Topic: Replacing cylinder liners CB750K

[timtune]

I have jugs with two bad cylinders (both outer). I have a line on some liners. I've been told they are not too hard to swap out.
Anyone care to add their first hand experience?

[MauiK3]

Never done this but I suspect heating the assembly and pressing them out would work. The tricky part would be honing or boring them all so they are in alignment. I imagine Hondaman or others have done this

[willbird]

The guys doing car, truck, farm engines full time bore them paper thin then use a pocket knife to remove what is left. Sometimes that reveals damage from prior sleeve replacements that used more abusive methods.

[PeWe]

Easy to take out after sitting in owen for a while. Sleeve/liner start to glide down on their own when cylinder sit upside down. I have done that.

When assemble again important to ensure it will sit all way down until it bottom out. I let my shop do that
If not, cylinder head surface milled flat, engine running getting hot sleeve will go down and that chamber will leak.

Important to use correct sleeve. Later, K3 and up has round corners for holes.

[timtune]

So with the jugs in their actual position the liners are removed and replaced from the top (head side). Correct?

[timtune]

Also can I replace only the two damaged ones?

[Remcod]

Yes, had 1 replaced on my f1 from another block.

Verstuurd vanaf mijn SM-A536B met Tapatalk

[MauiK3]

I guess I’m a “matched set” type of guy, I’d do all 4

[newday777]

Also can I replace only the two damaged ones?

Yes but you'll need to bore all 4 cylinders bigger.

[Remcod]

Depends on your plans and state of the bores. I just used the piston that belonged to the bore. Just crosshatching and new rings since all was within tolerance.

Verstuurd vanaf mijn SM-A536B met Tapatalk

[seanbarney41]

Depends on your plans and state of the bores. I just used the piston that belonged to the bore. Just crosshatching and new rings since all was within tolerance.

Verstuurd vanaf mijn SM-A536B met Tapatalk

Remcod, you have done this successfully?  The engine is running?

[timtune]

Also can I replace only the two damaged ones?

Yes but you'll need to bore all 4 cylinders bigger.

I'm trying to avoid just that. I can go 1st  or 2nd over and clean up what I have. North of $800 parts and boring is my guess.

[HondaMan]

You can get new liners from LA Sleeve in California. I've used them before and have 8 of them on hand for those cylinders with a rusted sleeve that has damage deeper than the oversize pistons needed for the other 3 cylinders. Mill the top of the deck -0.010" when done in any case: this is needed to make the O-rings seal where they pass oil thru the head gasket (because all modern head gaskets are at least 0.010" too thick). Some head gaskets require even more milling to make this seal, like certain MLS gaskets that are more than 1.0mm thick.

[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.

[Remcod]

Depends on your plans and state of the bores. I just used the piston that belonged to the bore. Just crosshatching and new rings since all was within tolerance.

Verstuurd vanaf mijn SM-A536B met Tapatalk

Remcod, you have done this successfully?  The engine is running?

Yes i have, runs great.

Verstuurd vanaf mijn SM-A536B met Tapatalk

[dave500]

dont #$%* around,if ya gonna do two,do all four,your only penny pinching otherwise!

[Remcod]

I did one, because one was damaged. I would do two if 2 where damaged. Nothing to do with penny-pinching.

Verstuurd vanaf mijn SM-A536B met Tapatalk

[timtune]

Remcod I agree100%. Replace only what you need. The rest is waste.
Did you do the swap yourself? Also did you mill the deck .010" as HM suggests?

[Remcod]

I did not do it myself, I had a trusted machineshop do it. I did not mill the deck, but did use the thicker orings as Mark suggested. I did have the head surfaced and valves cut also while i had it apart.

Verstuurd vanaf mijn SM-A536B met Tapatalk

[Don R]

 I removed a set of cylinder sleeves, baked the cylinder for 350* in the gas grille for a half hour.  I used welding gloves to handle them and I had some wood blocks set up to turn the cylinder over on to tap the sleeves out. One had previously been replaced and it came out harder than the three original ones.
 I have not had new sleeves installed yet, I mostly did it as a test and to prepare a cylinder for large bore machine work to be done in a shop. If I was putting sleeves back in, I'd reheat the block and freeze the replacement sleeves, and be ready with wood blocks to set the cylinder on to tap them down.  At any rate, they will need honed and new rings.
 I watched a video of a guy that used liquid nitrogen to freeze his sleeves, they dropped right in to a room temperature block.

[HondaMan]

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.

[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.

I have another cylinder with same type of pistons and fresh bore as a spare.
I told the shop to keep total clearance tighter than first time, under 0.02mm.

My K2 has 17:48 gearing that match gearbox very well. Not much more revs at 100kmh (60mph), ca +250rpm. Good when cruising on 5th gear, less need of gearing down.

My modified K6 has 17:48 too. This to let the torque easier for clutch.
Same bike with 836 in the 80's got 17t at front for max speed, easier to rev out.

Long tourings thru Germany to Jugoslavia, Italy and Spain worked fine on 17:48.
2 young persons and lots of luggage. Good acceleration important in the alps as well as highways.

[MauiK3]

Amazing how well these bikes do with two up and luggage.

[HondaMan]

My K2 has 17:48 gearing that match gearbox very well. Not much more revs at 100kmh (60mph), ca +250rpm. Good when crusing on 5th cear snd less need of gearing down.

My modified K6 has 17:48 too. This to let the torque easier for clutch.
Same bike with 836 in the 80's got 17t at front for max speed, easier to rev out.

Long tourings thru Germany to Jugoslavia, Italy and Spain worked fine on 17:48.
2 young persons and lots of luggage. Good acceleration important in the alps as well as highways.

I've lon gthought that the idea gearing for these bikes was that K1 gearing of 17T/48T with the .400x18" rear tire. Today's tires are larger OD (metric carcasses) so the more common 18T/48T gets to be pretty tall. This usually shows up as a lower top speed by a few MPH in the American West (where speeding starts at 90 MPH) from being a bit too tall.

[timtune]

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?