Oil Fed Tensioners

[chris_seven]

I have just been offered a pair of used oil fed tensioners that look as if they are in reasonable order and the price is quite good.

They have been de-pressurised by being clamped in a vice and are now quite soft and easy to move.

I don't want to put them in a motor and find out that they don't work.

Is there a simple way to fill them and see if they are good or does forcing the oil out with a vice ruin them?

I thought they were supposed to be de-pressurised by opening a valve.

Thanks for any info.

[lindy 911]

The only way I know to collapse them for installation is in a vise and then they are pinned until bolted in. I don't know any reason why compressing them slowly in a vise would hurt. I don't know of any good test...

[Walt Fricke]

Chris - the early (~1965) tensioners, not pressure fed, had a spring loaded ball bearing valve down somewhere inside, and the manual showed sticking a stiff thin rod down a hole to open this and to allow oil to fill the gravity reservoir.

The next generation of tensioners, and the next after that (the "Turbo" tensioners) did not have this feature as I recall. And the pressure fed ones certainly don't.

You will find a variety of opinions about some of this. Some say that when you have new tensioners you should immerse them in oil and, with suitably large water pump pliers, exercise them until they are stiff and no air bubbles come out. Of course, for installation they need to be compressed, which reduces the amount of oil inside, so you can get the wire lock in place for easy of installation. As soon as you pull that grenade pin, the tensioner will spring to full height, which must leave some air void somewhere inside. But this does not affect things.

Not knowing any better, when I have installed new tensioners (as one does when upgrading, often with the engine in the car), I didn't bother with any pre-oiling. And never had any issues - the pressure feed mechanism quickly gets things to where they need to be. The external relief valve is going to allow any air in that chamber to escape at once. And the pressure cylinder and piston are designed so that the pressurized oil will slowly leak out through a hole in the central shaft which ends below the hardened steel cap. When you squeeze a used set in a vice so you can install the pin, you see oil coming out (slowly) these orifices.

Since the oil only serves as a damper, and the spring is what produces all the real pressure on the chain idler (I assume we are talking pre-964 here), it is easy enough to test to see if the spring has somehow gotten weak. I can't imagine how that could happen, though - it is just a spring, and its travel is very short in operation. No where near coil bind.

I don't know just how tensioners fail, short of the two spring/ball valves failing. One is external, on the reservoir, and if you knock the little stamped metal cap off, you have a dead tensioner unless you can reinstall it.

There is a similar spring/ball/cap inside at the base of the pressure chamber. It insures that oil can enter from the reservoir, but not go the other way. Hard to see why this would fail either, but it could. I have had iatrogenic injuries to both of these, one due to prying to install a tensioner, and one due to trying to disassemble it by driving the circlipped base out from above without realizing what was down in there.

No seals in these, so I don't know how otherwise they could fail than as described. I suppose somehow the shaft and cylinder wall could wear enough to lose the seal they otherwise naturally have. Dirty oil? No oil?

These can be disassembled for inspection, though I found it a bit more difficult than I thought.

I think a pragmatic test would be to immerse in oil and exercise until no bubbles (so full of oil). And then put in vice and squeeze. If you can only squeeze slowly, as small amounts of oil slowly ooze out below the tip, I'd call them good.

[trond]

immersing in oil bath and excersising does not always work, the tensioner will not always fill up that way. I had to give up on a new one and finally called the Porsche shop to seek advive. The mechanic there advised me to instead use a regular oil can (thumb operated) with a hose arrangement. I got a crossover and a large ID hose that fit over the stub of the tensioner. Bleeding with an oil can is eas. Even better you can actually see what happens as air is displaced AND you get to fill up the tensioner after installing if you want.

I feel much better after verifying they actually work before closing up the engine

[chris_seven]

Thanks, I am now confident to buy them and try to use them.

We have built a small air over oil intensifier so we can pressurise them before the cam covers are put in place and make sure that the are working.