cylinder bore

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Peter Restaino

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I just came back from my local harely maching shop to show him my .020 over 1970 commando barrels. One cylinder is in good condition, the other has heavy deep pitting about an inch down. he thinks after going to .040 some the pitting will still be there. He says I could just try it and see what happens. He calls me a doctor because I want perfect bores. Getting a replacement will not be easy because all the ones on ebay look hammerd . Any words of wisdom will be appreciated.
 
Other alternatives you might consider are:
1. Spun-cast liners could bring it back to your .020 (keep same piston/rings - available from RGM and probably others
2. Silicone Carbide impregnation of the bores. Laystall Engineering (UK) offer this service - probably others too. Used to be Bore Tech in Ohio US but I think they closed.
Cheers
 
I just got a used set 850 cylinders from John at Motoparts in Edmonton. He only had two sets of used 850 cylinders. I suspect he has more of the 750.
Dennis
 
Peter Restaino said:
I just came back from my local harely maching shop to show him my .020 over 1970 commando barrels. One cylinder is in good condition, the other has heavy deep pitting about an inch down. he thinks after going to .040 some the pitting will still be there. He says I could just try it and see what happens. He calls me a doctor because I want perfect bores. Getting a replacement will not be easy because all the ones on ebay look hammerd . Any words of wisdom will be appreciated.
Click to expand...
Run away from the "harely shop".

Did he use a dial indicator to evaulate depth of pitting in the bore? Or just calibrated eyeball?

Without pictures, we are expected to give precision machining advice based on layman's verbiage. A lot of variables.
I work in this scenario daily, except eventually I get to see the actual problem, and fix it.
 
Last edited:
you tube bearded mechanic, he goes to a nickasill cylinder shop. very interesting but dont think they do all iron cylinders. everything in the video was aluminum 2 srokes.
 
Welding cast iron creates hard spots, so I wouldn't personally.
New liners would be my preferred option for a road going motor.
 
I wouldn't even consider putting liners in a 750 barrel.
Boring to .040" will leave the casting 0.20" thinner than standard
Boring to .060" will leave the casting 0.30" thinner than standard
Boring for a liner will require boring to 76.5mm which will leave the casting 0.069" thinner than standard
 
Stephen,
I am also in Vancouver. My cylinders were very heavily worn and already at 0.040 and likely could not be cleaned up with plus 0.060 so I bought a used set that are now at Precision racing in North Van for boring.

Dennis
 
How did you get pitting in the bore - was the engine left sitting with water in the top of the cylinder ? Cast iron can be welded, but the results are always suspect. I certainly would not want weld where the rings do their business, but pitting should not be a problem - except if it is in the area where most wear occurs near the top of the bore - where the most rapid change of direction occurs. In that case I would find bigger pistons, and over-bore to remove the pits
 
The bike was a rolling basket and the cylinder was off but whoever pulled the cylinders beat one of the pistons with a hammer to get it appart so it was rings were rusted. and yes thats the company Power seal
 

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