Hirth transmission removal

[oldguy]

whoops.. forgot to include the picture of the damper plate I removed

 

[oldguy]

here is picture of damper I removed

 

[Witzend]

Yep, that the POS! Look at the side and see if there are any cracks in the ribbon.

 

[oldguy]

is this the R&D design? there are no markings on it. it looks just like the pictures of the Westerbeke 044624 sold by discount marine (http://www.discountmarinesource.com/p-9309-westerbeke-damper-hbw-044624.aspx). here is the picture of the Sachs 1866 061 001 that Jim apparently used http://www.findpart.org/part/sac-1866061001

It looks like pic didn't get trough on my last post. Here it is

 

[oldguy]

Yep, that the POS! Look at the side and see if there are any cracks in the ribbon.

Please excuse multiple submissions of damper pic. need to get used to this website.

Nope.. no cracks in the ribbon, but incredible wear in the teeth. The remaining teeth have lost about 70% of their form. Also the inside of the bell cover had a significant deposit of steel powder from the worn teeth!

My new friend (John the mechanic at Hansen Marine Engineering of Marblehead) says this happened because of excessive time at idle in neutral. Apparently the shaft chatters when in idle. I don't think this kind of wear should really occur with only 550 hrs on the engine. There must be an unfortunate torsional resonance with this engine and damper that exaggerates the chatter. Lesson learned: avoid idling in neutral for long periods of time and when doing it increase rpm to 1000 or so to avoid the resonance.

 

[Witzend]

You got it, do not idle this engine. The plate is too stiff.

 

[oldguy]

So I'm finally done. It seems ok.
Here is my very long story.. I'm a retired engineer and couldn't help myself.

 

[oldguy]

quick correction: the transmission has a 2/1 ratio so the spline shaft turns twice as fast as the prop shaft, so a backlash of 9 degrees at the spline shaft would be 4.5 degrees at the prop shaft. Other numbers that I mentioned were all referenced to the spline shaft and would be half as much measured at the prop shaft.

 

[rpwillia]

Allen wrenches on Socket heads

Those give you enough torque to remove the bolts. You do need to rotate the engine (use a socket on the front of the engine on the crank shaft) to get to all the bolts. Been there done that.

 

[oldguy]

Those give you enough torque to remove the bolts. You do need to rotate the engine (use a socket on the front of the engine on the crank shaft) to get to all the bolts. Been there done that.

I tried and couldn't. Just another sign of my declining powers.

 

[oldguy]

some test results

After a couple weeks testing:
1)engine - transmission - prop shaft run very smoothly. Very little vibration above 1000 rpm. I think I nailed the prop shaft align
2) Definitely noticed slight vibration on the wheel that I don't think was there before. Maybe due to the fact that the prop is 1" closer to the rudder.

 

[damauney]

Curious. What Hurth transmission did you have and what did you replace it with. Thanks

Good winds
DaveM

 

[c130king]

Pretty sure mine was a Hurth HBW50 and the recommended replacement when looking on-line was a ZF-6. However, when I ordered it the dealer recommended the ZF-10 as it was more robust. And it fit just fine.

Cheers,
Jim

 

[oldguy]

Curious. What Hurth transmission did you have and what did you replace it with. Thanks

Good winds
DaveM

The original was Hurth HBW-50.
The recommended replacement (which I used) is Hurth ZF10M.