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:confused: Can anyone tell me what knurling (pistons) is? My Son had this done for his 1200 conversion.(the story is actually longer than this) Thanks for any help.
 

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Oh man! Knurling pistons is old school. When the tolerances between the cylinder and piston were out of spec they would knurl the piston skirts to expand the surface enough to get an acceptable piston to cyllinder fit.

I read about this technique in old shop manuals for flathead motors and earlier harley engines. I 'm guessing it was a last resort when new parts were not available. The manual even stated that it was considered a temporary fix.

I 've also heard of sand blasting pistons with coarse media to achieve the same results.
 

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Like LE PEW said, old school as hell. I'd bet that it will be an oil burner in short order. I had a friend that had sloppy piston to wall clearance and he went the knurling route, boy did that sucker go through some oil after a few thousand miles. In my book I'd either spend the bucks on a slight over bore or poney up for new pistons and jugs.
 

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Discussion Starter · #4 ·
Thanks for the replies! I was afraid that knurling wasn't really in my son's best interest. He had a Buell conversion in his '94 883. It ran great except for what he thought was a "pinging" noise at certain times. He's had his bike back to the shop(Lancaster HD) so many times that I lost count. The tech finally admitted that pistons were on the upper limit for tolerances but that his boss(no longer working there) rushed the job and said that it would be alright. Well they planned on making it right for him at no cost to him. I guess some one that works there(the new boss?) and used to be in racing suggested knurling, probably to save the company money. Well it'll cost them more in the long run because he won't let them off the hook. Mabee I should e-mail the COMPANY and see how they feel about their shops doing this procedure. Thanks again for the help.
 

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scarpatchy said:
Thanks for the replies! I was afraid that knurling wasn't really in my son's best interest. He had a Buell conversion in his '94 883. It ran great except for what he thought was a "pinging" noise at certain times. He's had his bike back to the shop(Lancaster HD) so many times that I lost count. The tech finally admitted that pistons were on the upper limit for tolerances but that his boss(no longer working there) rushed the job and said that it would be alright. Well they planned on making it right for him at no cost to him. I guess some one that works there(the new boss?) and used to be in racing suggested knurling, probably to save the company money. Well it'll cost them more in the long run because he won't let them off the hook. Mabee I should e-mail the COMPANY and see how they feel about their shops doing this procedure. Thanks again for the help.
Motorcycle pistons are so highly stressed that there really is no substitute for a nice tight fit after a rebore. I've never even heard of knurling being used in a motorcycle engine and I'm pretty sure that Knurling hasn't been used in car engines for close to 40 years. They had some "cheepo" auto repair companies in Los Angeles many years ago that would actually advertise knurling your pistons and valve stems to do an "overhaul". An engine "rebuilt" like that would only be good enough to get you out the door. Oil burning was the rule of the day. All of those companies were put out of business after California set up the Bureau of Automotive Repair to cull them out.

I'd either get them to do a proper job or find another shop.
 

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Wouldn't knurling just cause the piston to scrape the sh!t out of the cylinder walls? I supose this is why they burn oil. This seems like a really stupid thing to do.
 

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Knurling would be a "short term fix". It increases the diameter slightly and would tend to hold oil around the piston{s}. A "time wasting" fix. {YOUR TIME}

Mention it to H-D Customers Service, call them.
 

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I believe but not an expert here it involves kind of bending the piston skirt to have a very slight oval shape to prevent piston slap. Think it was more used when the block could no longer be rebored for oversized pistons. Cant imagine it being used in this day and age unless someone bored the cylinders to large.
 

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Knurling pistons, I used to do that back in the old days on my Triumph T120R flat tracker motor. Knurling of the piston skirt was a way of getting another weekend or three of racing out of a worn out bore. New barrels and pistons were very expensive and while the old Triumphs were semi-reliable, they had a tendency to wear out real quick when riding WFO on a half mile dirt track with nothing but velocity stacks on the carbs.
 
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