Cant Believe This

[Phil C]

Good to be back on the board after a long break. The T500 has been second priority to a very demanding job but I managed to grab some time to work on her for a couple weekends.

The bike is a 74L T500 cafe racer with a fully re-built mildly tuned motor with Swarbricks spannies .Its been on the road a few times but always made a lot of smoke from starting. The bike had been standing for 18 months so I drained the transmission oil and found something really strange. The oil stank of fuel and was very thin. I concluded that a lot of fuel had been pouring into the engine due to a sticky carb float valve. I took both carbs off the motor and checked the float valves. They worked without leaking???

There was also a total about 75ml of fuel/oil that drained out of the crankcase. Similar amounts in each C/Case chamber.

Motor starts and runs fine after crankcase was drained with much less smoke.

How did the fuel get into the transmission oil? Did the gasolene do any damage to the seals?

I am totally stumped. Any advice greatly received. Phil C

[dinogt]

fuel is going thrugh the o ring that I speak about, just beetwin the 2 crankcases.

[Craig380]

How did the fuel get into the transmission oil? Did the gasolene do any damage to the seals?

I am totally stumped. Any advice greatly received. Phil C

Hi, the fuel shouldn't damage the seals at all, they're designed to run in a rich fuel / oil mix. The excess fuel has just seeped past the seals over time because it's very light and thin.

One of the float valves may have had a tiny bit of crud on it that was allowing fuel to pass, but the quantity of fuel probably wasn't enough to completely flood the motor. When you removed the carbs, the crud could have been dislodged. If the valves seal OK when you test them, then no worries.

Hopefully it's all done a good job of keeping the crank seals wet Just keep an eye on the smoke and tranny oil levels on your first few runs. Good luck.

[Phil C]

Thanks guys for the advice.The crank was re-built withall new parts apart from the main bearings. I took great care in putting the motor back and checked that the two case halves were properly mated. Took my time but was not rewarded with a nice oil-tight motor. I am not goping to do anything on impulse but I will check out the carbs again for sticky floats.

Cheers one again for the support!

I know this bike would not be around if this forum did not exist!

Phil C

(Hope you guys are having a play with the CDI that I reverse -engineered. Its almost a straight copy of the original design and should be reliable if the componenets dont rattle around )

[Phil C]

I gave the job to Chris Applebee Engineering.The first attempt was a joke so they had take it back and re-do it.

I am quite a good mechanical fitter and finally got Mr Applebee himself to build it after complaining a lot. He was surprised to see that the seals were compleetely wrecked on the first attempt and looked ike they had been installed with a sledge hammer. Obviously gave the job to an untrained guy.

The crank was visibly very much better the second time around and it ran freely when the cases were torqued down (which was not the case on the 1st attempt.

Your Comments Pedro?

[rbond]

Phil, great to have you back on the board!! Your CDI is still working great on my bike. I have gotten the cost down to about $20.00 USD. It sounds though that the middle seals or the right one is letting tranny oil into the engine to smoke that much and at the same time allow fuel to get into the tranny.. If it is smoking the same on both cylinders, I would suspect both center seals, a common source for both.? You may need to get the crank resealed again somewhere else to fix that problem. Probably just some trash in the carbs or possibly the needle tip has a groove that is slowly leaking. I have seen this on a lot of motors that especially ran rich, two and four stroke. One of my other jobs is small engine repair (30 years) so I have seen almost everything