I would like to hear from people who have tried different ways to vent their gearbox.  I know Jan has used a few different designs in recent years and it would be helpful to hear from people which ones worked best for them.  

I see the new gearboxes have an oil separator ports on them and that may work well.   

Also, do most find that 8oz of 75w mobil one full synthetic is working well?    Any issues with foaming at high RPM?

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Add as much oil as the system will accept.  Usually 12oz is good.  Drain and replace often to keep a close view of the condition.  

Tie an old sock around the vent until everything has settled down and you are familiar with the venting.  


Thanks.   I have  noticed over recent years of different venting routes on the gear boxes.    Can  you share what you have learned.   How important is it to vent both of the holes on the upper face of the GB?   Is is always best to vent the one at the top, or will one or two of the ones on upper face suffice?    

I only have a few hours on mine and I have experience some slight overflowing of the 75w mobile one synthetic, but I think this will be manageable with a few minor changes in the vent line routing.

P.S.   Are you OK with clear polyurathane tubing?   (Not PVC).

I hope other builders jump in here and comment too.  We are here to share ideas and experiences and help each other out...


(move to bottom of page.)

We have only done a few short test runs. With that in mind, here's some photos showing what we have observed.

This photo shows how our system is set up.

Here's a photo after adding 16 fluid ounces of 75W-90.
Here are three photos of what appears to be some aeration after a short test run:
Contacted Jan and he said it's not a problem.

More photos here ––> https://www.facebook.com/Experimental750ES/posts/501307906916339

Sam, I appreciate you posting the info and pics. I only have a few hours on my gearbox too.

Is your oil level about 2" above the bottom Port while cold and at rest? Jan's been very helpful.

I'll try to post a pic of my current vent set up. I may have to switch to a larger reservoir. The small one in my pics is actually a Yamaha mater brake reservoir I had, and at high RPM it gets filled. And I do not think I have too much oil in the GB...Charlie

Picture of my gearbox and current venting solution....


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