...I don't remember seeing it mentioned in the book.

-h
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Old 04-01-2005, 05:38 AM
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I'm still not sure why the old tensioner failed - I should have removed the little oil feeder line to ensure that there was pressure, although I'm reasonably sure there was.

The new tensioner is in and she's all nice and quiet now. I'm going to speculate that something probably worked its way into the tensioner and caused the valve to remain closed, not letting new oil in.

Next time I'll know better....

JB
Old 04-01-2005, 06:45 AM
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Did you fire it up and make it through the first 20minutes?
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Old 04-01-2005, 01:29 PM
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Quote:
Originally posted by hcoles
I also wonder what Wayne thinks of the Woods slugs...I don't remember seeing it mentioned in the book.

-h
I like the idea - didn't hear about it though until after the book was put to bed...

-Wayne
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Old 04-02-2005, 01:44 AM
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Where do I find info on the "Jerry Woods slug Mod"? Willymakit
Old 04-03-2005, 08:46 AM
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