Anyone running a chain drive magneto? I've seen old adds for that set up for Bosch magneto? What chain size, sprocket diameter, tension and what ever you know.PK
I do - and I like it, mainly because it's much cheaper than the old gear driven alternatives. Some tinkering needed and I still haven't found out if there are better quality bicycle size chains out there, like the o-ringed chains for motorcycles.
I use the standard bicycle chain size because it's the only type sprocket that'll fit between the crank shaft pulley and the timing gear cover. First I looked for 20 tooth sprockets, but when I found a couple of new regular bicycle rear wheel 19 tooth sprockets on a swap meet for $2, I used them - and 19 tooth is about the smallest you can use behind the later large style crank shaft pulley. The sprockets are fastened with two screws through existing holes in the sprockets - they're hardened and though to drill.
First I made the magneto shelf with the engine out of the car and didn't give enough room for the radiator to engine inlet pipe, so I had to run the water through a flexible hose. Worked just fine, but didn't feel right, so I rebuilt the magneto shelf last winter higher up, so the ordinary radiator pipe would fit. Thus I needed a longer chain and noticed how worn the chain had been from only about 500 miles of driving. Well, I put a new high quality chain (that's what he said in the bike shop) and have driven another season with about 800 miles and it works fine, but the chain needed frequent adjustments. Then I thought maybe the now rather long free sections of the chain tends to whip at certain rpms, so I made a tensioner for the chain. I haven't driven all that much with the tensioner yet, so I'm not sure how much it helps the wear issue, but hopefully it'll help some.
If you have a magneto that turns the other way around, you can drive it from the cam shaft. Since the cam shaft is running half speed, you need twice the # of teeth on the cam shaft sprocket compared to the magneto sprocket.
Here's a picture of the chain tensioner I made in late september 2015. I have made shorter trips up through december - and the first trip in two months time last sunday, so it has tested OK, but the question of how much or if the chain will wear less isn't resolved yet.
And here's what it looks like installed from above (hard to get a good picture in the confined space)
No fan, but it's possible to fit one, should I ever need to drive in a slow queue (I tend to avoid parades)
I think there are conveyor chains that are much stronger than a bicycle chain yet the same or very similar size. If you could take a few critical measurements I can try and get a match for your gears.
Just let me know,
Once I know the chain and gear dimensions, I'll see if I can help you source them in the US. Should not be a problem.
I just sold the one which was fitted to my roadster when I bought it. It sat on a factory made cast aluminium platform which put it about 6" above the pan rail. The platform legs were bolted at the last bolt on the straight section the pan rail and then to the first one as it transitions around to the crankshaft. An arm at the top was bolted to the fan hub bolt to steady it.
The drive sprocket on the camshaft was keyed with the usual timer roller pin, but the gear could be timed on the hub by releasing a locking ring and rotating the gear on the hub. It was just an ordinary bike chain drive, linked to an English Fellows magneto.
I should have taken some photos before I took it off and sold it.
Allan from down under.
Bicycle chains are quite strong, yet I remember snapping one myself, and I am not.
Still, in this application it has proved to work fine. It is only driving a magneto after all.
My old motorcycle has a chain drive cam. That would need a stronger chain, but if you looked at it you'd think its a bicycle chain. The chain is a 06b-1 which is quite small, but available at conveyor chain merchants and others. On the clutch side it again uses an 06b-1 to drive the gearbox, but later the manufacturer switched to an 06b-2
These same merchants have all manner of gears too. With or without internal splines etc. You could machine to suit if you wanted to.
Anyway, I hope this helps,
i will have a bosch for sale at chickasha.charley
I have several mags to choose from all have the manual advance. I think I could use the stock advance lever. What did you use Roger. PK
The Bosch chain drive mag brackets used a silent(Whitney)chain to drive the mag. Most probably died from a lack of lubrication.
Thanks Justin, I'd say the size is 1/2"x1/8" - but the chain doesn't need to be any stronger, I would just prefer something more wear resistant. Maybe it's the initial stretch that was a bit more than I would have thought and it'll wear better after that. I use chain lube on a spray bottle for motorcycles frequently.
Pat - I use the stock advance lever, luckily I all I needed was a little piece of rod to connect the lever on the steering column with the advance lever on the magneto. There's an internal shut off in the magneto, so I have to advance a little just to get it to spark. But it's easy to start without any impulse, two priming pulls without spark but with choke, then two starting pulls with ignition and it'll run - even after two months like this sunday (they're horrible these winter months, really)
Haven't had the opportunity to fire up this motor, waiting for spring. Crank pulley is from Chaffin, sprocket added later.
Man, you'd be so much better off with a cog belt.. Hope you carry spare chain.
A cog belt would add too much modern looks - wouldn't want it in my T. Better an old technique that needs constant maintenance and works - well - ok, than a modern technique that works perfect without maintenance but looks - ugh - modern
This looks like what I would have liked to build if I had enough money for a 30's V8.. But I'm poor and love my T's ;)
I did take photos, and forgot them!!!!
In the first photo you can see the chain from the cam to the mag.
Being RHD, there was a long linkage from the control rod accross the front of the motor to an arm under the magneto. This was on a rod which ran under the mag mounting plate to the front of the mag. From here another short linkage was connected to the mag, all of which allowed the timing to be adjusted from the steering column.
Just for interest.
Allan from down under.
Great pics Allan. Helps understand what Roger was saying about sprocket size. I'll scout around using Justin's chain size info. PK
So, I assume we are doing a waste spark system with these 1:1 ratios? Why not a 2:1?
The Bosch mag I'm using, an AT4, produces a high tension spark every 180* and must be driven at engine speed, (crankshaft speed) for a four cylinder engine. I just changed the rotation on an AT4 from anti to clockwise rotation for my Case 12-20 crossmotor and found a Bosch service manual just full of great information! I've learned a great deal from this manual. Good stuff. PK
Hal, the sprocket on the camshaft on my motor is larger than that on the magneto. I did not check, but suspect it was 2:1 ratio.
you can see the linkage from the steering column across the front of the motor to the lever under the magneto. The shaft with that lever had another at the back end and a short linkage went to the magneto from there.
Allan from down under.
I'm not too familiar with these mags (Obvious, huh?), but the set up on Allan's is what I would have expected. Kinda like a distributor, driven at 1/2 engine speed, rather than 1:1. I guess the others have internal gearing that puts its "Rotor Button" at 1/2 engine speed?
Ok, I take it 1/2" is the pitch and 1/4" in the inside measurement of the chain. If so, it looks like you have and ANSI sized chain. I attached two Reynolds chain specs for you. The ISO chain would seem to be too wide in the inside of the chain, and the ANSI has two variants.
Obviously the best thing would be to see if the gear has any markings on it and to take measurements of the teeth pitch and width, and then to make sure you have everything matching, but I assume you have done this.
I don't know who in Sweden will carry this chain, but using the common name, you should easily find it. Also, calling around, you may find a company that will sell you exactly the length you need, avoiding having to buy 10 meters or more.
Hope this helps,