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Exploding Clutch Dog 1993 48hp Johnson

D

dogtired

New member
I had a lower end failure and upon disassembly found the Clutch dog in pieces and damaged gears. Replaced all, shimmed the pinion gear and reassembled. Ran engine gently for maybe 5 hours total, everything seemed fine. While engine was idling in NEUTRAL (3-4 minutes) engines suddenly stops. Flywheel does not rotate freely. Upon disassembly I find the clutch dog shattered in 5 pieces. Does anyone have insight into why I would experience while idling in neutral?
 
The thrust bearing that I replaced was either the forward or reverse. Nothing was changed on the driveshaft other than the pinion gear and shims.
 
In my 30+ years experience I have encountered a exploding clutch dog but one time... and never a repeat performance such as "dogtired" explains. Yeah "bullet", that makes me wonder OEM or aftermarket also.

In the back of my mind, a distant memory sits there... a graphic of a shifter clutch dog manufactured in sections, two parts I think, then fused together somehow. Does that ring a bell with anyone else out there?
 
Replacement was aftermarket. I have no idea about the first, I had run it for at least 6 seasons. Could the internal spring be weak allowing the Clutch dog to "float" around excessively? Failure while in neutral makes no sense to me.
 
Not Sierra, came out of a Wisconson Company. Unreal customer service. It took me almost a year to get to the lower and I noticed a chipped gear. They replaced it at no cost to me even though their warranty period had expired. I emailed them today to ask if they had any ideas why the clutch would shatter. They couldnt offer a solution but offered to send me a new clutch. AWESOME company. My concern is I reassemble and it happens again! Failure in neutral? What gives?
 
Good point Bullet, it will be a week or so to get my replacement clutch to check. Working with fragments says it is close. I also noticed vertical play in the driveshaft. What is acceptable?
 
Received my replacement clutch dog. The pinion nut and end shaft appear to just touch the clutch dog. Furthermore, upon looking at exploded clutch fragments, I can see what appears to be a "burnished" spot on a clutch dog fragment. It appears that while the motor was idling the shaft was making contact with the old clutch dog. My understanding is that shimming controls upward travel of driveshaft. What controls downward travel, Gear mesh? Any help is greatly appreciated. I can try and post a picture of clutch fragment if that will help.
 
Downward travel of the drive-shaft is controlled by the pinion gears teeth contacting the driving gears teeth.

When the engine is running (even at an idle), hydraulic pressure is created that forced the drive-shaft upwards, hence the shimming to create a limit for proper gear teeth clearance.

There should be just a very slight bit of prop-shaft play... In-Out. If excessive, I'm wondering if this would have any bearing on that shifter dog problem?
 
I took about .005-.010 off the driveshaft end. It visually appears to not make contact with my new clutchdog. I also cannot feel any "contact" via the propshaft if I rotate the driveshaft while pushing down on it in neutral. I think I am going to just install it and pray.
 
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