August 2025
1969 BSA Rocket 3 750
The owner of this bike queried a member of the local BSA owners club regarding having some work done, and wanted to know who to entrust it to. My name came up, having recently performed a few minor surgeries on that man's Rocket 3 as well.
Six or seven months later and having completed the bike rebuild that had taken that long and had now vacated the required workspace, he brought the bike around today. Very pleasingly he rode it here, so I heard it running and have a number of suspicions about the reported ills already.
Aside from that, this bike is in equally fabulous condition to that one, and it makes it a pleasure to assist in making them go as well as they look.
Of course I soon made it look a lot worse.
Having given the head and barrels close scrutiny I found a number of loose items, like rocker box screws, which made me think that maybe things had loosened off since the last rebuild. As I was going to check the head bolt tensions I started there. Sure enough, the bolts all tightened singificantly more than I loosened them off, and this is a legacy of non solid rocker box base gaskets. Such are fitted to this engine, but they look quite substantial and have no external signs of deterioration, so may prove to be viable despite the fact.
The spark plugs were all quite sooty, and checking the carb pilot screws showed that they were set somewhat richer than one would expect. As the idle had been off when the bike arrived, it may prove to be mostly solved with a careful tune.
During the course of moving things around to retorque the head, one of the spark plug caps fell off, and as they screw a long way onto the lead I figure it has been loose for a while. Checking the coil end of the leads there was a loose terminal on the top coil, so we have a number of reasons why it might have been off song.
Another issue was the throttle linkage, which was missing a spacer that should reside within the return spring. Removing the spring tension showed that there are no internal springs inside the carbs, so it seemed that I needed a spacer of some sort to improve the throttle action.
I found some small bore fuel line which had the correct dimensions, so that got fitted inside the spring, which also got reshaped at the operating arm end to make it line up in a more agreeable fashion. I had a lighter weight spring, but in the absence of internal springs this stronger version is necessary.
The oil lines and spark plug leads were not happy with each others presence, and also obstructing the choke cables, so I rearranged them all to cohabit happily. It will also assist access to the inlet rocker box to check the valve clearances, which should have closed up a bit due to the extra tightening of the head bolts.
