My XL2 chainsaw needs caps for fuel and bar oil. I have found two caps that fit but am not sure if the caps should be vented. Noticed that bar oil enters carburetor unless oil cap is loosened. Should caps be vented?

 

The fuel cap is a little more obvious vent. The oil chamber may have a little different way of venting the oil reservoir, but both reservoirs have to have some way of getting the air in to allow the fluids out.

I don't know of any way for the bar oil to get into the carburetor, though, unless something is cracked/broken.

 

Bar oil reservoir has two lines going to it. I think air enters the oil tank from one of the lines and pushes the oil into the other line where it enters the engine. There is a third line close to the two above that goes from one part of the engine to the carburettor. Fuel tank has its own line and must be vented to allow air to replace used fuel else fuel flow is hampered.

 

The fuel tank is likely vented through the cap. I'll have to look at a diagram on that one to sort out the two lines for the bar oil. If you have one of those going back to the carb and the oil goes into the carb through that line, then there would have to be a check valve malfunctioning that allows the oil to go back up the vent tube.

Editing this: A lot of chain oil setups have a pump driven off a spiral gear on the crankshaft.

I suspect that oil pump is a crankcase pulse driven affair with the diaphragm in the carburetor. It shouldn't allow a backflow of bar oil into the carb. There must be a problem with that part of the carb. It may be something a kit would fix pretty cheap.

Just pressurizing the oil reservoir gets oil onto the bar, but the overrun would present a problem. If pressurizing the chamber was part of the design, then you wouldn't have a vented cap. If that system is set up to move oil onto the bar in a metered way (which it should be), then you would need a vented cap.

 

"I suspect that oil pump is a crankcase pulse driven affair with the diaphragm in the carburetor."

The diaphragm is on the side of the crankcase under a flange held in place by 4 screws. Only the line goes from the crankcase to the carburettor.

Want me to photograph it and post a picture?

One other thing I noticed is that if you loosen the oil reservoir cap, the idle speed of the engine changes very noticeably.

 

When you get the rpm change, that says vacuum leak. The diaphragm is either leaking or ruptured.

 

In looking at another IPL for that saw it looks like:

The line you're describing as going to the carb would be the source line for pressurizing the oil tank. It should only feed air one way, controlled by a checking device, and driven by the crankcase pulse diaphragm assembly you're describing on the crankcase.

That setup provides the oil feed going to the bar/chain. It also has some checking and metering devices in the way of a plunger and ball check. I'm not sure what moves the plunger to allow the metered flow of oil. The ball check would shut it off.

 

I used the saw a while today. The chain temperature was only tepid. The chain is getting oil but it does not sling it off the chain when I position it near the ground and rev the engine. However, when I remove the bar and chain, I can see where oil has come out of the hole on the crankcase side of the bar and drips down to get on the chain. I am using some extra transmission fluid as the bar lubricant. The diaphragm looks ok. Earlier today I removed the cover that holds it and a spring located between the diaphragm and the cover. The diaphragm has a small rod attached to it that enters the crankcase. Unfortunately I could not completely remove it because it does not clear the centrifugal clutch. I cannot remove the clutch because I cannot get the retainer clip off without damaging the clip. But the diaphragm looked OK as best I could discern.

 

I would be careful using transmission fluid where it is not intended. By design tranny fluid is highly detergent and acidic, and not compatible with most rubbers, seals and gaskets.

 

Try doing the same thing close to a lightly colored wood and see if you notice any oil coming off. Even the slightest should be all that is needed. The oiler is only intended to lubricate the chain in the track of and the bar, not the teeth of the chain cutting the wood.

 

I'll remove the tranny fluid and replace with bar oil or straight 30 weight. Thanks.

 

Usually the bar oil is fed through a hole on the side of the bar to get in the chain guide. From there it pretty well goes everywhere it's needed.

The whole chain oil setup is unusual from everything I've seen with the pressurizing the oil tank, etc. Apparently the tank air pump is mechanically driven with the rod to the diaphragm. It must have been a good idea, though or they wouldn't have done it.