Scored piston

b7hs · Scored piston

After pulling off the pipes to clean them up a bit, I kinda wished I hadn't peered into the exhaust port of the center cylinder:

I noticed that one of the studs seems to have been helicoiled. I'm wondering if bits from that endeavor ended up in the cylinder and caused the scoring.

With the pipes off, I can see how the front of the engine got covered with oil:

I suppose pulling off the top end is in my future... or will I end up having to pull out the whole engine anyway?

So what do you guys think? Over bore and new pistons? All three? I'll have to measure the cylinders first for a previous over bore I suppose. I wonder why the pipes were pulled resulting in the knackered stud mount to begin with.. unless it was leaking and the guy just cranked on the nut until the stud ripped out of the cylinder.

Any recommendations for a shop to do the machining in the US?

<sigh>

kas750

250 pistons are cheap as chips.Pull it NOW and do the work before something drops into the crankcase and does damage in there...

g6mow

simonh

its not as bad as it looks, you may get away with a new piston and rings, depends how worn the bore is.

99% of the problem is worn rings/piston and a leaking exhaust port, tons of carbon build up there so it hasnt been running right for a while.

But if all three are the same worn out condition worth going for a new bore and pistons/rings

My centre pot was much much worse, i honed it and put a 2nd hand piston and rings in it and it ran fine, but sounded like a bag of hammers, see my avatar

kas750

b7hs

Sorry, 'forgot to mention that it's a kh400 engine.

With the rings chewed up as bad as they are on the center pot, I'm expecting to see a dinged up cylinder wall too. I'm wondering if I'll be able to find a cylinder with the studs intact. I just got the bike last April and I haven't gotten to the point of starting it yet. I just finished cleaning the tank and carbs and I was planing on covering the ports and degreasing/scrubbing down the bike/engine before re-mounting the carbs, tank and pipes.

I was tempted to skip the scrubbing down part and just get her running for the summer, but things have a way of snowballing I guess. :(

I also noticed that the side of the other pistons (as much as can be seen through the exhaust port) looked pretty oily for an engine that hasn't ran for a few years. I gave the starter a gentle kick, but I didn't see any oil spit out.

In for a penny, in for a pound.

Thanks for the info guys.

simonh

that cylinder is about to go the same way as the centre, see the erosion on the top ring groove, and the blowby of the rings.

I would do a rebuild matey, the bore should be ok, just worn hopefully

b7hs

simonh

the exhaust - weigh them!

if new rings were freely availble a clean up and ringset might be ok, but g6mow can supply pistons and rings for less than you could find a kawasaki ringset for

left looks alright just knackered rings, so blowby
if its on std, get your bores measured and checked for ovalness, mite have to bump to 1mm

b7hs

simonh

doesnt sound too bad, i'll weigh mine next week

ErlingW

Weight!!! Good idea. But I don't think I'll wait for my Higgsy ones to get to 9 - 10 lbs...

ErlingW