Scary Random Engine Clank/Tap

[Jon B]

I will have to double check if I could even get slow motion movements- that’s good info thanks...

Yes, the tensioner pistons are extremely slow to depress when functioning properly. You can use a large pair of channellock pliers to compress them.
The manuals say the piston should not depress more than 10 mm after 5-10 minutes, with 12 lbs of weight applied to the piston.

Your idler arms are the original type for your 73.5 engine, without bushings. You should upgrade those.
The divots are normal contact wear after 45 years.

Here are two early 930 tensioners like yours, still with 901 numbers on the castings, and a later 930 tensioner disassembled.
These are excellent tensioners, in my opinion, and I used to rebuild and re-use them quite often.

There's a lot of information in the factory manuals.





Jon B.
Vista, CA

[Jerry L]

Chickenstrips, There are several sources that will machine your idlers to add the bronze bushings as well as add to the width to match the later wide base idlers which is a good move in keeping things in alignment and better loading. Cant tell from pic if you have wide base idlers.

Jon, in using the 930 tensioners do you run mechanical stop collars in case of failure?
My 71 2.2 T Targa had a fresh rebuild prior to my purchase with some nice upgrades including the 930 tensioners and wide base idlers, was happy to see that in inspection, some recommended the Carrera hyd set up, I kept it as it was with the addition of stop collars, wondering your use.

Regards

[Jon B]

Jon, in using the 930 tensioners do you run mechanical stop collars in case of failure?

Jerry, I use the collars unless there's not sufficient clearance underneath them. The collar kits come with a 3.5 mm tool for checking this.
Sometimes, with new chains installed, the clearance isn't sufficient.

I think the 930 tensioners unfairly acquired an iffy reputation for various reasons:
There were a lot of iffy repro tensioners being marketed in the 70s & 80s, many with Porsche numbers or saying "Made in Germany"...
The 70s idler arms without bushings would gall and not pivot smoothly...
The tensioners weren't being bled correctly, or were not being rebuilt correctly.

In my opinion they're fine to use when they're genuine Porsche tensioners, bled or rebuilt correctly, and used with bushed idler arms.

Jon B.
Vista, CA

[gled49]

I started using pressure tensioners when they were introduced in the 80’s, after rebuilding tensioners in the 70’s. Went back to rebuilding them with all the late restoration work we did, for correct appearance. The most seen failures were the divider piston rising above inter chamfer and cutting the outer O ring leading to failure. The special tool for setting the divider piston height is important. I find it nearly impossible to pass on 40 years experience, trial and error in a sentence or maybe a paragraph. My experience follows Jon to the letter. G

[Chickenstrips]

I started using pressure tensioners when they were introduced in the 80’s, after rebuilding tensioners in the 70’s. Went back to rebuilding them with all the late restoration work we did, for correct appearance. The most seen failures were the divider piston rising above inter chamfer and cutting the outer O ring leading to failure. The special tool for setting the divider piston height is important. I find it nearly impossible to pass on 40 years experience, trial and error in a sentence or maybe a paragraph. My experience follows Jon to the letter. G

So I was onboard with the idea of rebuilding the 930 Tensioners and liked preserving the original, not to mention saving $1,500, but after reading the service manual about how you can't even press down on the piston with a screwdriver or you may deform the tensioner housing and cause the piston to seize, and here I was being not super gentle so now I am paranoid. And thank you- the service manual is good on this, I followed it to a T and I can't get the piston out for the life of me. These are scaring me now. The thought of a potentially compromised critical part is more than I can handle. thanks for the info. Maybe they are seized? or is there a trick to remove the piston? thanks

[Jon B]

I followed it to a T and I can't get the piston out for the life of me. These are scaring me now. The thought of a potentially compromised critical part is more than I can handle. thanks for the info.
Maybe they are seized? or is there a trick to remove the piston? thanks

In the illustration above, if you've already removed parts #4 through #9, then remove the #1 bleed screw, and pop the #10 circlip off through the screw bore.
Put something over the tensioner so you don't lose the clip.

As I said before, you can also bring or send them to a Porsche specialist to disassemble and inspect, or to rebuild them for you.
Or, of course, you can purchase new tensioners instead.

Jon B.
Vista, CA

[Jerry L]

Jon, Thank You for the reassurance!

And a bump to see what was the result here.

Regards

[Chickenstrips]

Let me be the first to say, replace chain ramps. Just to get going if you want, update idler arms and tensioners, confirm cam timing, if noises are gone drive it.

Let me be the first 100th person at least to say this forum is priceless! You and EdMayo had it right about the ramps. This is the inner bottom left ramp that gets replaced with the brown ramp. I am guessing the chain must have been slapping the inner most part of the guide levering it over the bolt as fulcrum. holy crap! Like hearing a bullet whiz by.

[Chickenstrips]

In the illustration above, if you've already removed parts #4 through #9, then remove the #1 bleed screw, and pop the #10 circlip off through the screw bore.
Put something over the tensioner so you don't lose the clip.

As I said before, you can also bring or send them to a Porsche specialist to disassemble and inspect, or to rebuild them for you.
Or, of course, you can purchase new tensioners instead.




Jon B.
Vista, CA

Many thanks for the input. I feel like after rebuilding so many similar parts (some super crusty brought to perfection) I really ought to be able to have done that, but if I have the slightest fear, and I do, that I handled them like a chimp with tools, then there is no chance they are going in my engine however likely it is they are fine. Bought new tensioners. Almost done installing new ramps.

[Chickenstrips]

So to close this one out, I ended up doing the carrera tensioner upgrade. I did the step where you dunk it in oil and pump by hand until bubbles were out, but it never really firmed up so that might have been a fail. So I gave it a lot of engine turn over without spark to pressurize. I started it up yesterday and am happy to report the problem is solved not the slightest sound. My only problem now is a weird one, it is missing on 1-2-3, exhaust headers are barely warm while 4-5-6, are hot. About to go on the hunt with elec diagram, but any ideas what that could be? is there a separate ground for the ignition on those? Every once in a while 1-2-3 fire up and the rpms pop up and misfires go away. I replaced distributor and rotor and checked to see that the all the plug wires are seated. The plug wire from coil to distributor seems poorly seated, but does not want to come out, seems unlikely to be my problem because it would affect all 6 right? any thoughts appreciated