348 Cam Drive Chain Tensioner.

This type of chain tensioner, with identical body and piston but with a few size/shape variations of the pad, were used by Triumph (Stag & Dolomite), Rover, Peugeot and probably some other cars. I think it was originally "invented" by a British company called Renold. And yes, the hole through the pad is very important for the chain lubrication. Otherwise, the tension of the tensioner is, I think, more controlled by the spring and not so much by the oil pressure. The inlet and outlet (through the pad) holes are usually of the same diameter and some even have the inlet hole smaller than the outlet. This means that the oil pressure in the tensioner piston is rather small (but the oil will still flow to the chain) and it seems that the oil in the piston, as far as the tensioning operation is concerned, acts more as a damper to prevent the tensioner vibration as the chain links go over it. The picture below shows a Peugeot tensioner.

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What year is your car and mileage?

Fwiw, my 92 (Dec 91 build) has NO hole in its original cam chain tensioner pad or assembly.

 

Interesting. Ive just measured my old one and its only a tiny hole, 1.2mm diameter.

 

Probably why my tensioner was so worn after such little mileage!

 

Excellent write up Steve!

 

Excellent stuff and something I'd never of known about

 

Anyone selling those aftermarket pads?


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That's what the 348 Brotherhood is all about. Helping each other so that owning a 348 is much easier.

 

One thing I can't seem to understand on this type of tensioner, is that there is a gap between the shaft and the tensioner pad, therefore Im not sure how oil would pass through the hole under pressure. The Peugeot one in the photo has a solid base so can understand that.

 

Looking at the tensioner picture in the first post here, it appears that the original Ferrari rubber pad is fused to the metal base (like the Peugeot one) so the oil has no other escape but through the hole and to the chain. The Stanyl pad, although not fused to the base, seems to be sitting fairly tight against the middle raised portion of the metal base where the oil hole is. If a corresponding hole is drilled through the Stanyl, the oil will flow through it. The oil is at rather low pressure inside the tensioner cylinder and at no pressure as it exits the hole in the metal base towards the hole in the Stanyl pad. As long as the Stanyl pad is in contact with the metal base raised portion, the oil will go to the chain. It is not a high pressure oil squirt anyway but more like just continuous wetting/flooding of the chain, and the face of the pad, with oil (which very well serves the purpose).

 

That makes sense, thank you.

 

Reversal of my post above. I came across my original pad last evening, and much to my surprise, noted that there is indeed a hole in the original pad, obscured on the face by the wear from the chain.

'92 car, Dec 91 build. Orig pad w/37k mi at time of removal. Image Unavailable, Please Login Image Unavailable, Please Login

 

As some foks asked me about this.
Is there a way oil under pressure can get inside the hollow shaft ?? I don(t remember, to long ago.

For me as the chain is inside the oil pan i think there is way enough oil for lubricating the chain. This little squirt hole won't make a lot of difference in my opinion.

"Im not sure how oil would pass through the hole under pressure" very simple : not.

There is so much motor oil flying around in that area that the little squirt means nothing and is not needed at all. My opinion.

 

"the original Ferrari rubber pad" i am not so sure this is correct. Mine ( from 9/1992) is 100% original and Stanyl.

 

I have the drawing if interested. But there is one dimension not correct !!!!! I will look it up.

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Also correct.

 

Yes, I see that now. My pad was completely blocked. How to blow it out with compressed air!