cb77E cylinder diameter

[Brian Foose]

hi everyone,

i recently acquired a CB77 and am going through my top end. i am a machinist, so i took the cylinders to work to measure bore diameter and runout and all of that using our fancy inspection equipment. every manual ive seen so far has my bore diameter at ~2.126.....mine are a whopping 2.3642...oversize pistons come in thee steps of .0098, so i figure i must be looking at the wrong reference material or something. any help you guys can give me is greatly appreciated!

Brian

[Tim Miller]

Brian,

Those manuals are for cb72 (250cc) with 54mm bores. Cb77 have 60mm std. bores. You will need .002" clearance at bottom of skirt. Make sure sleeves have .003 to .004 interface or you won't get heat transfer.

Good luck,
Tim

hi everyone,

i recently acquired a CB77 and am going through my top end. i am a machinist, so i took the cylinders to work to measure bore diameter and runout and all of that using our fancy inspection equipment. every manual ive seen so far has my bore diameter at ~2.126.....mine are a whopping 2.3642...oversize pistons come in thee steps of .0098, so i figure i must be looking at the wrong reference material or something. any help you guys can give me is greatly appreciated!

Brian

[Tim Miller]

Brian,

Those manuals are for cb72 (250cc) with 54mm bores. Cb77 have 60mm std. bores. You will need .002" clearance at bottom of skirt. Make sure sleeves have .003 to .004 interference or you won't get heat transfer.

Good luck,
Tim

hi everyone,

i recently acquired a CB77 and am going through my top end. i am a machinist, so i took the cylinders to work to measure bore diameter and runout and all of that using our fancy inspection equipment. every manual ive seen so far has my bore diameter at ~2.126.....mine are a whopping 2.3642...oversize pistons come in thee steps of .0098, so i figure i must be looking at the wrong reference material or something. any help you guys can give me is greatly appreciated!

Brian

[Brian Foose]

do you mean the sleeves should have .003 to .004 interference fit with the aluminum cylinder casting? because mine slide right out....

thanks for the reply! i figured i was looking at the wrong manual...dang thing even says cb77 on it but i had my suspicions.

[Tim Miller]

That's correct, otherwise your wasting your time making a perfect bore job because you will seize pistons. The loose fix is to copper plate sleeves or go with oversized sleeves.

Tim

do you mean the sleeves should have .003 to .004 interference fit with the aluminum cylinder casting? because mine slide right out....

thanks for the reply! i figured i was looking at the wrong manual...dang thing even says cb77 on it but i had my suspicions.

[Brian Foose]

copper plate the outside of the sleeves!? holy smokes...thats a bit more involved than i had originally anticipated. how do you copper plate the outside but not the inside of the sleeve? (when you say "plate", im envisioning some sort of electroless immersion bath.) i assume trying to wedge some .002 shimstock around the sleeves is a complete waste of time, as would be trying to use a center punch and dimple the aluminum casting in a bunch of places so the sleeves are an interference fit....so what do you reccommend? i dont know that i have ever seen sleeves that are oversized on the outer diameter before.

thanks again for the help, i really appreciate it!

Brian

[Tim Miller]

Yes it's a little involved, but it's doing it right. I have a chrome plater that does mine and yes the complete sleeve gets copper. In your case at standard bore now, after getting sleeves fitted I would probably bore to 2nd over and see if it cleans up first before acquiring Pistons. Otherwise finding NOS aftermarket oversized sleeves are hard to come by. Or you could get a lot more involved and install custom big bore sleeves to except 66mm custom Pistons.....like I do. If you need more help PM me.

Tim

copper plate the outside of the sleeves!? holy smokes...thats a bit more involved than i had originally anticipated. how do you copper plate the outside but not the inside of the sleeve? (when you say "plate", im envisioning some sort of electroless immersion bath.) i assume trying to wedge some .002 shimstock around the sleeves is a complete waste of time, as would be trying to use a center punch and dimple the aluminum casting in a bunch of places so the sleeves are an interference fit....so what do you reccommend? i dont know that i have ever seen sleeves that are oversized on the outer diameter before.

thanks again for the help, i really appreciate it!

Brian