Piston Rings are shot

[gtosteve65]

Hey everyone, my buddy has a 1982 Yamaha Seca 550. He missed a shift recently and over revved the engine. Piston rings are fried. So we plan on replacing the rings, and a good old honing to clean up the cylinders. The problem is he is going to spend about $130 just for 4 sets of rings. Turns out that they don't make those guys in high numbers anymore. We are both engineering students and broke so I started thinking if we could just use ordinary rings that are the same thickness and for that bore size. Pretty much buy rings without buying the general Yamaha rings. Has anyone ever tried something that seems as dumb as this :spank:? After doing some research we think it will work as long as we get the measurements perfect. The original rings didn't have any special design to them(at least from what we could tell).

Worst case we buy the correct rings, but this was something we are now both pondering as being capable of working if we do it correctly.

 

[FinalImpact]

There is a lot more to it than that. Tension, gap, thickness, bevil or cut appropriate for that piston as cylinder pressure is used to expand the top ring to build compression. Top ring, second ring, and oil scrapper set are all very specific for piston and cylinder wall material.

That would be a big gamble....

JM2C unless the pistons are damaged, the rings are not the weak link in an over-rev situation that would fail.

What are the symptoms?

Over-rev can take out any of the following:
Valve springs, spring keepers, bent valves from hitting pistons, wrist pin, piston skirt, rod stretch are among the top casualties when this happens....

When it goes real wrong the rods, crank, wrist pin and piston break and parts go everywhere....

What has been inspected so far?
How did you conclude the rings are bad?

If it ran low on oil, that could damage a lot more components...

Good luck!

 

[TownsendsFJR1300]

+1 ^^^^

A missed shift from a simple over rev won't toast 4 sets of rings...

As FI asked, how did you come up with that conclusion?

**A LEAK DOWN test (if the engine isn't broken down yet) would be very informational...

Again, what are the symptoms and can you post an audio / video of it running


Rings are available BTW, search is your friend:

1982 Yamaha XJ550J Crankshaft Piston Xj550h J K | Babbitts Online

 

[gtosteve65]

So we did a compression test, and the compression on cylinders 2, 3 and 4 was about half of what it should be. Put some oil in the cylinders and repeated the test. Compression went up a significant amount.
Started to take the bike apart so that we could get to the rings and check them out. This is what they looked like and you can see the blow-by. The rings also have a decent amount of what looks like melted metal on them. Pistons themselves look alright as of now (still gotta clean them) and the valves are also looking ok (again, still gotta clean them).

 

[TownsendsFJR1300]

That carbon, etc has happened over years, not from an over rev.

I would first pull the rings, put them in each bore (top/middle,lower) and check ring end gap vs spec's

Your going to have to measure the bore(s) as well. If out of spec, punching them out .010 with new pistons and rings would be next..

It's hard to tell in the pic's but is the carbon holding part of the compression rings IN the groove?, IE, they can't fully expand???


Worse case scenario, if their just carboned up badly, ring end gap is still within spec, you may be able to get by with what you have.

I got 64,000 miles out of OEM Kawasaki KLR 250 rings (from 1989) and they were just barely out of spec(pulled apart for a failed crank bearing)

 

[FinalImpact]

Looks like is sat and moisture/corrosion attacted the piston and cylinders. Adding to that, the pure amount of varnish could really be hurting it not to mention the carbon deposits....

Do you have the before and after compression ###'s?

The used to sell gallon containers of Gunk engine degreaser and they came w a strainer basket. Let them sit in there for week, wash and dry, scrape off any carbon / or blast it off with walnut shells through sand blast setup....

Agreed, if the rings didn't break from piston rock in the bore, it wasn't over-rev that made it loose compression.

Maybe previous owner thought it was a diesel tractor motor and lugged it up and over steep hills in 5th gear at 17mph??? J/K.... but...

What do the holes look like?

 

[gtosteve65]

So the bike ran great until the over rev. Luckily for now he has an extra motor we are going to put in the bike. In the meantime we are going to clean everything and check all the parts to confirm they are in spec. We don,t have before compression numbers before the over rev, but it ran really strong. I'll try to get some more pictures from him of the engine.

 

[TownsendsFJR1300]

You didn't happen to check cam timing before pulling it apart did you?

 

[gtosteve65]

Timing was good. After the over rev it sounded like an old man. It ran like crap. Cleaned the carbs thinking he might have backfired some **** into them during the over rev and didn't hear it over the engine, and then that's when we checked the compression and found it to be bad. Looked at the timing before we pulled it apart and it was good still.