BSA Owners' Club Forum

The BSA Workshop => Bantam => Topic started by: Mike Farmer on 15 October, 2021, 14:38:14

Title: Bantam "Newy"
Post by: Mike Farmer on 15 October, 2021, 14:38:14
 :) :) :) :)

Greetings. I have never had anything to do with Bantam---Bushman/D7?? and have been asked by a friend to try and solve a problem. This is bike he bought many moons ago and has never had running.

New petrol, assumed correct mixture, Timing apparently correct. Big fat spark at the plug. It has been kicked over, sworn over and probably prayed over and pushed round and round the yard with not the slightest inclination to fire up. Fuel is definitely getting to the combustion chamber.

As said I have never had anyting to do with this marque but under any other circumstances my first suspicion would be condenser.

So may I please hand this over to the men of Bantam experience. Any assistance or advice gratefully accepted----Thank you.

Mike 8) 8) 8)
Title: Re: Bantam "Newy"
Post by: Stubaker58 on 15 October, 2021, 16:10:43
Hi Mike,

It will depend a bit on the type of Bantam you are looking at. The early engines, up to D7, are very different in the ignition department from the D10/14/B175s. If itís a Bushman it will be a later engine.
Any pictures?
Title: Re: Bantam "Newy"
Post by: idie on 15 October, 2021, 18:01:34
Maybe the crankshaft seals are worn.
Title: Re: Bantam "Newy"
Post by: Dean Southall on 15 October, 2021, 19:30:34
Agree that Crankshaft seals likely to need replacing (,ake sure to get viton ones (available from Rex Caunt).
But even with good seals my Bantam takes 20 or more kicks, lots fo floading and even more swearing if laid up for a month or two.
Title: Re: Bantam "Newy"
Post by: Mike Farmer on 15 October, 2021, 21:01:25
 :) :) :) :) :)

Thanks for your replies. This is taking me down untrodden paths and into the Bantam wilderness

Sorry no pics, I've never seen it just this prob has gently eased up and blindsided me. Like quote" you're a BEESA bloke what do you reckon". Cant just walk away can you.

So I think its manual time and I think I have a damn good idea who will be doing the reading. A point, I am told that the compression appears OK. Would this be the case if the seals were seriiusly poorly. Recommended manual please.

Please keep your thoughts coming.

Mike 8) 8) 8)
Title: Re: Bantam "Newy"
Post by: idie on 15 October, 2021, 21:50:25
The compression that you can feel is that over the piston. When the piston comes down mixture is compressed in the crankcase and forced up the transfer ports to the combustion chamber above the piston where the mixture is detonated. If the crank seals are worn the mixture cannot be compressed due to air leak so the bike will not start. I am sure someone can explain this better than me.
Title: Re: Bantam "Newy"
Post by: Stubaker58 on 16 October, 2021, 07:02:19
The seals are always worth checking for wear and/or incorrect fitting but that does involve a full engine and gearbox strip.  Before you go down that route itís worth double checking the ignition especially as you say it doesnít even cough.

Sparking outside the cylinder does not always equate to inside the cylinder. Ensure the plug cap does not have a resistor in it and swap out the plug for a trusted genuine one. As you say replace the condenser, check the points themselves are working as they should. All normal stuff.

The wiring, especially on D7s is complicated as the switching tries to match generator output to load. The different wiring harnesses look the same but arenít. It might be worth hot wiring the ignition ie by-passing the ignition switch completely to see if it makes any difference.

Then ..

Is it a ďmagnetoĒ ignition ie spark direct from the coil on the left side of the engine? If so you could rig up a constant loss external coil and battery to see if the bike will start, if it does then suspect the internal coil or the magnetism in the rotor (can be re-magnetised by Villiers services).

Next ..

On these earlier engines with generator and points on the left the keyed shaft can turn in the crankshaft flywheel as a result of a seizure. If this has happened then the timing will be out. (The rotor will also be out of sync with the magneto coil which will also affect the spark). To add to the confusion the D1/3 crankshaft assembly looks the same as the D5/7 assembly but isnít as the angle of the woodruff key slot in relation to TDC is different. This can all be checked by removing the left hand side cover and the generator stator plate and measuring the angle of the key BTDC. The central bush in the stator plate is also suspect, if very worn it will allow the crankshaft to whip and affect the timing but this will usually only be an issue at higher revs.

Or ..

If the points are on the right the cam is not keyed to the shaft but is held by a taper.  This means that itís possible to have the timing 180 degrees out.  Worth checking.  These bikes have an external coil so this can be swapped out to check.  Watch out for the low tension feed to the points as it runs under the engine and is very vulnerable to damage.

Bantams can be (are?) infuriating but do start reliably once set up properly (mines a first or second kick starter).  They seem very simple but things are of course fifty years old, Iím sure a methodical approach will have things running.


Title: Re: Bantam "Newy"
Post by: Mike Farmer on 16 October, 2021, 11:50:23
 :) :) :) :)

Thanks for that. A lot to digest. I am fairly upsides with 2stroke theory and so am able to follow what you have said. However as you will appreciate I have slightly less than no practical experience other than horizontally opposed diesels and even that is limited and many years ago.

What you have written is much food for thought and I may be back here lots of times. I am not able to do much to it at the mo, but expect to "get my hands on it" about February time. Thats if the said gent doesnt change his mind, like saving it as something to do in his retirement.

In the interim, have a nice weekend and enjoy your bikes.

Mike 8) 8) 8) 8)

Title: Re: Bantam "Newy"
Post by: AdrianS on 16 October, 2021, 14:38:40
Squirt a bit of mixture into the plug hole and then see if it fires. It should run for a second or so.
That will tell you if the spark is ok inside the cylinder and timing roughly right.
I would drain the crankcase ( there is a small drain under the engine ) to make sure there is no build up of old oil etc. Clean the carb out in case jets are bunged up. 2 stroke oil separates if left in the carb and will clog the main jet. Leaking seals will make the bike hard to start but unless really bad you should get it to fire.
Unlike 4 stroke engines you need to remember that the engine needs to be filled with fuel mixture before the engine will fire so the way I start mine is as follows :
Turn on fuel tap and press carb tickler till fuel runs out. Put choke on and kick over 2 or 3 times with no ignition. Flood carb again and then turn on ignition and kick over with some throttle opening and mine fires immediately. Each engine has its own character so you need to find out what works.
Do all the above and try and get it to fire and run.
Failing that I would double check timing but these engines are not too fussy with timing to start and run. If no joy, take the engine out and strip and rebuild. Need a couple of tools to make life easy but I recon I can get an engine out and completely strip in 1-1 1/2 hours.
Good luck with it!
Title: Re: Bantam "Newy"
Post by: Mike Farmer on 16 October, 2021, 19:42:51
 :) :) :) :)

Allgood stuff. Thanks

Mike 8) 8) 8) 8)
Title: Re: Bantam "Newy"
Post by: bluebell on 19 October, 2021, 13:24:38
i will try to precis this,,,d10 onwards one cam profile  on a taper can be set at any crank position some say 18 deg some say 30  deg BTDC,,,,, havnt played with one of these yet to get answers,,,excluding the early d1 lucas,,,,d1 to d7 the cam is held in position with a tiny  woodruff key, early wipac  magneto  had a 12 o clock keyway in relation to the crank pin, the cam looked  lumpy,,,later ones up to d7 had 2 types of cam and 2 diameters of magneto bowl wit a slight difference in advance of the magnet positioning,,,,all of these had a 11 oclock keyway position both d7 cams would work   but try setting the points to  .005 thou to see if it runs,,th long duration cam d7 was for the trickle charge small rectifier, nif you have  two much clearence on your spider to magnets the spark could be weaker  and have less output for your lights,  with magnetos,, no  plug suppressor cap!!
Title: Re: Bantam "Newy"
Post by: cdsdorset on 01 November, 2021, 21:54:25
You can test the seals by pressurising the barrel and see if you can hear the air escaping.
Title: Re: Bantam "Newy"
Post by: bluebell on 04 November, 2021, 08:54:50
take the crank case plug out  squirt some petrol in the spark plug hole   turn the engine over a few times to blow the crap out of the crankcase bung  hole, replace crank case plug  turn engine over with your finger in the spark plug hole  you will know what your compression is like  fit known good plug  gapped to   019  thou,   if a bantam has just been left in an out building for  more than 10 years the chances of  the crank seals detetioration goes up drastically  and the engine may start and run to  up to an hour  but on restaring from cold later the seals just give up the ghost through static hardnening over the long period of inativity,,,