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Old 06-02-2018, 06:12 AM
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tail shaft - how much wiggle?

Hello all,

I had a leak at the rear of my reversing gear and am tackling the repair this year. So far I have lifted my engine forward into the "salon" and removed the output coupling and thrust bearing.

The spring was broken in the oil seal so I am hoping that was the root of the problem.

while i am in there i decided to replace the thrust bearing as well.

My questions.

1) Should there be any side-to-side play in the tail shaft with the output coupling removed? Mine has a fair bit of wiggle - maybe 1/4" or 3/8"?

2) Would this suggest a bum pilot bearing?

3) If so, can i remove the reversing gear with the thrust bearing plate removed?

4) Is this all covered in the reversing gear video?

Looking forward to your wise council.


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Old 06-02-2018, 09:02 PM
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The output coupling rides inside the rear bearing. With the coupling removed, the tailshaft will have some motion - can't really say whether 1/4" is too much. Check again with the coupling in place - should be fine.
Replacing the seal should stop the leak. First overhaul I did consisted of new rings and a new output seal. Engine is still in the boat to this day, and just completed a run from CT to Rockland, ME - including about 30 hr of continuous running (at reduced throttle, burning 10 gal of fuel). Only issue was an exhaust system failure, repaired class A in 9 hours at Burr Bros in Marion, MA.(yes, this is a plug - they're good and fast).
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Old 06-07-2018, 07:09 AM
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To close the loop on this, I examined the tail shaft on a blown engine I have kept for miscellaneous parts and trying out repair procedures on.

The tail shaft on that engine wiggled about the same as the one in the boat.

I concluded that is the normal amount of wiggle. I suppose they both could be bad too...

I finished the repair and cannot recommend the MMI Tech Video on rear seal replacement highly enough.

Transmission seems to work fine now - no leaks and much quieter with the new thrust bearing.


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