Author Topic: Stuck piston in BSA B21 (like a B31 sort of)  (Read 1313 times)

Online KiwiGF

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Stuck piston in BSA B21 (like a B31 sort of)
« on: 05.10. 2019 05:32 »
Hi, after accidentally ending up with a B21 project as a local auction, I’ve decided to have a look inside the engine before selling it to someone who I guess will know what they are doing with pre-war BSA’s. It’s missing quite a few parts and I don’t fancy sourcing them.

I only discovered the crank cases had a hole in them after buying it, and I think I owe it to the next owner to see what horrors lie inside! (See pic). This could be external damage, or “internal”  *eek*. The cranks looks rusty but not like it’s been “submerged”.

I struggled but eventually got the cylinder through bolts undone, it’s the same system as in the b31/33 engines, I didn’t think these bolts would undo, but heat and oil and an old fashioned beefy BSA open ended spanner eventually did the trick.

Next up is freeing the piston, it’s well and truly stuck in the barrel near TDC. The crank seems free to turn.

Anyone come across a similar stuck piston issue and got advice on how to free the piston without wrecking it?

So far I’ve tried heat, oil, turps, and it’s now got a mixture of turps and oil on its top, and is sitting with a clamp providing some down force.

Should I try to split the cases and then remove the barrel?
Should I try to remove the piston upwards, or downwards? (To minimise damage?).

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Offline Swarfcut

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #1 on: 05.10. 2019 09:02 »
Kiwi, of all the parts available for this engine, the piston is possibly the least difficult to replace,  even so it would be good to get it out in one piece.
 So, a good soak as you are doing, then a few cycles of heat and cooling, then a few smacks on a wooden block to spread the load on the piston crown.  If the barrel and crank can be removed, then access to the underside of the piston is possible to knock it upwards, with less distance to go, but in practice supporting this big lump of floppy heaviness will present a challenge. You can smooth the bore above and below the piston, so it stands a better chance of movement once freed. If you do dismantle the cases, the barrel can stand upside down for a while with the magic mixture soaking the piston skirt and rings.
 So alternate up and down blows, load spread on wooden blocks, heat and lubricant should do it. If not, sell as is, and let the next owner struggle.

Swarfy.
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Offline Rex

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #2 on: 05.10. 2019 12:39 »
Get it to the barrel/piston/crankshaft stage and leave it to soak in diesel for a couple of weeks, and if you rig up a jig to keep the pressure on the piston crown while it's soaking so much the better.
Failing that find a local garage with a hydraulic press you could use. Nothing will withstand that pressure but it would be worth turning up a collar to support the whole base of the barrel when it's in the press.
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Offline A10 JWO

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #3 on: 05.10. 2019 18:14 »
I use my log splitter to press in bearings and do jobs like freeing up stuck pistons. I agree with previous entry, soak in diesel for a long time. 
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Offline chaterlea25

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #4 on: 05.10. 2019 19:46 »
Hi All,
A word of warning  *ex*
Once I split a cylinder trying to press the piston downwards
It was corroded below the piston
For that BSAengine I would split the crankcases, then dismantle the flywheel
Leaving the rod piston and cylinder as one lump,
If it's rusted underneath the piston,
Soak in vinegar or use electrolys to get rid of the rust.
If the piston need sarcraficing , a gas axe can be used to melt it (with care)

John
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Offline muskrat

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #5 on: 05.10. 2019 20:47 »
G'day fellas.
Not knowing much about the singles. Are the cylinder studs removable with the cylinder still attached to the cases? If not it would be nigh on impossible to split the cases if the piston is near the top of it's stroke.  *dunno*
Cheers
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Offline Bsareg

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #6 on: 05.10. 2019 21:02 »
I have used caustic soda when all else fails. Takes time but disolves the piston (and rod if aluminium ) leaving the barrel pristine. Dump in a tub and check every few days.
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Online ironhead

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #7 on: 05.10. 2019 22:46 »
I had a piston so badly stuck in a barrel once due to years out in the weather. wouldn't budge after using all the above methods ( except caustic, must remember that.) so I drilled a series of holes as close as possible around the crown just inside the outer diameter. Then broke through them with a cold chisel *work* & removed the crown. This then gave me access to the skirt,  then carefully sliced through it with a die grinder. Took a fair bit of time but I needed the barrel .   As Swarfy says pistons are readily available for these engines.
After reading Bsaeg's method I'll go with that one next time, a lot less hassel. All the early singe rods are steel.
  Just have to make sure no caustic gets on the cases.
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Offline berger

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #8 on: 06.10. 2019 00:51 »
due to elf and safety the caustic sold over the counter is no where near as good as it was "back in the day" *whistle* even the stuff I got from a mate in industry was only about a third as good as it was "back in the day" *lol* so what I did was helped it a little bit by heating it up. but not in an ally pan *grins* . yes I still use ally pans for cooking sometimes , I think that is why I am a loon ;D O well I take that back according to the health thingy on googly it is a 1970,s myth that ally sends you doolally. so I will have to do some research as to why I am a nutjob. it could be the stone jar of mercury that I used to empty out and play with when I was a young en.
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Offline Gerry

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #9 on: 06.10. 2019 04:19 »
due to elf and safety the caustic sold over the counter is no where near as good as it was "back in the day" *whistle* even the stuff I got from a mate in industry was only about a third as good as it was "back in the day" *lol* so what I did was helped it a little bit by heating it up. but not in an ally pan *grins* . yes I still use ally pans for cooking sometimes , I think that is why I am a loon ;D O well I take that back according to the health thingy on googly it is a 1970,s myth that ally sends you doolally. so I will have to do some research as to why I am a nutjob. it could be the stone jar of mercury that I used to empty out and play with when I was a young en.
Ha ha Burger, Weren't we the kids that chewed the lead based paint off our cots?? I also used to chew on air rifle slugs when I had a air rifle and yes played with mercury. I once had a B25 single with a stuck piston. Nice big block of hard wood and a club hammer got the b#^*ard moving and even got it running after God knows how long it had been standing. Usually the rings rust up before the piston but depends how long its been standing. As for caustic, had a mechanical engineer at work came in all "sunburned" he had boiled some water and chucked a big lump of caustic into it and it blew up into his face. Or maybe the other way round, poured the water over the caustic. Anyway same result. Cheers Gerry
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Online KiwiGF

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #10 on: 06.10. 2019 05:09 »
I had a piston so badly stuck in a barrel once due to years out in the weather. wouldn't budge after using all the above methods ( except caustic, must remember that.) so I drilled a series of holes as close as possible around the crown just inside the outer diameter. Then broke through them with a cold chisel *work* & removed the crown. This then gave me access to the skirt,  then carefully sliced through it with a die grinder. Took a fair bit of time but I needed the barrel .   As Swarfy says pistons are readily available for these engines.
After reading Bsaeg's method I'll go with that one next time, a lot less hassel. All the early singe rods are steel.
  Just have to make sure no caustic gets on the cases.

Well that’s good news on the piston availability, I assumed a piston and/or rings would be hard to source, I’m assuming there is no chance of saving the rings, and only a remote chance of avoiding a rebore and subsequent oversized piston, which company sells the pistons please? (It’s a 1937 B21 deluxe), 250cc).
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1956 A10 Golden Flash (1st finished project)

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GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife)

Online KiwiGF

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #11 on: 06.10. 2019 05:12 »
G'day fellas.
Not knowing much about the singles. Are the cylinder studs removable with the cylinder still attached to the cases? If not it would be nigh on impossible to split the cases if the piston is near the top of it's stroke.  *dunno*
Cheers

Without doing it ....yes it looks like the 4 through bolts can be unscrewed from the cases, and the  cases then split.
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New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife)

Online KiwiGF

  • Last had an A10 in 1976, in 2011 it was time for my 2nd one. It was the project from HELL (but I learned a lot....)
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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #12 on: 06.10. 2019 05:14 »
Hi All,
A word of warning  *ex*
Once I split a cylinder trying to press the piston downwards
It was corroded below the piston
For that BSAengine I would split the crankcases, then dismantle the flywheel
Leaving the rod piston and cylinder as one lump,
If it's rusted underneath the piston,
Soak in vinegar or use electrolys to get rid of the rust.
If the piston need sarcraficing , a gas axe can be used to melt it (with care)

John


Thanks, I like the idea of splitting the crank, I can’t see how rusty it is yet, but the big end is moving freely.
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New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife)

Online KiwiGF

  • Last had an A10 in 1976, in 2011 it was time for my 2nd one. It was the project from HELL (but I learned a lot....)
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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #13 on: 06.10. 2019 05:17 »
Kiwi, of all the parts available for this engine, the piston is possibly the least difficult to replace,  even so it would be good to get it out in one piece.
 So, a good soak as you are doing, then a few cycles of heat and cooling, then a few smacks on a wooden block to spread the load on the piston crown.  If the barrel and crank can be removed, then access to the underside of the piston is possible to knock it upwards, with less distance to go, but in practice supporting this big lump of floppy heaviness will present a challenge. You can smooth the bore above and below the piston, so it stands a better chance of movement once freed. If you do dismantle the cases, the barrel can stand upside down for a while with the magic mixture soaking the piston skirt and rings.
 So alternate up and down blows, load spread on wooden blocks, heat and lubricant should do it. If not, sell as is, and let the next owner struggle.

Swarfy.

Thanks, I’ll try the heat/cool thing a few times (it takes 30 mins to get the barrel smoking hot with my heat gun). I’m pretty determined to see the inside of the engine, albeit I guess I could split the cases anyway.
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New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife)

Online KiwiGF

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Re: Stuck piston in BSA B21 (like a B31 sort of)
« Reply #14 on: 06.10. 2019 05:19 »
Get it to the barrel/piston/crankshaft stage and leave it to soak in diesel for a couple of weeks, and if you rig up a jig to keep the pressure on the piston crown while it's soaking so much the better.
Failing that find a local garage with a hydraulic press you could use. Nothing will withstand that pressure but it would be worth turning up a collar to support the whole base of the barrel when it's in the press.

I’ve got a home made 10 tin press, but I’m hoping to not resort to that as it will damage the piston for sure, but as a last resort I’ll use it
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New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife)