Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A10 Motor mystery

I bought a running A10.After restoring the frame etc.I replaced the motor in the frame without changing the motor at all.Now when I rotate the crank it will only turn about 180 degrees either way and then stops.It is a firm stop not just sticking.What should I look for that is in the way of the rotation.As I said this motor ran when removed from frame.

ATEN -

Does it do that with the primary chain connected to the engine (so that it is also turning the clutch and transmission), or with the primary chain disconnected so that only the engine is turning?

Also, did you happen to replace the spark plugs? Plugs with too long a reach will hit the piston and do just what you're noticing, especially the 180 degree part ...

Lannis

Or a stuck valve.

It sounds to me like you left outthe spacer between the engine and inner primary chain case , or you have possibly installed the wrong hardware at this joint. with the correct hardware , if the spacer is missing it will allow the bolt to contact the flywheel in the crank case causing a very scary clunk and dead stop as you describe, dont wanna disclose how I know this .

FWIW-BONZO

It's what Bonzo says. Don't ask me how I know...

Guy The inner primary,primary chain is not installed I am turning the shaft with a wrench.It does it with sparkplugs in or out.I have to think something is hitting the flywheel but what? thanks for the ideas,any more?

I would also guess that a bolt is touching the flywheel, but since, as I understand you, you don`t have any of the primary chaincase bolts mounted that can`t be the problem. Don`t ask me why that was my first guess.

Take a look at the rocker box, What is happening there when you turn the engine? can some of the pushrods have been misplaced?

The oil pump and it`s drive sprocket can also cause that kind of trouble I guess. Take a look at all the timing gears, any teeth that have fallen off/cracked ?

Which parts have you worked on since the engine was in the frame ?

Question for the group - A couple of posts here have implied that if a valve is in the open position when the piston comes up (either stuck or with the valve train "out of time") that the piston could interfere with the valve and cause this problem.

I've never heard of a pushrod gas engine that had "interfering" valves and pistons before, let alone a 1950s 7.5:1 compression Brit. It'll happen with automotive diesels, or with OHC engines driven by chains or belts which, if they break, your entire engine is hosed, but is it true on an A10?

I woulnd't think so, but I'm open to hearing different.

Lannis

Group NORBSA had it right Stuck Valve.Pulled the rocker covers off and two of the four valves were not moving.I eliminated any possible bottom end causes and concluded it had to be in the valves,it was.Thank you for all the ideas and help. Bill

At least you didn't break a rocker finding out. I hope...