Drive Problems
 

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?

Sounds like it sheared the teeth in the forward gear.

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

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

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.
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interesting....what are the fixes??

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.

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.

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

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.

What about using a exact fit tab washer behind the nut. Pull the tabs down to lock against the nut after proper torque. Wonder if stage eight would have anything that works for that app. No offense, I would rather use a chisel to get a nut off rather than notch hitting to keep in place. I would think you might be loosing some integrity of the nut itself.

I had kicked around a lot of ideas on fixing this. An old auto wheel brg style lock washer would work but you would have to machine a slot or flat edge on the shaft. That would not be easy and might compromise the strength of the shaft. My mechanic, who posts on here and I trust very much has had success with the red loctite and a few extra crimps around the nyloc. I like the idea of shimming it to proper pre-load so that the nut can be tightened down properly. The nut on mine had backed off about 1/8 inch and could almost be turned with your fingers.

Dick,
Not trying to hijack the thread, I have a upper gear cut apart and the cut polished and always wondered if one would ever let go there at the weld. How many inertia welds have you ever seen let go ? Just curious.
I build a lot of SV and SVL, P3 and 4 drives and think mine don't see the load some of yours might. Orrr I'm just plain lucky
Thanks in advance.
WB

WB,
I have seen a couple of clean breaks, all the way around. Then some break half way around and splits the ring gear into multiple pieces. I have seen more "one tooth snapped off at the root" than the weld failing.
I recently removed the inner bearing on a gear to replace it, I attempted to pick up the gear and ended up with only the hub. The bearing inside was holding the gear together. Gotta love it.
The SCX doesn't have that problem.. :)

Thank God the SCX doesn't have that problem , just converted from SC to SCX , the SC had all XR stuff in it .

Dick
Thanks for the info. I guess the race drives I build for these offshore classes aren't heavy enough to stress the welds or I'd seen one by now. Any chance there were just a bad batch of sets sent out?
WB

I think every 4th or 5th one is a bad one. You just don't know, from snapping teeth to ring gears breaking loose. I put two SC's together last winter and they lasted all season for a guy. He had fun with it, the way you are suppose to. Others aren't so lucky. But I never saw these two problems before 2006. I have to believe Merc changed suppliers and the new generation doesn't know how to forge them like the old duffers did..
Not too many ring gear failures, more teeth snapping at the root than ring gear problems.
Dick