Engine oil smells like petrol

Allan.Atherton · Post by **Allan.Atherton** » Sun Jul 20, 2008 3:10 pm

Perhaps you left the petcock open and the gas went through the carbs and into the cylinders. Change the oil and be sure to keep the petcock closed.

EuroIron · Post by **EuroIron** » Mon Jul 21, 2008 4:47 pm

yeah keep the petcock closed and also check to make sure that closed or off really means fuel isn't still flowing

many of those petcocks need recorking and it can be done even if somewhat tedious and painful

anyhow, make sure the valve/petcock is turned off while sitting and make sure when it's off it really is not flowing fuel

not the worlds greatest fuel taps and the float needles and seats in those carbs are pretty third world crude if you ask me

if severe fuel contamination of the oil indeed happened while the engine was running so very rich in operation

it would wash the oil off the walls and wreck your rings and cylinder walls at the least

and it would not be running nice at all

as in you know something would be causing very lumpy/rough running and copious amounts of black exhaust smoke

and that is possible too but you give no indication of any symptoms which would point to rich running conditions, fouling, or running worse hot than cold,. or difficult starting once at temp......

schrader7032 · Post by **schrader7032** » Mon Jul 21, 2008 5:34 pm

Michael said he ran the petcock outlet into a can and there was no leaking or drainage past the closed petcock. Sounds like that's not the problem.

If the petcock is closed at all times when the bike is not running, and it's open (obviously) all times that the bike is running, then the only way for excess gas to get into the oil is from a very poor combustion process. Coupled with bad rings, allowing the combustion gases to pass into the crankcase, contaminating the oil.

Kurt in S.A.

Allan.Atherton · Post by **Allan.Atherton** » Mon Jul 21, 2008 9:05 pm

... check to make sure that closed or off really means fuel isn't still flowing.....
His first post says he closed the petcock and piped it into a can for 2 days, and no gas came through the petcock.

EuroIron · Post by **EuroIron** » Tue Jul 22, 2008 11:36 am

I know but unless the bike has previously set with the petcock not turned off.....

and if it is not clearly exhibiting very noticeable drive-ability symptoms

we have an inexplicable anomaly or perhaps there has been some level of sabotage

Micha · Post by **Micha** » Tue Jul 22, 2008 11:52 pm

Thanks for the help, guys.
Well, I'm starting to suspect the carbs, as they are old and maybe not gas tight. I've changed oil now, and hope to exchange to new carbs the moment I can afford it. I think that after closing the tap, the fuel that still is inside the rubber hose is getting through the filter and down to the carbs, passing the carbs needle and from there into the heads and down the liners. What do you think?
Cheers, Michael.

Allan.Atherton · Post by **Allan.Atherton** » Wed Jul 23, 2008 10:54 am

... suspect the carbs, as they are old and maybe not gas tight.... hope to exchange to new carbs the moment I can afford it. I think that after closing the tap, the fuel that still is inside the rubber hose is getting through the filter and down to the carbs, passing the carbs needle and from there into the heads and down the liners....
I think new carbs will be extremely expensive and an unnecessary waste of money.
Gas that enters the carb must flow through the float chamber. If the float rises and the float needle does not shut off the flow, the gas overflows out of the float chamber onto the ground. I don't think the gas can also get into the intake of the cylinder. Many people have leaky carbs, but nobody finds gas in their oil. I think the gas must pass through a jet to get into the cylinder and into the oil. I just don't think it happens unless perhaps the bike is constantly kick-started without firing, and even then the amount would be insignificant.
There is many a leaky petcock, and many a leaky carb, all putting gas on the ground, but not into the oil sump.
You have tested your petcock, and it is gas-tight.
You have never reported gas overflowing from your carb float chamber, so your float needle also appears gas-tight. But if you want to test it, leave the petcock open overnight and see if gas leaks from the carb. If the float needle leaks, it is only an inconvenience and can usually be fixed with a kit from Bing.
But when Bing sends you anything, there is always included a yellow warning sheet saying the the carburetor itself (i.e. the float needle) is NOT a fuel shut off device, so always turn of the petcock.
Sometimes on a hot engine the gas in the float chamber will expand when stopped, and leak out of the carb. To avoid that, turn the petcock off as you are riding into your driveway and then let the engine idle for a half minute to draw down the level of gas in the float chamber.

EuroIron · Post by **EuroIron** » Wed Jul 23, 2008 3:22 pm

why not simply convert to the later (R69S?) float bowl tops with the seat on the side which also uses viton tipped needles?

should cure what is ailing your ride

EuroIron · Post by **EuroIron** » Wed Jul 23, 2008 3:23 pm

and I think they merely screw in place with no modifications required

Allan.Atherton · Post by **Allan.Atherton** » Wed Jul 23, 2008 5:35 pm

why not simply convert to the later (R69S?) float bowl tops with the seat on the side which also uses viton tipped needles? should cure what is ailing your ride That is called the "lever top conversion", and it appeared on all the late-60s bikes. It is available from the Bing Agency (google that). But it only shuts off the gas from overflowing the float chamber. It prevents dripping carbs.

Micha has not reported dripping carbs. And even if he were to report dripping carbs, that would not put gas in the oil.

I must say that I have not heard of gas in the oil of a BMW, and wonder if Micha is perhaps incorrect about that.

Vintage BMW Motorcycle Owners