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Messages - martinh10

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Singles / Re: B32 compression
« on: 27 July, 2022, 18:05:45 »
I put a new piston and rings in my B31 as the existing +.020 bore seemed OK. I was disappointed with both compression and performance and had a look inside after 100 miles and found that the rings were not making good contact all around the bore. I managed to find a NOS +030 Hepolite piston and rings and had a rebore. Compression was improved a bit but now after about 700 miles the rings are bedding in and compression is about as good as I remember it should be from my youth (allowance made for some weight gain in the intervening years). I assume your valve lifter is properly adjusted.

Singles / Re: B31 oil leak
« on: 01 July, 2022, 17:00:31 »
What makes you think it's coming from the engine? Does the oil level in the chaincase rise? I have had oil leaks in the past in the region of the gearbox sprocket and these turned out to be  chaincase oil due to a poor chaincase sliding plate/cork/felt seal and gearbox oil from between the gearbox mainshaft and pinion sleeve (worn bushes). Of course, as Idie says, check your crankcase breather first.

Singles / Re: B31 spares
« on: 08 June, 2022, 08:46:54 »
Dennis, I have tried on two occasions to respond to your PM but it does not appear to have worked. If you want to send me an email ( I will be happy to respond.

Singles / Re: B31 spares
« on: 06 June, 2022, 14:14:22 »
Draganfly have them - got mine there.

Singles / Re: B31 Dirty Oil
« on: 05 April, 2022, 18:13:14 »
Thank you for those replies which are quite reassuring - which I suppose is what I was hoping for.
In response to some of the comments:
I was imprecise about the oil changes - I think there were probably three upto 450 miles and the sample shown is 50 miles after the last change.
I do have a magnetic sump plug fitted and there was a small amount of black gunge attached to it after the last 50 miles which must be ferrous but I am reassured that the consensus is that these are quite dirty engines, particularly when running in. I will be changing the oil quite often and may see some improvement after a few more miles.
Several decades after my last B31, and more recently being more familiar with FireBlades and R1's, I find myself constantly having to recalibrate my expectations of B31 engineering and performance!

Singles / B31 Dirty Oil
« on: 04 April, 2022, 20:10:38 »
I’ve done 500 miles now since a complete engine/bike rebuild and changed the oil a couple of times. On draining the sump just 50 miles after the last oil change I was slightly alarmed to find how dirty it has become – no bits in it just dirty – see photo new oil v 50 mile oil.
If it wasn’t for wet sumping and my practice of draining off before a run I would probably be blissfully unaware of the situation – as I was in my youth when I hadn’t heard of wet sumping. The engine and oil tank were meticulously cleaned on rebuild but maybe the rings, particularly the oil ring are not fully bedded in yet. Your opinions welcome.

Singles / Re: Preignition
« on: 31 March, 2022, 16:30:08 »
It's a 5/8" 20 tpi thread, the same as the the cylinder head bolts (in the crankcase). If you have a spare/scrap cylinder head bolt just tap a thread for a 7/16" BSF or whit bolt in it and you've got a mag pinion puller - see photo.

Singles / Re: B31/B33 primary chain oil
« on: 21 March, 2022, 15:17:43 »
BSA Service Sheet 312 for S/Arm B31/33 gives 1/7 pint (80cc) for magneto models and 1/2 pint for alternator. Service Sheet 701 for plunger doesn't give a chaincase capacity but I have always filled to level plug which is 120cc - what else could a level plug be for?

Singles / Re: 1946 B31 oil feed pipe in timing cover
« on: 17 February, 2022, 12:30:15 »
I would try tapping a thread in the bore and draw it out with a short piece of tube (I/D a bit bigger than oil pipe O/D), a bolt with sufficient thread length and a crossbar or washer and nut. A bit of heat may help.

Singles / Re: B31/M20 Gearbox
« on: 18 September, 2021, 10:58:19 »
Rog/Calum, thanks for your inputs. I'll assume they are the same cogs for the time being unless I hear otherwise.

Singles / Re: B31/M20 Gearbox
« on: 17 September, 2021, 13:18:14 »
I'm afraid I did not pay close enough attention to your original reply Rog. The M registered but not the 33, I was thinking 20. Your gearbox will be the same as a B33 which has the same cogs as a B31. So if there's any M20 gearbox experts out there .......

Singles / Re: B31/M20 Gearbox
« on: 17 September, 2021, 08:47:26 »
Thanks Rog - finally got my head round that. That strongly suggests that I have the M20 internals in my box as first and second seem way under-geared whereas third and fourth seem about right on standard B31 sprockets. When I strip it I can confirm this if the number of teeth on the cogs are not on line with my B31 data but if anyone has the numbers for an M20 box I would appreciate it.

Singles / Re: B31 smoking
« on: 16 September, 2021, 19:26:09 »
I replaced the rocker oil feed banjo bolts on my B31 recently with the correct 65-317 items which have a 1/64" dia hole. The drain pipe bolts have 3/32" to 1/8" dia holes, ie many times the area of the two rockers combined.

Singles / B31/M20 Gearbox
« on: 16 September, 2021, 16:54:04 »
My 1950-ish plunger B31 bitsa has M20 stamped on the inner gearbox casting. My B-Series spares book gives me the number of teeth on each gear but I cannot find the same information for M-Series (I should have counted them when I rebuilt it - dammit). Are they the same with different gearing requirements taken care of by the engine/clutch/gearbox/rear wheel sprockets?

Singles / Re: BSA B range gearboxes
« on: 07 September, 2021, 09:19:57 »
Rupert, you think that the taper/keyway are the same as the M series gearbox mainshaft, in which case primary chain alignment would appear to be the main issue. Do you know by how much inboard or outboard your taper is compared to the M series?
I fitted a Triumph-type clutch to my B31 M series gearbox and only to find that the clutch sprocket was 0.2" outboard of the engine sprocket (maybe I have a 1946-48 mainshaft in it - I don't know if that's possible).
If yours is the same issue let me know and I'll explain how I resolved it - I wont bore you with the details if it is not.

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