BSA 420. My first engine!

Hi, this is my first post so forgive me if the pics don't appear.

I saw this engine on ebay for what I considered a very reasonable price, put a bid on it, was outbid, raised my limit and hey presto won it for just over twenty pounds.

It's my first engine so it will be a learning process.




First I took the spark plug out and poured a drop of petrol in and left overnight.  The morning after I tried turning the flywheel by hand and it moved nicely without any nasty noises. Next I removed the cowl and head, bore looks passable valves are moving, put the head back on and tried turning over to see if ther was a spark with the spark plug against the engine.  There is no spark so next job is to open the magneto and have a poke around. I'm a bit nervous about this as I've never seen a magneto.  Doing some research on 'tinternet and then will post further with my findings.

Oily Fingers crossed, Simon

Hopefully it will be just dirty points in the magneto.

Neat looking unit hopefully easily sorted!

Alan

Looks like you got a bargain there. It appears to have a reduction 'box on it, now you just need something to drive with it...

Hi Simon and a very warm welcome to the forum. Good luck with your first project - plenty of knowledgeable and helpful members here.
First off, I'd suggest you invest in a cheap digital multimeter to check magneto HT winding resistance.

PM me with email address if you need a copy of Service Sheets.

Robostar5 was right, I gave the point surfaces a light rub with wet and dry paper, put the magneto cover back on and hey presto I have a nice strong blue spark at the plug.

The next job is to get some fuel line and rig up a temp petrol tank.

Someone pointed out that the engine has a reduction gear box fitted and when I looked closer near the output pulley there is a casting with 2-1 stamped on it.  Just wondering with a belt drive to whatever you are running why go to the expense of reducing the drive speed with gears. Why wasn't it just done with the pulley sizes and belt.

Thanks all Simon.

a 2:1 ratio could involve several pulleys and belts particularly with a high reving engine like yours and a reduction box saves a lot of space and increases the torque on the final drive.
Maryalice

Looking good, I’m not sure that when you get it running wether that bench will stand up to it though, mines on a metal stand/trolly and even then it moves about a fair bit.

Finally found the other topic - maybe you two should get in touch - if you haven't done already.

https://ukengineforum.forumotion.com/t10580-bsa-engine-number-info