16V collapsed chain tensioner?
07-09-2003, 03:26 PM
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16V collapsed chain tensioner?
I saw the recent post on the cahin tensioner for the 944S and had some questions.
Is the tension maintained by oil pressure or spring pressure?
If the chain stretches will there be a problem with valve clearance on the camshaft thats driven by the chain. Or does the cam start to lag behind and increase valve clearance?
If the plastic ramp is worn out or wearing out what kind on noises might you hear?
I saw Seggy's post about his bad tensioner and it got me to thinking about my engine problems.... My 87 944S starts up and idles fine with good oil pressure. But as soon as I raise the RPMs a little I start hearing distinct and loud knocking/tapping sounds from under the valve cover. It sounds very high up in the engine and more towards the middle of the head.
I originally thought that this was the sounds of the valves starting to "kiss" the piston but now think it could be maybe the chain and or tensioner making the noise.
Is the tension maintained by oil pressure or spring pressure?
If the chain stretches will there be a problem with valve clearance on the camshaft thats driven by the chain. Or does the cam start to lag behind and increase valve clearance?
If the plastic ramp is worn out or wearing out what kind on noises might you hear?
I saw Seggy's post about his bad tensioner and it got me to thinking about my engine problems.... My 87 944S starts up and idles fine with good oil pressure. But as soon as I raise the RPMs a little I start hearing distinct and loud knocking/tapping sounds from under the valve cover. It sounds very high up in the engine and more towards the middle of the head.
I originally thought that this was the sounds of the valves starting to "kiss" the piston but now think it could be maybe the chain and or tensioner making the noise.
07-09-2003, 04:49 PM
#2
Race Car
Don't run the car until you've lifted the valve cover to inspect the tensioner. The sounds you describe are EXACTLY what a cam chain/tensioner assembly sounds like before repair becomes one hell of a lot more expensive.
The 944 S/S2 tensioner loads the cam chain using spring pressure. The 968 uses oil pressure.
As the plastic ramp wears you run the risk of having it break. We're talking grooves of ~0.5mm but as the plastic ramps age they become brittle...if a ramp breaks the chain will become caught on the metal tensioner and you risk breaking the entire head, particularly the tensioner mounting points on the casting.
As the chain stretches it will lash the cam gear teeth and either wear them down or break them off...hopefully this isn't what you'll find because a repair will involve purchasing new cams, in addition to a new tensioner and cam chain.
Good luck!
The 944 S/S2 tensioner loads the cam chain using spring pressure. The 968 uses oil pressure.
As the plastic ramp wears you run the risk of having it break. We're talking grooves of ~0.5mm but as the plastic ramps age they become brittle...if a ramp breaks the chain will become caught on the metal tensioner and you risk breaking the entire head, particularly the tensioner mounting points on the casting.
As the chain stretches it will lash the cam gear teeth and either wear them down or break them off...hopefully this isn't what you'll find because a repair will involve purchasing new cams, in addition to a new tensioner and cam chain.
Good luck!
07-09-2003, 04:50 PM
#3
Nordschleife Master
If the valves were kissing the piston you would probably know about it big time!
If you value your S, don't start your engine again until you've pulled the cover and checked your tensioner and pads. When these things let go it gets very expensive fast. A worn pad doesn't make any sound, and even if not super worn, I'd replace them. They get brittle when they get old.
There is a big difference between a knock and a tap, so you'll have to be more specific there.
The tension is maintained by a spring.
If you value your S, don't start your engine again until you've pulled the cover and checked your tensioner and pads. When these things let go it gets very expensive fast. A worn pad doesn't make any sound, and even if not super worn, I'd replace them. They get brittle when they get old.
There is a big difference between a knock and a tap, so you'll have to be more specific there.
The tension is maintained by a spring.
07-09-2003, 09:42 PM
#6
Nordschleife Master
How much pressure loss, and for how long, and why?
Depending on your response, there are other things that would be damaged first, like bearings, cams, lifters etc. etc.
Bader, I didn't think the tensioner on my S was pressurized by oil. Sure it was lubricated, but pressurized? Are you sure?
Depending on your response, there are other things that would be damaged first, like bearings, cams, lifters etc. etc.
Bader, I didn't think the tensioner on my S was pressurized by oil. Sure it was lubricated, but pressurized? Are you sure?
07-09-2003, 11:54 PM
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According to the seller, he lost oil pressure turning a corner about a mile from his house. The next day the engine made all kind of knocking sounds. A mechanic came over and said "rod bearings" so he decided to sell the car...that's his story.
I towed the car home and found it to have only 2 quarts. My guess is that while turning the last corner, the oil pump pickup went dry and the oil pump lost its prime. So thats one mile with no oil pressure. The lifters bleed down overnight and collapsed...thus all the rattling.
I reprimed the pump, got full oil pressure back and the lifters appear to have pumped back up. But now there is that loud knocking in the top end that I can't identify. The car has never been driven since I got it, only idled. The knocking is only heard above idle speed...
Is one or 2 lifters still collapsed or maybe the tensioner collapsed?
I'm going to completey rebuild the engine when I get garage space. Just don't know what I should expect or look for.
I towed the car home and found it to have only 2 quarts. My guess is that while turning the last corner, the oil pump pickup went dry and the oil pump lost its prime. So thats one mile with no oil pressure. The lifters bleed down overnight and collapsed...thus all the rattling.
I reprimed the pump, got full oil pressure back and the lifters appear to have pumped back up. But now there is that loud knocking in the top end that I can't identify. The car has never been driven since I got it, only idled. The knocking is only heard above idle speed...
Is one or 2 lifters still collapsed or maybe the tensioner collapsed?
I'm going to completey rebuild the engine when I get garage space. Just don't know what I should expect or look for.
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07-10-2003, 12:06 AM
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Its really easy to pull the valve cover off these engines, just be really careful with loosening the bolts. I found out that the bolts are tapered in the center which makes them weak and prone to twisting in half ( I BARELY got one of them out and it looked very twisted up, probably as it was breaking loose) But getting the cover off is simple except for the bolts, and then a visual inspection will tell you all you need to know.
07-10-2003, 12:09 AM
#9
Burning Brakes
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by odie:
<strong>Just don't know what I should expect or look for.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">expect the worst
I remember your old poats and thought the PO beat the thing to death
<strong>Just don't know what I should expect or look for.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">expect the worst
I remember your old poats and thought the PO beat the thing to death
07-10-2003, 12:32 AM
#10
Race Car
odie,
for a visual inspection of what chain tensioner failure looks like on a 944S, see my webpage at the bottom of my signature. i just received my 944S back from the mechanic three weeks ago after having the tensioner fail and the head crack. $3200 later and car is finally running again. maybe my photos will help you understand a bit.
for a visual inspection of what chain tensioner failure looks like on a 944S, see my webpage at the bottom of my signature. i just received my 944S back from the mechanic three weeks ago after having the tensioner fail and the head crack. $3200 later and car is finally running again. maybe my photos will help you understand a bit.
07-10-2003, 03:22 PM
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Tom...I don't think the PO actually abused it. He only had it for a few months. I'm thinking he just never had the sense to check the oil (16 year old kid). Overall, the car was in excellent shape so it was well cared for before he got it.
It idles pretty quiet and smooth so I don't believe any major damage has occured...yet. But something is coming loose or about to have a major failer.
Joseph...what indications did you get when your chain tensioner failed? What was the actual condition of the related pieces? Was the plastic shoe all worn out or did the tensioner itself structuraly fail?
It idles pretty quiet and smooth so I don't believe any major damage has occured...yet. But something is coming loose or about to have a major failer.
Joseph...what indications did you get when your chain tensioner failed? What was the actual condition of the related pieces? Was the plastic shoe all worn out or did the tensioner itself structuraly fail?
07-10-2003, 06:11 PM
#12
Nordschleife Master
Sounds like the tensioner is the least of your worries. There could be a lot of damage that hasn't had time to surface yet. You'll want to have a good look at your bearings, pistons, lifter bores, cam etc., etc. Good luck!
07-10-2003, 09:06 PM
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Peckster - Don't be such a Jonah.
Odie COULD be one of the lucky ones - sounds like all it needs is a new tensioner.
It would't idle well with all the problems you're giving it.
Odie lift the cam cover and have alook don't spend $$$$ until you need to.
Odie COULD be one of the lucky ones - sounds like all it needs is a new tensioner.
It would't idle well with all the problems you're giving it.
Odie lift the cam cover and have alook don't spend $$$$ until you need to.
07-10-2003, 10:41 PM
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Thanks for the uplifting words...
But I DO VERY MUCH appreciate all the pessemisim (can't spell).
I have already planned on a complete engine rebuild (bearings, rings, belts, seals, etc). It would just be great if I don't need any "hard" (I don't mean difficult to find) parts.
I'm really hoping to just replace all the "soft/service" parts and basically have a brand new engine.
If I find structural damage I might just have to sign "take this Porsche and Chev it, I ain't PCAing no more" LOL
But I DO VERY MUCH appreciate all the pessemisim (can't spell).
I have already planned on a complete engine rebuild (bearings, rings, belts, seals, etc). It would just be great if I don't need any "hard" (I don't mean difficult to find) parts.
I'm really hoping to just replace all the "soft/service" parts and basically have a brand new engine.
If I find structural damage I might just have to sign "take this Porsche and Chev it, I ain't PCAing no more" LOL
