The crank oil seals perish over time. On the right hand side that means it sucks in gearbox oil into the crankcase and either burns it off (white smoke from exhaust) or spews it out if the combustion isn't too good. The combustion won't be great if the seals are in poor condition as the engine will be sucking in extra air as well as oil, so the fuel mixture will be incorrect.
You can see this on my bike here. I didn't overhaul the engine at first, just got the bike back on the road and got an MOT for it (roadworthiness test). This was its first outing, to the test centre. You can see the excess white smoke on the right hand side but it passed the test.
That means an engine strip down and a crank overhaul. I'm guessing you are not set up to do that yourself, as the crank has to be pressed apart and rebuilt on a jig, so it needs to go to a specialist. The tough bit is finding some of the oil seals, you have to dig around a bit and keep searching, unless you get lucky.
No i will call around and see if I can find a dealer that will do the work. Do you know how many seals it takes? I have found some on line, but looking at some videos it looks like several? Cant find a good video though. Thanks for your help! Kim
If you have a look on the t20 site, t20suzuki.com, under "restoration" you will see pictures including the crank. There are 4 seals. From memory the two centres are the same and the left and rights are both different. So three sizes.
I can't think how there would be back pressure that would blow the cap off
Does it happen immediately? Just wondering if it happens later, when the engine has been running, if heat from the engine is warming the tank enough to cause a bit of pressure in the tank.
Is the gas cap the simple rubber bung one that just pushes in? If so, you can get it to fit by soaking the rubber in petrol overnight. I thought I actually had the wrong cap on mine, or I was missing an insert in the filler neck, it was rattling around so loosely. After 24 hours in a bowl of petrol (might have been longer, I don't recall exactly) it had swelled so much it needed a real push to get it in again. A year or so later and its still good.