examine my piston top

[Guest]

Head gasket was leakin bad on my 80 gs 1100. Pulled engine, head, cylinders. Piston tops were all sticky and black. Used some Big Orange cleaner and the stuff melted off , I rubbed it with my finger and this is the mostly cleaned result. The top of piston is all scratched up, and there is a dark ring around the surface about a quarter inch from the edge. It almost feels like a slight groove, but then again not really. The rings (top two) have about a three eights gap between the ends. I have read the owners manual, and measured the cylinder bore and it is actually a hair smaller than the listed range of acceptable limits before reaching the service limit. I measured the piston diameter and it seems to be in the accepted range, this measurement I must look into more, making sure I measured the right spot. The engine is of questionable mileage. odometer says 22,xxx but think it has been rolled over, Is it possible this thing has 122,xxx? Oh, the cylinder walls have cross-hatch marks on them, maybe suggesting a past rebuild or cylinder work? Any insight on all this appreciated.
I have much more engine work ahead of me and will search forums for info, just puttin this pic and info up to see if yall see anything bad or smell anything fishy with this engine story. ****** I recently bought it, had it running pretty good, but have not ridden it yet. It blew black smoke when I rould rev it up hard, and the cam cover vent tube puffed black smoke, which I gathered is normal. third cylinder stopped firing at some point, spark but cold exhaust pipe. in process of rebuilding carbs and cleaning up engine for paint/polish.

[Nessism]

Looks fine.

What tools did you use to measure the bore and piston?

[loud et]

Looks fine.

What tools did you use to measure the bore and piston?

a digital slide , with inner and outer jaws

[Nessism]

a digital slide , with inner and outer jaws

What is a "digital slide"? Do you mean a set of calipers?

[Big Jay]

a digital slide , with inner and outer jaws

That is not accurate enough.

[loud et]

What is a "digital slide"? Do you mean a set of calipers?

yeah, calipers

[loud et]

That is not accurate enough.

I know it is "accurate" enough, but it probably lacks the ability to access the areas that need measured....is that what your saying? I will look into engine measuring tools from the people i know.

[Nessism]

That is not accurate enough.

Agree. You need a bore gauge and micrometer.

[loud et]

Agree. You need a bore gauge and micrometer.

copy that. thanks

[Guy]

If the (standard) bore measures inside the service limit and the cross hatch marks are still visible, then it's unlikely the odometer has rolled over. The ring gap will give you a good idea of the mileage/wear.

[Steve]

The rings (top two) have about a three eights gap between the ends. ... odometer says 22,xxx but think it has been rolled over, Is it possible this thing has 122,xxx? Oh, the cylinder walls have cross-hatch marks on them, maybe suggesting a past rebuild or cylinder work? ...

The only proper way to measure ring gap is to remove the rings from the pistons, push them down into the cylinder just a bit and measure the gap. If you were measuring the gap with a relaxed ring, it is totally meaningless.

I recently had the opportunity to see the cylinder walls on my wife's bike. Cross-hatch still plainly visible, 64,000 miles.

.

[loud et]

The only proper way to measure ring gap is to remove the rings from the pistons, push them down into the cylinder just a bit and measure the gap. If you were measuring the gap with a relaxed ring, it is totally meaningless.

I recently had the opportunity to see the cylinder walls on my wife's bike. Cross-hatch still plainly visible, 64,000 miles.

.

thanks for the info, I jumped the gun in noob style with my thread, I have not been on long, but I too already marvel in disbeleif at some of the questions other new members ask, I know you long-timers on here get pretty crabby sometimes.... I get it. I will be tracking down proper measuring tools, and am getting quite familiar with the service manual from Cliffs site. I know how to do the ring end gap measurement and the milti point cylinder wall I.D.
Thanks all for your responses, I got a little manic after midnight. I have stars and GS's in my eyes. new and obsessed with my rebuild/ mod project.

[DanTheMan]

An FYI on a couple of things you mentioned: Black smoke out of the tailpipes=fuel mixture too rich. Black goo on top of the pistons=fuel mixture too rich. Black blowby coming out of the crankcase vent=fuel in your oil and the crankcase is venting it as blowby.
How did you determine it needed a headgasket, let alone a complete rebuild? It probably only has 22,000 miles on it, it's barely broken in. My 850 is pushing 94k right now, replaced the head gasket because it blew at 64,500 after a few very hot days running in slow traffic in the desert. I knew it was blown because it spewed oil all over my left leg.
I know it's too late now, you've got it all apart on the work bench and most likely have parts ordered, but this info might be good for the next time.

Nothing at all wrong with your piston, by the way, unless the skirt is broken.

[loud et]

An FYI on a couple of things you mentioned: Black smoke out of the tailpipes=fuel mixture too rich. Black goo on top of the pistons=fuel mixture too rich. Black blowby coming out of the crankcase vent=fuel in your oil and the crankcase is venting it as blowby.
How did you determine it needed a headgasket, let alone a complete rebuild? It probably only has 22,000 miles on it, it's barely broken in. My 850 is pushing 94k right now, replaced the head gasket because it blew at 64,500 after a few very hot days running in slow traffic in the desert. I knew it was blown because it spewed oil all over my left leg.
I know it's too late now, you've got it all apart on the work bench and most likely have parts ordered, but this info might be good for the next time.

Nothing at all wrong with your piston, by the way, unless the skirt is broken.

thanks for your response, yeah, It has oil bubbling out from between the cylinders and the lower case on the left side . The 10 mm bolt right near the 1075cm3 stamping is broken off,(on the very left side of the cylinders) have to extract it. So i have to do gaskets. I just got paranoid. I will do the ring gap measurement , make sure they are good and clean and paint the engine and do gaskets and be on my merry way. this is not a high end restoration, I am just poking around in the engine while its opened up making sure nothing is seriously broken/worn. thanks again.

[DanTheMan]

Well, that's good anyway. I hate to see someone doing a complete rebuild on an engine that's barely broken in, unless it's for class or something. Just don't get your pistons, wrist pins and rings mixed up.