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clank or snap sound when turning engine over by hand GT3

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Old 03-10-2021, 01:47 PM
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Doug DeArmond
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Default clank or snap sound when turning engine over by hand GT3

So I pulled my 2005 996 GT3 motor to get the trans rebuilt and replace the crank seals. Been sitting for about 8 weeks on the bench. Took my ratchet and decided I would turn it over a few revs with the crank pulley bolt. When rotating I get a loud metallic clunk/clack from the crankcase area, sounds like toward the rear of the motor but definitely inside. I only turned it a couple of times and it will make this loud single clunk/clank sound 2 or 3 times per revolution. Fairly loud scary sound. Ran fine before I pulled it out. Ran it after an oil change before I pulled it. It is a new track car to me. Only have driven it a couple of miles after purchase and decided to tidy things up before tracking it. Now it is making this scary noise. Rotating the crank with a ratchet the engine seems harder to turn over than I would have expected with the plugs out. Any advice? Anybody know of a GT3 engine guru in the midwest?
Old 03-10-2021, 02:13 PM
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theprf
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Originally Posted by Doug DeArmond
So I pulled my 2005 996 GT3 motor to get the trans rebuilt and replace the crank seals. Been sitting for about 8 weeks on the bench. Took my ratchet and decided I would turn it over a few revs with the crank pulley bolt. When rotating I get a loud metallic clunk/clack from the crankcase area, sounds like toward the rear of the motor but definitely inside. I only turned it a couple of times and it will make this loud single clunk/clank sound 2 or 3 times per revolution. Fairly loud scary sound. Ran fine before I pulled it out. Ran it after an oil change before I pulled it. It is a new track car to me. Only have driven it a couple of miles after purchase and decided to tidy things up before tracking it. Now it is making this scary noise. Rotating the crank with a ratchet the engine seems harder to turn over than I would have expected with the plugs out. Any advice? Anybody know of a GT3 engine guru in the midwest?
The chain tensioners have bled off and what you're hearing is the intake cam lagging the crank and then being snapped to lead the crank by valve spring pressure. I had the same plink-snap sound on my Turbo engine. When I retimed the cams and installed the heavy spring loaded tensioners used for setting time the plink-snap went away. Then when I put the actual tensioners back in the plink-snap was back.

Side note, the tensioners don't wear our or break which is a good thing as they're 959 parts and over $500 each. So don't worry about the sound, the tensioners are vastly different from those used in the M96's which do wear out and fail.
Old 03-10-2021, 02:46 PM
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Doug DeArmond
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Thank you! That makes some sense from what it is doing. Sure is a scary noise not expecting it to do that.
This a new track car to me and it has had a rough life and poor maintenance. Not sure of the actual time on the engine.
I can do air cooled 911 engines in my sleep but this is my first water cooled
Is there any wear items in the valve drive like chains or rails or tensioners that I should worry about? Something I should do or check or service while I have the engine out?
I want to run a couple track events this year before doing an engine refresh next winter but not at the expense of hurting something in the meantime.
Thanks for sharing your expertise. Much appreciated.



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