Stuck piston in BSA B21 (like a B31 sort of)

[KiwiGF]

Whilst waiting for my B31 frame section to get posted to me I thought I’d better see if the soaking in diesel trick has worked magic on the b21 stuck piston.

No good news unfortunately, it’s still stuck and hitting/pressing/heating still had no effect, so its back in the diesel soaking again 

I was amazed at how much smoke it made when heated up by a heat gun, I was a bit nervous the smoke/vapour  would light up..which would REALLY have heated it up 

[muskrat]

G'day KiwiGF.
Is there anyone near that has liquid nitrogen? Put barrel in oven (or BBQ if the wife's home) to as hot as it goes (300C should do). Turn it upside down and pour in a little into the underside of the piston.
You could try dry ice if no nitrogen is available.
Cheers

[KiwiGF]

G'day KiwiGF.
Is there anyone near that has liquid nitrogen? Put barrel in oven (or BBQ if the wife's home) to as hot as it goes (300C should do). Turn it upside down and pour in a little into the underside of the piston.
You could try dry ice if no nitrogen is available.
Cheers

Hi musky, I tried something on similar principle, emptied half a can of brakeclean onto the piston which boiled away nicely then hit it big time with wood/hammer, no joy, I think the issue is the rings have bonded with the barrel. I’ve ordered some carbide die grinder bits as the probable “ultimate solution” 

[duTch]

 Maybe try it in a tub of molasses solution- doesn't need to be strong mix- maybe  a cup in a bucket...I've had some in a bucket for about 15 years and it still works to various degrees just takes longer

[Klaus]

Hi Kiwi GF

if the piston is not in TDC, fit the head on with the valves. Make an adapter to the plug hole and a grease gun, and try it this way. A good grease gun is able to pump to 140 bar pressure. While pressuring heat up the barrel with a gas torch.

cheers Klaus

[berger]

I have not been to the pub, maybe that piston heat seized last century and has been left since but I would be giving it some grief by now having read back through all the posts, I don't think it can be made a bigger wreck than it is , but that's just me   so here's a pic of my puddy who doesn't know either, and no he hasn't been to the pub but I am on monday

[Joolstacho]

Kool Kat.

[Klaus]

To surrender is not a solution.

[RDfella]

Seems to me we’ve drifted off the diagnosis.
As I understand it, the piston is at TDC and the rod is still attached (otherwise the barrel would pull off with the piston inside).
Which, if so, means no amount of pressure / violence on the piston will make any difference – because the rod prevents it.
What is needed is pressure between piston and barrel only. There’s only two ways I can think of achieving this at present. One would be to carefully drive wedges between the crankcase and cylinder. The other would be to wedge the engine under a bench or similar, put an appropriate sleeve on the crank with a large pair of stillsons on the sleeve. Then attach substantial weight to the stillson to achieve at least 100lbft torque. And then heat / cool the piston until it moves. I believe the rings have rusted to the bore rather than a piston seizure, as the latter rarely happens at or near TDC.

[KiwiGF]

Seems to me we’ve drifted off the diagnosis.
As I understand it, the piston is at TDC and the rod is still attached (otherwise the barrel would pull off with the piston inside).
Which, if so, means no amount of pressure / violence on the piston will make any difference – because the rod prevents it.
What is needed is pressure between piston and barrel only. There’s only two ways I can think of achieving this at present. One would be to carefully drive wedges between the crankcase and cylinder. The other would be to wedge the engine under a bench or similar, put an appropriate sleeve on the crank with a large pair of stillsons on the sleeve. Then attach substantial weight to the stillson to achieve at least 100lbft torque. And then heat / cool the piston until it moves. I believe the rings have rusted to the bore rather than a piston seizure, as the latter rarely happens at or near TDC.

Thanks for putting a lot of thought into this but it’s not quite at TDC (maybe 2mm short) and the crank does move a few degrees so the big end is not seized.

I am concerned I will damage the barrel and/or the cases by putting sufficient force on the piston to move it.....I’ll give it a few more weeks in the diesel and try again. I’m becoming resigned to trashing the piston!

[Joolstacho]

Well. you've tried almost everything. the final thing is to sacrifice the pistons, easy. Drill and bash them out, then clean up the rest that's sticking to the walls. If you're careful with it all, worst case scenario is you need new pistons and the barrels rebored (possibly re-sleeved).

[KiwiGF]

Hi Kiwi GF

if the piston is not in TDC, fit the head on with the valves. Make an adapter to the plug hole and a grease gun, and try it this way. A good grease gun is able to pump to 140 bar pressure. While pressuring heat up the barrel with a gas torch.

cheers Klaus

It’s a good idea but I think the 4x through bolts holding the head and barrel on won’t take the pressure!

[Swarfcut]

I like the idea of the grease gun trick, but maybe a blow torch and hot grease  has major personal injury writ LARGE. Pulling threads in cases is also an additional load of extra unwanted hassle.

So, I reckon it is time that defiant chunk of alloy and its cast iron friends were put to the sharper tools in the box. Assuming, of course, that a replacement is available.

Swarfy.

[BSA_54A10]

As Klaus has already said
Drill a 14mm bolt to take a grease nipple
Give the valves a quick lap so they make a good seal.
I like to fill the head with old ball bearings as it reduces the amount of grease needed
Then fill the cylinder with grease through the plug hole.
You can use any grease or any other liquid for that matter.
Once full as you can get it screw the adapeter in loosely and pump more in till it starts to ooze up the thread  then tighten the adapter.
Pump as much grease in as your gun can then add heat.
I use a gas torch.
The person who originally showed me this used a BBQ set to 200 C .
Never had one that would not come loose but some did take a day or two.
Once you get it apart play very close attention to the crank case between the cam holes
They are prone to splitting.
When the B series was redesigned post WWII they moved them further apart and of course added the outrigger support plate.
You can modify a B/M series plate and the timing cover to make it fit and if you intend to do any sort or spirited riding it is worth while doing.
M/B series cams can be made to fit but they need to be ground smaller or the followers will foul on the cases.
And yes the frame is very light , although BSA called it the "medium weight" frame and they do go like the proverbial scaled cat  .
Std C series wheels drop right in as B series wheels are near impossible to find.
No one was too worries about offering the 250 for war effort scrap so there are not many around and very few in the UK.
Early C or B ( tapered mainshaft ) clutch fits and it is a single plate job.
I think the early 2 plate B series clutch will fit  but the latter one will foul the chain case.
And we are talking about the single spring clutch here.
One member cut down a WM20 clutch to fit

Without checking I am fairly sure they used the same "medium weight " 4 speed box as BSA revived for the 46-48 B31/33 ( probably found a stillage full of them round the back of the factory ).

[RichardL]

I've lost track of this, a bit, but, after all this time and the various methods, why not just destroy the piston by whatever means and move on? Others may correct me, but it seems to me that attempting hydraulic means of loosening the piston has as good a chance of fracturing the barrels as moving the piston.

Richard L.