Removing material from lifter tunnels

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Nov 14, 2009
How much material can I remove from the lower edges of the lifter tunnels (located on the cylinders) with out effecting anything? (1970 750 Commando) The reason I ask is that I have some rough edges on my cylinders in this area where it looks like it has fragmented away. I can also see some hairline cracks that i would like to remove now before putting the motor back together. Better now than it breaking away while its running and a smoother edge just seems like good practice. It is my understanding that this area must be relieved in order to run radical cam shafts. I just want to get some more info on this subject before I start removing any material.


If not too serious (1/8" or less), i would definitely remove the cracked piec(es) and file the edges clean. The other option would be to weld them, but you'd need to do a careful re-bore to ensure that welding didn't warp the material into the bore.

Those little bits of steel floating around in the crankcase can do an inordinate level of damage to the whirly twirly bits.
Those were my thought exactly - get rid of it now if at all possible.

Thanks for the advise Paul, an 1/8" should clean it up nicely. I'll refrain from using the welder and stick with a hand held die grinder. Periodically cooling it down with water to avoid and warpage. I'll buff it smooth when finished.

On another note, is the groove in the lifter that is typically matched up as a pair and positioned forward for oil flow or just proper alignment in the cylinder?

Thanks again,

The chamfer in the tappet is definitely there for the oil to run down. I put them in backwards many years ago and it made quite a mess of the head!
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