Oil Starved Engine Disassembly.

Yorkie

Yorkie

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I could use some advice. I have an 850 motor that ran out of oil and seized. The pistons are stuck in place at nearly TDC. I am trying to get the cylinders off the crankcase so I can separate them and unbolt the connecting rods. However, the position of the pistons prevents the cylinders from clearing the crankcase halves. I have tried everything imaginable to push the pistons down but they have galled and seized solid in the cylinders. A mix of diesel and acetone doesn’t move them. I believe I need to collapse the piston by drilling holes in the crown. Has anyone tried this before and can they provide any advice?
 

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Not clear what methods have already been used, but I would pack timber between the cylinders and crankcase, heat the cylinders, and whack the pistons with hammers of increasing sizes…..
Other method could be to clamp a bar across the cylinders with sockets or something between that and the cylinders. Put some strain on, then hit with a hammer….
 
DougC said:
Not clear what methods have already been used, but I would pack timber between the cylinders and crankcase, heat the cylinders, and whack the pistons with hammers of increasing sizes…..
Other method could be to clamp a bar across the cylinders with sockets or something between that and the cylinders. Put some strain on, then hit with a hammer….
Click to expand...
Thanks Doug but I’ve tried all those. I welded up a clamp bar and applied beaucoup pressure via a couple of 5/8” bolts. I went through numerous heat cycles and got medieval with a block of wood and a sledge hammer. I’ve only ever seen this level of seizure with a H2 750 two stroke that locked up due to oil starvation.
 
Oh well..
How about a hole saw to cut out most of the piston crown? Not sure if that would cut the gudgeon pins as well, or if they're hardened.
That might allow the lower half of the piston to break off and get forced down..
 
Yorkie said:
Thanks Doug but I’ve tried all those. I welded up a clamp bar and applied beaucoup pressure via a couple of 5/8” bolts. I went through numerous heat cycles and got medieval with a block of wood and a sledge hammer. I’ve only ever seen this level of seizure with a H2 750 two stroke that locked up due to oil starvation.
Click to expand...
was it a anti-sump valve that caused the oil starvation? Just curious.

The pistons can be drilled & cut out. Do you know a talented fabricator?
 
Looks like it was pulled out of a dried up wash in Death Valley CA.

As far as getting the barrels off the pistons goes. I'd bolt the crankcases back together in a bolted down engine stand, then start the hammering, heating, or whatever technique one prefers. It would prevent potential binding of parts not aligned properly and the hammering would be more effective. That is what my brain is telling me. That said I have only worked on locked up V8's and not any locked up motorcycles that I can remember.
 
As I view pics...have you determined or really know if the crank is seized at the mains, connecting rod bearings seized, wrist pins seized?
Cut the connecting rods, you've probably stretched them with all the effort to separate the components...it looks like there is access based on the view of 1 photo...judging from initial appearance that old power plant might be better off as a boat anchor.
 
Last edited:
Yorkie said:
I could use some advice. I have an 850 motor that ran out of oil and seized. The pistons are stuck in place at nearly TDC. I am trying to get the cylinders off the crankcase so I can separate them and unbolt the connecting rods. However, the position of the pistons prevents the cylinders from clearing the crankcase halves. I have tried everything imaginable to push the pistons down but they have galled and seized solid in the cylinders. A mix of diesel and acetone doesn’t move them. I believe I need to collapse the piston by drilling holes in the crown. Has anyone tried this before and can they provide any advice?
Click to expand...
Use a doorknob drill on the piston tops, and chop out a large enough circle to avoid the small ends of the rods. Just a little at a time till they pop thru.

Start with the center bit in place until you have a significant depth on the outer circle. Then remove the center bit so as not to hit the rod.

Oil Starved Engine Disassembly.
 
Use a oxy/Act welding tip to poke a hole in the top of the piston. Front or back. Wash out a line down the skirt. Lower heat would work best. Act. rich, as to not cut into the carbon of the cast iron, with excessive Oxy.
 
Consider bolting a head back on, make plug inserts with grease zerks and pump grease into the head barrel piston chamber until the pistons free.
 
ilikevelos said:
Consider bolting a head back on, make plug inserts with grease zerks and pump grease into the head barrel piston chamber until the pistons free.
Click to expand...
That's a common technique for the John Deere two cylinder crowd. It takes a few tubes of grease to fill those big barrels.

I'd be inclined to take the whole mess to a machine shop and get it chucked level up on a Bridgeport and use an end mill to cut the pistons away perpendicular to the wrist pins. Cut close to the barrels the piston should be weak enough to further destroy. It might take a bunch of cuts getting as close to the pin as possible but it's aluminum and an easy cut. Piston rings may be a problem.
 
If the pistons are all the way up then pounding them won't help. I would use some real penetrating oil like "deep creep" and let it sit for over a week. Then try heating and moving the pistons by either using the rear wheel to turn the crank or a big wrench on the drive end of the crankshaft.
I had a small compressor seized like this (all the way up) and after weeks of soaking I finally got it to break loose by turning the crank.
 
Once you have the pistons destroyed enough to remove the barrels then all the alloy fused to the barrel can be removed with Muratic acid otherwise know as Hydrochloric acid. The cast iron will be untouched, have used it to removed smeared alloy on crankshaft journals and no regrind needed.
 
kommando said:
Once you have the pistons destroyed enough to remove the barrels then all the alloy fused to the barrel can be removed with Muratic acid otherwise know as Hydrochloric acid. The cast iron will be untouched, have used it to removed smeared alloy on crankshaft journals and no regrind needed.
Click to expand...
Common way back in the day to remove the smear of a seized two stroke piston from the bore. Biggest problem is storing the muriatic acid. Can't be stored in glass and plastic jugs are somewhat permiable so metal close to it rusts.
 
ilikevelos said:
Common way back in the day to remove the smear of a seized two stroke piston from the bore. Biggest problem is storing the muriatic acid. Can't be stored in glass and plastic jugs are somewhat permiable so metal close to it rusts.
Click to expand...
Respects but hydrochloric acid doesnt react with glass Hydrofluoric acid does though but thats not an acid one would want to play with!
 
A big temperature differential has worked wonders on locked-up stuff I've had to separate. I can't think of anything it didn't get free. Steel surrounding aluminum alloy is an ideal situation Get the barrels very hot, like 350F plus, then drop ice, or even better, dry ice on the pistons to 'shrink' them. I'd add some Berryman's B12 Chemtool or acetone/ATF in the bores and have a big fan blowing away from me for the sizzling vapor. Maybe somehow lift the barrel and knock on top of the pistons at the same time with some hardwood and a hammer?
 

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