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1981 CX100 Breather Box-excess oil blow out

motoguzzian

motoguzzian

Just got it firing!
GT Contributor
Joined
Mar 25, 2012
Messages
10
Greetings!
Ongoing issue prior to replacing top end last month (MG cylinder/piston kits both sides, new valve guides and seats)….
No issue under 3k rpm, but who rides there....its a "bits-a-bike" so mileage on" bottom end" is 45K plus....I'm sure the rings were installed correctly and that each rings seam was installed at 120 degrees from the other. Check for blockage in the drain tube from box to crank. On a 22 mile, conservative run, it puked out 2-3 oz. (best guess...enough to put oil out the vent hose just under the seat). She still put out more oil than the Exon Valdese.

Set up: Old LM 1 breather box with punched out flapper/new "ball" check valve / K&N pods/VG engine/ Mikuni 38s.
So, after reading the Guzziology section on "Breathers" for the thousandth time, I thought I would throw it out to you-all for any suggestions....I am hoping for an experienced explanation and possible solution from the community.....not that Dave Richardson (DR) doesn't go a great job.

I understand the issue of air-volume in the crank case (a 850 breather system for a 949 system), but if the "vent-to-road" tube is coming from the top half of the LM box, and the top of the box sealed from the crank-vent and drain tubes, then all the oil that is venting to the road from the box is coming from the valve cover drains....if I understand DRs diagram....or....are the bottom half and the top half of the LM box connected/sharing the "vent to road" tube? IF that much oil is coming from the valve covers, and all the top-end was done correctly, where is the oil coming from????

Thanks for any suggestions, ideas, words of encouragement, or support.....I still have the 2007 Griso, and the ST1300 to keep out of the cage!
Ian

A First cleaning
 
It takes time for the rings to seat. Which kit did you install? My suggestion is to do a leak down test to see if the rings are seating.
 
Thanks John....will do. The cylinder/piston kits came from MG cycle (Gilardoni set for SP/CX100/G5). As noted, first ride was 22 miles keeping between 3-4.5K RPMs, and to be honest I didn't consider seating (first time doing a top end, didn't think to run it by my tutor in all things mechanical....). Would you suggest taking it out for more road time (higher RPMs maybe) before doing the leak down? If so, what would be good target for miles?
I was dealing with excessive blow-by for a long time, and was putting all the "chips"on the new rings (wasn't really planning on pistons and cyclinders, but when one old piston turned out broken, busted rings and scored cyclinders…..ya gotta do what ya gotta do).
Might be a few days before I can get to the leak-down, so will post results at the end of the week....Ian
 
Will do...Maybe drop out a pint of oil from the sump? I understand that some people ride the CX at a little less than the factory suggested oil level.
 
The engine will seek its' own level. That is it will go down so much then stop. That is the level you should maintain. If you add more it will just blow it out.
 
Hi Ian, you say your breather system includes a "new "ball" check valve." Is your ball check valve a recent reproduction with an internal o-ring seal? I had a similar oil puking problem with my 1974 Eldorado, and found the problem to be the o-ring seal was not properly seated in the groove, and thus the ball was not fully seating. I chased this problem for a while, even installing a catch bottle in the vent line, but once the o-ring was properly seated, the problem was solved - no oil in the catch bottle.
 
Thanks John...
I will double check for proper seating. Took out 10oz of oil but continues to blow. Because it was a problem I was trying to resolve when doing the top-end, so I'm pretty sure I did a pretty thorough check of the valve and lines....but will do again!
Did a compression test....110 psi on both at 5000 feet above sea, so conversion is close to 150 psi at sea level.
Thank goodness I have the Griso!
Ian
 
I don't know if you have solved this. I agree with John that the first thing is to do a leak down and also check how much blow by is happening. The ring orientation axially doesn't really matter - the rings rotate with each revolution. Yes it is good practice when building an engine to space them but debatable whether it can actually has much of an effect during break in. I know a lot of engine builders who don't bother and lots who do.

In my experience Nicasils don't require gentle breaking in - in fact the opposite seems to be true. Nicasils are the best improvement you can make to your bike - your compression numbers seem a bit low to me but I don't know what you put in. I would not assume that the PO did it right and whipping off the cylinders is an hour job at best.

A sump extension if not fitted is also good.

Gutting the breather box is a good move. I would lightly stuff the breather box with stainless steel or brass wool - it will greatly increase the efficiency of the box as an oil-air separator. I would remove the PCV valve altogether as a test and aim it at a catch can. If it stops puking oil either the PCV was too small for the job, stuck closed or in backwards. If it continues puking then either the oil level is too high or your rings aren't sealing.

The Lemans 1 had a very nice 'worn oil ring' gauge - Guzzi directed the blow by at the rear tire. Move pipe and direct it into a suitable catch can. I use an old Brio bottle for italian flavour.
 
Have a leak down test performed. It sounds like you are building up too much crankcase pressure.
I had a CX100 as well, loved it, My Griso now that’s a different story. Get that CX of yours to new engine condition & keep it. Ride it it will be the best Guzzi you may ever own, especially if you buy newer. The Older Guzzi’s would last forever.
 
Just curious, do the valve cover breather lines attach to the front of the cover or the back? They were originally set up to come off of the front of the valve cover, and if they come off of the back, the valve covers have been swapped side to side at some point. We had an 850 LeMans endurance racebike back in the 70's that would puke oil if those lines were vented out the rear of the head. We figured that since there is an incline from front to back of the head, we were getting too much oil towards the rear of the valve galley and it was being pushed out the vents. We swapped the valve covers to get the breather line towards the front of the head and it helped a lot.
 
Sorry about the long delay is reporting back....but it looks like the I have finally put the blow-by issue to rest...I double checked the breather box check valve for proper installation and obstruction (all good, stuffed the lower section of the breather box with a stainless steel mesh (a woven mesh designed for oil separation for tractors...on sale at Tractor Supply!), switched the valve covers so the vent lines are now located in the front...(makes sense if your venting vapor.....), and running about 1/2 qt less than the book.....So far all good...thank you all for the suggestions and help...now if I could get the new Mikuni VM32 carbs dialed in......
 
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