Questions? Looking for parts? Parts for sale? or just for a chat,

The WD Motorcycle forum

WD Motorcycle forum
Start a New Topic 
Engine oil being forced into primary chain case

I had noticed that my primary chain case had begun to fill up with engine oil. So I decided to drain the primary case completely of oil and then went for a 60 mile ride, not exceeding 45 mph.

On my return I managed to drain about 120 mls (4 fluid ounces) of oil out of the primary case after the ride. I then checked the breather assembly and found it to be completely blocked.

Would a blocked breather be responsible for allowing this amount of oil to be forced out of the crankcase into the primary or should I be looking at a problem inside the engine?

I might add that I also conducted a compression test on the engine and at operating temperature with the throttle wide open on the first kick of the pedal I obtained a reading of 300 kpa (43 psi) and with a second kick the reading went up to 400 kpa (58 psi).

Cheers, Neil

email (option):

Re: Engine oil being forced into primary chain case

If the bike has been left standing for a while, it could have wet sumped (Oil dribbling past the oil pump into the crank case) The level can rise and flow through the drive side main bearings into the primary case.

The first indication would be low oil in the tank. The immediate cure is to take out the drain plug in the sump, and collect the oil in a clean container and return it to the tank. Was there lots of white smoke on start up?

The breather issue needs to be resolved also. Ron

email (option):

Re: Engine oil being forced into primary chain case

As you drained the primary case but had the problem again after 60 miles, wet sumping isn't the cause I suspect..A blocked/non functioning breather will lead to the crank case being pressurised (however good/bad the bore is) and that is probably the cause of the problem...The first step would certainly be to repair the breather and then repeat the test I'd have thought...One problem at a time and all that!!...

Compression readings seem to vary considerably and I don't usually bother with them as a means of diagnosis....If the kickstart will more or less take your weight when the engine is moved onto the compression stroke and the bike is running as expected out on the road it's probably OK...

Have you had this problem previously or has it appeared recently?....Dropping off of compression as a result of wear, by its nature, occurs over extended periods of time/use and isn't a sudden problem generally.. A mechanical failure, the tappets have adjusted themselves (not likely) or the valve lifter not being set correctly (recently) are also possibilities for you to consider if repairing the breather fails to cure the problem....Ian

email (option):

Re: Engine oil being forced into primary chain case

As per Ians reply
Just a note about compression teting
1) no two gauges ever read the same
2) throttle position is not important, but a WOT will take less time
3) compression is a MAXIMUM reading so you keep on kicking till the gauge no longer goes up

BEcause of this for a single cylinder motorcycle you need a screw in type

The most valuable strait compression test readings are the ones done over time and hopefully plotted
On new rings & bores the readings will rise over the first few months as the seal becomes better then plateau for a considerable time followed by a slow decline as the rings start to wear then when the decline curve changes slope & becomes steeper it is time for new rings

All this assumes you are getting a good seal around the rings which for side valves is rarely the case as they tend to errode around the exhaust port

If you want to test perssure, do a leak down tests which will test gaskets, rings & valves

Re: Engine oil being forced into primary chain case


If the engine breather is blocked then the pressure from the descending piston and the oil vapor has to find its way out somehow. The obvious route (it seems to me) would be through the main bearings on the primary side, causing your primary to fill with oil. A clear breather valve will help prevent this.

Others may disagree, but I think I'd try clearing the breather first.

I hope this helps.


email (option):

Re: Engine oil being forced into primary chain case

So the engine breather is blocked and you are wondering why it is pumping oil in to the primary?

What do you think the engine breather is there for?

Nieuwe pagina 1