The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Goldy on 04.04. 2011 09:37

Title: BTH Magneto
Post by: Goldy on 04.04. 2011 09:37
Has anyone got one of these on their machine. Expensive but looks good.
Title: Re: BTH Magneto
Post by: olev on 04.04. 2011 12:18
Gday Goldy,
Orabanda in Kalgoolie is sticking one on a super rocket.
If he kept away from Hay street and changed his drink to XXXX, he might get it finished.
Title: Re: BTH Magneto
Post by: orabanda on 04.04. 2011 13:42
You are a disrespectful boy!

Update on the SR Special is that what with moving house, (building new bigger shed too), running a business, remembering I have a family, taking teenage daughter to hockey training 3 times a week, finishing off yamaha restorations, musical interests, etc, the project had stalled.

However, back into it now, and hope to have SR running soon!

For Goldy's benefit, I am posting pics of maggie, and how I mounted the coils (no welding required; bracket clamps to frame tube). I still haven't worked out how to shrink these bloody pics, which is one reason I don't post much these days, as I hate getting told off!

Title: Re: BTH Magneto
Post by: alanp on 04.04. 2011 16:33
Just when you think you've done a good job of building your bike along comes some pictures of a higher level of build/creativity to put you in your place!
Very nice work Richard.
2 questions - 1) What type/supplier of belt drive is that? 2) The clutch looks superb but looks very deep (front to back), will the standard inner and outer covers fit over it?
Title: Re: BTH Magneto
Post by: orabanda on 04.04. 2011 22:49
Hi Alan,
The clutch is a spare one I had from a Suzuki PE400.

It fits within the primary cover, no problems.

Title: Re: BTH Magneto
Post by: orabanda on 05.04. 2011 00:34
The clutch machining was done by Colin Tie (the Mundaring Fossil!).
He has been making them for years, initially for his impressive collection of Gold Stars.

All my swing arm A10's have Colin's clutches; he uses Suzuki GS550 clutches.

This is fitted to my RGS Replica


This is Colin, with one of his beloved GS.





Title: Re: BTH Magneto
Post by: Brian on 05.04. 2011 02:35
I have a friend who has just fitted a belt drive/clutch conversion from the bloke in Melbourne, I think its Lytedrive or something similar. Anyway he reports after a couple of hundred miles that it is very good although I tend to think the clutch is the big improvement rather than the actual belt drive. The main improvement as you would expect is with gear selection.

Richard do you have a belt drive primary in any of your bikes yet or just the clutch conversions ? What I am keen to find out is if the belt is much of an improvement over the clutch.

I have the four spring in my bike so will leave it as is cause' it works well, however if I get a bike that has the six spring it will get replaced with either a four spring or an alternative like the Suzuki clutch.
Title: Re: BTH Magneto
Post by: orabanda on 05.04. 2011 02:50
The SR Special is the first one with the belt drive, and I am yet to get it running (give me a couple of months!).

However, Colin Tie has converted all of his Gold Stars to belt drive now, and loves them! Previously he had fitted the Suzuki clutches but chain drive, then modified them to belt.

He says they are a smoother drive (but the bely must be correctly adjusted, with sufficient slack).

He rides a bike every weekend on club runs.

Interestingly he fitted a clutch from a GN250 Suzuki which I had lying around, to his 350 Goldie and it handled the power very well.

Title: Re: BTH Magneto
Post by: orabanda on 05.04. 2011 03:21
Re the maligned 6 spring clutch.

I got conned into sorting out one on a B31 about two years ago (it was the tip of the iceberg; the whole bike needed going over).

After a lot of work on the clutch (and finding info on sites like this forum), it has been performing as good as the 4 spring for two years now.

The clutch is light, doesn't slip, and he can always get neutral.

My opinion; the 6 spring is an inferior design to the 4 spring, and I wouldn't fit one out of choice. They are very finnickey and are relatively difficult to set-up, but they will work!

Title: Re: BTH Magneto
Post by: Brian on 05.04. 2011 04:02
G'day Richard,

I have some of those six spring ones in my other bikes, B33 etc. Like you have found they can be made to work ok but they are a very poor design from a engineering point of view. One thing that does seem to help them is the new type bearing that is available, the alloy ring drilled full of holes to hold the balls. The thing I dont like is for them to release properly a chain driven sprocket and basket is asked to move sideways to release, hence the miserable bearing set up they have which allows lateral movement.

On a different subject my current research subject is using a ball bearing main instead of a roller. A ball doesnt have the radial load capability of a roller but it eliminates end float which seems to be a major consideration in bottom end design. All modern bikes like CRF450 Honda's etc use ball bearing mains. I might bite the bullet and put one on my 61' and see what happens. I'm doing about 10,000 miles a year on that bike so it wont take too long to find out if its a good or bad idea.

Its all good fun.
Title: Re: BTH Magneto
Post by: Goldy on 05.04. 2011 12:28
Nice workmanship Orabanda. You will have to let us know how the mag performs.
Title: Re: BTH Magneto
Post by: orabanda on 05.04. 2011 12:30
Thanks Goldy,
I will also post the dyno chart!
Title: Re: BTH Magneto
Post by: KiwiGF on 07.10. 2012 05:46
Sorry to restart such an old post but this topic is relevant to my question ...which is did you (orabanda) or has anyone else have issues with the timing method of the BTH mag

I've fitted the same Mag as in the pics and found that the 6mm rod does not lock the mag completely like you would expect and the result is that I can turn the crank (carefully) even with the mag locked equivalent to 2.8mm of piston height (measured with a dial gauge).

I'm wondering ill have to find a more accurate way of setting the timing eg setting up degree wheels and strobe etc

Or have I got a faulty mag!

Adding to my woes is the aluminium gear i bought from draganfly to suit the mag only engages 2/3 of the width of the teeth of the camshaft gear and almost jams as it's turned almost like it's not round or the teeth are not cut correctly.

Title: Re: BTH Magneto
Post by: orabanda on 07.10. 2012 10:15
I did not have problems setting the timing; used the 6mm peg to lock the mag, and a timing disc on the primary drive.
Title: Re: BTH Magneto
Post by: KiwiGF on 07.10. 2012 11:30
Hi orabanda thanks for the quick reply
I guess I have a faulty mag then, I've got about 2mm movement on the circumference of the mag gear When it's locked which equates to a lot of piston height, The upshot is that I have no idea where the mag is firing between about 6 and 9 mm of piston height.

I think I'll ask BTH what's going on.

And also Draganfly ref their ally mag gear, it's about 0.5mm mm bigger in diameter at the root of the teeth than the cam gear but it should be the same i reckon, not my day really. I was hoping to be riding it this month!
Title: Re: BTH Magneto
Post by: groily on 07.10. 2012 17:35
Dunno about the BT-H thingy, but ref the alloy pinion Kiwi, just went and had a look at 2 of mine. Exact same thing as yours - maybe a tad worse even (these were SRM-supplied but likely the same maker?) - I have to admit I never even thought to check that carefully before fitting. One's plain, one I attacked to mount an ATD on, and they're both the same.
The good thing is, they've run fine, the plain one for a lot of miles. No weird wear patterns either on the teeth.
So maybe they're all like that?
Just checked them for mesh by running them round a cam gear on the bench, and they seem smooth enough. So with any luck, not a problem.
Cheers, Bill
Title: Re: BTH Magneto
Post by: KiwiGF on 08.10. 2012 02:47
Hi Orabanda (plus anyone else with a BTH mag).

I think I've found the explaination to the problem I observed, mainly because I found an "Ignition Timing in mm Before TDC Calculator" on the net. The link is below if anyone is interested.
Eyeballing the mag pinion there is about 2mm movement at the pinion perimeter when the BTH mag is locked, I calcualte this equates to about 3 deg, which in turn equates to 6 deg at the crank pinion.

Using a dial guage, and after locking the mag and setting the timimg to 8.73mm (11/32") I observed the variation in piston height between magneto stops was 6.15mm to 9mm (2.85mm variation). In a perfect world the crank would of course be locked by the mag and not move at all.
According to that calculator using  rod length 165mm, stroke 84 mm
34 deg btdc is 8.86mm
28 deg btdc is 6.10mm

So this more or less proves that the (observed) play in my new BTH mag locking/timing mechanism can result in the timing being up 3mm out.

The 3mm that really surprised me, that such a big piston height difference results from just 6 degrees crank rotation.

Anyway, I guess this is just something to be aware of if your (new style) BTH mag has any play in the stops like mine has. I'd still buy the BTH mag knowing this.

I'll just experiment with the timing once the bike is going, I'll just use the mags slotted mounting holes to make "fine" adjustments to the timing should the engine pink etc. 
Title: Re: BTH Magneto
Post by: orabanda on 08.10. 2012 09:41
Interesting feedback; Mine does not show this problem.

I assume you will make timing adjustments with a timing (strobe) light?

32 BTDC was best for me!
Title: Re: BTH Magneto
Post by: KiwiGF on 08.10. 2012 11:14
Hi orabanda, I probably won't do the strobe thing, I might but I'll probably just set the timing so it's 11/32 in the middle of range allowed by the mag stops.

It does not make me feel great that my BTH mag is not quite right compared to yours  *rant*. I'll mention it to BTH.

Groily /Bill I persisted with The alloy gear after your findings (thanks!) rather than send it back, and with some wet and dry wrapped a lolly stick and a couple of hours "fettling" it now fits ok without binding. Levering the mag away from the camshaft gear and then doing up the mounting bolts helped a lot towards getting it to fit.

So onto the primary drive next assuming no issues with the dynamo drive....

Ps sorry about the lamberetta link just avert your eyes from anything else in that site  *razz*