Technical > Matt Shaff's Engine Shop

Cause of fretting on main caps?

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gordon:
Spot on by duster Dave. Tune up allowed Detonation,too much timing and or not enough fuel. Even a little will fret the caps. If you have to run that close to detonation , try to find an old can of dutch boy white lead. Used to be sitting next to lathe for dead center work.  Put a small amount on mating surface then torque as usual. Takes just a small amount. I believe Gene Adams now uses a very pure form of lanolin as it is easier to find. The lube that is sold for use with thread go, no-go gauges is lab grade lanolin. See MSC catalog .

Frontenginedragsters:
Like it has been already said:
 Lean, too much timing advance, too much engine load.
The crankshaft is being pushed counter-clockwise during detonation while the momentum is clockwise.
You need to richen up the fuel and back off the timing and sneak it back in a little at a time.
Get some help reading the plugs and pull the pan during the week and look at your bearings.
Sooner or later detonation will also crack the crankshaft.

Dunc the Funk:
I would say we only did one run where it was lean. This took off the plug plating much further than any other run we've done, as I said, down to the top of the first thread. Maybe that's when it did the damage. The motor was much hotter than usual after the run. Previously we'd not done more than about half way round the face. I recall the 'timing' bar on the plug ground was usually near or just down from the corner. We didn't realise how bad the pump was til we put a new one on & it's been so rich we have not coloured a plug since. We went from having less & less fuel in the oil to having a shed-load. We won't be running again until April at the earliest.

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