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Thread Like Summary
Allan G, Beach, BSA_WM20, gavin eisler, leon bee, MarcB, Nick H
Total Likes: 20
Original Post (Thread Starter)
#811309 06/03/2020 1:40 PM
by Nick H
Nick H
I so hate to need to make this thread.
I certainly don't know it all but I've been around long enough to know the basics and then some.
Engine has new standard size pistons and rings. Lapped the valves, head appeared in good shape.
Tappets at .008" and .010"
Using this style coil, same one in my running Triumph.
[Linked Image from]
Spark looks good, big.
Points ignition. Timed with advance locked to 34 BTDC (tricky since I found out too late the flywheel was put on wrong so no timing slot available)
Swapped out Monoblocs (Did try them) for a pair of Concentrics since I'm more familiar with them. Pilot jet clear.
Cold (obviously) compression is 90 both sides. I know that is low but my Triumph is the same and runs fine. Maybe its the gauge-maybe not.
Tried new NGK plugs and new Champion N3.
Starter fluid or gas sprayed in carbs and still not even a pop.

Obviously doing something wrong. Deja vu for the Triumph which I struggled with for longer than I care to say.
Turned out I had a bad Boyer box. Put in points and Vroom!

Any ideas or direction most appreciated.
Liked Replies
#818474 Aug 2nd a 11:07 PM
by quinten
allen covered this , so mostly saying the same thing in a different way

Are all rotors supposed to have an advance mark from the factory? I have a Sparx on my Triumph and it doesn't.
Also, don't T120's and A65's have different timing advance degrees?

a rotor can go on either way , but only one face is usually marked .
early rotors had no mark ... later ones had 1 mark ... and the last ones have 2 marks , 180° apart .
but these are not timing marks
they are .... Centerline of the rotor-keyway marks .

its the crankshaft and its corresponding rotor- keyway
that has ... a degree angle ... to the cranks TDC

the rotor is a generic part that can transfer the ...crankshaft keyway slot .. to a readable line
on the face of the rotor . .. the same rotor will work with various timings of a BSA , Triumph or Norton

The primary cover holds the last part of the timing information .
with no cover ... the rotor mark has no reference .
2 members like this
#811391 Jun 3rd a 11:47 PM
by gavin eisler
gavin eisler
Not so long ago I had an "issue" after a rebuild when the bike would only run on one cylinder, on investigation I found a rag still blocking the inlet port, whoops!
Measuring piston height to guestimate firing angle is not as accurate as using a degree wheel zeroed at TDC using a fixed stop to calibrate. Still it should be close enough to make it run. Are you sure the correct points are firing the correct plugs when the correct cylinder is on comp.?
1 member likes this
#811399 Jun 4th a 02:18 AM
by Danam
When I first got my A50 I didn't realize the cam pinion rotates in the opposite direction of the crank so I had the points 34' after TDC. wouldn't start.
1 member likes this
#811619 Jun 5th a 11:49 PM
by gavin eisler
gavin eisler
That 15 thou thing, that not Gavins method, RTFM.
1 member likes this
#812039 Jun 9th a 11:27 PM
by NickL
Originally Posted by MarcB
Originally Posted by NickL
[quote=Nick H]
Spend a couple of hundred bucks on an electronic ignition and life will be simpler.
Hmm, not necessarily. If the timing marks are non-existent then it's possible that nothing is lining up. Nothing will line up with EI either. Don't get me wrong, I'm a big proponent of EI but replacing points with EI shouldn't be "to make it work" but rather "to improve on the working process".

If replacing the points with EI helps in this case, then the original parts were wrong (either points or AAU) and a different set would have helped as well.

You can get it running with an EI by putting a screwdriver down the plug hole and marking it at somewhere around 8mm.
It's a bloody site easier than messing with the points cam, replacing springs, checking wear on advance assembly etc..
When i see a points plate/mech advance that isn't worn or clapped out on one of these old crates i'll advise to use it.
1 member likes this
#812982 Jun 18th a 01:15 AM
by koan58
You should care about the springs as well as every other part of the motor, but the immediate issue seems to be with valve/seat sealing.

The springs may or may not be ideal, but are unlikely to have much relevance to your leakdown observations.
1 member likes this
#812986 Jun 18th a 01:59 AM
by koan58
Well hopefully they will, but while they're out, now is the time for a little wiggling to see how floppy the valves are in the guides ( any more than about 10 thou head shake is worn) but more relevantly now is the time to examine the valve and seat surfaces.

If in any doubt it is time to try a little lapping with fine paste.

Then look at the surface of the valve, if it shows just one patch of grinding, the valve is bent.

If the valve is straight, continue with careful lapping to get a good contact surface, using the finest compound. Don't be tempted to use coarse to speed it up.
You should end up with something like a continuous smooth contact surface between valve/seat at least about 1/16+" wide.
1 member likes this
#813234 Jun 20th a 02:06 AM
by Ignoramus
lots of good comments about mechanical side of things but none of these should stop it actually starting or at least attempting to start (other than the obvious timing) . that said friend of mine with a Goldie drove himself round the bend chasing his tail till he found melted alloy under one of the valves (he has cooked a piston and blew a hole in the top) ......but that was a i said to him 'well the melted alloy has to have gone somewhere"

so lets take a look at some of the obscure stuff

pretty high up my check list would be stale fuel ( you said, i think bike had been off road for a bit) ....sorry if you have already filled it with new fuel, ......try disconcerting the tank and filling just the carb bowls with some new fuel ......if it still doent at least fire up i would be starting to look for electrical faults

like they say 80% of carburation problems are electrical
1 member likes this
#813991 Jun 25th a 09:07 PM
by gunner
Sounds like you local machine shop is taking the p*ss, there is no way it should cost that much, shop around for some better deals.

The process of installing new guides goes something like this:-
- old guides are punched out of the head
- guide bore in the head is checked for size in-case oversize guides are needed
- head is heated in an oven, new guides are cooled in the freezer and the guides are then installed, hopefully using a guide tool to align them with the valve seat
- valve guides are then honed to match the valve stem diameter
- the valve seats are then cut ideally using 3 angle cut
- some modern machine shops using Serdi and other valve guide honing and seat cutting tooling claim that their accuracy is so good that no lapping is necessary, assuming the valves are in good condition

This type of renovation is standard business for many car engine re-conditioners so with only 2 valves instead of 16 or 32 I don't see how they can charge that much. Maybe you could try a motorcycle specialist such as E&V engineering who have huge experience with BSA's etc. see
1 member likes this
#814828 Jul 2nd a 10:12 PM
by Nick H
Nick H
WhaLah! She started!

Put in new valves and springs. Cold compression was still low. Put some oil down the plug holes which if you've ever done it, makes the bike hard to kick. Had to do the jump kick and Vroom! Lots of smoke of course. Ran it for a couple minutes and when I turned the key off, she kept running. Had to pull off the plug wires. I guess it was dieseling.

I think compression is the issue. I'll see how things go with the ignition strobed and the carb dialed in and a bit of break in.

1 member likes this
#814917 Jul 3rd a 08:13 PM
by Ignoramus
sure sounds like an intermittent electrical problem to me (those can be a real [***]) wire it to by pass the switch and see how you go then ...........i did suggest electrical problem like 20 posts ago but that didn't seem to attract any comments
1 member likes this
#815069 Jul 4th a 07:33 PM
by quinten
Would it help if I installed +.020" rings and gapped tighter

Not in my opinion .
Larger rings will impart more friction throught all 4 strokes ... not just the power stroke .
ring drag is necessary to seal but it's also a waste of power .
spring load is supposed to be just enough
compression and power stroke get behind the rings and add to the rings spring-seal .

Someone else , the engine designers and ring- manufacturers have already done the hard thinking on this .
each oversized is designed to work in a bore-range .
1 member likes this
#815086 Jul 4th a 08:48 PM
by Beach
Originally Posted by Nick H
Rode the Lightning around the yard today. Clutch is easy and shifts without any effort or noise.
Had to oil the pistons for compression to start it though. Gasket seal is good but apparently I have leaks past the pistons and rings.
Or the valves still or both. New valves fit the guides better and the head held kerosene overnight, something the old valves didn't do.
Leakdown test was only slightly improved though. I could hear leaking past valves and inside case both.

The bores are 2.95" everywhere with little variation so my standard pistons and rings should be correct.
Ring gaps were .016"-.018". Would it help if I installed +.020" rings and gapped tighter?

Pleased to know my carbs, timing, wiring etc are good though. Big thrill to finally hear it fire up.
It's hard to get a correct measurement on the cylinders unless a somewhat experienced machinist. If your clearance was correct for std pistons, you wouldn't be losing compression and have too large end gap on rings. Just for a ballpark I'd put pistons in and push to one side and measure clearance with feeler gauge. Myself, I leave that part to the shop I use and save myself the heartache. You know all about that by now. Surprising how much one can learn with a battle like this.
1 member likes this
#815082 Jul 4th a 08:29 PM
by quinten
you can put larger rings in , you wouldn't be the first guy ,
but its not a magic solution .

once the bores get oversized ... they can really benefit from a Machinist
that can return the cylinders to a real geometric cylinder shape .
sometimes they didn't come from the factory cylindrical
... just within whatever tolerance was acceptable .

My old machinist , who is now retired , would show me
how are out of round my cylinders were ...
with the bores first pass as the base line . and they show/tell what he planned to do .
1 member likes this
#818051 Jul 30th a 03:26 PM
by Beach
Your compression after rebore may not be much . Seat the rings in, then check the compression. I would almost bet your problem has finally been solved. Fingers crossed.
1 member likes this
#818174 Jul 31st a 01:23 PM
by Beach
Originally Posted by Nick H
Thanks, i understand the timing and the advance. Not asking about that.
I must have a problem getting my message across.
I like having the 34 degree advance mark and the TDC mark visible as a reference knowing that at idle the pointer will be a bit counter clockwise from TDC.
I suppose it would be smarter to make a mark at 10 degree BTDC (34 minus 24) where timing should be at idle but as I have been reminded several
times here it is the full advance point that is critical.
As NickL mentioned this is only a start point and many variables such gasoline used, carb setup,compression, altitude, etc., etc. will effect and determine the best points timing. Can I get an "Amen"?
Looked back through this whole thing and looks like you're sure of timing marks being correct and it strobed at your mark. If all these thing are correct, why don't you just ride it and enjoy. If you're not sure of timing marks, use piston stop and degree wheel to verify.
1 member likes this
#818116 Jul 30th a 11:21 PM
by NickL
Yes, the line on the raised segment is the fully advanced mark.
It can be a bit confusing as there is the other hole in the cover
for the pointer, for the ET setup etc.
Just like the trumpet stuff, all lucas junk.
1 member likes this
#818392 Aug 2nd a 08:18 AM
by Allan G
Allan G
Nick, I think you over reacted to Gavins comment about the manual, so many will ask a question before reading the manual, I’ve even been guilty of that myself. If you read the manual and go through it properly there is little reason for anyone to ask most questions on the forum.

I could be wrong but I Believe the early rotors are thinner, you might want to check this as it might effect power output.

The above comments are also correct, the Fully Advanced Mark should be right of the TDC mark, as the crank turns in a forward motion it will spark before TDC is reached, as the crank rolls as if it was pushed forward on the ground, the mark right of TDC will reach the top before the other mark will.

If the magnet is good on the other rotor, fit that... otherwise buy a new one, it’ll save you a lot of headaches.

Also, if your timing light has an advance dial on the back, turn it fully left and glue it in position, some (least mine does) has the habit of moving too easily and you find the timing is way off when you have set it. A glue gun is ideal for the job wink
1 member likes this
#818454 Aug 2nd a 07:45 PM
by Allan G
Allan G
The marks on the rotors came about the same time they put inspection windows on the primary covers, I think this was c1967. As all rotors with timing marks are made equally The factories had to either index the position on the primary case to suit alignment of the timing mark on the rotor. Another thing worth adding is that the early cranks with 2 sludge trap plugs, do not have the same key way position on the crank as the later cranks, why bsa couldn’t have kept this the same and used a different position for the pointer is anyone’s guess, however they didn’t and if using an early crank this part needs to be made aware of.
1 member likes this
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