30-05-2021, 08:09 AM
Hi flywheel1935
I'm in agreement, I can only think of three ways neat petrol can reach the sump:
1 Past a hole/tear in the pump diaphragm
2 Down the inlet valve stems from the inlet manifold
3 Past the pistons/rings
2 and 3 will be aggravated if the mixture is rich (choke for cold start) and if the engine is cold (incomplete evaporation of fuel to vapour). 3 will be aggravated if the rings/bores are new and not bedded in. Once the engine is running and warm then these leakage sources should be very small unless you have a carburation fault causing excessively rich mixture.
I once had an engine with an incorrect compensation jet fitted to the zenith 26VA carb, which gave a very rich mixture at part throttle. Enough over a week or two to cause the oil to thin and smell of petrol due to route 3, but not enough to cause the level to rise on the dipstick.
How much petrol is reaching the sump, and how much cranking without starting has happened ?
I'm in agreement, I can only think of three ways neat petrol can reach the sump:
1 Past a hole/tear in the pump diaphragm
2 Down the inlet valve stems from the inlet manifold
3 Past the pistons/rings
2 and 3 will be aggravated if the mixture is rich (choke for cold start) and if the engine is cold (incomplete evaporation of fuel to vapour). 3 will be aggravated if the rings/bores are new and not bedded in. Once the engine is running and warm then these leakage sources should be very small unless you have a carburation fault causing excessively rich mixture.
I once had an engine with an incorrect compensation jet fitted to the zenith 26VA carb, which gave a very rich mixture at part throttle. Enough over a week or two to cause the oil to thin and smell of petrol due to route 3, but not enough to cause the level to rise on the dipstick.
How much petrol is reaching the sump, and how much cranking without starting has happened ?