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1967 BSA 441 shooting star-lock up rear wheel #783074 08/30/19 6:31 pm
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TBC Offline OP
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We just recently completed a restoration on my girlfriend's late fathers '67 BSA. It took a lot of work to get it back to mostly original shape. On the very first ride we ran into a huge problem that we can not seem to solve. While riding the bike in top gear, at cruising speed (45-50 mph) the rear wheel locks up solid skidding to a stop, almost crashing the rider(GIRLFRIEND). Once the bike stops everything is free wheel again, able to restart and go again like nothing happened. It did it twice in about a 6 mile ride, then we trailered it home. We pulled the transmission apart, everything looked fine there. Wheels, brakes, clutch etc, all fine. I am at a stand still for ideas. Has anyone else came across this problem that can help?

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Re: 1967 BSA 441 shooting star-lock up rear wheel [Re: TBC] #783075 08/30/19 6:50 pm
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quinten Online Happy
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Yes , sounds like piston seizure .

Lugging the bike in 4 gear ...
, bad timing , wrong mixture ... lack of piston clearance .
A lot of things can over heat the piston ,
Causing it to seize onto the cylinder wall .

When the piston cools ... the seizure is released .

What ignition... the 4ca points cam ... run on 12 volts ... was know to cause seizures ... and worse.
.

Re: 1967 BSA 441 shooting star-lock up rear wheel [Re: TBC] #783076 08/30/19 6:55 pm
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Allan Gill Online Happy
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Unless your pulling the clutch in as soon as this happens. It’s more probable that the engine is getting too hot and nipping up. A 4 corner seizure can be common on a new build, especially if.

The engine is lugged in too high a gear
Air leaks at the carb causing the engine to get too hot.
Piston to cylinder clearance is too small (general rule is 0.0015” per inch of bore and your running a 3.5” piston. So you want a minimum of 0.005” clearance.

Or the carb is completely wrong for the bike and denning very lean (had 2 strokes do this)

As a safety tip, if the back wheel does lock up at speed and your on a straight, don’t apply the brakes, pull the clutch in. Most importantly continue to steer the bike as normal. It will eventually stop!

The back end may squirm/weave a little on the tarmac but keep your head together and you’ll be ok.

Last edited by Allan Gill; 09/05/19 9:03 pm.

beerchug
Re: 1967 BSA 441 shooting star-lock up rear wheel [Re: Allan Gill] #783519 09/05/19 2:54 pm
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thank you for the ideas, very much appreciated

We did rebuild the motor. New piston and rings. We had to get a new jug from overseas. The old one was at max bore. It took like five months to get it(they had to make it).

The posts here make sense. It has the original AMAL carb. but, we are also having issues with the fiberglass tank shedding materials clogging up the in-line fuel filters. So, possibly while riding the filters are restricting the flow. I am in the process of cleaning the tank and using caswell to reline it. Is that the best stuff to use? I know not to use ethanol gas to help 'slow' the erosion.

After fixing the tank, and checking to make sure it isn't lean. Do you think riding it at slightly higher rpm, no lugging for a while would help break the motor in?

Re: 1967 BSA 441 shooting star-lock up rear wheel [Re: TBC] #783523 09/05/19 3:50 pm
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kommando Online Content
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The jets in the carb will be filling up with resin so they need cleaning, the pilot needs drilling out with a #78 drill, also you need to check the inlet valve for resin too, if its there then it may be in the valve guide.

After that and the tank being fixed then how long is a piece of string ref bedding in, you have to try in case it can be bedded in but watch for blue smoke in the exhaust and keep the revs up.

Re: 1967 BSA 441 shooting star-lock up rear wheel [Re: TBC] #783528 09/05/19 5:53 pm
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I'd pull the barrel and hone it, recheck ring end gap. If you think about it, not all that big a job. If it's too tight, riding around gently isn't going to do it in my experience.


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