Hi,
I'm glad your oil pump gasket area is oil tight. But why did you hone a standard but used bore ?
Why not move to the 0.25 mm oversize ? A used cylinder, were honing is necessary isn't round anymore, and the honing stones do take metal from the walls. The piston clearance should be 0,01 mm to 0,03 mm, and that will never be achieved when honing a used bore, never.
If the standard bore was used, and the honing structure was gone, it had certainly more that 2000 miles after new. When you hone that again, it will never have the right piston to cylinder clearance.
I, for one, never hone a used bore, but always bore and hone, and use the next piston size.
Piston to cylinder clearance always between 0.01 and 0.02 mm. Make the bore fit the piston, and mark which piston should be in which bore, don't interchange them. Piston sets usually differ 0.01 (if you're lucky) to 0,05, so your machinist should bore the cylinder to match the piston, and that will mean two different bores, for two different pistons.
This is what I do :
Buy a piston set, and mark them with L and R. Write the measured size on the piston.
Make the pistons equal (weight). Give the pistons and cylinder to the machinist with the spec you want. Make sure he does the measuring of the piston size with room temperature, don't make them warm with your hands. Bore the cylinder to spec, and measure the end gap play for the rings. Make the end gap play to spec (not to small, otherwise they will snap when warm, not to wide otherwise the compression is lower. After starting the engine, don't let it idle to long (just a minute), then ride.
Jensen
1962 CB77 Restoration underway
JENSEN!!!!!!!!!!!!!!!!! AS SAID DOWN THERE WHERE MY CHUMS EXIST "IT'S JUST A FUXXING MACHINE !!!!!!
YA AIN'T GOIN TO LIKE THIS!!!!!!!!!!!!!!! BIG WHITE HORSE??????? AT TIMES YA REALLY TEST MY MECHANICAL KNOWLEDGE AND COMMON SENSE WITH YOUR MESSAGES!!!!!!!!!!!!!!!!! Tom's answer was polite to ya. Your way to rebuild a CB77 engine may work for you. However we "who aren't into the 00000.1 tolerance world of machines" and $$$$$$$$$$$$$ know that MOST ENGINES especially a CB/CL72/77 can be rebuilt with no more than a Good Ball Hone job and a new set of rings to fit that bore. (even use the same pistons!) It may interest ya to know that the 1963 CB77 I ride (THE MOUSE THAT ROARS) after 27,000 "MILES" is on it's 3rd set of rings and "ball honed each TEAR DOWN using the same pistons. Lets face it that engine exploded and the fault is yet to be determined but to do as ya say for any engine is a """"""""""LOT FOR ME!.""""""" IT'S YOUR $$$$$$$$$$$$ AND TIME. I'm happy to know how through ya are with your work but I have learned how to accomplice spending the $$$$$$$$ US the same end without wasting $$$$$$$$ and time. May I ask if ya really have determined that we ride, repair, and enjoy these bikes and don't have the access to all technologies and equipment where we live! $$$$$$$$$$$$$$$$ Like a fire in a structure. The reason may never be known why it BLEW but ?????????!!!!!!!!!!!!!!!!!!!!!. YA are a SUPER engineer but "Need To Get The Real World with others on this forum. My Thanks to TOM for being polite. Love ya there Jensen. .............................LM
Tom
I'm sorry to see your unfortunate pictures but you have given us something to think about. It does seem very unusual to loose the shoulder (top piece) of each liner when each piston is traveling in opposite directions on this motor. I don't see any real marking on your pistons and the bottom of the liners seems to still show the honing marks. It takes a lot of force to take the shoulder off the top of the liner and for it to happen on both, more or less simultaneously suggest something that's common to both. Having rings break on both pistons at the same time is unlikely unless they were the wrong rings or perhaps broken when they were inserted? I would look to see if there is something that is common to both cylinders, such as lubrication or fit of the liners in the cylinder block. Are the liners tight now? Could we see some close-ups of the pistons, the liners and the shoulders? Looking at your pictures again, I would think that the top ring dropped into the gap between between the shoulder and top of liner. Also (from the very small picture) the edge of the valve pocket on those pistons looks battered. What did that? Let's make sure it doesn't happen again...... 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
Hi LM,
Of course I know that Tom's answer is polite, that's why I didn't responded, because it's ok with me. I explained to him what I do, not what he should do, so no harm done, no one offended, I guess. An advice let people free to go in any other direction, and that's exactly what Tom answered to me when he answered polite, thanks Jensen, but I'm going another way, and that's his own direction. It's how a forum should work, someone writes about something and he hopes he gets as many good advices, so he / she can pick the right one for him / her. I understand that my advice isn't mainstream, as I often see things from a different perspective. The US is a big country with all kinds of people, some people pay a lot of money for anything, some not. I only know the US by stories from the people I talk, never bin there myself. Indeed it's difficult for me to understand that people living in the richest , most powerful country in the world, don't have access to high end engineering facility's like we do here, or cannot / will not pay for these facility's. It's good that you pointed out to me that my knowledge about the US isn't correct, thanks, really appreciated, I have to go there myself to see it sometime. I like to ride my bikes too, instead of wrenching again and again, and I do the riding this season on my CB450 K0, lot's of fun, but next season or the end of this season I'll ride the CB72 '67 again.
The first thing is a challenge, the second I don't know. No offense here, Cheers, Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
When I removed the old liners I found evidence that the liners had been removed before- gouges in the aluminum cylinder. When I dropped my liners I ground the damage caused by the the crank weights smooth and after being in the oven for a while they slid right out. I did not bang, beat or pry on them. When I bought the bike several years back the old man that owned it said he had it rebuilt, rode it a couple times then put it away. Maybe the previous wrench beat on the liners when he was taking them out/putting them in, causing a stress fracture. I don't know, really don't care at this point. Old liners out, replacement liners in waiting to go to get bored.
HT
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
