A solid chain tensioner??

mark 74 carrera · mark 74 carrera's Garage

While I was visting Dave White's Racing once I saw what Dave described as a solid chain tensioner. He said they used them in race motors because they were always in the engine working on things.

Why would my car have these? What are the advantages or disadvantages to running a street car with solid tensioners? I am at a loss.

Leland Pate · 02-16-2004, 07:09 PM

I've often wondered that myself. It seems I see other brands that use a fixed position chain tensioner... wonder why they need to move in a Porsche...

I can think of half a dozen reasons... but I haven't a clue as to which one is right.

markwemple · 02-16-2004, 07:14 PM

It places less stress on the rest of the engine, including the chain, which we wouldn't want to break. Racing engines get broken down and checked regularly. They don't need to last 100-200k. I think yours might have them because, they don't fail and they were once cheaper!

Jkaser · 02-16-2004, 07:20 PM

I found these units in my '75. It must have been a pre-'84 "bombproof" fix. I've finally broken down and ordered the Carrera tensioners due to the many warnings I've read in searches here and on Rennlist. Too much about chain stretching and cam sprocket wear from improper adjustment. I have never come across any quantitative value for proper adjustment of the mechanical tensioner, either. I guess the racers are in there so much that they develop a "feel" for this adjustment. So, I expect to be a little more comfortable with the higher revs, etc. when I get this upgrade done. Good luck with the rebuild!

Paul Valcourt · 02-16-2004, 07:36 PM

I also found solid chain tensioners (see pic) in my 75. They were in there for awhile with no problems but I changed them out to hydraulic anyway.

Leland Pate · 02-16-2004, 07:41 PM

Must be because of the long length of chain in 911 engines... pushrod V8's don't have a hydraulic/mechanical tensioner.

David · David's Garage

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markwemple · 02-17-2004, 01:21 PM

Another option , which is cheaper, is to go to the old style hydrolics. By this I mena the non-carerras. If you install a fail safe or "hydra-stop" they are actually a better alternative. Both style of tensioners have a "lifespan". The carerras have failed. Bruce Anderson even addresses this issue (can't remember where). With the faiil safes in place, the chain will not drop to a fatal point. Once you get cahin noise, just replace them. Better yet, get into the habit of changing tensioners and rails every 50k like a timing belt. Porsche should list them as a regular service item as both have a safe life of about 50k. Oh well.

Bill Verburg · Bill Verburg's Garage

The solid chain tensioners were marketed extensively in the "Bad Old Days" i.e. pre "84. Back then tensionor failure was common, if not caught in time serious damage would result.

The down side to them is they only tension the chains properly in a single temperature regime, usually ~200&deg F. This means that when cold the chains flail and slap unmercifully. This is Ok on a race car wheich is tended to very well, but not so good for street use.

Mr9146 · 01:40 PM

The mechanical tensioners work great ... I've had 'em in my 2.4S daily driver with no issues for 10K+ miles.

They're also in my dad's 2.8RSR daily driver with more than 50K on it ... no problems.

The reason the factory went to hydraulic tensioners is, basically, a matter of maintenance. With Carrera style tensioners there's less overall maintenance because they automatically take up slack as the chain stretches with wear over time. Mechanical tensioners, obviously, do not; but I've NEVER had a problem with solid tensioners and would recommend them to anyone building a race motor without hesitation.

HarryD · 02-17-2004, 01:58 PM

If anyone wants a set of the non-carrera type, I have a pair available. I interested, E-mail me privately.

Paul Thomas · 02-17-2004, 02:16 PM

Is there any reason why you couldn't upfit an older engine with 964 style "tensioner" chain ramps? Aside from the fact that you would have to do it during a rebuild?

Paul

Oldporsche · 02-17-2004, 03:25 PM

I have converted a lot of old failed chain tensioners to sold types. I have them in my 911E at the moment. This is not a set and forget item. I was into my chain boxes about every 6 mos. anyway. (Autox a lot!)

When I get that car back on the road, I probably won't use them.

Good luck,
David Duffield