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Old 26-04-2012, 16:08   #1
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Join Date: Oct 2009
Location: Redondo Beach, CA
Boat: 1990 Oyster 55
Posts: 288
Hurth HBW250 to Bell Housing Torque

I am currently replacing my Hurth HBW250 and I can't find the torque spec for the six bolts which hold the transmission itself to the adapter plate which fits into the bell housing.

I am not talking about the six bolts which take the round adapter plate and mount to the bell housing on the engine.

These are going into an aluminum transmission through an aluminum plate and do not want to carried away tightening them.

Additional question: When I pulled the six bolts out to seperate the transmission itself from the adapter plate two small pieces of what appear to be aluminum shim material appeared on the matt I was working on to make sure I did not loose anything. The two pieces are about 1/8 - 3/16 in thickness and a quarter inch thick, an inch long, scored and tapered on one side like a serated knife. They look to be shims or wedges which showed up after I pulled the adapter plate off the transmission. I am almost 100% sure they were not loose on the transmission before I pulled the bolts. The only place I could see for them would be on either side of the lower square bearing cover (toward the engine not the output shaft) between the bearing cover and the adapter plate to keep the transmission from rotating.

With the 6 bolts through the flange into the transmission finger tight I can rotate the transmission a few degrees so the only thing preventing a slight motion is the friction between the adapter plate and the transmission with the bolts tight.

The pieces of metal shim appear to be low strenght "pot" aluminum and have a small curvature to them as though you would tap them into place.

Anyone seen something like this or am I missing something failed on the other side of the flywheel which is very tight in the bell housing.



p.s. the fun started when I was chasing a noise in gear under reasonable load (1400 RPM ish) pulling on dock lines and hear a knock from what appears to be inside the transmission. I assumed the damper plate, pulled it and it is an R&D linear elastomer damper plate, checked entire drive train, pulled off rope cutters, re-greased max prop, rebuilt Aquadrive system, etc. Noise is very intermittent, can take 10 min to show up but with mechanics stethascope on transmission housing can generally hear it so most likely transmission at this point. The "extra parts" was a last minute surprise!
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hurth, hbw 250

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