Topic: CB750 pistons to match bores 67,53mm that need refreshment of another 0.1mm

[PeWe]

I have a cylinder block I measured today with a micrometer. All bores have same sizes. Around 67.52-67.535. Measured around 20mm from bottom, middle and 10mm from top.

The bore have some scratches and need to be refreshed. Maybe another 0.1mm bore will fix it. This will end up in bores of 67.73mm
I guess that there are no pistons that will match that bore, right?

I have old Henry Abe pistons to the cylinder, old boring flat model that I doubt will work with high lift cams when the pockets are almost nothing.

The sleeves are the tapered model without need of case boring. Thickness today where enter the case is 1.23mm, OD 70.0mm.

I need a complete piston kit with new sleeves, right?
915 must be the better choice, but that will end up in case job too.

[BPellerine]

is 915 not 68mm?,the 915 kits have the same type of sleeve as the ha sleeves so no case work.cycle x is also making a 900 kit but don't know the piston size.billp

[hotdog]

Nice bore mic

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[PeWe]

CycleX is not correct on their website when they say that 67.5mm is 915cc. (901.75cc) 68mm is 915cc that need larger sleevesand case job.
http://www.cyclexchange.net/Engine%20Parts%20Page%20(Non-Cafe).htm
The tapered sleeves are 70mm and the case is just a little bit more, less than 71mm.

Not a cheap quick solution then...new sleeves (+ work replacing them). I'll take the engine apart so I have possibility to bring case to the tuner for case bore just for sure...
67.6mm pistons would be fine if existing.  I guess I need to find a good  later cylinder with  pistons for a low price
I have to take her apart today and check the 836 bores while I have the bore micrometer home. Difficult to move my ass from the sofa

[mick7504]

Correction
69mm 68mm plus a whisker
The old fat finger strikes again. 

[madmtnmotors]

Nice bore mic

I was admiring that too!

[BPellerine]

CycleX is not correct on their website when they say that 67.5mm is 915cc. (901.75cc) 68mm is 915cc that need larger sleevesand case job.
http://www.cyclexchange.net/Engine%20Parts%20Page%20(Non-Cafe).htm
The tapered sleeves are 70mm and the case is just a little bit more, less than 71mm.

Not a cheap quick solution then...new sleeves (+ work replacing them). I'll take the engine apart so I have possibility to bring case to the tuner for case bore just for sure...
67.6mm pistons would be fine if existing.  I guess I need to find a good  later cylinder with  pistons for a low price
I have to take her apart today and check the 836 bores while I have the bore micrometer home. Difficult to move my ass from the sofa

pewe,not disputing you,but I thought that cycle x made a 915 kit that you do not have to bore the cases,comes with tapered sleeves,you could also just put new sleeves in your barrels and flycut the valve cutouts on your pistons,which upon reflection was done to mine to run a bigger cam.

[PeWe]

Yes, the bore tool is really nice! I'm happy I can borrow it from my job. Measured my 836 cyl today too when open the engine. Bores better than I thought when I measured in the abs bottom where it should not be any wear, 4 points in each bore. The rest were almost the same, maybe 0.01mm more wear.
Edit: Moved cams to the 315 thread...

[PeWe]

CycleX is not correct on their website when they say that 67.5mm is 915cc. (901.75cc) 68mm is 915cc that need larger sleevesand case job.
http://www.cyclexchange.net/Engine%20Parts%20Page%20(Non-Cafe).htm
The tapered sleeves are 70mm and the case is just a little bit more, less than 71mm.

Not a cheap quick solution then...new sleeves (+ work replacing them). I'll take the engine apart so I have possibility to bring case to the tuner for case bore just for sure...
67.6mm pistons would be fine if existing.  I guess I need to find a good  later cylinder with  pistons for a low price
I have to take her apart today and check the 836 bores while I have the bore micrometer home. Difficult to move my ass from the sofa

pewe,not disputing you,but I thought that cycle x made a 915 kit that you do not have to bore the cases,comes with tapered sleeves,you could also just put new sleeves in your barrels and flycut the valve cutouts on your pistons,which upon reflection was done to mine to run a bigger cam.

No problem. I was a little bit short. The recommendation about new complete kit with sleeves is highly appreciated!
When changing sleeves, its easy to think about more cc when the job has to be done with re-sleeving

I got the idea today to bore my upper cases to fit 74.5mm sleeves, just for sure and finally ensure the bottom end. I'll continue with the 836 unless I find something bigger for a really good price. I can change cyl with engine in frame.