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Reassembly Woes: Stuck pistons

  • Thread starter Thread starter ameen
  • Start date Start date
For the future, there's a thread here on using some wooden blocks for holding up the barrels and large ring clamps as piston ring compressors. It worked like a charm for me my first time.

As to the current situation, most everyone who does mechanical work has been in this kind of situation. Seems to me you need to decide that a cylinder bore and new piston/rings will be required, and use whatever force is necessary to get the stuck piston out.
 
Think positively. You may have only damaged a section were the piston and rings does not ride. ;)
Then, you will only need to hone and clean up the damaged area. Also, as mentioned earlier, the lower part of the cylinders is tapered to ease the install process.
Taper the taper a little bit more where it meets the cylinder bore and when you go to re-install, smear plenty of white assembly grease in the taper and on the rings and piston skirts.
You may only have to do minimum work and only need a couple of sets of rings in parts. Still cheap!

Eric
 
On my 850, The pistons sometimes tipped on the way in, jamming them. In that state, they didn't want to come out either. If this is the case, you'll be able to see one side of the piston skirt looks to be sticking out less. A little tapping with the handle of a screwdriver freed mine so I could try again. But then, I never whacked the cylinders with more than the palm of my hand. I hope that's all you used.

(New to this thread and just skimmed it. Sorry if I missed a relevant detail somewhere.)
 
unfortunately i pushed a little harder than that...

here are some pics
 
Jeez that sucks, man.
Have you tried blocking the cylinder up with a 2x4 or something and turning the crankshaft?
 
Yea, I'd wrap shop cloth around the bottoms of the pistons then block the cylinders up and hit the tops of those pistons with another piece of wood driven by a hammer.

The reason for the shop cloth is to keep the pistons from hitting anything after they come loose and causing additional damage.

The cylinders are pretty sturdy and I doubt you've damaged them so far. Light scratches can be honed out. Check everything over when it's disassembled and perform a ring end gap measurement to make sure they are the right size.

Get another pair of hands when putting it all together next time. Don't force anything. If it feels like it's binding start over.
 
Number 2 is in cockeyed. Try tapping the bottom of the skirt and see if you can straighten it out. Try using a small ball peen hammer if you have one.
 
chef1366 said:
Number 2 is in cockeyed. Try tapping the bottom of the skirt and see if you can straighten it out. Try using a small ball peen hammer if you have one.
Click to expand...
Ah, I wouldn't strike the piston skirt with a ball peen hammer.

Those pistons are in pretty far to be cockeyed. If they are, I'd try using the handle of a ball peen hammer on the crown of the piston on the opposite side of way it's in cockeyed.

My guess is you have a oil ring that's not in it's groove and is wedging between the piston and the bore. That would give the appearance it's in cockeyed. If that's the case you'll need to bang it out as mentioned earlier. There is no being kind to animals. It's gotta' come out and you can access the damage from there. It will come out harder than going in. It's kinda' like the Chinese handcuffs you had as a kid.
 
Look at the crank rod and the piston in post #24.
I'd say it's cockeyed.
I would "tap" not rap. :D
 
chef1366 said:
Look at the crank rod and the piston in post #24.
I'd say it's cockeyed.
I would "tap" not rap. :D
Click to expand...
Yea, but even tapping a hard metal object against a softer, possibly immovable thin metal skirt is a dangerous proposition. If it's merely in cockeyed it won't be hard to budge and tappin the piston crown is far safer.

Hey, just my opinion.
 
How about a block of wood and a rubber mallet. I think I like that ideal better.
You're right about the hammer on the skirt.
 
chef1366 said:
How about a block of wood and a rubber mallet. I think I like that ideal better.
You're right about the hammer on the skirt.
Click to expand...

Use a piece of wood with a steel hammer to bang on top of #2 & #3 pistons. A rubber mallet onto the wood won't apply enough energy to the piston crowns.

Before you do that, pack some timber pieces between the cases and the bottom of the cylinders. You need to support the cylinders so that the impact is transfered through the piston crowns without any energy being lost by the cylinders moving. Don't be too brutal, just good firm blows to the crown areas.
You should have the pistons free in no time. You'll probably only need to re-hone the bore and fit new rings. Pay careful attention to any ring land damage that may have occurred. You can fix this by careful filing of the damaged groove.
 
I think what Chef is referring to is to hit the piston skirt with a rubber mallet and hit the piston crown with a block of wood by a steel hammer. ;)

Eric
 
block the cylinder with blocks and cloth to prevent further damage.... wooden hammer handle to knock.tap/hit the crown to get it out... hit ali with wood and nothing harder as the softer material will deform to a degree.... hit it progrssively harder til it comes out as ultimately.... it HAS to come out or it'll be a paperweight.

i'll bet the pistons looks wonky as an oil ring is bent over and has create a nice solid wedge in there... only way out is to hit.... then hit harder until it pops out.

good luck
 
Yeah, it has to come out, but he's already been hitting it a lot. The problem is it's seesawing back and forth. I would cut a piece of 2x4 to fit tight on one side, then hit on the other. Repeat for the other side. I would also consider using jacks, blocked so they are not directly on the head or cases. A ram system for pulling dents would work well, but so would a screw type car jack, like old VWs had. 2 jacks would work best, but 1 will do if you block one side with a 2x4 like above. IMPORTANT! If you jack on one side, do not go more than 3/8" before switching to the other side. Take your time and bring it up evenly.
 
using this (the rock)

and this (yeah that deformation came from the piston)

i ended up with this




i have two new pistons in the mail, but the cylinders are fine : )


 
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