A couple of weeks ago, after two years work and a lot of cash spent, I finally finished building my beautiful BSA Rocket Gold Star replica (see pic).
She started first time, and sounded great.
Given that I hadn’t yet got her registered, all I could do was ride her up and down my (private) road to get the bugs ironed out. So each day for the following week, you’d find me, chuffed to bits, riding to and fro, until one morning she wouldn’t start and was spitting back through the carb. I also noticed that the compression was nowhere near what it was when I first started the engine.
I went through all the normal checks – fuel, spark, plugs etc and everything was OK, but when I came to check the compression, there wasn’t any on the left-hand pot.
So, off with the rocker covers to make sure the valve clearances hadn’t closed, only to find that as I turned the engine over on the kick start, only the exhaust rockers moved! The inlet rockers just stayed where they were!
At this point I decided to take the bike back to the guy who built most of the engine for me for him to diagnose the problem.
After taking the rocker box and head off, he found that both inlet valves were stuck fast in the guides, and that there was a hard, sticky residue on the top of the guides (see pic).
On top of that, both inlet pushrods were badly bent (see pic).
After some cogitating, he realised that the Petseal sealant that had been used when the petrol tank had been restored was being dissolved by the petrol – now known as the ethanol problem. So the fluid reaching the carbs was a very sticky solution of petrol and Petseal, which had built up on the valve stems and set hard. Finally, enough had been deposited to cause the valves to stick, with one partly open, bending both pushrods.
In addition, the back of the inlet valve heads and the inlet ports were coated with the stuff and the carburettor completely gunged up.
After an awful lot of work including using strong solvents to remove the deposits from the valves and ports, reaming the guides to get rid of the stuff from there, stripping and cleaning the carb, fuel lines and filters, removing the rest of the Petseal from the tank, fitting 4 new pushrods, reassembling the head and putting everything back together again, the bike is now back to first class running order.
So my advice to anyone with a bike that has a tank that has previously been sealed with Petseal is DON’T START THE ENGINE until you’ve removed all of the Petseal from the tank. Chris Williams at Autocycle Engineering can provide a solvent to remove it. If you still need to seal the tank, Tank Care Products (
http://www.tankcareproducts.co.uk) claim to have an ethanol resistant sealant, although I cannot verify that – you’ll have to make your own mind up.
I hope that my experience will save many of you similar or even worse problems.
Alan
