WCAC

Mirage 257, blown 502, MC XR drive.

Went out today. Running about 5k rpms in light chop. Everything was hooked up good and going about 75mph. All of the sudden sounded like it popped out of gear. Once i stopped i put it in reverse, no problem. Reverses fine. Put it in drive (forward) and it sounds like it popping between " in gear" and nuetral. I made sure the cable is going fully in forward in drive itself. Still popping and grinding like its halfway in gear and halfway in nuetral.

Any thoughts?

indysupra

Sounds like it sheared the teeth in the forward gear.

Mr Gadgets

It is possible that you broke the ring gear off the hub on the forward gear. I have seen this before. The ring gear is fusion welded to the hub on all the bravo merc upper gears. There is an air space that circles around the gear where it is welded. The last one I saw didn't damage anything else, very lucky in that situation. Only way to know for sure, what happened, is to have it torn down and inspected. Gotta love the Merc gears to keep you on your toes, or on the beach..
Hope that helps.
Dick

WCAC

Yea. Sounds about right. What would be a logical upgrade for my drive to try to hold up to this?

thirdchildhood

This nut is used to adjust the input bearing pre-load. It relies on nyloc to hold it in place. Even if loctited it can easily back off. There are fixes for this design flaw. I lost an XR upper this year because of this. I wonder how many people have blown XRs because of this which would have otherwise held up. Once that nut loosens the input shaft can wobble and causes uneven gear wear and eventual failure. Mine broke the case when it let go.

pqjack

interesting....what are the fixes??

JaayTeee

If you hard shim it, that will take care of it.

I had the cone shear off the gear like Dick mentioned...it actually started with a crack in between the teeth and as it flexed, it eventually broke....that God for rev limiters.

thirdchildhood

That seems to be the preferred fix and that is what Victory Marine said that they did with my replacement. I'm going to have it checked before the 90 day warrantee is up. You can also loctite it and use a blunt chisel to put a few crimps in the nut. I also thought that maybe a tack weld would be a good fix but my mechanic doesn't like that idea.

dereknkathy

as long as you aren't planning on ever disassembling it again, welding the nut to the shaft is a good idea...

Mr Gadgets

With new bearings they will loosen up as they break in, usually .001" or so to tighten them back up. So I wouldn't recommend welding them. Shims behind the pinion gear to set the preload and tightening the nut against them works. Imco came up with this process years ago.