Chain Tensioning (not Tensioner) Question

[Steam Driver]

I think I have seen this discussed, but I have a question about chain tensioners and valve timing.

Why is it recommended that mechanical tensioners, C-clamps, etc. be used to tension the timing chains when setting camshaft timing? It seems to me it would be simpler just to use the tensioners themselves. This is certainly the way it is shown in the Bentley manual; I don't see any mention or trace of mechanical tensioners or other means there, nor was there as I recall (from long ago) in the 914-6 shop manual. When I rebuilt that engine I added the Carrera tensioners to it and used them to provide the tension for cam timing.

Since the chain is running under the tension provided by the spring in the tensioner itself, why isn't this now deemed enough when setting cam timing? And let's not hear anything about pressure feeding; the pressure feed is to keep the tensioner filled up so it hydraulically resists collapse. It does not appreciably add any tension at all.

Just curious. Clamping, swapping tensioners, etc. seems a lot more risky than just installing the tensioners one intends to use and be done with it.

[snbush67]

The purpose of using a solid surface during cam timing is to avoid tension as the process requires exact conditions. It is not used to simulate the tolerances in tension required in a running engine.

[Flat6pac]

I'm sorry, if it so exact, or needs to be so exact, why does the settings come in a window of upward of .3mm. With chain jammed up tight, it will never be duplicated in a running motor, so, the number set on timing is "in the window".
Bruce

[cgarr]

Can't let perfect get in the way of done! quote"Bob Witzel"

[prschmn]

Originally Posted by cgarr

Can't let perfect get in the way of done! quote"Bob Witzel"

Good one!

Remember that cams can "cog" ahead at times which I suspect is the reasoning
in insuring a hydraulic tensioner cant back off. Once the engine is turning at any reasonable RPM there's effectively constant tension on the chain-one of the reasons
why before the pressure fed ones they almost invariably failed at or near idle.

I remember hearing the "it was fine all the way down the highway until I stopped at the exit ramp" a whole lot of times.

[bpu699]

I asked in another thread, but its buried at the end... I kind of have the same question. I did my cam timing for a 930 with a mechanical tensioner, and got perfect spec (goal 0.6-0.8 for a 930), I got 0.7. Put the tensioners in, rechecked, now its 0.6...

Clearly the mechanical tensioners stretches the chain a bit more... So, do I redo the timing with the tensioners in? Or, go with the timing as set with the mechanical tensioners (clamp)?

Thanks

[Bigtoe32067]

Leave it