Stuck Piston in a Cyclinder, best way to unstick

[Bruce Young]

This is a subject I have not seen covered very much. As most of us know when a engine sit,s out in the barn or behind one for very long, or just out in the weather, or even in a garage, the engine parts and pieces become very very stuck, rust frozen and not even arust remover seems to work in UN-sticking it or the rod from the crank or the cylinder studs from the cylinder. They just don,t budge.

What step by step methods or trick tools have the Hodaka world used or made to make it possible to remove the cylinder off first the piston, and then freeing up the rod and crank. I know many of you have done this and we might try to help the newbys out there that have found a project bike and need to get the engine unstuck. Bruce Young

[matt glascock]

Hi Bruce. There are two fluids I use. For smaller jobs (studs, wrist pins, etc) I use Kano Kroil. A bit spendy but an excellent penetrant. I use some rendition of apply, let it sit, apply, let it sit, apply, let it sit for several cycles before I test for movement. For motors, I fill the entire motor, cylinder, and transmission case with a 50:50 blend of dino ATF and acetone. Again, fill, let it sit, agitate, let it sit and repeat this cycle for a week or two before testing for movement. Keep the motor in a tub and away from sources of ignition during the process. The solution will most likely leak out of the motor during the process. Obviously, a torch plays no part in this technique. I might do a little rapping with nothing more aggressive that a nylon dead-blow hammer or the like. The key here is patience, patience, and more patience.

[viclioce]

I’ve even used WD-40 if I know the engine wasn’t rusted shut.

I have an Ace motor now that’s been sitting for over a month with PB Blaster and it still hasn’t broken free. I’m not too worried about it because the cylinder is a .080 overbore, so there’s not much left to the cylinder. But I wonder, can you split the cases if you can unbolt the threaded rods which hold the cylinder? Just to try and get it apart? Victor

[Bert44]

Victor, as long as you unscrew the cylinder studs that should work. There’s an article in the latest “Classic Bike” British magazine showing exactly that process. The crank, rod cylinder was then placed in a hydraulic press to separate the piston/cylinder.
I always like to use a bit of heat before separating frozen parts, the differential expansion rates seems to get the ball rolling and a spray of your favourite penetrant can then penetrate the cracks.
Bert

[viclioce]

Thanks Bert. My only concern at this point is to save the connecting rod & crank. Can’t pull the wrist pin until I can separate the piston/rings from cylinder. I’ve thought about just drilling the piston and breaking it since the piston/cylinder are a .080 over bore. Not much cylinder to save. Better off getting a less devoured one! Victor

[Bert44]

Victor, the idea is to hang the crank and con rod between your two steel bases on the press and rest the cylinder on top of the bases, then press on the piston (preferably via a block of wood) and hold the crank with one hand so it doesn’t drop on the floor.

[viclioce]

OK. I’ve sprayed it several times with PB Blaster but it hasn’t freed up. Which is why I was going to try to remove the cylinder studs, separate the cases and take the cylinder with the crank and do what you’re suggesting. I don’t have a press, but my son in law does & I hope that it will push the piston free. Victor