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Discussion Starter #1 (Edited)
Pull the head off.

Clean everything out of the bores and measure the position of the pistons in the bores.

If you have not yet done so, mix acetone and ATF 50/50, and fill the bores; let sit overnight.

If more than 2.5" from crown to top of cylinder, you have very little downward travel left (3.2" total stroke), so proceed with caution! If measurement is anywhere near 3", skip to paragraph below that starts with "DO NOT PROCEED".

We know any penetration possible has likely occurred by now, so consider the problem MIGHT be compound. Remove the primary cover and make sure the chain isn't rusted frozen. Shift the transmission while rotating the rear wheel to ensure you are in neutral. Remove the timing cover and remove the idler pinion, for nothing else, see that the cams spin freely.

If none of the above has given any incremental progress in freeing up the engine, proceed to the instructions below...

OPTION A:

Take a large wooden peg about 2.5" diameter and insert it atop one of the pistons, and smack it sharply with a 5# sledge hammer or the biggest ball-peen hammer you can find.

Check the measurement from piston crown to top of cylinder and see if the piston budged at all (unless it is obvious that it freed off already).

If not freed up, move the peg to the other bore and give it a smart whack. Measure again, and continue opposite side whacks for several turns each, measuring between whacks.

DO NOT PROCEED once the measurement is approaching 3". At that point, remove the cylinder base nuts, wrap a zip-tie, rubber band or small o-ring around each pair of cam follower shanks, and lift the cylinder up; crank should rotate relatively freely (best if you've already removed the primary chain, and timing pinion). Take at least 4 same-length shallow sockets (3/8" drive) and set them with the 3/8" drive hole over 4 opposite side cylinder base studs, stuff some rags in the crankcase mouth, then set the cylinders back down on top of the sockets.

Now you can continue whacking away. Once you approach 3", and the pistons still aren't fully free, change the shallow sockets to deep sockets. That ought to do it.

OPTION B:

Make a 1/4" steel plate tool, patterned after the head gasket (with no piston cut-outs). Purchase a large enough piece of steel plate to also cut a few other bits mentioned below.

Over-cut the gasket pattern into a rectangle (round the corners), then drill out the 8 main bolt holes in your plate tool; next, drill one hole in the center of each bore with a proper hole for a 1/2" fine thread tap. Tap the two center holes.

Obtain (2) 4" long 1/2" dia fine thread grade 8 bolts, and fashion (2) 2" diameter plates from 1/4" steel. Weld a 9/16" nut in the center of each 2" round plate.

Drop the 2 discs into the bores, centered, then place your tool over the cylinders and fasten it down, with the (2) 4" bolts centered into the nuts on the 2 discs.

REMOVE ALL 8 CYLINDER BASE NUTS, and wrap the cam follower shanks so they don't fall into the cases.

Start cranking on the bolts, 1 turn each, equally. You MIGHT need a cheater bar on your ratchet!
 

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I'm having the same situation with my 1966 Tr6r . Heads off, and they don't move with a good whack. 50/50 mix of acetone and atf is in the bores now. Hopefully tomorrow they will budge! Someone should make the Plate tool you describe and sell it. I'd buy one!

Thanks for a great article. I'm certain it's helped a load of peeps!
 

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I’m not fond of beating pistons except as last resort. I first try filling the cylinders with mixture of choice, then put the bike in gear and rock it forward and backward. If this doesn’t work I heat the cylinders and do it again, adding penetrant as necessary. Usually, but not always, works.
 

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There is no question that what GPZ has posted has been proven by many over the ages to be the very best method for dealing with badly stuck pistons.

But I would note that in my experience, most cases do not require so much effort. Of course it will vary and will depend on how long the engine has been frozen and its environmental conditions.

I have found that for most cases, if you do not have the acetone and ATF, several long good squirts (couple tablespoons I'm guessing) of PB B'laster in the cylinders left for 48 hours does the trick. Then use the kickstart to see if things break loose. Or rock the bike in 2nd gear as duc96cr has suggested.

If this doesn't work, proceed to GPZ's steps above.

GN
 

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On 2 separate ocassions, I have freed an engine by boiling olive oil with a torch in a tin can and pouring it in the spark plug holes. In both cases, I could hear the rings ping and was able to gently work the engine back and forth until it was free. Both times I got the engine to run. For what it's worth. Maybe I just got lucky.
 

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I’m not fond of beating pistons except as last resort. I first try filling the cylinders with mixture of choice, then put the bike in gear and rock it forward and backward. If this doesn’t work I heat the cylinders and do it again, adding penetrant as necessary. Usually, but not always, works.

I am trying to get my 70 Bonneville loose, It was a running machine before extended storage. How much heat and where? Thanks, Mike
 

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Heating the cylinders with PB Blaster and rocking in 4th gear didn't free up the pistons-- disassembly will commence after haying is done.

Added Idea: I am thinking about machining air valves the same size/pitch as the spark plug thread. Putting 100 lbs of air pressure while rocking the bike in 4th gear. Some of the problem might be that the pistons are very high on the stroke.
 

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Better than air, grease, modify a spark plug to take a zerk, grease nipple , then pump away, much higher pressures than 100 psi can be achieved.
 

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I've lost track, but it sounds like you need the head off anyway. Hard to know if you have the pistons coming UP, or going down, unless you get the cylinder base separated from the cases and peer in with a flashlight.
Agreed, I appears that the quick and easy approach is not working! Disassembly with lots of questions on this forum
will proceed!
 

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I recently read a test on penetrators. The best performing was seafoam penetrant.The next was dot 3 or 4 brake fluid.
 
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