Engine blown - Cylinder spigot fractured

[Duncan R]

Hi All,

My engine let go yesterday - the right hand spigot on the cylinder fractured and caused the piston to shatter. Any idea what caused something like that? Flange has broken off the cylinder as well. Is it possible to weld the flange? Cylinders seem a bit thin on the ground, wondering if it is possible to get the liners pressed out and cylinder repaired and new liners and pistons fitted. After Initial checks the rods seem to have survived but obviously need to split the cases.

[Duncan R]

Photo of damage

[chaterlea25]

Hi Duncan,
OUCH!! 
From your photo, it looks like the liners fitted were thick walled, so much so that there is nothing left of the original
bsa below the base flange ??
Normally the liners fit into the extension below the base flange
In my opinion this has weakened the structure too much and hence the failure
Look at the amount of metal left on the cylinder wall above the flange and below the fins (V little!!!)
I think you will have to find another cylinder  ????

I cant see why the piston let go ( no photo??) If the piston failed this would have stressed the weakened cylinder
Beware of any pock marks on the rods as this can lead to failure 

Regards
John O R

[Duncan R]

Thanks John,

I will start a search for a new cylinder, also obviously split the cases and get everything checked and cleaned

Photo of what's left of the piston

[bsa-bill]

Hi Duncan - sorry to see this, I have a question for John though
John am I missing something here, I cannot see evidence of a liner in the other cylinder (perhaps it's not always visible) or is all the spigot liner?
I had liners fitted to my flash and you could tell they were lined and also you could see quite plainly where they had been ground out for the conrod.
Never thought of this before but are the barrels bores machined from the whole cast lump or are they lined from new??

best of luck with your search Duncan

[Duncan R]

Thanks Bill,

I am hoping crank/rods/bearings are ok then money wise it won't be too bad. I was hoping to get the gearbox overhauled over the winter but that's out the window now.

[Topdad]

Hi Duncan, so sorry to read of your trouble. I've spoken to SRM re getting a set of barrels resleved some time ago .They ,if I recall correctly use an adhesive between the liner and the bored barrel. I'm reasonably sure the guy said they did that to stop fracturing which could be the same as looks to have happened. I know they are thin on the ground but I'd try to get thick flanged saves a bit of worry. regards and comisserations BobH

[RichardL]

Just chatting here. John and others will be sure, but I pretty certain the original bores are in the cast iron. It looks to me that only the right cylinder was lined. Also, am I correct in believing that is  a thin-flanged base? It's a bit hard for me to to tell from the photo. I was expecting to see higher compression ratio pistons, but considering what John pointed out about the remaining cast iron surrounding the sleeve, I really didn't matter.

Richard L.

[dpaddock]

What was the engine doing when this happened, Duncan?
To my knowledge, A7/A10 cylinder blocks are one-piece items. Any linering would have to be a post-factory mod which would endanger the integrity of the spigot.
In any event, your barrel is toast. You'll need a replacement (preferably not linered).
Good luck!
David

[RichardL]

Ya know, looking closely at the photo, it is really hard to see where the spigot (cylinder skirt?) broke off. It doesn't make sense to me, but it gives some creedence to the idea of the spigot and sleeve being one and the same. For instance, why is the spigot smooth wall on its O.D.? Where do you see a fracture line for the spigot separate from the sleeve? (Look closely at the broken off piece of flange.) Who knows the truth and, if this is not the case, how do you answer these questions?

Richard L.

[Duncan R]

Bob - Thanks, read your PM before your post

David,

I was doing less than 30MPH when it went, no horrible noises to warn of impending disaster.

Richard,

As I may have mentioned before in previous posts the bike is from India and lord knows what's been done to it the past. It had car pistons in it before!! that's not a dig, they just keep things going with the available bits

[bsa-bill]

how do you answer these questions?

Yes it looks odd, looks like its been sleeved on one pot only, one suggestion might be perhaps a liner from a single was available, perhaps not the right size.

[chaterlea25]

Hi All,
Have a look at this ebay cylinder, number 200657953496
The cylinder walls below the base flange are as cast on the outside, not smooth as Duncan's are
So I believe that both sides were sleeved????
That cylinder on ebay looks not bad value??? it may be possible just to enlarge and blend in the damaaged cutaway??
If "modern" rods are used the cutaways need enlarging anyway
And Duncan has now gotten enough fins to repair everyone elses damaged barrels 
I bought an old Bantam barrel to provide fin material  and silver solder the repair pieces in place

After seeing the second photo of the piston, I think that the bottom of the liner may have fractured all around its circumference, this droppped off and wrecked the piston??
Why?? the sharp join where liner and base meet??

Duncan, I have a pair of secondhand +.020 pistons, 8 to 1 comp, (Hepolites?? not Taiwan)
they would be fine if you were boring a cylinder to suit,
I probably have good conrod as well??

Regards
John O R

[Duncan R]

Hi John,

I was going to bin that barrel, never thought of using as a fin donor - thanks.

A friend is on the look out at the Kempton auto jumble at the weekend for a set of cylinders(i am away at the weekend) I will keep the pistons in mind -thanks. I was hopeing to get  lucky and get some + 20's barrels

Any one had much success with re lining? I was thinking of getting any intact thick flange  barrels and having them re lined. I saw some liners made by Westwood for £65.

Thanks

Duncan

[bsa-bill]

I had mine relined Duncan as they were on +60, no problems at all although up till now I haven't got to ride as much as I'd like, no project next year though so hopefully more time on the road.

John I understand what your saying re the spigot on the good side but in photo one there is a distinct surface to the broken liner and similar on the broken bit of barrel suggesting  the spigot bit was separate to the liner (does that make sense), otherwise it's a liner in a liner - now there's a wild conjecture