Topic: Replacing cylinder liners CB750K

[willbird]

I had to get 2 liners replaced when cyl 2-3 had too deep rust.
An otherwise good looking cylinder I intended to use with +0.50 mm pistons.

My nearby shop bored to oversize 0.50mm to fit my pistons, but the rust pits were too deep. +1.0mm pistons needed. (+0.75mm not available)
Shop replaced the 2-3 liners only.
I bought 2 liners from a friend.

I used cheap pistons from Cruzinimage to my CB750 K2.
K7-K8 pistons that give a little higher compression.
Total bore-piston clearance 0.020-0.025mm.
Very low oil consumption in 5500 km. Max 10mm on dipstick. Spectro 20W-50 oil that still looked good (viscocity) when replaced.

https://www.cruzinimage.net/page/2/?s=cb750+piston

I had earlier a honed cylinder with Cruzinimage stock size K0-K6 pistons. Total clearance closer to 0.05mm. That smoked in higher speeds, around 140kmh. Not nice for riders behind that complained.

A hint of what I've done: my own 750 has clearances of 0.0005" (0.015mm) in 3rd oversize pistons, It makes more power than ever, easily tops 100 MPH with the Vetter aboard and has enough extra torque to pull a 19T front sprocket (48T real) to redline in 4th gear. The CB350F, while having smaller bores, needs this 0.0004" clearance to run right, and that one is a 10k+ RPM engine.

Makes me wonder what size the hole is when the engine is warmed up.

[PeWe]

I had to get 2 liners replaced when cyl 2-3 had too deep rust.
An otherwise good looking cylinder I intended to use with +0.50 mm pistons.

My nearby shop bored to oversize 0.50mm to fit my pistons, but the rust pits were too deep. +1.0mm pistons needed. (+0.75mm not available)
Shop replaced the 2-3 liners only.
I bought 2 liners from a friend.

I used cheap pistons from Cruzinimage to my CB750 K2.
K7-K8 pistons that give a little higher compression.
Total bore-piston clearance 0.020-0.025mm.
Very low oil consumption in 5500 km. Max 10mm on dipstick. Spectro 20W-50 oil that still looked good (viscocity) when replaced.

https://www.cruzinimage.net/page/2/?s=cb750+piston

I had earlier a honed cylinder with Cruzinimage stock size K0-K6 pistons. Total clearance closer to 0.05mm. That smoked in higher speeds, around 140kmh. Not nice for riders behind that complained.

A hint of what I've done: my own 750 has clearances of 0.0005" (0.015mm) in 3rd oversize pistons, It makes more power than ever, easily tops 100 MPH with the Vetter aboard and has enough extra torque to pull a 19T front sprocket (48T real) to redline in 4th gear. The CB350F, while having smaller bores, needs this 0.0004" clearance to run right, and that one is a 10k+ RPM engine.

Makes me wonder what size the hole is when the engine is warmed up.

Piston will swell when warm, hopefully not quicker than the cylinder.

[Don R]

 Aircraft guys repair just one on a four-cylinder engine all the time. That blows my mind. How far behind in wear can the other three be? That said, I honed and re-ringed my 836 myself. I'm sure the hone job isn't perfect. I could still see rust stains, but I got the bike running again and so far with a couple hundred miles it isn't smoking and pulls hard.

[Don R]

Would you folks be ok with tapping in the liners and then checking them with a straight edge and if they looked good call it done?

  I would if I was confident that they were all the way down. A hot block and cold liners will put them in without moving metal. Be ready to tap them down quickly in case of a sticky one.
  I did buy a bike with an 1124 stroker motor that had two dropped cylinder sleeves that could not make compression. That was likely caused by improper machine work.