Clattering Sound in 5th Gear

[dps650rider]

Was out for a leisurely evening cruise and suddenly started hearing a clattering sound. At first I thought it was a valve but as I played around with it I discovered it didn't make a sound under any other conditions except in 5th gear. Rode the rest of the way home in 4th without a bit of unusual noise.

Looks like a transmission tear down is in order but I am a bit mystified how a gear problem could make such a sound. I tried several times to recreate this sound in 4th at the same RPM and at various throttle settings but it was silent.

Anybody have any ideas?

 

[TwoManyXS1Bs]

Hey, dps650rider. Last time I got a clatter in 5th was last November.

It was my teeth.

There's several reports here on the adjacent (driving, mainshaft) 3rd gear slider weakness, busting off a dog or two. Could try draining the rear sump and magnet/fish for stuff...

 

[dps650rider]

Sorry about the duplicate post, I forgot to add the engine tag and there doesn't seem to be any way of changing that once the new thread is saved.

Anyway, went on a fishing expedition and found a tooth from a gear in the sump. Given the symptoms and the lack of notches ground into the tip of the tooth I'm pretty sure this tooth is from the Mike's 5th gear I installed back in '07 which now has 46K miles on it. Will find out for sure in the next couple days after I tear it down.

So now it looks like I have a choice to make, if this is in fact a failure of Mikes gear I will not be putting one back into it. I really like the ratio change but not as much as I dislike having to tear it apart during our relatively short riding season. The choices are:

* Just replace the gear with the original one after inspecting the trans for damage.
* Get another complete transmission from Ebay and swap the whole thing.

I'm leaning toward the second option fearing that there could be a crack in the mating gear that I cannot see.

Opinions?

 

[TwoManyXS1Bs]

Yep, bad news.

The grainy appearance of the fracture looks like MIM (Metal Injection Molding) manufacture. Not unusual, most complex parts made that way, just not strong like billet.

The 'ding' marks on that tooth make me think that some other foreign matter was circulating in there prior to the incident. May have caused it. So, more surprises may be waiting.

Of course, the opposing 5th (wheel, driven, countershaft) gear may need to be replaced.

 

[TwoManyXS1Bs]

Sorry about the duplicate post, I forgot to add the engine tag and there doesn't seem to be any way of changing that once the new thread is saved?

Way at the bottom of the thread is the 'tags' and 'edit tags' hyperlinks.

I edited this thread's tag list (which was empty) to include "engine". As I understand it, anybody can edit the 'tags' list.

What I DON'T know is if that is the same as the 'tags' you enter on thread creation...

 

[dps650rider]

Do you think this is an indication that this replacement gear was weaker than the OEM?

I was thinking the ding occurred after it broke but that is just a guess.

 

[dps650rider]

Way at the bottom of the thread is the 'tags' and 'edit tags' hyperlinks.

I edited this thread's tag list (which was empty) to include "engine". As I understand it, anybody can edit the 'tags' list.

What I DON'T know is if that is the same as the 'tags' you enter on thread creation...

OK, thanks I see the links.

 

[TwoManyXS1Bs]

Do you think this is an indication that this replacement gear was weaker than the OEM?

Dunno. MIM manufacturing has its specs and procedures to achieve material properties. Sloppy manufacturing and shortcuts don't help.

The cracked tooth looks like it was adjacent to one of the engagement slots, obviously a weaker zone. But that weak zone would be thinner/weaker on the smaller OEM gear.

Have yer eyecrometers calibrated before teardown.

I'm seriously curious. Post up some pics when you get in there...

 

[dps650rider]

Here is another pic of the tooth showing multiple dings. Looking at this I now think that you may be right, that the gear was damaged (cracked) by debris and then broke as a result.

A couple years ago I had a big end rod failure that I attributed to valve seal debris (don't ask how they were destroyed). What I am thinking is maybe this gear was cracked a while ago and finally let loose now.

I have ordered a transmission from Ebay and am now trying to decide on getting another Mike's gear. I really like the ratio change so if am reasonably sure that this failure was the result of debris I will order one now.

 

[TwoManyXS1Bs]

Yeah, lotsa dinging there. If it was debris causing that, then I'd expect to find similar dinging on all the other gears. If the other gears and the opposing gear don't have that dinging, I'd suspect a weak/soft OD 5th gear. Check primaries too...

 

[dps650rider]

Can't imagine how all of that could have happened after the tooth broke off. Another thing, under magnification the edges of the dings look worn like they had been there quite a while.

Hopefully it comes apart tomorrow...

 

[pcoumbe]

Please post what you find once you tear it down with pictures. I'm very keen to see the outcome. There's been much discussion about these gears but I haven't seen much in the way of reporting on failures. I'm running these gears also and have done about 10k on them now without an issue. Like you I really like the split between 4th and 5th and reckon it was one of the best changes I've made to my bike. I sure hope your problem is from the previous failure with debris running through the teeth and not just another inferior part from Mikes.

 

[dps650rider]

Got it apart, all gears look OK except Mike's and the mating gear. Check out the bearing race for the main shaft, this bearing is right next to the 5th gear pair.

Does this look like galling?

 

[weekendrider]

It does to me.

 

[TwoManyXS1Bs]

There's a lot of pitting and spalling on those 5th gears, destructive pitting on the mainshaft end, and what appears to be signs of light brinnelling on the drive faces of the other gears. Galling will usually have scraping trails, most noticable in stainless-to-stainless sliding action.

Bearing failure analysis is a career path of its own, gets quite involved. I'd have to say that multiple things are at play here.

First is bearing life expectancy, they eventually succumb.
Second is lubricant contamination, suspected in the light brinnelling of the other gearfaces.
Third is a wild guess at the OD 5th gear. It's surface may have started pitting, then spalling, from surface hardness insufficiency. Then again, if the opposing (driven) 5th had pre-existing spalling damage, it could have taken out the OD 5th. Chicken and egg kinda thing.

I guess you'll have to call it as you see it. You've had the bike for quite awhile, and did your own oil changes and filter cleaning. So, you have a better idea of any contaminate history.

You could try to closely examine the spalled surface textures on the OD 5th and its opposing 5th gear using an eyeloupe or good magnifying glass. The one that's grainier would likely be the one that fracture/spalled from improper surface hardness. And, the one with the smoother surface would most likely have brinnell/spalled, from compression/displacement caused by contaminates.

If MikesXS had a Failure Analysis lab, I'm sure they'd like to receive those gears for examination...

 

[dps650rider]

This transmission has a lot of miles on it, probably around 80000 (bike has 130000 all from me ). Could that be a factor here?

 

[TwoManyXS1Bs]

I hope that's an extra zero in your 130000 miles.

So there's 67,000 miles of Previous Owner usage?

That's quite a bit. But that comes from my '70s thinking.

I worked on a lot of blown trannys back then, most had much less than 20,000 miles.
That's just the way things were.

For a pampered bike, 80,000 miles may not be too bad.
For the abused stuff we ran into down here, 15,000 miles was near impossible to achieve...

 

[dps650rider]

I am the original owner, 129,450 miles.

 

[TwoManyXS1Bs]

Holy crap!

You, my friend, have a bike that's well beyond my comprehension...

 

[dps650rider]

So, I dug out the original 5th gear from the transmission currently in the bike and look what I found. This gear had damage similar to what is seen in the failed gearset. If you consider that the mating gear to the OD gear probably looked a lot like this when the OD gear was installed, and that it ran for 46K miles before failure I don't think I complain about Mike's OD gear. That's a real good thing considering the improvement it gives and the fact that I have already ordered a new OD gear and a used gearset from Ebay.

Lesson learned: before installing one of these gears inspect the mating gear very carefully for damage.

BTW, thanks TwoMany for the helpful tips!