Smokin'

Wotcha.

Here's a nice little problem for you. I bought a BSA B31 ( well someone had
to ), all very jolly apart from it has a nasty habit. It smokes. It smokes
like it is going out of fashion. This was first thought to be a loose
exhaust valve guide - so an oversized one was made and fitted. It still
smoked. Upon examining the oil tank, I found the standpipe for the oil
return was missing - this would allow oil back into the crankcase when the
engine was stopped. The back was cut out of the oil tank, and a new return
standpipe was made and fitted - then the tank was brazed back up, powder
coated and fitted. It still smoked. The bore and piston were new ( or at
least they looked new, and they measured up OK ). The piston rings were
changed, seeing as we suspected the original ones were those cheap Italian
things that have been flooding the market. It still smoked. Right - lets
take the oil pump out and check it. Seems OK - made sure the pump seating
faces were clean and free from burrs. Put it all back together and left it
overnight with a piece of glass under it. No oil at all was passing back
through the pump - so that ruled out wet sumping. Now the strange thing
is - it only smokes badly when on the side stand - which made me think the
oil was being thrown up by the flywheels and hitting the bore walls. Next
plan - a new piston. A nice new +060" piston, of reputable make , and a
rebore. Now I've put the whole plot back together again, and it still
bloody smokes when on the side stand. I'm running out of things to try. My
other B31 doesn't do this - and I can't see any difference between 'em. (
The smokey one is a 1959 alternator and the other is a 1954 dynamo )

What the Hell is causing this ?

Cheers in advance.

 

Does it smoke from cold, or just after the exhaust has warmed up?

 

Wild guess #1 of thousands based on total ignorance of the bike in
question: blue or black smoke? If black, could it be the float not
floating properly?

Wild guess #2: could it be a breather/oil trap problem?

I won't be offended if you snort and laugh derisively.

 

Wotcha.

I can get it to do both. I did think it was 'old oil' in the exhaust, but
I've covered enough miles to burn that out.
Just got back in, and in the two or three minutes it takes to unlock the
garage, it started smoking. The new barrel / piston has now covered a grand
total of ten miles. As far as I can see, the bike doesn't blow any smoke
out whilst being ridden.
Most odd.

 

Wotcha.

Blue - well, white actually.
It is set a tad rich on the pilot jet, and I can get a faint trace of black
smoke when ticking over . . . that is when ticking over and no white smoke
is bellowing forth.

Thought that. Some of the later engines have a timed breather that operates
off the ignition cam spindle - the drive peg has to line up with up with the
left hand screw hole when on TDC. Mine is one of those that doesn't have
this breather. ( bugger ! ) The timing side non-return breather is working
as it should.

Indeed not. It's always good to have another straw to grasp at - and, like
in so many cases, it's all too easy to miss the obvious.

Maybe the bike is trying to tell me that a new Pope has been elected ?

 

[snip]

Tried new valves as well as the guides? Could the oil in the rocker box
be by-passing the valve on the induction stroke?

 

Worn inlet valve guide?

Ron Robinson

 

Wotcha.

I couldn't see anything wrong with the valves - maybe if I take the head of
the "good" B31 and swap it.
At least that will prove if it's the head.
<<wanders into garage>>

Cheers.

 

message
Wotcha.

I couldn't detect any wear in the inlet guide - but I'm going to swap heads
with my other non-smoking B31 just to see what happens.


Watch this space.

Cheers.

 

Wotcha.

<<wanders back out of the garage>>

Bugger !

At least I know it's nothing to do with the head.

 

Its often said you should run a newly re-bored engine at 4000rpm for the 10
minutes of its life to ensure the rings and bore do not glaze,
Personally I could see this

happening in reverse with a SO,BSA

;(
-

 

"TMack" <tonyREMOVEmackin_at_bigfoot.com> wrote in message

Wotcha.

I've been running it with no oil in the primary side - in fact without a
primary case on at all whilst I've been buggering about with the alternator.

It's not as if this prevents the bike from being used - but it's totally
screwing my head up as to why I can't stop it from happening. I thought I
was fairly good when it came to sorting BSA pre-unit singles, but this one's
giving me a good run for my money. I can't think of anything else to change
.. . . . apart from the whole bloody engine.

Cheers.

 

Wotcha..

With a SO,BSA this is known as "running out" ;-)

Ooh - I like that, and so will my mate who runs a Starfire.
Strangely enough, a rather special "Starfire" will be on show at Malvern
this weekend. It has a Desmo head, amongst other things, and goes rather
well.

Cheers.

 

Strike one suggestion.

 

Mmmm. Okay, you've swapped the head, and that didn't cure it. It's got a
new barrel and piston, so it's unlikely to be coming up the bore.

I'm assuming it doesn't have an airbox with a crankcase breather feeding
into it, so there isn't an oil feed of any sort into the carb.

Is it possible that there's oil in the petrol, or contaminating the inside
of the tank somehow? You could try swapping the tank from the other bike.

 

Heh. Does than mean the Pope is now a Geordie?

back to your original thought: the crankcase is 'definitely' not
running wet? Have you tried undoing the drain bolt immediately after
running it (I assume it has one)?

 

Wotcha.

The tank is new - well, it's just been chemically stripped, then powder
coated - then Petsealed for good measure. Filled up with fresh petrol - in
fact I had to stop for petrol on the way home.
I've been for a run out to a bike show at Malvern today - no smoke at all
when the bike is running, and no smoke when ticking over, but the within a
minute of it being left ticking over on the sidestand it looks like a steam
engine. As far as I can tell, the left hand flywheel then throws oil up the
side of the barrel. The thing that's really bugging me is that my other
bike never does this, and, as far as I know, it's not a 'feature' of BSA
pre-unit singles. My 'project' B33 isn't up and running yet, or I'd have
another engine to compare things with.

Cheers

 

Wotcha.

When you start it, with deliberately too much oil in the crankcase, you see
the oil return out of the standpipe in the oil tank. Within a few seconds,
the steady stream of oil starts to splutter, and a mixture of oil and air
bubbles start coming out. This proves the scavenge side is trying to shift
more oil than is available - hence the crankcases are dry. If you lean the
bike on the sidestand - then the oil return stops for a while, until the
level reaches the pick up pipe on the oil pump, and at roughly the same time
it starts to smoke. I know the flywheels run damn close to the crankcase
walls, and I can well imagine the left hand one could now be flinging oil up
the barrel wall. At least that's the only explanation I can come up with.
The moment you pick the bike back upright, the oil return becomes stronger,
with no air bubbles until it has once again emptied the 'sump'. I've done
around a hundred miles today, and when running there is no smoke - even when
sitting at traffic lights and the like. In the time it takes to get my keys
out and unlock the garage, the bugger is chuffing away like an eighty a day
chain smoker. Maybe it's just the nature of this particular beast - but
it's sure got me scratching my head. There again, I'd only be bored with a
bike that ran 100% perfect.

Cheers - again.

 

Relocate the oil pickup, or relocate the sidestand. Then again, you're
getting regular upper cylinder lubrication - you could tell people it's a
feature...

 

Wotcha.

You don't know how close to relocating the oil pump pickup I've been.

We made an extended "sump" and a longer oil pickup for a rather trick B50
engine, and that worked well.

I just can't see why this particular engine does this - and that's the bit
that bugs me. Once I know why it's doing it, then I can set about trying to
stop it.

Ah well, I suppose I'll just have to keep riding it until I find out ;-)