Pistons #1 and #4 lodged on reinstall

[redfenix]

On my GS850 rebuild...

Okay, I messed up pretty bad here. After putting new piston rings on and lightly honing the cylinders, I was putting the jugs back on. I rotated #2 and #3 up and got them in without much trouble, then I slid the cylinders down further to #1 and #4 and got the rings started in the bottom of the cylinders, but they were tougher to get in. Long story short, I resorted to tapping with a mallet on the cylinder block to get it seated and I now realize that was a big mistake.

Fast forward, the #1 and #4 pistons are lodged firmly in their cylinders and I can't seem to get them unstuck, no matter what I try. I'm guessing they're misaligned in there and that's why they're stuck. I'm afraid to use any more force on them for fear of irreparably damaging the cylinders (I know the pistons may be unsalvageable at this point). Even if I wanted to try to get at them from the underside, I'm not sure how because these piston rods don't come apart and it looks like it's not even possible to disassemble the crankshaft with the #1 and #4 pistons engaged.

Sorry guys, I don't mess up like this very often and I think this is the worst I've messed up on a vehicle I've worked on. I should have known better than to use any force at all on reinstall, but I got too eager to get it back together.

Is there anything I can try at this point? Or am I looking at getting another engine altogether here?

 

[chuck hahn]

Can you get to the wrist pins still? Remove the circle clip wire and lift pistons off with the cylinders. Bet you'll find one of the thin rings on the oil control rings has wedged itself. A block of wood should smack the piston out. It's happened to me. There was a little nick on my piston but it filed right off. These things rings can be a pain to get in at times...this my asking for ring compressor suggestions a while ago. My fat fingers are a hindrance and not a help

 

[chuck hahn]

Might be a mark on the liner too. Might have to run a ball hone to freshen it up. Hopefully it doesn't dig into the liner. If a mark is below the area the piston will travel I don't see any reason to do anything than sand it smooth so it won't snag rings when putting cylinders on.

 

[redfenix]

Can you get to the wrist pins still?

Unfortunately no, they're too far up in there to get to them. I've tried a block of wood from the top, but even then I get nominal progress (like 0.1mm, I measured it with the tail of a digital caliper) I'm afraid if I smack any harder on the top of the pistons it will just dig in more.

 

[chuck hahn]

Well. As I see it, you've gotta do what ya gotta do. 2X2 dead center of the piston and put wood under the bottom of jugs and have at it.

 

[redfenix]

Well. As I see it, you've gotta do what ya gotta do. 2X2 dead center of the piston and put wood under the bottom of jugs and have at it.

Yeah, I'm coming to that conclusion myself. If the only other option is another engine, what do I have to lose? I'll give it a try and report back. Thanks!

 

[jsandidge]

I had a similar problem. In getting it loose, I busted a piece off of one of the piston skirts. No other damage. Bought a used piston off of e-bay for $10. That was over 5000 miles ago.

 

[chuck hahn]

Yeah....is what it is now.

 

[Grimly]

This is not an uncommon occurrence.
Last year I did almost the same, but just as they started to go cock-eyed and jam I recalled the last time that happened and stopped. They weren't stuck by much, so I was able to put a piece of 2x2 down from the top and whack the cocked side of the piston to attempt to right its alignment. Resist the temptation to clout the piston skirt, but it will show you what part of the piston crown to attack.
It will also help to put a broomstick under the barrels and exert some upward force, just be careful to not destroy the base gasket.
Once it's out, dismantle it again and check for damage.

 

[redfenix]

Great news! I was able to drive both pistons back out the bottom of the cylinder liners. Chuck called it, both of them had oil rings folded downwards. This is the #1 piston which was the hardest to drive out.



After looking over the damage, I think I can file down the rough spots on the pistons and hone down the cylinders. There’s just minor surface scratches on all parts involved.

Thanks for the support and encouragement!

One more note for others who might read this. Measuring the position depth with the tail of a digital caliper made this a lot easier to tell if I was making progress and which side was higher or lower.

 

[rphillips]

Congrats & thank goodness for no major damage.

 

[Guest]

learning a valuable lesson here eh? you'll get there

 

[redfenix]

learning a valuable lesson here eh? you'll get there

Definitely. I'm just glad the lesson wasn't more expensive. I just ordered another set of piston rings and a base gasket from PartsOutlaw, which I feel isn't very costly in comparison to what it could have been!

 

[rapidray]

Just out of curiosity, did you clean the carbon out of the ring grooves before you installed the new rings???

 

[redfenix]

Just out of curiosity, did you clean the carbon out of the ring grooves before you installed the new rings???

Yeah, there wasn't much carbon in any of the grooves to begin with, especially the oil ring groove. I think I just didn't have the oil rings compressed enough and forced them in.

 

[chuck hahn]

Be sure the ends of the wavy rings are setting perfectly together and not overlapped....then put on the two thin rings.

 

[wymple]

I always make sure the rings will compress far enough into the grooves to begin with. Manufacturing mistakes happen and I've seen it 2 or 3 times in my years. I've had to cut bit off the expansion rings under the oil rings because they would not compress to a small enough diameter. Most recently on my AMC Javelin 401, once that I recall on a 2 stroke bike, as well. I've had piston grooves on new slugs that were not milled deep enough.

 

[redfenix]

Be sure the ends of the wavy rings are setting perfectly together and not overlapped....then put on the two thin rings.

I did put on the thin rings after the wavy ring, but maybe I should have inspected it more closely? I'll definitely do that this time around.

 

[redfenix]

I always make sure the rings will compress far enough into the grooves to begin with. Manufacturing mistakes happen and I've seen it 2 or 3 times in my years. I've had to cut bit off the expansion rings under the oil rings because they would not compress to a small enough diameter. Most recently on my AMC Javelin 401, once that I recall on a 2 stroke bike, as well. I've had piston grooves on new slugs that were not milled deep enough.

Good tip, thanks. I'll definitely check that on each piston before installing this time.