bad noise in reversing gear

[irtrimble]

I'm hearing a loud tap or clunk in the gear box which diminishes in forward and gets worse in reverse. Nothing looks loose in gear when I look inside. Local mechanic says it's in transmission, must pull engine. Any ideas, Don?

[Don Moyer]

For now, please do not pull the engine until we have a chance to kick around a few things:

1) The rear thrust bearing could have had a massive failure, in which case you should be able to grab the prop shaft and pull up and down (as hard as you can) and feel noticeable play. If this turns out to be the case, you could (depending on access to the aft part of your engine) replace the bearing rather easily.

2) One of the pilot bearings supporting the tail shaft and gear cage assembly could have failed, in which case you should be able to reach inside the aft housing (through the access in the top) and grab the gear cage assembly and pull up and down as hard as you can. If either of the pilot bearings had failed, you should be able to feel some play in the gear cage assembly and tail shaft.

Try to grab the back of the forward clutch assembly and then the tail shaft itself. If the forward pilot bearing failed (OREV_08_228 in our online catalog), the whole assembly will appear to be loose in the front, where the gear cage slips over the rear of the crankshaft. If the inner pilot bearing failed, the play will feel more like a "bending" in the center of the shaft (at a point just behind the gear cage itself).

Don

[irtrimble]

I tried your suggestions. No apparent play in propeller shaft. More difficult to evaluate play inside gearbox; lying on my side on quarterberth, reaching into engine compartment and down into gearbox, it was hard to get much force on it, but not obviously loose at either end. Where does this leave me?

[Don Moyer]

Before giving up on something outside the reversing gear assembly, I'd disconnect the prop shaft and then see if the noise is still there when you run the engine in forward and reverse. You'd have to disconnect the prop shaft in any case if you decide to move the engine forward, so this is not wasted effort.

Don

[irtrimble]

At this point my boat is up on stands in Nova Scotia, Canada, and I am home in California, unable to try any more experiments on the old engine. I am thinking that it's time to replace with a rebuilt engine. The present engine went in in 1983, I think, and aside from a new carburetor hasn't had much maintenance.
Have you had engines shipped to you from Canada for rebuilding?