I was changing the oils in my 2005 4RT today. I found that the engine had over 900 cc of oil in it and the gearbox had about 5 cc. I don't think this is a good thing. How did all the gearbox oil get over to the engine? I found an earlier post about engine oil going into the gearbox due to a pinched breather tube. All my breather hoses are open. I put 540 cc in the gearbox and left the engine cover off to see if any gearbox oil is going to run through to the engine overnight. Does anybody have any advice or opinions?

Yeah, had that situation on my previous '05 and my friends '06. The problem was the oil seal between the gearbox/clutch and the engine. Change the seals and you will have it sorted. ps if you run all the std breather hoses you will more than likely find a residue of oil in the air box ?

Yes, I found oil in the airbox after the first oil change. I must have over filled the engine at the time. Then, it happened again after the gearbox drained into the engine.

Yep - sounds like the exact same thing we had. The oil seals sorted our bikes out and the problem went away. At the time though no-one had actually seen this problem either as most answers came back that the engine oil was over filled - trouble was we had changed the oil a couple of trials before the oil in the air box appeared.

I let it sit for 24 hours with a full gearbox and no oil leaked into the engine.

Changing out that seal is at the edge of my knowledge, skills, and collection of special tools. I think I'll finish the oil/filter change and carefully avoid overfilling. I'll check the dipstick frequently during rides. If it starts sucking gearbox oil again, I'll contact my dealer and let him do the dirty work. Thanks.

How did it go ? did you get to the bottom of it ?

Yeah, had that situation on my previous '05 and my friends '06. The problem was the oil seal between the gearbox/clutch and the engine. Change the seals and you will have it sorted. ps if you run all the std breather hoses you will more than likely find a residue of oil in the air box ?

Which seal (Partnumber) must be changed ??

Seal clutch / Gearbox

Update: I added oil very carefully until I reached the upper level with the stick screwed in, which was a total of 440 cc (oil had been drained and filter changed).

I have now ridden the bike several times and used one tank of gas. So far, the engine oil level has not changed. Replacement of seals has been postponed until more exciting oil things happen.

Couple of points/questions

I thought oil level should be checked with out screwing in the dipstick - is this right or wrong

My second hand 4rt has crankcase breather running to atmosphere which seems to be a common mod. Is this true and does it help avoid the seal issue. Beter crankcase breating???

Couple of points/questions

I thought oil level should be checked with out screwing in the dipstick - is this right or wrong

My second hand 4rt has crankcase breather running to atmosphere which seems to be a common mod. Is this true and does it help avoid the seal issue. Beter crankcase breating???

The manual says without screwing in the dipstick, but I recall that ferret flasher suggested that the full mark when screwed in was what he used.

In regard to breather venting to atmosphere, I reckon there is a big problem with this in allowing contamination into the crankcase. Crankcase pressure is not positive all the time and the idea of terminating the breather in the airbox on the engine side is that only filtered air is drawn back into the motor.

Some other motors use a pcv valve to prevent back flow into the motor others use a breather filter most does as Montesa does in venting to the filtered side of the airbox.

If you think about it the airbox has a small (if the filter is clean!) negative pressure on the engine side and therefore probably breathes slightly better than to atmosphere. If you do choose to vent to atmosphere don't forget to plug the entry into the airbox otherwise you will draw crap into the motor at both ends!

Edited March 3, 200719 yr by oz thumper

Not sure about the dip stick idea as this means running less oil than recomended.

Breather point is very valid, why do people mod from the standard set up????. Not seen much discusion on this.

Hopkins..... bet you feel a right one now that you realise you were draining the wrong oil .. ....... it happened to me one sunday morning, rushing around trying to change the oil befor a trial .... felt a right noob when i realised what was going on ..

the measurement is dip screwed in .... checked wit sandifords

Edited March 5, 200719 yr by daggs888

Now i am confused. just checked in my 4rt 07 manual it says to check oil level without screwing in the dip stick???do sandifords mechanics recommend something else??

Surely the nice folks at montesa know how to measure the oil (in manual) , though you are a special chap paul...... or get a beta and you get a sight glass in the gearbox.

My shop manual and these postings disagree on whether the stick is screwed in or not. However, the manual says that an oil and filter change require 440 cc to replenish the engine oil. On my bike, 440 cc makes the level read on the upper mark with the stick screwed in. I think my problem started on my first oil change when I kept adding oil until the level reached the upper mark with the stick out and I hadn't measured the total added. It's all getting very fuzzy, if not fussy!