Topic: Cylinder rust damage

[cafeviking]

I'm not sure what to do about this. I took these photos after polishing so the contrast is really high and makes the pitting look more severe than I think it really is. One of the photos shows something that looks like a really big deep crack but it's not any deeper than the rest, which are almost undetectable by hand (the colour really is more oxidation presence than it is shadow).

Is there any chance I can rebuild and run as-is?

If I do, what is the result? Significant loss in compression? Smoky exhaust? Other?

I just don't have a grand to spend on doing a big bore kit.

[tomkimberly]

Instead of polishing, have you tried using a cylinder hone?

Then place a ring about one inch from the top and measure the gap.


Tom

[cafeviking]

Instead of polishing, have you tried using a cylinder hone?

Then place a ring about one inch from the top and measure the gap.


Tom

Looking into it. Measure the gap and then? This would determine maybe a piston ring size or something?

[uksparky]

Hone it yourself or take it to a machine shop to do...also they can measure the bores for any oval wear, if the grooves are too deep they might interfear with the rings....if no good you can find one on e bay ...ask for pictures..

[bollingball]

Give it a mild hone then you need to mic. the bore. I'm not sure what good checking a ring gap would tell you about the bores. This is usually done after the bore is in speck to let you know if you need to file the ring to fit a good bore.

Ken

[tomkimberly]

Give it a mild hone then you need to mic. the bore. I'm not sure what good checking a ring gap would tell you about the bores. This is usually done after the bore is in speck to let you know if you need to file the ring to fit a good bore.

Ken

Measuring the ring gap will tell you if you need to rebore.


Tom

[bollingball]

Give it a mild hone then you need to mic. the bore. I'm not sure what good checking a ring gap would tell you about the bores. This is usually done after the bore is in speck to let you know if you need to file the ring to fit a good bore.

Ken

Measuring the ring gap will tell you if you need to rebore.


Tom

So you make the bore fit the ring. I thought you do the bore and file the ring fit it?
Ken

[tomkimberly]

Give it a mild hone then you need to mic. the bore. I'm not sure what good checking a ring gap would tell you about the bores. This is usually done after the bore is in speck to let you know if you need to file the ring to fit a good bore.

Ken

Measuring the ring gap will tell you if you need to rebore.


Tom

So you make the bore fit the ring. I thought you do the bore and file the ring fit it?
Ken

Honing the bore does not mean re-machining the bore, but you already knew that.

Quit being a dick, and help this guy out.

Tom

[matt mattison]

If the cylinder doesn't completely clean up after the hone and tolerance check, you really should get it bored or re sleeved . After honing, if a rust stain is left inside the bore, but "feels" ok, it's best to rebore or sleeve.

[dave500]

you can get away with murder with these engines,,hone/deglaze and new rings,new gaskets/o rings through out,thats what most shops will call a top end "re build"?you dont want a shiney/polished bore man!

[Xnavylfr]

If the RUST is deep enough that you can see PITS in the sleeves, then chances are you WILL have to go oversize.  For the cost of boring and ring sets ,I would go ahead and go to an 836 KIT.... NO REPLACEMENT for DISPLACEMENT!!! I run with a guy that installed one of those 836cc kits from JAPAN off E-BAY , NOT a problem with quality of rings or pistons.
The first OS you can get is .25mm larger than stock . If you HONE the sleeves and you still have pits then you will have loss of compression AND burn oil.
 I'm not sure about how a machine shop charges for boring or if they have to bore in small increments to final size but if you were considering going to a big bore I'd do it now since your engine is apart.
Most of us chopper guys/gals have one of our members do the machine work. Great quality and fast turn around so you can get the engine back together.

Contact  http://cycleonemanufacturing.com/  and ask for KATE they've done hundreds of these CB engines and at a fair price..

Xnavylfr(CHUCK)

[ekpent]

Looks like he has a 78 F2 so there may be some compression number issues if he went with the cheapie E-bay 836 kit.

[Xnavylfr]

Yes he would have lower compression in the F engine. From what you can see in the pictures, some of those sleeves are rusted pretty deep!! I don't think a single OS will clean them up!!


Xnavylfr(CHUCK)

[754]

Any engine shop can tell you approx how much has to come out.. Looks like 2nd over wont clean it.

[Xnavylfr]

Might be able to get a "T" bar micrometer down in that one jug and find out how deep that gouge is!! MAYBE!!!



Xnavylfr(CHUCK)

[754]

Not. Tbar..too fat..try spring caliper with pointy end.
 If you put it in drill press, you can run a small dial test. Indicator down the wall over the spot and see what it indicates. ..
 It really only looks good as a core for a bigbore...to me..

[Xnavylfr]

YES it looks like an 836cc would clean it up. If he is wanting to stay stock then why not get a set of jugs (GOOD ONES) Run a hone up/down to get swirl marks and put it together!!  Probably the cheapest way to go. I know I have three sets of jugs but would have to see what they LOOK like inside!!!



Xnavylfr(CHUCK)

[CB750F2]

I am assuming that the motor is a 1978 F2. I would do a clearance check first up and if the clearance is well within specs I would then hone and recheck clearance. At this point if clearance is still well within spec and all of the pits in the cylinders are gone then re-ring and reassemble. If clearance is not within specs or you still have significant pitting I would start looking for a good set of used F2 barrels that can be honed to take your pistons. The only other option would be an aftermarket 836 F2 Piston kit. These kits are expensive and you would need to add the cost of re-boring your cylinders to 836.
There are not many options for oversized pistons available for the F2. Its either stick to standard bore and use your pistons with a new set of rings or one of the 836 F2 Piston kits. I would not consider using the cheap 836 piston kits that have been available on Ebay. They are a good kits but the pistons are flat topped - yours are domed - and you would loose too much compression. You would have to mill the head a lot to get an acceptable compression ratio.
I would try very hard to find a good used set of cylinders in standard bore. Try and find a set that you can have a look at before you buy so that you can check clearances and bore condition. Ebay is a source but it is risky because you cannot check clearances and bore condition. Good Luck, Pat