Topic: 1978 Cb750 K Rebuild Questions

[jmelton]

That's good to know, I put them in the oven at 250 (the temp my paint required for heat curing) for an hour or so when i was trying to reset them. I'll give 350 or maybe a little hotter a try, fingers crossed that sets them flush!

[bryanj]

Liners should fall out at 200 celcius

[jmelton]

I'm working in Fahrenheit. At 350F I was able to get 3 of the 4 pretty close to flush but still a bit of distance to go. I'll probably do a few more heat cycles and maybe add a little persuasion with wood and a hammer or maybe a dead-blow hammer.

Just as a last double check... How do we feel about the scratch coming 32mm from the top of cylinder 2, little bit of low compression maybe some oil burning but nothing major?

[Don R]

 I'd send it at this point. It isn't very often we get one of these old motors in perfect condition, but they rarely seem to complain.

[bryanj]

You need 395 fahrenheit for the liners to move without problem then leave the block supported with liners not touching till cooled

[scottly]

At 350F I was able to get 3 of the 4 pretty close to flush but still a bit of distance to go.

Just as a last double check... How do we feel about the scratch coming 32mm from the top of cylinder 2, little bit of low compression maybe some oil burning but nothing major?

Just how far to go? You mentioned .005" before. Remember, the metal "fire ring" in the head gasket that seats against the top of the sleeve is what holds all the fire and pressure in the head. It compresses a fair amount when the head is torqued, allowing for minor differences. The concern with the sleeves is that if not fully seated, they may drop in use, and since the gasket has been compressed, it might not seal as well. This is also why it's not advisable to reuse a head gasket.
Regarding the scratch, I doubt you will notice much loss of compression or much oil consumption. The engine isn't going to explode in a ball of flame, at least due to the scratch.

[jmelton]

I was able to just barely fit a .003" feeler gauge under a straight edge in some sections last night. I'm giving the cylinders one more bake at 400f this morning and i think i may call it good. When checking last night cylinder i also put a feeler gauge next to the cylinders and could feel the lip on 1,3 and 4 sitting proud .0015 to about .003". Honestly after this bake i'm just gonna call it good, as even last night it looked like i as just barely under the service limit of .0039".

I did find another glaring issue last night when i was looking at the valves and guides... I think my new "exhaust" valves are actually intake valves, so that might be a bit of an issue .

[MRieck]

You need 395 fahrenheit for the liners to move without problem then leave the block supported with liners not touching till cooled

I'd also put some weights on the sleeves so they don't creep back up. It will need to be decked too if you want it correct.

[newday777]

"I did find another glaring issue last night when i was looking at the valves and guides... I think my new "exhaust" valves are actually intake valves, so that might be a bit of an issue ."

Who supplied the parts?

[jmelton]

Its on me. I went back through our messages from a few months ago, the original intent was to replace both the intake and exhaust guides but when it came time only the exhaust guides and valves were replaced and i unfortunately ordered intake valves instead of exhaust.

On the bright side of things i may just go ahead and replace the intake guides as i have brand new valves to go in them and will probably need to potentially replace and definitely recut the seats for the exhaust side 

[Tracksnblades1]

Its on me. I went back through our messages from a few months ago, the original intent was to replace both the intake and exhaust guides but when it came time only the exhaust guides and valves were replaced and i unfortunately ordered intake valves instead of exhaust.

On the bright side of things i may just go ahead and replace the intake guides as i have brand new valves to go in them and will probably need to potentially replace and definitely recut the seats for the exhaust side 

Atta Boy,

Do it right once..
If you max out your kitchen oven. With your block at temp and your sleeves taken out of your deep freeze, they should home in the block by hand..

Follow the other guys’ advice and have the bottom of the block propped up above sleeves bottoms.
And weight the tops of the sleeves to hold them down as mention to prevent movement as the temps equalize.
Having the top of the block with the sleeves all seated deck a minimum is good insurance that all if flat, true, and square with the world..😁

PS… when, if your sleeves are all out be sure and check aluminum sleeve bores for any burrs or rough spots that would keep the cold sleeve from falling (hand) in place when the block is at temperature. Making sure the block is actually at temperature..

[Tracksnblades1]

You, your self could put some dykem on your new exhaust valves faces and by hand lightly pop them down against the seats.. then look at the dykem to see the if the witness mark of the seat is continuous all the way around the new valve faces. And whether the vitness mark is at the ideal location on the valve face…

They used to call the procedure “slamming the seats. It was a quick check, especially when you ground your valves with interference angles to the seats to prevent lapping. And avoiding the augment of lapping compound residues prematurely wearing your freshly ground seat.. And now there is Serdi, until it is destroyed by the new truth…cs…🤫