Fuel Draining Into Crankcases?

  • Thread starter Thread starter Harry Lime
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Harry Lime

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Strange days at Chateau Lime this morning.

Drained the oil off the 3C this morning. Hmm. Rather a lot of oil!! About 4 litres. Certainly more than the 3 litres I'd put in there and certainly looking a bit thin!

So I'm guessing that at some point about a litre or so of fuel has got into the crankcases. Not good.

Fuel taps were off and are sealing OK. Still gas in the tank too.

What baffles me is how this happened? The bike hasn't been ridden for a few months (been having fun with the SF1). But as I said, the taps were off and fine.

So I'm guessing this happened when I was last out on the bike.

The plan is to drain the engine and filters thoroughly and do a quick fill with oil, run, then another rapid change of oil.

But has anyone got any idea about the causes? Float height? And how can I check / rectify the problem?

Help and advice appreciated

H.

 
Harry,

This sort of thing only happens when the bike isn't used.  Definitely something leaking, either taps, float valve or both.  Probably both...

Incorrect float heights will cause an over-rich mixture, I'm certain you would have noticed that when the bike last ran. ;)  If you have neat fuel getting into the crankcase, the engine will have a hard time to run at all.  Should be permanently belching plumes of black smoke! :o

At a standstill, even too high float settings should cut off the fuel supply.  Taps likewise.  An ever-so-slow leak at either point will fill the carbs, and due to the rather hefty downdraught angle, it will over-flow (more like seeping actually) into the inlet port, past the valve and piston rings and eventually into the sump.

Once had a triple in the shop with about 20 litres of "oil" in the cases, guy had filled up to prevent the tank rusting during lay-up, over winter the entire contents had seeped past taps, float valves, etc.

piet
 
1000/3C_Stefan said:
Rich carburation combined with rather short riding trips could have caused that, Harry. I have observed it relatively often on cars of old ladies which drive them solely within the city limits, usually only for a few hundert meters of total driving distance. Always the same, level on the dipstick over the top and the oil running like water. Checking mixture screws and float height settings might be a good idea.
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So have I Stefan.

But when asked when they return the choke knob, I always got a blank stare and "Choke?  What's that?" (quite few years ago, lots of similar problems with automatic chokes on Fords in particular)  Modern fuel management systems very rarely pose these problems.

Quite sure that does not apply to Harry... :D

piet
 
OK. That makes sense. I've only owned the bike about 9 months. When I got it, I checked the oil level (and appearance - looked new-ish).

The bike was running as rich as Hell and hunting furiously when I first got it. I don't know how the DPO rode it like that (if he did). I've since backed off the jets (sizes are in my notes), down to standard pilots and mains for a 4C equipped 3C and the bike is a lot happier. This process involved changing the jets and mixture screws and doing quite a lots of short runs (say about 20km). So I'm guessing the fuel draining happened during this period as I jetting down from the original (huge) jets in stages.

I then put the bike away for a few months as things (like April May and June in the UK) were not suitable for motorcycle activities.

So I'm guessing one or the other, or maybe both, caused the problem.

I'll also purchase another set of fuel taps from Phil as the left hand one is old and may be leaking a little. The right hand one I replaced when I got the bike.

Thanks guys.

H.
 
just  a thought is there  a remote chance petrol leaking into the oil may lead to a crank case explosion ?    BIG "T"
 
i think it is known as "hydraulicing" (sp?) isn't it? If the crankcase is full of fluid, the piston has no where to go when you start the bike up. Remember the Laverda has a very strong starter motor, and if you crank the engine over with a full crankcase and if the engine fires you can end up with a bent rod or twisted crankshaft.
Dennis
 
Hydraulicing is when the petrol is on top of the piston and has no where to go,it would be very unlikely to bend rods if the petrol was in the crankcases.
Neale
 
nealebms said:
Hydraulicing is when the petrol is on top of the piston and has no where to go,it would be very unlikely to bend rods if the petrol was in the crankcases.
Neale
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... and after the conrod has been bent it doesn't take overly before things go horribly wrong.  :(

In my case is was 50 miles later that the conrod snapped and punched a hole out the front of the crankcases.  :'( :'(
 
It only takes one time forgetting to turns the petcocks off when parking.. usually after a lager or two. A few days later your oil level is up a quart..hardly enough fuel to miss seeing in the fuel tank. Not good for your favorite 20w50.

Probably just jetted too rich though and now corrected..
 
Leaving the petcocks open shouldn't cause a problem. If it does there's a problem which needs attention.

Leaky carbs can cause serious problems as outlined in the various posts above. One possible diagnosis to Harry's problem [as suggested by Piet] would be a sticking needle jet allowing fuel into the cylinder and its leaking down past the rings into the sump. The first job is to isolate which carb is causing the problem and the easiest way to do this is remove the bank of carbs and set them up on the bench at the same angle as they sit on the bike. Connect a fuel supply and then wait and see if any fuel starts dripping from the throat of one of the carbs. Easy enough to sort out once you know the source of the problem.
 
OneThinBloke said:
nealebms said:
Hydraulicing is when the petrol is on top of the piston and has no where to go,it would be very unlikely to bend rods if the petrol was in the crankcases.
Neale
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... and after the conrod has been bent it doesn't take overly before things go horribly wrong.   :(

In my case is was 50 miles later that the conrod snapped and punched a hole out the front of the crankcases.  :'( :'(
Click to expand...

and in my case it was the perfect excuse to fit brand new shiny Carillo rods with new bearings into my high comp "1200" RGS......... :D

Paul LeClair
 
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