‘56 AJS model 30 600 twin

mdt-son · Mar 13, 2022

I understand it's the corroded pistons which prevent further progress. Pistons are probably of the wire-wound variety, so in addition to aluminum oxide, you will have a steel to iron rust bonding.
Why not take the lump to a blacksmith and let him heat the barrels with an acetylene torch. If that doesn't work, you can still drill and grind the pistons to pieces. Those pistons have to be scrapped anyway.

If pistons are not in TDC or BDC, another option is to drill a recess in the piston center and use a jack hammer at one piston a time (engine has to be fitted to a stand of course). Depending on the impact energy I am convinced the impact force will break the bonds. Long term soaking may or may not work.

- Knut

N0rt0nelectr@ · Mar 14, 2022

ILLF8ED said:
This is last resort…I ordered a 20 gallon polyethylene bucket and lid from Amazon today. It will probably take 5 to 10 gallons of diesel oil to submerge the entire engine. How long to soak it…maybe a year.

Thanks

Months at least. Take your time and don't force it.

ILLF8ED · Mar 14, 2022

It went into the 20 gallon container today. 7 gallons of diesel covered all of the engine. The container top has a steel band that clamps to seal the whole thing. Months in the soup sounds right. It probably sat with water in the sump for years. I was inclined to part out this machine, but it’s now a challenge…I like it.

ILLF8ED · Mar 14, 2022

I already broke open the piston crowns just to see inside. Makes the diesel flow better as well.

ILLF8ED · Jun 3, 2022

June 3 today. The engine is still submerged in diesel since Mar 14. I did pull it out a few weeks ago to check….was still solidly locked up.

mdt-son · Jun 7, 2022

Obviously piston walls have corroded by oxidation, which makes them swell. Even IF diesel is able to penetrate the oxide layer by capillary effect, I doubt it will reverse the oxide layer formation.
I think you should try to melt piston bosses. This will free up piston pins and you should be able to remove each barrel. Once removed, the piston remains can be removed by boring barrels to the next O/S.

- Knut

Shelby-Right · Jun 8, 2022

Make a thick plate 12-16mm that is drilled for head bolts , mark the bore centre's using head gasket, drill and tap thread like ½ unf , make up two slugs about .020 smaller than bore size ,½ thick ,drill a centre dimple so the screwed stock will stay in the centre , make sure all barrel bolts are out , Jack barrel off . Just adding an edit , this will work if bolting plate to barrels , not so well if the studs go down to block !

sorry not familiar with your AJS twin.

baz · Jun 8, 2022

Shelby-Right said:
Make a thick plate 12-16mm that is drilled for head bolts , mark the bore centre's using head gasket, drill and tap thread like ½ unf , make up two slugs about .020 smaller than bore size ½ thick drill a centre dimple so the screwed stock will stay in the centre , make sure all barrel bolts are out , Jack barrel off .

I did similar with my rust seized b50 plus plenty of heat
A +40 bore cleaned it up

mdt-son · Jun 8, 2022

Shelby-Right said:
Just adding an edit , this will work if bolting plate to barrels , not so well if the studs go down to block ! sorry not familiar with your AJS twin.

The AJS/M twins had proper through-studs, as every well-designed engine should have.

Shelby-Right · Jun 8, 2022

If your pistons are right down , not much point beating on those pistons , can you lift barrels i:e turn crank and chock barrels with hard wood , then it will give your pistons room to move down . Cheers .

mdt-son · Jun 9, 2022

Shelby-Right said:
If your pistons are right down , not much point beating on those pistons , can you lift barrels i:e turn crank and chock barrels with hard wood , then it will give your pistons room to move down . Cheers .

This is a twin cylinder engine where both pistons are frozen. Turning the crank is impossible even if it may turn eventually (not likely though due to corroded ball bearings).

- Knut

Richard Tool · Jun 10, 2022

Have you tried agitation while soaking ? Vibration of engine lump may be even better if it can be engineered somehow ..

Shelby-Right · Jun 10, 2022

What i sort of meant , is if the pistons are at bottom dead centre or close to that , then you cant move them any more , but by using a stillsion wrench on an old sprocket with some med force back and forth then maybe the barrel will lift , if there is a lot of rust in there , maybe soak it for a week in 9% vinegar the cleaning stuff, good at removing rust , then another clean out and back in the diesel .

Shelby-Right · Jun 10, 2022

If the barrel stud holes are sized close to a tapping thread , can you thread them , and then make a puller plate , you might have to sacrifice something to move forward ?, but looking at your picture barrels don't look rusty.I looked at some AJS barrels and they quite deep skirted , could be hanging on down there , so some good generalised heat in the cases with a large headed propane torch , anyway good luck .

ILLF8ED · Jun 11, 2022

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mdt-son said:
Obviously piston walls have corroded by oxidation, which makes them swell. Even IF diesel is able to penetrate the oxide layer by capillary effect, I doubt it will reverse the oxide layer formation.
I think you should try to melt piston bosses. This will free up piston pins and you should be able to remove each barrel. Once removed, the piston remains can be removed by boring barrels to the next O/S.

- Knut

OK this one is interesting. How do I melt the piston bosses? And I believe the cylinder skirts are corroded to the engine case. The engine is a big ball of corrosion…aka boat anchor. Already sold the front wheel. All other parts are on the market if anyone needs something.

mdt-son · Jun 11, 2022

ILLF8ED said:
How do I melt the piston bosses? And I believe the cylinder skirts are corroded to the engine case. The engine is a big ball of corrosion…aka boat anchor. Already sold the front wheel. All other parts are on the market if anyone needs something.

An acetylene or plasma cutter will handle this easily. Aluminum melts at about 660 deg C (1220 deg F). Pour water into the crankcase before starting the cutter. If you prefer a cold process, a dremel or pneumatic die grinder and a milling bit should do the trick as well (carbide bits are effective and come in a variety of shapes).
As for barrel skirt corrosion, iron and aluminum will not bond but there may be an oxide layer at the cases. The clearance is much larger than the piston/bore gap though. Cast iron corrodes slowly, and cylinders do not look too bad above the pistons. Gently heating the cases (the lump) to 100-120 deg C may ease separation of barrels and crankcase once rods are free.

I think you made a sensible decision to part out the bike. Some bikes are simply too far gone.

- Knut

Shelby-Right · Jun 11, 2022

Sell it as is , don't worry about it .

Shelby-Right · Jun 12, 2022

Put two long tuff bolts down a couple of the barrel stud holes , leave an inch sticking up , heat the cases put a 3 or 4 foot bar through the two bolts , if they have no dowels you might just get a couple of mm movement each way , then it might come free . Cheers .

cjandme · Jul 5, 2022

As mdt-son said earlier, a dremel or die grinder would be the way to go IMHO. Not having a plasma cutter or acetylene , I usually go the "cold route". You seem fairly close to getting the pistons separated from the rods. Even if it's too far gone for a rebuild, it would be interesting to lift the barrels and see the bare bottom

ILLF8ED · Aug 1, 2022

I have scrapped this project.