I want to do this right, but I don't want to break the bank.
I've got a cylinder that has some scuffing and scratches from a piston that looks to have overheated.
I can get a good set of used stock pistons and honed cylinders for around $125 on Ebay.
I can also get new .25 oversized pistons and matching rings for around $175, and that doesn't include the labor for a rebore.
What would you do?
Bad piston. Should I replace with used or rebore and OS?
First job - find out why that piston overheated. Timing? Fuel? Lubrication?
Next, take it to a machine shop to get the cylinder measured / honed. Then look around for suitable parts depending upon the advice you get from the machine shop. Don't spend any money until you know why the problem happened first time around..... G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
I'd love to know why it happened, but I bought it used and I've run it for less than an hour, so I'm pretty sure the damage pre-dates my owning the bike. It's a single-carb bike, with one piston fried and the other fine so I don't think it's a fuel issue. Timing was set according to the manual, so unless someone else ran it advanced before I got it, I don't think that's it. Lubrication? I don't know. What would cause oil to get into one cylinder and not the other? There's also the possibility that someone ran it low on oil at some point and it didn't get enough splash into the cylinder. Wrist pin looks fine. It slides into the rod with slight resistance and has a hint of play in the up-down axis, exactly like the other wrist pin. Examining the piston, there are raised spots where aluminum has been re-deposited on the skirt, leading me to believe that this was an issue of overheating. Rings are properly loose in the grooves and have no damage except for blackening along one face indicating blowby. You folks have a lot more experience with this than I do. Any suggestions as to why this might have happened? I will take it to a machine shop Monday to see if it needs a rebore or perhaps just a honing. Anyone know the maximum allowable bore size for standard pistons? Thanks CylindersShop manual says wear limit is 54.1 mm
Max out of round and taper is .05 You may want to get a shop manual for reassembly. Do you have Bill Silver's CD? G-man is right. You need to figure out why that cylinder galled that piston so badly to avoid a repeat.
Re: CylindersI've been working from the Clymer Vintage manual that has CBs, CLs, and CAs in it. I ordered Bill Silver's book a couple of days ago. I'll have the bore mic'd at a machine shop. Believe me, I'd love to know why that piston did what it did but I'm at a loss. On a one-carb bike, I can't see any reason why one piston would seize and the other wouldn't unless the engine overheated and the right piston happened to be the one that gave up first. Valves look great, cams are beautiful, all valve guides are in place and won't deflect to the side. What else should I be looking for?
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