What wears first, piston rings or cylinder?

[One1]

I’m about to stick my 657 back together and I’m deciding on the last part. Let me tell you my issue and get help deciding the best move.

First, i asked which wears first because I’m thinking of dropping some new rings in a used jug that has good compression. Curious which will last longer.

I bought a new old stock oem piston, jug, rings, wrist pin for cylinder #1 and cylinder #2 is untouched with good compression, but not perfect. It’s original to the ski and has hours on it. Since the original will have less compression than the new, I’ve been looking for easy ways to get it to match the new one as closely as possible. I do not have a machine shop that can help me bore it so it’s down to what i can do here. There’s no need to buy another complete set for cyl #2 since it’s high compresion and looks excellent. I was thinking of throwing new oem rings in.

Stock 78mm bore. All oem parts.

 

[mikidymac]

SInce the pistons are the same manufacturer and size there will be no issues for balance. You wouldn't want to use two different size pistons or brands because the difference in weight could throw the rotating balance off.

If it were mine I would hit the #2 cylinder with just a flex ball hone and an new set of OEm rings and be done with it. The old rings in it will loose tension and compression before the new ones you are installing in #1.

 

[Chester]

The piston wears out first. Replace both pistons and the crankshaft seals. Make sure you check the piston to cylinder wall clearance.

 

[One1]

Actually I am going to change the crank seals since I saw a little bit of oil in the stator cover, but I was going to ask .......I’ve heard this is incredibly hard to remove the flywheel, so should I just let somebody else pop that fly wheel off for me or is it something I could pull off with a little heat and a puller or without too much chance of messing up the crank?

 

[GGuillot]

Actually I am going to change the crank seals since I saw a little bit of oil in the stator cover, but I was going to ask .......I’ve heard this is incredibly hard to remove the flywheel, so should I just let somebody else pop that fly wheel off for me or is it something I could pull off with a little heat and a puller or without too much chance of messing up the crank?

May want to get someone to do it, I've pulled 2 off, both 787's, I almost got a hernia and bent a 1/2" breaker bar the first time last year, heat didn't do anything. Wrestled with it for over an hour and got nowhere. I turned to the Auto Skills center on the Army Post I work at, they had a massive vice to hold the crank, 3/4" impact tools and breaker bar and a 4 foot cheater pipe. It broke loose fairly easy that way, but it's no joke, you need the heavy stuff, no mickey mouse tools will cut it.

Some people like to use a chain wrench, but the impeller tool worked fine for me.

 

[mikidymac]

The big problem you or anyone is going to have is you have no way to stop the crank from turning now that the cylinder is off.

The correct way is to use rope or even better a block of wood in the rear cylinder with the head on to lock the crank to be able to unscrew the rear PTO.

Heat and a chain wrench is the easiest. I have actually broken a few impeller tools and you can damage the splines too.

 

[One1]

I’ve removed the bolt, what else turns? I was thinking the flywheel balancer came straight off? I haven’t looked into it past being told it’s a pain.

 

[IDoSeaDoo]

Personally, I've never had that big an issue removing these PTO's. I use propane to heat it up, put a piston and jug onto one side (temporarily) with some rope in there to stop it, strap the whole thing down with ratchet straps and use my electric impact gun and/or Harbor Freight 1/2" breaker bar with a spline tool. I work mostly on 787's, and haven't ever needed more than a little propane to coax it off. I'd try to get it off myself first.

 

[mikidymac]

I’ve removed the bolt, what else turns? I was thinking the flywheel balancer came straight off? I haven’t looked into it past being told it’s a pain.

What bolt? The rear, white round flywheel unscrews from the crankshaft.

 

[One1]

That’d be what i was curious about. Lefty loosey?

 

[mikidymac]

Yes, standard threads.

 

[Sportster-2001-951C-Stock]

Yep, new rings and light hone at rhe correct angle. The cylinder ports need to be chamfered so the rings won't snag in the ports so check that too. New outer crank seals stop air leaks, inner seals stop oil leaks.
This is why I prefer remanufactured warranty engines, too much to go wrong.

 

[One1]

Ok i put the stator flywheel back on and locked it, but even with heat (250 degrees) I couldn’t turn the balancer left and screw it off. I’m able to get a grip on it, though I don’t see why there isn’t a point to put a breaker bar and get leverage, however I’m unable to muscle it loose. Is there any technique that works for getting enough leverage to spin it off?

 

[mikidymac]

Are you talking about the PTO?
You can't hold the flywheel and then unscrew the PTO or you will twist the crank out of phase. If the crank is junk then don't worry about it but you still could shear off the flywheel key.

THe key is lots of heat on the PTO then a chain wrench around the outer diameter of the PTO and a cheater bar then constant pressure and hit the bar with a hammer to shock it and break it free.

 

[One1]

I’m going to have to put it back together. I didn’t have a good reason for it other than checking for debris and I’ve seen enough to know i can flush it clean from here. I only grabbed and tried to turn it once so i doubt i did anything to hurt it, but it’s a good engine and I can’t afford to make a mistake just for curiosity in checking the bottom end when it runs great.

 

[Sportster-2001-951C-Stock]

I agree, definitely don't take it apart if it runs good and compression is reasonable. Once compression drops too much, excessive blowby can torch a piston and throw debris everywhere thus it's better to rebuild or at least do the top end.

If the engine hesitates in the water, it's usually a sign of running too lean, fuel system issues. I can't count how many 2-strokes I've seen killed from running too lean.

 

[One1]

I planned on doing a pump bypass for the oil while I had it down and it looks like that was a good idea.

 

[One1]

Ps- there’s been a lot of grit settle in the bottom end since it's been apart for a few months. I poured a gallon of mixed 2 stroke to rinse. Also learned the question i asked on here many months ago and didn’t get an answer...... the cylinders are independent of each other in the crank area. You can pour 2 stroke down one crank side and fill it up without it coming into the other crank area. So if you blow one cylinder you only have to worry about THAT side. That’s very helpful when assessing damage and cleaning up after a problem. None of the piston from the back could have gotten into the front when i hooked the exhaust.