Cylinders - Do I chance it...

[yesterdayze]

So here's the deal. I bought my wife a 91 Bandit GSF400. Needed motor work but everything was there and in really good condition other then faded paint. On to the engine... Nothing blown, nothing cracked, no thrown rods or anything... BUT it had sat for years with moisture in the cylinders. Well, they rusted. So, I pulled the engine apart and cleaned out the rust. It is freaking near impossible to get the stupid cylinders so I am hoping to save the one I have. Here's the gotcha.... I need to hone it a hair more to get it all hatched properly but I just put a bore guage to it....

Service limit is 56.080

In most parts I am fine and the bore specs in at 56.02... there is one section though where it is out of round and specs in just between 56.04 and 56.05 which is still well inside the 'out of round tolerance' limit of .2 and still .030mm within spec (Note, mm not inches... in inches that is .00118...).

So here is the gotcha.... the cylinders walls while mostly smooth, still have some ugliness going on. Normally I would hone this out myself with a stone, but I tried that and had miserable luck. I can have a machine shop do it for me on a professional machine but I am concerned they might get overzealous. I'm contemplating just using a ball hone and calling it good.

Anyone have any experience having this done at a machine shop when you are this close to the service limit? Anyone know anyone that can do a bore of .010mm - not inches - decently? I have a mill, it has that tight a tolerance but there is no way in hell I trust myself to attempt the job.

Thoughts, ideas?

[SSearchVT]

If you're looking to just have a decent bike to run around I'd run a ball hone through it, and put it back together with a proper sized piston and ring set (you didn't mention if it was stock bore - safe bet that it is). Being an air cooled inline twin - there's a good chance the cylinders change shape a little when the motor warms up. If the ugliness section you mentioned is that bad - boring it out might not clear anything up for you.

[FTMS]

Can you feel the "ugly" with your fingernail if you run it over the spot or is the cylinder wall just stained from where the rings where?

[Cerberus]

good point on the shaping of the cylinder as it gets hot.. manufacturer may have had a way to simulate head-bolt-torque induced cylinder deflection, as well as compensate for heat shaping..
bottom line i'd probably just..
oh hell, truth is i would probably bore it to just this side of service limit, hone it out to spec, re-ring reassemble and be done with it.

ok, i miised the millimeter versus inches clarification the first read through.. still need coffee..
i don't think doing a .001 of an inch bore job is even possible...

ball hone and reassemble while you hunt down a new cyll

[yesterdayze]

yeah, it is still stock bore. You can't really feel the ugliness with your fingernail. If you really pay attention you can tell that it isn't as smooth, but it doesn't drag or catch or anything. It looks more like stain from where the rust and rings were.

Yeah, I didn't think that a .001inch bore was possible but I figured I'd ask. On something that wasn't my cylinders I would chance using my knee mill to try to bore it, but that is such a minuscule amount there is no way I would be able to keep it aligned closely enough.

Thanks guys! I think I will just ball hone it and call it good.

At worst I may have some oil sneaking by the rings but probably not enough to worry about.

[Kurlon]

Are the cylinders sleeved or is the block itself plated? If need be new sleeves can be pressed in, easy cheasy. You should be able to get the next oversize piston from Suzuki too as there will be plenty of meat in those sleeves to go that route (If sleeved).

[yesterdayze]

Are the cylinders sleeved or is the block itself plated? If need be new sleeves can be pressed in, easy cheasy. You should be able to get the next oversize piston from Suzuki too as there will be plenty of meat in those sleeves to go that route (If sleeved).

They are sleeves pressed in, but what I ran into is the sleeves haven't been made in years and I couldn't find new ones. I did find oversized pistons but only one place in the UK carried them (bike was more prevalent in the UK then here, pretty rare here) and they want 580 pounds for them, that's a lotta us dollars lol.

[butcher bergs]

A hone such as this one is how to get the cylinders back into proper shape. This style is the only hone which will return the cylinders back to round. Just push it thru a few times and that should do a fine job to clean up the cylinders.

As far as the spec, you may have to cross that bridge when you get there but, since there's already an issue with the cylinders, you may just want to run it and see how long it will last. I think you'll be surprised and since this engine is not being used in a race application, you may fair just fine.


EDIT: Double check to see if there is a special coating (Nikasil, for example) on the cylinder walls.

[stoinkythepig]

Being an air cooled inline twin - there's a good chance the cylinders change shape a little when the motor warms up.

It's a liquid cooled inline 4.

[Kurlon]

They are sleeves pressed in, but what I ran into is the sleeves haven't been made in years and I couldn't find new ones. I did find oversized pistons but only one place in the UK carried them (bike was more prevalent in the UK then here, pretty rare here) and they want 580 pounds for them, that's a lotta us dollars lol.

Northwest Sleeve and many other sleeve shops can make sleeves to fit, easy cheesy. If I get some time I'll dig around for pistons, odds are there is another bike with units that can be used as drop ins and possibly net you a small compression boost at the same time. : )

[yesterdayze]

Yeah, no special coating that I see so I think I'm good there. That hone is a lot gnarlier looking then the 3stone spring loaded one I have lol.

Northwest Sleeve and many other sleeve shops can make sleeves to fit, easy cheesy. If I get some time I'll dig around for pistons, odds are there is another bike with units that can be used as drop ins and possibly net you a small compression boost at the same time. : )

Sounds awesome man! I'll call up Northwest and see what they're at for prices.

The pistons stocks size is 56x40.4mm if that is any help.