Do we really need our oil filled tensioners?
10-13-2007, 06:48 PM
#16
928 Engine Re-Re-Rebuild Specialist
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My tensioner shoulder bolt failed last week. On start up. The belt slipped and shredded some of the belt. Ordered another belt, replaced the tensioner shoulder bolt. No problems since. Glad it was a non-interference engine. After 28 years I guess the bolt got a little weak. I am **** about keeping the proper tension on the belt and check it religiously.
10-13-2007, 06:49 PM
#17
Rennlist Member
10-13-2007, 07:45 PM
#19
Team Owner
I am going to throw this out there , for leaking tensioners I had a similar problem with leaking oil and i found that if i put engine oil in the tensioner it leaked out faster than the 90 wt , anyway going on that idea I got some STP oil treatment the stuff is thicker than molasses and filled a visene bottle with it after drilling out the tip, I removed both bleeders and began filling till the old oil was flushed out, the STP seems to be heavier than the engine oil so it fills from the bottom to the top and the old oil simply rinses out of the top bleeder hole I put a rag under the tensioner to catch all of the old oil, and after that i used some loctite pipe thread sealant on the threads of the bleeder screws, now the tensioner is dry and it is full of a liquid, so to keep the tensioner lubed and the heat transfer system working, I also checked the tightness of all of the tensioner mounting bolts . The biggest worry about the belt tension system is that a if the belt is over tensioned, a few unwanted things will happen quicker that is the wear of all of the pulleys in the belt run, the possiblity of damaging the water pump bearings and the worst thing is the possibility of snapping off the driverside cam at the pulley a known weak link in the system. The engine grows when it gets hot, the heads will be farther from the crank and the belt will get tighter. If you have any doubts about this just check out a 944 belt when its cold and then run the engine till its hot, the belt is considerabley tighter due to the engine expansion. .just my 2 cents
10-13-2007, 11:58 PM
#20
Rennlist Member
without the oil, the tensoner does it job, it just takes a little longer for the heat to transfer, but not much longer. think about it, you are kind of near the heads! those heads are REAL hot! i be surprised if with vs without oil costs more than 5 mins before they are equal
mk
mk
I am going to throw this out there , for leaking tensioners I had a similar problem with leaking oil and i found that if i put engine oil in the tensioner it leaked out faster than the 90 wt , anyway going on that idea I got some STP oil treatment the stuff is thicker than molasses and filled a visene bottle with it after drilling out the tip, I removed both bleeders and began filling till the old oil was flushed out, the STP seems to be heavier than the engine oil so it fills from the bottom to the top and the old oil simply rinses out of the top bleeder hole I put a rag under the tensioner to catch all of the old oil, and after that i used some loctite pipe thread sealant on the threads of the bleeder screws, now the tensioner is dry and it is full of a liquid, so to keep the tensioner lubed and the heat transfer system working, I also checked the tightness of all of the tensioner mounting bolts . The biggest worry about the belt tension system is that a if the belt is over tensioned, a few unwanted things will happen quicker that is the wear of all of the pulleys in the belt run, the possiblity of damaging the water pump bearings and the worst thing is the possibility of snapping off the driverside cam at the pulley a known weak link in the system. The engine grows when it gets hot, the heads will be farther from the crank and the belt will get tighter. If you have any doubts about this just check out a 944 belt when its cold and then run the engine till its hot, the belt is considerabley tighter due to the engine expansion. .just my 2 cents
10-14-2007, 12:18 AM
#21
Team Owner
Mark even though your running your tensioner dry and it seems to be working, the reality is that it isnt working as it was designed to. The oil in the tensioner also adds a dampening effect and it provides lubrication for the tensioner where the bellview washers are rubbing on the inside bore of the tensioner housing. as the washers warm up they also flatten out increasing their diameter, I have rebuilt a few tensioners that were bone dry and full of worn aluminum particles from the washers rubbing on the bore without lubrication. Anyway if your worried about leaking oil why dont you try using the STP oil in your tensioner, it seems to be working well for me without any leaks, what would it cost you to try??. Id hate to see the engine fail due to improper servicing. Stan
10-14-2007, 01:16 AM
#22
Under the Lift
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Mark:
How many miles do you put on the Holbert car between belt changes? The effects of a dry tensioner are not an overnight problem. It's more like the belt and other components may not last 60K miles. I had a problem at 25K miles when the tensioner would not hold oil.
How many miles do you put on the Holbert car between belt changes? The effects of a dry tensioner are not an overnight problem. It's more like the belt and other components may not last 60K miles. I had a problem at 25K miles when the tensioner would not hold oil.
10-14-2007, 03:04 PM
#24
Race Director
It just seems risky to me.......afterall they did design it to work WITH oil...on every 928 ever made..... If you change the belts much more often and don't care about the possible increased wear on the cam gears & everything else....then I guess its okay...
10-14-2007, 10:33 PM
#25
Rennlist Member
ive got 20,000miles that i have put on the holbert car, including the 90+ race days.
maybe ill try that STP treatment.
mk
maybe ill try that STP treatment.
mk
Mark:
How many miles do you put on the Holbert car between belt changes? The effects of a dry tensioner are not an overnight problem. It's more like the belt and other components may not last 60K miles. I had a problem at 25K miles when the tensioner would not hold oil.
How many miles do you put on the Holbert car between belt changes? The effects of a dry tensioner are not an overnight problem. It's more like the belt and other components may not last 60K miles. I had a problem at 25K miles when the tensioner would not hold oil.
10-16-2007, 10:14 AM
#27
Mike
Last edited by mj1pate; 10-16-2007 at 10:14 AM. Reason: spelling
10-16-2007, 01:22 PM
#28
Inventor
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What about some sort of (low temp?) grease? Pack the housing before installing, then stick a grease gun on there.
10-16-2007, 06:28 PM
#29
Chronic Tool Dropper
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The design of te later tensioner looks like it has a bit of check-valve action going on, with a limited amount of oil passing around the piston when the unit is under compression, with the little check valve in the bottom of the seal plate closed. On rebound/extension, the little brass check valve opens so the piston will move more outward quicly. This is all in addition to the basic spring function provided by the Belleville washers. So the viscosity of the oil plays a key part in a properly-functioning tensioner, since compression requires oil to leak by the piston in the bore. IMHO, grease would never flow back around the bypass port to the space under the seal plate and the piston, so aftre the first compression action you'd get no more damping.
This is all based on my analysis of how the damper part functions of course. Other opinions may vary... a lot!
This is all based on my analysis of how the damper part functions of course. Other opinions may vary... a lot!
