Box Stock

Side Cover Failure

T

Trailduster79

Member
Was doing some backyard racing yesterday and had a engine failure. Thought it was the rod, but when I pulled it apart, it appears that the cam boss in the side cover let go and then the compression release came apart and held the valves open. Only minor damage to the cam gear, and no visible damage anywhere else.

Maybe compression release came apart and caused the damage?

Any idea what would cause this?

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Anything loose in the crank case?
If something got between the cam and crank gear that would do it.
Actually looks like the cr release weight ran through there.
 
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Nothing that I saw. Only thing laying in the bottom of the block was the parts to the compression release.

It was running quiet when it went. Just died and lost all compression.
 
That's it. Never did a clone with out one. Was it high lift modified cam?.
Flathead got me once hurt for three weeks.
If basically stock , side cover and cam is cheap in comparison.
 
Kart43 said:
From your picture are you sure that side cover bearing is properly seated?
Click to expand...

The bearing was seated, and I shimmed for proper crankshaft end play. The bearing slid out of the case when I took it off.

The bottom end had been together for two race days and it was fine the day before.

We have electric starters, so I may throw it back together without the compression release until I settle on a new cam.
 
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Wow I always remove the comp.release for this reason, but was getting ready to install a new stock cam with it on because of tech. And to ease the starting especially with a timing key. I like how it's spring will allow the comp.release to be disabled after starting up.
 
I don't see how the block cam boss is not destroyed. Is that the shim you used laying behind the crank? We always found they needed more clearance never had to shim them tighter.
 
I will take a look at it tonight when I get home.

I did shim it to about .007 endplay. Was my understanding that the goal was .005-.010 endplay.
 
Seems when I've used shims between bearing and crank they get beat up pretty bad to the point I won't use them .
 
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