Possible Preventative Quick Fix for DR350 Crankshaft / Counterbalancer Problem

Some DR350s have self-destructed when the pin that locks the counterbalancer timing gear to the crankshaft moves and releases the gear. This allows gear to rotate freely and the crank and counterbalancer collide. See the catastrophic results here.

Jesse Keinz of Keintech Engineering has developed a permanent preventative fix for the problem but it requires splitting the cases and removing the crankshaft. I'm sure that's the right thing to do but it is a whole lot of effort, particularly on a motor that's otherwise working fine.

I recently had the cylinder off my '97 model to refresh the top end and could clearly see that the crankshaft in this motor was drilled all the way through as described in Jesse's writeup and hence is a candidate for the problem. I considered spliting the engine and sending the crank to Jesse, but instead, I decided to try to an easier fix. As I understand the problem the locator pin works fine unless it moves (about 1/4") and releases the gear so my thinking was that I might be able to "glue" it in place using a metal reinforced epoxy. I've used JB Weld in many hot oil contact environments and have found it to be amazingly durable even under those adverse conditions. So, I decided to try it here. The idea is that by filling the hole with JB Weld, the locator pin won't be able to move and release the gear.

My motor is out of the bike which allowed me to move it around easily but this procedure could be done with motor mounted - it would just be a more awkward place to work with the bike laying on the floor.

The steps were:

1. cleaned the area and particular the inside of the hole carefully - first with carburetor cleaner (spray straw) then followed that up with a couple of teaspoons of lacquer thinner - let the excess drop into the crankcase where it exited through the drain plug hole
2. blew the area completely dry with compressed air
3. oriented the motor on the right side
4. mixed up my JB Weld and used it quickly (while it was still "flowable")
5. using a long flat blade screwdriver, I carefully dripped and packed the epoxy into the hole being as sure as possible that I wasn't trapping an air bubble - sort of like the way a dentist fills a cavity.
6. after about an 2 hours when the epoxy was no longer liquid but was still soft I pressed it down into the hole with my finger as firmly as possible to force out any voids.
7. let it sit for 12 hours to harden

Since the solvents stripped away the oil from everything they touched, all the bearings were manually re-oiled before re-assembly.

The JB Weld plug is visible here

Only time will tell if this works or not. Although the cured epoxy is pretty tough stuff, it is still far softer than the metal parts so I'm guessing it won't do any harm. Even if the JP Weld plug were to escape, it would most likely just lay in the bottom of the crankcase or, at worst, get ground up by moving metal parts. The risk of that is probably no greater than the pin releasing the gear and we already know the outcome of that event!

Post Script: In the FWIW department, it was necessary to pull the head at about 5K miles for another reason so I went ahead and pulled off the cylinder to check the status of the "plug". As can be seen in the photo below, the JB Weld was still solidly in place so this appears to be a long term "quick fix".

The JB Weld plug after 5,000 miles

Post Post Script: I haven't had a reason to tear down this motor so I haven't actually looked at the crank; BUT, approximately 2 years later and 15K hard miles later this motor is still going strong. It may not have failed without the epoxy but a few minutes of extra work during a simple top-end rebuild provided some extra insurance.