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[Wheaters]

Dai, It appeared to be caused by deformation rather than loss of of material, unlike what usually occurs in cases like this. The surface of the damaged seat was smooth, with a clearly defined ridge where the valve contacted it, looked almost machined.

As I wrote, I had a new valve seat fitted 8,000 miles ago and it’s not recurred since, In fact the tappets haven’t needed any further adjustment. So I’ve no real need for a fuel additive. However I was brought up with 4 stroke grass track racers running on methanol and castor oil so a very small amount* of Castorene might soon occasionally get added to a full tankful, just for the aroma, for old time’s sake.

*I’m aware of the possible consequences (sticky piston rings) of adding castor oil, btw. It would be a very small amount, just to “flavour” the exhaust.

[Daiwiskers]

Wheaters I have to admit that I have used a drop or two of Castrol R in the tank now and again Just for the smell

Asbo 30 had a valve eating it's way into the head sorted by Paul (B. W.)(for the life of me I can't remember which one it was)

If I am planning any long runs involving motorway work I use two stroke mix just a cap full to a full tank

[ChrisD]

Thanks guys - I knew there'd be some useful comments. Of course, you're right, the petrol this bike originally ran on was appallingly low octane and it did OK. Cheers, ChrisD

[Wheaters]

Chris, my bike is an Indian home market one. I don’t know if there’s a critical difference between Indian and UK petrol, or if I was just unlucky and bought a bike with a sub-standard, soft seat. I think probably the latter is true.

The bike had just three thousand miles on it when I bought it but four previous owners. It must have suffered ongoing compression problems from new and the others gave up with it. Certainly the previous owner hadn’t ridden it and he’d apparently been unable to start it, but he was more into cars, he’d taken it in part exchange for a car he’d sold. I serviced the bike when I first bought it and set the valve clearances, it then ran OK. First time I took it out I rode with a bunch of mates and it died on me, the power just faded away to nothing then I couldn’t restart it, no resistance on compression. I reset the tappets at the side of the road and got it going again but the exhaust valve clearance closed up again on the way home. I realised what the problem was when I saw how little adjustment was left on the pushrod.

[ChrisD]

Wheaters - yes, the same issue with mine - and it too was an Indian home market version from 1996. The seat just disappeared next to the valve - a smooth new surface several mm away. I'd never heard of this before. If I had known it was not a UK export model, I wouldn't have worried about it sawfu l;ack of power - instead of spending thousands to make it go like a Redditch one. It could barely make 60mph then - now I chicken out at 80 mph 'cos steering and suspension cannot handle such speed.
I have discovered another issue with the 1951 G2 bike. It looks like someone has dropped the barrel at some point (probably when they smashed off a large piece of the top fin). The barrel had been resleeved with a ~1mm thick sleeve back to standard size and then a chip of the sleeve broken off the base - far from the rings fortunately. Now it is all cleaned (preparatory to rewelding a piece of fin cannibalised from the old Indian barrel). I note the barrel itself is cracked about 4mm up from the base - call for JBWeld to fix the hole. Now I know where the large thin piece of steel (4mmx5mm) that I found in an oilway in the timing chest came from. Ah well, it is keeping me from feeling unwanted during our interminable lockdown (now 7 weeks and counting here in RSA). Cheers, ChrisD