BSA B44 problem

[KiwiGF]

Thanks for that story, Mike. So, when you say the rally was put on by the "BSAOC," I take it you mean the NZ version and not an international event? I was thinking, "wow, that would be really hard to get to" (not that every one of us doesn't wish we could have been there).

Richard L.

Better start saving everyone, the International rally IS being held in NZ, in 2026 😆 hopefully the flight cost will have reduced by then, I am visiting the UK in April and the cost is circa double what it was pre covid 

https://www.bsaownersclub.co.uk/interrally.php

My guess is that a lot of visitors will want to borrow bikes.

PS It was my B44 that suffered a major engine failure after 40 miles and whilst cruising at 100 kmph  …..I already know there is a “morbid interest” in exactly what has happened to it 

Any theories? 🤨

Small hole in piston, exhaust valve cut out, crack through gudgeon to skirt, bore  looks ok.

Japanese plus 020 piston, cast or forged? Dunno, comp ratio unknown.

Black marker pen dots show crack direction.

Pic of bike on trailer of shame also 

[KiwiGF]

More pics

[RDfella]

Seen many seized / melted / damaged pistons over the years, but never seen that happen before. What's with the drilled holes? Looks like improper choice of material / fatigue to me.

[KiwiGF]

Seen many seized / melted / damaged pistons over the years, but never seen that happen before. What's with the drilled holes? Looks like improper choice of material / fatigue to me.

I’m puzzled for sure, I expected signs of melting, but one side of the hole is straight which (I think) eliminates that. The drilled holes? You mean under the rings? (Or do the dots made by my marker pen look like holes!)

I am fairly sure this a manufacturing fault in the piston, rather than detonation or pinking, but I just thought I would ask in case this is a known fault with the TNO piston brand, or B44’s in general.

I am lucky the piston didnt break up, its possible to see where the crack has caused the skirt to expand and rub so there are shiny patches, one can flex the skirt with finger pressure and see the edges of the crack move, the pics dont really show the crack around the gudgeon pin area inside the piston.

Wassel and Draganfly don’t list the B44 piston, but I see Feked (gandini 129 quid) and PES (220 quid, forged,   ) list them.

[muskrat]

G'day KiwiGF.
Wow, yes your lucky it didn't break up all together. It's a cast piston and not as strong as a forged one. Could possibly a flaw in the casting starting at the valve pocket.
Cheers

[KiwiGF]

G'day KiwiGF.
Wow, yes your lucky it didn't break up all together. It's a cast piston and not as strong as a forged one. Could possibly a flaw in the casting starting at the valve pocket.
Cheers

I have found out that JE Pistons in the USA make forged B44 pistons (just) for EandV engineering in Howard City, a B44 specialist, so I might give them a go, HOWEVER I found a very small imperfection in the bore, affecting just the top ring seal, most probably damage from a fragment of piston, and now I will investigate getting a rebore and plus 040 piston 

Companies that do (good) reboring on old bike engines are getting harder to find in NZ, that may affect what I do next.

https://shop.shopevengineering.com/eandv-engineering-ev-b44-piston-assy-detail.htm?productId=-282299

[muskrat]

G'day KiwiGF.
When boring a ci sleeve in alloy barrel it's a good idea to bolt it at required torque value to a plate, I've used 1" steel plate (destroyed in fire). Sometimes if just clamped to a boring machine table (or 4 jaw chuck in a lathe) and bored it may distort the bore when bolted to the cases. Not all the time but I have seen it happen.
Cheers

[KiwiGF]

G'day KiwiGF.
When boring a ci sleeve in alloy barrel it's a good idea to bolt it at required torque value to a plate, I've used 1" steel plate (destroyed in fire). Sometimes if just clamped to a boring machine table (or 4 jaw chuck in a lathe) and bored it may distort the bore when bolted to the cases. Not all the time but I have seen it happen.
Cheers

Thanks I will discuss this with a reboring outfit…assuming I can find one willing to do the job (nearest place does v8’s mainly, so this a piddly job for them 😏)

[muskrat]

G'day KiwiGF.
Find a place that does HD's. If they go by the "book" it must be done for HD barrels.
Cheers

[CheeserBeezer]

I have fond memories of the International Rally in 2010. My wife and I stayed a couple of days in Rotorua as we toured New Zealand for three weeks after the rally. Happy times, lovely people. Greetings!

[KiwiGF]

G'day KiwiGF.
Find a place that does HD's. If they go by the "book" it must be done for HD barrels.
Cheers

Hi Musky, I am still “conflicted” as to what to do, either hone and bung in a new 020 piston (and risk it not lasting long due to the slight gouge affecting the top ring), or rebore and use a 040 piston.

The barrel is pretty flimsy, and through bolted (or more correctly studded), more than half the bolt diameter is drilled through the fins so there is not much metal taking the forces of bolting or combustion. A liner is cast into the barrel as std, sometines that can go to plus 060, sometimes not if BSA got the liner in offset, or a bad rebore was done off centre.

Could you explain the 1” plate method given the above? Is placed on top of the barrel or bottom or both?

Simon

[muskrat]

G'day Kiwi.
I moved and re-named topic s it may be lengthy.
As explained previously once the barrel is fitted and head is torqued down here can be distortion to the bore (can be witnessed by shiny spots n the bore).
The idea of compression plates is to replicate the mounting of the barrel and give a true bore.
Pics of plates, pic #2, I would make them myself, if you have a mate with a lathe and a bit of 1" plate, would only take an hour or so.
Cheers

[Rex]

As used by Americans when reboring high-power V8s etc.

[muskrat]

G'day Rex.
Yes in any race/drag motor is a must. I built 350ci speedway motors years ago.
With cast liners in alloy barrels even on cooking models is recommended. When I dropped new liners in the Honda CB1100F I made plates to do the job.
Cheers

[RDfella]

That 'imperfection' is - IMHO - too much to ignore.
Qu - are those barrels 'ALFIN' or are the liners pressed in? If the latter, I'd replace the liner if boring looks like making it too thin.
Remember if replacing it, to let it 'rest' for a day or two before boring to size. Things move and I've been caught out myself by boring immediately after liner fitting (cast liners in 6 litre cast iron block).