Dang Convert TC drive failed AGAIN

[brider]

I JUST finished a great week on my Cal 2 Auto on a trip up to New Hampshire and Maine, even made it to the top of Mt. Washington (and slapped the testimonial sticker to my saddlebag), but just today on my way home from work the dreaded slippage began. For the 3rd or 4th time I've had it.

All the way up Mt. Washington I was gritting my teeth waiting for the drive to start slipping, but it held fine. Guess I should be happy it got me home.

Fluid level is fine, caught it before I could cook it, but I'll bet 98% it's the hex drive interface in the timing cover. I replaced it once (the hex shaft). I thought once you replaced them with a tool-steel part you were good for life.

Who was that Convert-guru member who experimented with an electric pump?

[StuCorpe]

I think it was "Road Kill" or something on that order (RodeKill).  Made a trike out of a convert drive.

[John A]

Rodekyll I think, I’ll see if I can find him. I haven’t talked to him since last year. Talented guy, knows Converts alright.

[Antietam Classic Cycle]

Bought my '76 Convert with 18k miles on it. During the refurb to make it roadworthy again, I checked my original hex piece which looked worn on the edges. I replaced it with one made from an good quality allen wrench. Didn't even last 2000 miles - I was stranded one rainy Sunday in Punxsutawney, PA. Fortunately, I was rescued by Ralph Poole and family. At Ralph's I installed another allen wrench section to get me home.

Investigated why it was happening, at home in the shop. In my case, an M6 allen wrench fit very sloppy in both the cam and original pump coupling. To fix it: a) I swapped to the later pump with deeper "socket" in the coupling (approx. 8 mm vs. 12 mm) for more interface between the coupler and hex. b) I cut a piece from a 1/4" Bondhus allen wrench and had my friend Curtis surface grind each side until it was 6.2 mm. That fit snug in both the cam and pump.

18k miles later, it's still working fine, but at some point I want to remove the timing cover for an inspection to see if there's any wear. Maybe once the Convert Cafe' is on the road...

[brider]

18k miles later, it's still working fine,

I was hoping I'd catch your attention, Charlie. I went thru this on a '76 also, but my current PIA is an '85 version, and I don't recall measuring the pump depth when I had it apart last.

My history:

Original failure was at a predictable 20k miles. Replaced with 6mm allen hex piece. Bike was way out of tune after that for a long time and would backfire regularly as part of the starting procedure, and whaddya know the hex failed again ~3k miles after that. I learned then (from Rodekyll?) that backfiring was the kiss of death for the hex drive (and I have no other explanation for why mine failed so soon).

Fixed AGAIN with either an MG cycle or Moto Int'l-purchased hex piece, and that's the one now that is suspected of failing.

More history: Since my backfiring days, I took meticulous care to make sure the timing was right, and I never had another backfire UNTIL this past week while in Maine. Hot start under weird conditions, and one "bang!" occurred. Hard for me to believe this one event led to a rounded hex again, but still.....

[fotoguzzi]

I bet the one big backfire “could” ruin the drive piece.


I called this one the SPEVert.

[brider]

I bet the one big backfire “could” ruin the drive piece.

You think? That's a BIG weak link if so.

I called this one the SPEVert.

Yes, my eyes bugged out like a cartoon the first time I saw a pic of your creation (they're bugging out now). I call dibs if you ever decide to sell.

[wrbix]

As a new Convert owner, please educate me: what are the preceding symptoms and final failure SYMPTOMS of a failing hex drive.
I’ve put a temperature sensor on the TQC case but due to other unrelated (electrical) issues don’t have a feeling for what I’m seeing yet. Suspect flow failure would lead to rise in temp in the TQC….?

[Antietam Classic Cycle]

As a new Convert owner, please educate me: what are the preceding symptoms and final failure SYMPTOMS of a failing hex drive.
I’ve put a temperature sensor on the TQ case but due to other unrelated (electrical) issues don’t have a feeling for what I’m seeing yet. Suspect flow failure would lead to rise in temp in the TQ…..?

In my case, there was no warning or symptoms preceding failure. I had just passed some slower traffic going up a hill, and then could barely pull away from the stop sign at an intersection about a mile later. Managed to creep into an Advance Auto parking lot. Opened the ATF tank - fluid looked like a strawberry milkshake.

[brider]

The hex failure can happen suddenly without any prior symptoms, although I have never had it happen when under way at cruising speed. I can only assume that's because the load on the ATF system (pump pressure) is very low @ cruising condition. When you come to a stop, however, the load to get going again suddenly exceeds the ability of the worn hex edges to engage the female pump and the slipping begins to occur. As Charlie has indicated, the bike revs freely but there is very little forward motion. Screaming the bike WFO in an attempt to "get it going" just rounds off the hex piece faster, and you get nowhere faster. VERY gentle coaxing with the throttle can move you along temporarily, but the reduced pumping of the ATF means whatever is in the TC is just sitting there shearing away and eventually boiling.

In my case, a week prior I was grinding up Mt. Washington in low range, working the entire system harder than I think it's ever worked, for like 8 miles. I am astounded that the hex did not decide to round off then and there.