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Blind Cast Iron Motorcycle Cylinder Honing

samclampett

Plastic
Joined
Jul 5, 2022
Greetings-

After performing a search for shops that do blind cylinder honing in the NE OH area I found this website. I own a couple old metal lathes and a Super Max vertical mill and have machined a few things for my personal use over the years but have never done anything very elaborate. An antique motorcycle came into my possession a few years ago that has an engine with blind cast iron cylinders. It's known as an F head or intake over exhaust. The head and cylinder are cast as one piece. The cylinders have been bored and need honed to the proper clearances for cast aluminum pistons. All of the engine machine shops I've called in my area aren't familiar with blind cylinder honing. The cylinders bores are roughly 6" long and the i.d. is around 3.5". If someone knows of any job shops within driving distance of the Akron / Canton, OH area that have the capability to perform blind honing please post a reply or send a PM containing contact info. Thank you for your time.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Last edited:

john.k

Diamond
Joined
Dec 21, 2012
Location
Brisbane Qld Australia
Every auto engine machinist has horror stories of the heads being bored off Harley pocket valve cylinders,or heads popping off when the engine fires up......harleys were very prone to massive scores in the bores caused by piston pin retainers failing.
 

john.k

Diamond
Joined
Dec 21, 2012
Location
Brisbane Qld Australia
The first time I rebored pocket valve Harley cylinders,I got them way oversize to what the owner requested for the cast iron pistons.....didnt attempt to hone any more out of them,just stuck the motor together ,and no more was said........they are a loss oiling system,so no one is gonna comment on smoke,and the bike was still running years later...........incidentally,the cylinders were supposed to be incredibly difficult to cast ,due to eggshell thin ness.....but are now being remade in Oz .....price will be up there ...but you dont buy five pocket valves for $80 any more either.
 

john.k

Diamond
Joined
Dec 21, 2012
Location
Brisbane Qld Australia
Incidentally ,the cylinders were ground ,and a 004 taper was included which made the bore parallel at operating temperature.......which was very high......couldnt ride the bikes in shorts ,heat from the rear cylinder would burn you.....a very fast bike with no brakes .
 
Aircraft shops can grind them with a planetary set up.
As John K notes, aircraft cylinders, and i believe most integral-head cylinders have choke.
If not, when the upper cylinder heats up, it will already be the shape it takes when worn out.
Correct choke is essential if you really want to the piston and rings to seal effectively and wear appropriately.

Be sure to fit the rings down in the tightest part.

smt
 








 
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