Chain broke!

[Minto]

Well after a lot of cleaning oil up from under the bike, I drained the sump and left it over night ready to start ripping the engine out again, but...this morning it was bone dry, not a drip. Must be leaking when the crank case is pressured...go for a 5 mile ride, still dry (apart from a couple of drips from the Speedo cable and one from the timing case.
So, bugger it off for a proper ride, 3 miles later pulling off from some lights rattle rattle, no power. Pulled the clutch in quick and came to a stop. I knew instantly it was the chain.
Everything seems ok, apart from my back, bloody hell that last hill is steeper than I remember it. Just glad I didn't get down into Ironbridge before it went.
It is a ,530 I need isn't it?
Cheers
Jase

[Billybream]

5/8 × 3/8, type 530, approx 97 links

[Minto]

Nice one thank you.
I'll give the chain man a shout in the morning.
Jase

[Brian]

If its for your plunger then make sure you get a std width chain, not a heavy duty one. They cant take a chain that is wider.

[Swarfcut]

 Did you loose the chain?  If you still have it, it will be just a split link you need unless the chain is so worn that it warrants replacement......and of course, for longer life the new chain likes new sprockets.....Change the gearbox one if it looks worn, and the box is coming out anyway.

   BSA list Plunger the chain as    5/8" x  3/8"  X .400" roller. Roy Bacon's book says  0.625" x 0.400" x 0.380"  Solo 42 teeth rear sprocket  takes 100 pitches, Sidecar 49'er takes 104.

  Measure the teeth width on existing sprockets to make sure they are the right parts. Some folks end up with the narrower teeth used on the B Series. Typically  from EBay sellers offering B31 rear sprockets as A10.

 Swarfy

[Black Sheep]

Changing the gearbox sprocket is, without doubt, the worst job on a plunger BSA. But if you must, you must...

[Minto]

Thanks very much all for the info and responses.
I'm no longer convinced that the lump needs to come out after all, it was all nice and dry after a ride apart from a couple of hopefully easy to sort drips, going to just keep an eye on things after fixing the other drips.
The drive sprocket got checked while the gearbox was off last week and was in excellent condition anyway, the rear sprocket got changed for an new, more appropriately geared one about 30 miles before the engine got stripped, the chain however, didn't because I was too cheap.
I've still got the chain, and the joining link though that's a funny shape now. But I'm not sure why it decided to give up so it's time to change it, besides my sprockets will be grateful.
Going to give the Chain man a ring now.

[Minto]

Got chance to have a better look at the bike this morning, my initial thinking that everything was ok, was it seems a little premature.
Everything does seem mechanically ok, gear box still seems to operate ok, engine still runs without loosing any more oil than usual. However, where the chain had apparently smacked just above the final drive sprocket there's a section been smashed out. About an inch and a half long just in front of where the chain guard attaches to the rear of the primary case. This section doesn't seem to have any purpose other than to cover the sprocket and stop s**te from the chain being flung all over the place. I've had a good look with a torch and a dentist's mirror and can't find any other damage, and it doesn't look like it's weakened any other part of the castings. (No cracks, scoring, scratches, gouges or dents).
So, course of action... Got some chemical metal stuff being delivered tomorrow, and going to see if I can mould a piece in with a couple of bits of extra webbing above the break.
Anyone ever used this stuff for similar? Any tips?
Cheers
Jase

[RDfella]

I'd cut a piece of thin card to shape, with overlap at the ends, then transfer to 1/16" or 1mm aluminium sheet and cut out. Bend to shape as necessary and glue in place with suitable adhesive (sticks like sh*t or bonding silicon). I assume the material you're mentioning is metal-filled epoxy? Devcon is my favourite, either steel or aluminium filled. Great stuff but not sure it's appropriate in your case.

[Minto]

That does sound an easier proposition than trying to mould this stuff to shape. As a temporary repair til next time the lump is out, I could even make an extension to the chain guard to slide over the broken bit, fixed at one end by the chain guard bolt.
Good idea RD Fella
Jase

[Swarfcut]

Minto. A polyurethane sealer will bond metal to metal and will be fine to secure your temporary  guard. I've seen that damage a fair number of times, together with big chain gouges in the back face of the primary casing. Most common cause was worn sprockets and a loose chain.

 Swarfy.

[Minto]

Swarfy,
Yes there was already a semi circular gouge in the rear of the chain case, though it actually looked like it had been machined, very neat.
I'm hoping my new chain will be waiting when I get home from work later. Looking forward to some midnight garage time.
When you say a polyurethane sealer, would some Carbon petseal ultra do the trick? I have a can that someone gave me that is just gathering dust as it's no longer useful for sealing petrol/ethanol tanks. It would be nice to find a use for it
Jase

[Swarfcut]

      Can't help with that product, but whatever method and design you use it has to be foolproof.  Fast moving chain means powerful forces, as you have found. Polyurethane is used for bonding steel pressings on car bodies, it's the stuff oozing between the bracing frame under the bonnet (hood).
    The chainguard may need a bit of additional support, depending on the damage. If the engine comes apart again it's a good chance to have some alloy welding done  and complete a relatively easy repair.   

 At this stage of ownership, building a spare engine starts to look attractive..........

 Swarfy.

[Minto]

Oh, Tigerbond or the like, not what I have on my shelf.
Been trying to find some guidance for chain tensioning on the plunger, as I want to rule out the possibility of the chain breaking as a result of me messing it up last time.
Inch n half play in the middle of the bottom run while on the main stand is how i set it last time. Is that too tight? Should it be set with the weight of the bike and rider on the ground?
Cheers
Jase

[berger]

minto you will lose most of the inch & half dropping it off the stand, it is best to get some weight on it