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Comparative analysis - tensioners
Posted by Gary Stottler (more from Gary Stottler) on Fri, 22 Jul 2011 12:23:51
In Reply to: That car ran several competition events, DrewP , Wed, 20 Jul 2011 09:32:14
All,

OK, I dug out a new Saab tensioner and a new MG tensioner and laid them
side by side. For good measure, I also threw in a Triumph/Saab 1.7/1.85L
tensioner I had lying around. For some reason Saabnet is giving me a Spam error message every time I try to put in an image or a link, so if you want the pictures, email me off line.

First, overall, all 3 tensioners have the same bolt pattern, the bodies are the same width, all have the same bore diameter, etc. So any of them will fit on a "B" block. The Triumph tensioner is just like the "B" tensioner except the shoe is narrower, so can't use that unless you can reuse your old shoe.

Second, The Saab tensioner does not use oil pressure at all to push out
the tensioner. It relies completely on the spring in the plunger. It
has a very small orifice (probably no more than 0.020")allowing oil into
the tensioner and a large hole in the face of the shoe (~1/8") letting
oil out onto the chain, so there's no pressure inside the tensioner
plunger - all this just provides a little oil for the chain. The MG
tensioner has a large orifice (~5/32") letting oil into plunger and a
little smaller one (~3/32") oiling the chain. Still not enough
difference to build up much pressure inside the plunger.

Third, the little dowel pin with the orifice in it will come out of the
tensioner (the last engine I took apart it stayed in the block). This gives us a solution to the use of the MG tensioner.

CONCLUSION: The large orifice in the MG tensioner will let a bunch more
oil out of the high-pressure oiling system (and onto the chain). So, it
is like having a leak from high pressure (galley) to low pressure (chain
cover/pan). The Saab pump may have some excess capacity, and this may
not be a problem under all conditions, but there's some risk of low oil
pressure, particularly as the engine gets older and other clearances
increase.

RECOMMENDATION: Go ahead and use the MG tensioner, but keep your old
Saab dowel pin with the small oil orifice in it. I see no reason not to
mix and match other parts among tensioners as well if nothing is worn.

Good Luck!

posted by 198.208.15...
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