I'm going to have the dealer do that. But what would you expect me to see in there? Some have said it could be a blown up compensator. Is that the thought here?

 

My guess would be a broken comp sprocket cam. Some have been known to break under higher performance motors. When it goes you lose the connection between the motor and clutch, hense it won't start. With luck it's an easy fix.

 

I’ve done a lot of research the past 2 days and I also lined up the pick up from the dealer. They will come get it Tuesday, provided MD doesn’t go full quarantine. And that’s possible.

It’s still coming down to these two main possibilities - the compensator or sumping/destruction. The fact that the oil was frothy (boiling?) and that there was a burning smell and that I lost the power and engine at high stress (70-80 mph, accelerating) leans towards sumping and destruction. I recall no chatter in the primary at startup(like a failing compensator would do) or any vibration or other sounds as if the comp socket had broken or jammed up.

But I also don’t recall any of the subtle performance problems indicative of sumping. Not that day or the day prior. When the problem occurred at speed, I didn’t lock up. So the engine didn’t seize. It DID die as I slowed (as if the friction finally overcame the power and it locked then) but even then it didn’t lock up the rear wheel, or experience engine drag, which I would have expected since I was in gear. These symptoms make the case for the compensator failing.

Either failure would keep the engine from starting. It just occurred to me, if the engine is locked, I shouldn’t be able to move the bike while in gear (while off). But if it moves easily, then the crank is probably disconnected from the clutch, because of the broken compensator. Does this reasoning make sense?

 

Yes, that's correct, with everything ok, switched off and in gear you might be able to roll the bike a few inches, before all the backlash in the transmission is taken up and the movement tries to turn the engine over. If you can just push it about in gear, it would seem to point to a problem with your primary drive.

 

First off it's not sumping. The bubbles you see are a characteristic of of a dry sump oiling system. The return pump has a higher capacity then the feed side so the scavenge pump pulls air besides oil. The problem is that you did not get the oil real hot so the bubbles stick around. Hot oil they disappear quickly.

Comps can fail more than one way. They can wear out (clatter common on 6 speed TCs) or they can break. I've not seen any M8 comps wear out yet tho I'm sure some probably have. The more common issue seems to be from what as been observed here is that the bigger M8 motors break the sliding cam. In that case there is no warning.

Someone with experience should be able to tell quickly whether it's the primary or motor. Motor could still be an issue. If the starter sounds like it is spinning freely, chances are it is in the primary. If spins but still seems like it has a load then it's more than likely something went in the motor. A possible issue is that the cam lost timing, say by the pinion sprocket coming loose. In that case the motor could bend valves and loose compression. Motor will turn over freely but not run. Motor can die this way without locking up.

 

Thank you. That is a fantastic explanation. The bike is getting picked up tomorrow (repair shops are essential) so someone more experienced will definitely look at it. Thanks for explaining the oil. I didn't like the look of it (still don't like to color, so I may change it myself when I get it back) but explaining the frothing makes sense.

As far as I can tell, there is no load on the starter when trying to start. It feels like it's spinning the starter but not the engine. That would be a best case scenario, I think. That should be a quicker repair than an engine tear down and replacement!

So, if it is the compensator, what's the repair solution? It seems silly to replace it with the same OEM compensator that just broke. Is there a better option?

 

There are aftermarket comps but I don't have any experience with them. My M8 is simply a stage 2 107 RK with stock mufflers. I've not had any problems.

Dark Horse Crank just came out with one. (no data)

Baker is on their second revision of the TC comp which they have a model that fits the M8s. (wonder what was wrong with their first, no data)

Vulcan makes a comp eliminator sprocket. (would tear up drivetrain IMO)

 

Yeah, I can't believe getting rid of a comp altogether would be a good move. Especially on a higher compression engine. It's in there for a reason, even if it's faulty. I know a lot of folks are skeptical about the MoCo, but being an engineer I do believe they engineered the system to include a comp for a valid reason.

 

So the dealer picked up the bike today. Did a few tests before loading.

First of all, the bike does NOT move while in gear. It wasn't off the ground, so I wouldn't expect it to move easily. But shouldn't it move some?

Second, we tried to start the bike again and this time the motor DID crank ... a little. The starter seemed strong - it sounded normal. And the bike lights didn't dim or anything, so the battery and electrical system is probably OK. (?) But the motor never spun enough like it was going to start. It moved, unlike before. But you guys all know what a bike sounds like when it *might* turn over. It wasn't rotating that much. Still, this was more than was happening before. And that would seem to imply that the engine isn't frozen . I don't know what (if anything) it says about the compensator.

 

That's been debated for years......

The comp definitely makes for smoother performance, when they work properly...

Some have eliminated the comp with rave reviews.... Some have eliminated the comp, hating the feel of engine pulses afterward...

Most will be wary of the MoCo cranks handling the lack of "cushion" from the comp.... Some claim to have eliminated the comp on OEM cranks, ridden hard and had no problem... Some will say that with hard driving, the comp is taking up its slack immediately and doesn't cushion anything...

In my reading about this issue, most who have good things to say about eliminating the comp, usually have big bore engines with improved HD cranks, or aftermarket cranks such as S&S, and they switch from 34 tooth, to a 32 or 30 tooth solid engine gear...

So you see, anecdotally, you can find someone to support whichever choice you decide to make.....