Tight Motor - Real Tight

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Cheesehead Commando

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Fellow Commando Fanatics -

Once again I turn to you for help on my maiden voyage with my first frame up rebuild. I have entrusted my 850 MkIIA to a trusted mechanic, but have decided to attempt this next project myself. Or at least as much as I can do...

The bike in question is basket case '72 750. It belonged to a dear friend who bought it new, but over the years let it slip into disrepair. The engine/primary/gearbox subframe spent some time outside, and the engine is stuck. Tonight I removed the head. Oh, my...... The pistons are rusted in the barrels. How bad, I don't know. But this isn't good. I sprayed around the pistons with penitrating oil, and will continue do to this for a few days. But I am concerned this will not be enough.

What else to do?? The barrels won't come off without the pistons free, and I don't want to risk damaging the crank by pounding on the pistons trying to free the barrels. Any suggestions or methods to try would be helpful. Thanks again to all that reply...!
 
If you're not in a hurry just keep doing what you are doing. If they aren't at BDC you can tap them down with a hammer and block of wood to loosen them.
 
Apparently ATF ( Automatic transmission fluid ) and acetone mixed 50/50 will give you the best option for penetrating rust, but any penetrating oil will suffice.

Do you have a butane torch ?.

Allow to soak for a few days, clean out the penetrating oil with a rag, heat the top of the piston ( say to 100-150 C), it will expand, pour in some more oil, let it cool, sit for a while, say an hour, then do it again.

Dis-similar metals, the piston will expand and contract each time you heat them, each time breaking a little of the rust and allowing the penetrating oil to soak in.

I would remove the drive chain and work the engine directly. ( best to remove any possible resistance to your work ).

Under no circumstance get heavy handed with it.

Another option is to pour in vinegar ( effectively a mild acid ) into the barrels, it will remove the rust, but is not good for many of the other components in the engine, I personally would not use this option.
 
Great suggestions! Thanks! The penitrating oil is highly enflamable, so I am guessing one needs to be extremely careful with the flame...? More concerned with the vapor. Stuff brings tears to my eyes!
 
if the pistons are really stuck , you should make up a thick steel or alloy plate to bolt up on the barell . In that plate make a hole and tap a thread in it (i use m6 ) . drill a hole through a m6 bollt and then screw the bolt into the plate ,with a nut both above and below the plate ,this because you could strip the thread in the plate .On top of this bolt you put some kind of tap . now connect a grease gun or another sort of pump but filled with grease and start pumping .Once the pressure is there close the tap and go out for a beer .after a while put some more pressure on etc It can take a few hours or days but it will become undone and your pistons might even be saved
If I write this step by step it is because I don,t understand some of the advice being given here (Hobot?)
 
Drop the whole motor in a drum full of deisel fuel for a week will losen up any motor, have done this to a fully ceased up outbord motor that had been smeaged in salt water and left sitting for a few weeks, freed it up and got it going again...

Ashley
 
Some John Deere mechanics that I had in class last year told me to use diesel fuel mixed 50/50 with brake fluid to free up a stuck Homlite chainsaw that I couldn't get loose with any of my favorite rust busters. I filled up the crankcase with the blend and let it sit for 3 days. I then broke it loose with a wrench on the crankshaft! Worked like a miracle, and wasn't expensive considering how much I needed. Hopefully your pistons are not stuck at TDC. I would advise that you take the barrel nuts off, block the barrel away from the crankcase, turn it upside down, and fill the barrels up with whatever" blend" you choose. Remember that there is far more "stuck surface area "below the rings than above. Let it sit for several days. Reassemble the barrel to the crankcase and "rearrange the molecules" by applying sharp blows from a mallot via a wood block placed on the piston tops. I like to turn a piece of hardwood on my lathe to the approximate diameter of the cylinder to assure even impact area to the piston. Be parient and good luck!

Mike
 
I have the same problem on an 850 motor that I will be tearing down this winter. When I got the bike home, the first thing I did was to flood all available spaces with the ATF/acetone mix. It will sit like that until I get fully into the tear down. My pistons are stuck low in the bores, so my theoretical plan is to see if I can get the barrel loose and lift it high enough to clear the pins. If I have to saw the studs off I will as they are cheap. This should allow the cases to be broken and the crank removed. The rods will be taken off the crank and this will alow me to work on the problem from both sides, or drop it in a bucket full of the next magic mix. I haven't tried this yet, but I think this is all possible. Some care will have to be taken not to bang things up. Worst case scenario is I shop for new rods, pistons and barrel!

This of course is assuming that the crank will spin.

cha-ching,
Russ
 
Marvel Mystery Oil is superb for this. I have personally used it/seen it used to release seized engines on several occasions.

However, I realize this is just another "opinion" of what to use, sort of like engine oil or anything else. ;)
 
I have had this problem several times over the years and the best method I have found is to make a plate that bolts onto the top of the barrels with a hole with a nut welded on concentric with the piston (something like the clutch spring compressor). Then, with the piston crown protected with a peice of wood or metal, screw a bolt in to press the piston down the bore. This should move the piston without damaging the piston, rings or bore. If the rings are stuck in their grooves then boil them in water and this should free them.
 
myjota said:
I have had this problem several times over the years and the best method I have found is to make a plate that bolts onto the top of the barrels with a hole with a nut welded on concentric with the piston (something like the clutch spring compressor). Then, with the piston crown protected with a peice of wood or metal, screw a bolt in to press the piston down the bore. This should move the piston without damaging the piston, rings or bore. If the rings are stuck in their grooves then boil them in water and this should free them.
Click to expand...

Very clever...I like that idea better than a hammer. Of course if you can get the thing into a hydralic press...

Russ
 
Lost of great tips for breaking the pistons loose. Are there any concerns, on a several day soak, with these fluids getting into the crankcase or primary and damaging seals, o rings, gaskets , clutch plates etc..
So far the list of recommended products includes: penetrating oil, ATF,Brake Fluid, Acetone & Marvel Mystery Oil and Diesel Fuel.
 
T95 said:
Lost of great tips for breaking the pistons loose. Are there any concerns, on a several day soak, with these fluids getting into the crankcase or primary and damaging seals, o rings, gaskets , clutch plates etc..
So far the list of recommended products includes: penetrating oil, ATF,Brake Fluid, Acetone & Marvel Mystery Oil and Diesel Fuel.
Click to expand...

If your pistons are stuck in the bores I think you will probably need to replace seals anyways!
 
Mix 8 oz. of Coke with 2 oz of 151 proof Rum then slam this down, wait 10 minutes then repeat. This will loosen you up.

When suitably lubricated, add an oz of diesel fuel to each cylinder and then curse the motorcycle like a drunken sailor. This must be done LOUD before the broken motorcycle will respond.

If motorcycle is still stuck, repeat the entire process.

When taking on a project like this, swear early and swear often; the more foul the better. Profanity is a tool. It’s as important as the torch, which you will be using later.

Glad I could help.
 
To add to spikes sound advice, you could always up the tempo a little with some italian influence, hand talking and crutch grabbing, preferably in public.

You should have to pay for such experience and knowledge........ :D
 
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