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Thread: Scary Random Engine Clank/Tap

  1. #11
    Quote Originally Posted by Chickenstrips View Post
    Quote Originally Posted by Chickenstrips View Post
    I was going To do the OEM Carrera upgrade even though it was more expensive Because I have been punished by not using OEM parts in engines before. But if the experts here say that the Pelican upgrade kit that is SEBRO brand is good enough I just might do that instead And save 800 bucks. Also it looks like the OEM option does not have a link chain so could not be done with the engine in place. Any opinions appreciated. thank you
    Your tensioners are early 930 Turbo-type. They're genuine Porsche replacements, and not original to your 73.5 engine.
    If this were mine, I'd rebuild those tensioners and not upgrade to Carreras.

    If you update the idler arms as Gordon suggested, which I'd also recommend, you'll have to modify those tensioner housings if you re-use them.

    And as Gordon and Ed have said, you should replace any chain ramp similar to the one in the lower picture, they're original to your engine and can break with old age.

    Jon B.
    Vista, CA

  2. #12
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    Quote Originally Posted by Jon B View Post
    Your tensioners are early 930 Turbo-type. They're genuine Porsche replacements, and not original to your 73.5 engine.
    If this were mine, I'd rebuild those tensioners and not upgrade to Carreras.

    If you update the idler arms as Gordon suggested, which I'd also recommend, you'll have to modify those tensioner housings if you re-use them.

    And as Gordon and Ed have said, you should replace any chain ramp similar to the one in the lower picture, they're original to your engine and can break with old age.

    Jon B.
    Vista, CA
    OK perfect! I will rebuild my 930 tensioners, get the improved idler arms, and install new ramps. I searched a lot of threads and can’t find anything on needing to modify the covers for the new idler arms. What do I need to do? Mill the cover? Thanks. Also is there a theory for how the old tensioners / chain are making the hammer-tapping-the-case noise? Thanks!
    Member #3896
    1973.5 911 T
    1974 911
    1974 CB750K

  3. #13
    member #1515
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    Have you done a leak down test or removed your valve covers to check the rockers? Have you gapped the valve clearances? I would proceed with caution. I had a tensioner go suddenly at speed, on my car when it only had about 30,000 miles. Not a happy occurrence, bent valves, broken rockers. Ever since I've been hyper sensitive to the issue. I first went with late 930 tensioners and now put in the hydraulic tensioners.
    David

    '73 S Targa #0830 2.7 MFI rebuilt to RS specs

  4. #14
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    Quote Originally Posted by RSTarga View Post
    Have you done a leak down test or removed your valve covers to check the rockers? Have you gapped the valve clearances? I would proceed with caution. I had a tensioner go suddenly at speed, on my car when it only had about 30,000 miles. Not a happy occurrence, bent valves, broken rockers. Ever since I've been hyper sensitive to the issue. I first went with late 930 tensioners and now put in the hydraulic tensioners.
    So far removed valve covers, boroscoped cylinders, and all looks OK. Next up is valve clearances and compression test this weekend. This is all just to carry me a few k miles until full rebuild. Thanks
    Member #3896
    1973.5 911 T
    1974 911
    1974 CB750K

  5. #15
    Quote Originally Posted by Chickenstrips View Post
    I searched a lot of threads and can’t find anything on needing to modify the covers for the new idler arms. What do I need to do? Mill the cover? Thanks.
    Also is there a theory for how the old tensioners / chain are making the hammer-tapping-the-case noise? Thanks!
    The chain housing covers don't need any mods for the newer idler arms. Early tensioners will need a simple mod to make the mounting support thinner.
    What's been discussed are reliability upgrades for your cam drives, which might be related to your noises. We haven't seen the condition of your parts, or the 4 chain ramps that aren't visible in your pictures.

    Jon B.
    Vista, CA

  6. #16
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    Quote Originally Posted by Chickenstrips View Post
    Also is there a theory for how the old tensioners / chain are making the hammer-tapping-the-case noise? Thanks!
    Well the chain is literally hitting/slapping the case. You will probably see some scratches where it’s been making contact. When the tensioner is bad then the piston in it loses pressure and it can’t hold the chain in taunt condition. This then allows the extra space for the chain to be able to become loose and contact the case. The nightmare is if the loose chain comes off the sprockets and causes all manner of destruction. I’m sure when you get the tensioners out out and compare the force needed to push down a new vs a failed tensioner you will understand.
    Early 911S Registry#3437
    1971 911E

  7. #17
    Quote Originally Posted by ZombieBranz View Post
    When the tensioner is bad then the piston in it loses pressure and it can’t hold the chain in taunt condition.
    The chain is tensioned by the coil spring under the piston, while the hydraulic element dampens the piston's movements.
    When these tensioners go bad, the hydraulic dampening element malfunctions or fails.

    Jon B.
    Vista, CA

  8. #18
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    I pulled the tensioners and idler sprocket arms after zip tying and scribing the chains and sprockets. I think Both tensioner pistons are totally seized up. I put them in a vice and tried pressing down with a foot of 2x4, and repeated rounds of PB Blaster, propane and tapping with hammer would budge the pistons - even with 5o plus pounds of weight on the 2x4. It can't be that they are under that much pressure under specs correct? I think the source of the tapping/klink sound was the idler arm snapping down on the piston, because the idler arms both have been peened with a divot in the shape of the piston top.see pic. No sliding marks on the case - this would explain the distinct tink/tapping noise and none of the sliding sound I would hear in videos of failing tensioners. I am very happy that I think I found the source of the sound and have a path to driving before a full rebuild, but happy also to have my ballon popped if this does not sound right. Also found oil-starved scoring on left idler sprocket arm bore. See pic. Do I just polish the axle it spins on and the new bronze bushings solve that problem?
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    Member #3896
    1973.5 911 T
    1974 911
    1974 CB750K

  9. #19
    Quote Originally Posted by Chickenstrips View Post
    I think Both tensioner pistons are totally seized up. I put them in a vice and tried pressing down with a foot of 2x4, and repeated rounds of PB Blaster, propane and tapping with hammer would budge the pistons - even with 5o plus pounds of weight on the 2x4.
    It can't be that they are under that much pressure under specs correct?
    The tensioner pistons are extremely slow to depress when functioning properly, due to the hydraulics involved.
    It's very unlikely they're both seized. It's possible that someone purposely disabled them, but I suspect they were probably fine. I wouldn't have gone near them with a propane torch.
    They should be carefully disassembled and inspected. If you're not sure how to do this, then bring or send them to a Porsche shop familiar with earlier Porsches.

    Jon B.
    Vista, CA

  10. #20
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    Quote Originally Posted by Jon B View Post
    The tensioner pistons are extremely slow to depress when functioning properly, due to the hydraulics involved.
    It's very unlikely they're both seized. It's possible that someone purposely disabled them, but I suspect they were probably fine. I wouldn't have gone near them with a propane torch.
    They should be carefully disassembled and inspected. If you're not sure how to do this, then bring or send them to a Porsche shop familiar with earlier Porsches.

    Jon B.
    Vista, CA
    I will have to double check if I could even get slow motion movements- that’s good info thanks And with the propane I was committed to a rebuild anyway so figured a little heat would only be a problem with soft parts and am a little on the fence with them versus Carrera upgrade. If they were fine would those divots from the pistons be on the idler arm? Maybe that’s normal? Thanks
    Member #3896
    1973.5 911 T
    1974 911
    1974 CB750K

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