Hydraulic Chain Tensioners in HP Motors?

[Jim F]

Hello:
I just finished installing a new high output motor that I had built for my 70 911t and am concerned about the decision the engine builder made to not installing hydraulic valve chain tensioners in the motor when it was built. The engine builder told me that he was worried about the motor grabbing r's way too fast for the hydraulic chain tensioner's to keep up so he went with mechanically chain tensioners and told me a keep religious valve train maintanence schedule. is this really the case? I've heard many horror stories about Mechanical tensioners. I am reasonably mechanical and am comfortable with adjusting the valves and tensioners, but don't want to go this way if it isn't prudent.

For some background, I started w/ a 2.7 case. the case was properly machined, shuffle-pinned and boat tailed, A forged crank was straightened, Knife-edged, and micropolished. 2.9liter Mahle barrels and pistons were fitted and the heads were milled, ported and polished with oversize multi-seated valves installed. I used Porsche 906 camshafts, and put 44PMO carbs on it as well as a MSD ignition system. Even though this is a very high reving motor, it will be driven on the street occasionally but was built for time trial and autocross events. Any informed opinions please?
Thanks

[jluetjen]

Interesting. Looking at some pictures I have of different 911 race motors (906, IROC RSR, etc) I don't see any sign of hydrolic tensioners. I wonder if it was the issue you described Jim or just a desire to remove anything that could break and that is not specifically required in order to improve the reliability of the motor.

Hmmmm....

[Wayne 962]

High horsepower and race motor are two different things. You should only use mechanical (non-spring) tensioners on race motors that will be run for a few hours.

That said, I would go with the hydraulic tensioners. The fellow rebuilding your engine seems confused, as the hydraulic ones are actually spring-loaded as well - they are just supplemented by a dampening feature that is supplied by the hydraulic oil.

Does PMO make 44s? I thought it was only 46s?

-Wayne

[BBShriver]

If the hydraulic does have a spring backup (my Jag XK has this as well, so that's what I'd expect) why would you use mechanical at all given the option? i.e. why is mechanical better for race engines?

Originally Posted by Wayne at Pelican Parts

High horsepower and race motor are two different things. You should only use mechanical (non-spring) tensioners on race motors that will be run for a few hours.

That said, I would go with the hydraulic tensioners. The fellow rebuilding your engine seems confused, as the hydraulic ones are actually spring-loaded as well - they are just supplemented by a dampening feature that is supplied by the hydraulic oil.

Does PMO make 44s? I thought it was only 46s?

-Wayne

[Flat6pac]

The mechanical tensioner has a correct setting only once over a warm up and run. Once the chain has stretched with the thermal change the setting is no longer correct. If your concerned, install collars on the hydraulic tensioners and all is well, if you rev too fast the ttensioner will drop down to the collar but the rest of the time support the chain.
Bruce

[kenikh]

I only use 930 tensioners w/ collars now. Simple, reliable and they don't break. If they do, you have a collar to save you.

[longhornchris04]

Remember, the hydraulic chain tensioners didn't debut till '84 (so says our host's page selling them), after a number of the race motors that were mentioned in the OP.

The only reason I can think of for using the purely mechanical ones is on a race motor that will be torn apart anyway. My assumption is that you can use a higher pressure spring to ensure the chain doesn't ever get loose, and reliability is a non-issue as race motors are rebuilt - well before spring failure. That, and mechanical tensioners are probably marginally cheaper.

Now, for a straight, "high HP" configuration, I'd stick with the hydraulic. If you are that concerned, add collars to be safe.

[Flat6pac]

You are confused on the terminology I think.
Mechanical are a block and a threaded bolt with a lock nut.
Hydraulic is the tensioner off the 64 to 83. These can get the collar.
Carrera or oil fed are from 84 and the collars wont fit..but these will fail on occasion even that they were thought to be perfect in the introduction.
Bruce

[longhornchris04]

Makes sense, and a block, threaded bolt, and lock nut would need adjustment periodically... which is a non-issue in a race motor that is torn down on short mileage intervals.