crank vent

[mjean22140]

Hi Guys,

I'm new to this post but have a question that I hope someone can help with. I have a Combat Wombat that I just finished restoring and ran for the first time last year. I had the motor completely rebuilt by Roger Lappiatt about 6 or 7 years ago, maybe longer... but never ran it until last summer. It fired on the first kick an appeared to run fine apart from some needed carb adjustment. I think I have a total of maybe 20-30 minutes run time on it right now. What I'm noticing is that after warming it up and taking a lap or two around my house I'm starting to see a bit of frothy crank oil escaping from the crank breather. My first thought was that I may have over filled the crank a bit so I drained it and refilled it with correct amount as stated in the manual. After running it for a few more minutes and a couple laps I see the same results.

I sent an email to Roger to see if he had any thoughts but never heard back from him.

Does anyone have any thoughts on this? Is this just a possible break-in issue???

Thanks

Mike

[BrianZ]

What brand of oil are you running? Does the level show correct on the dipstick?

Brian

[socalhodaka]

non-detergent oil.

[Bullfrog]

An "in the bike" transmission oil drain and replace calls for 16 oz of new oil since you can't drain all the old oil out. So, if you drained, then added 20 oz -- you ended up with about 4 oz of over-fill.

While you need to keep an ear tuned for symptoms of a leaking crankshaft seal (detonation, accelerating idle, engine "run on" (keeps running for awhile after you turn it off)) - it is quite possible that the following three things are causing your problem:

1. Mid to high rpm before the oil warms up. Cold oil gets thrown up to the base of the transmission vent and then warming air inside the transmission expands and pushes the oil up and out of the vent.
2. Choice of oil. While non-detergent 30 wt is what the Owner's Manual specifies -- you'd be better off with Silkolene or Bel Rey 70 or 80 wt motorcycle transmission oil.
. . . and then (after the drain and refill)
3. Too much oil (possibly).

Items 1 thru 3 will cure themselves by a good warm up and running time. The engine will "eject" enough oil to cure any over-fill. BUT . . . IF . . . there is a crankshaft seal leak, the oil ejection will stop when the engine seizes (not good). No.

Ed

[admin]

Roger really does not do emails. When his wife Nancy checks for him might be once every three weeks. If you need something just give him a call !!
Paul

[mjean22140]

Thanks guys. I’m using Lucas SAE 80W-90 high performance oil and the level looks ok. I haven’t had a chance to run it this season yet but I don’t recall any of the leaking crankshaft symptoms, that you mentioned ED, the last time I did. I’ll make sure I pay attention to it when I finally drag it out of the garage. Hopefully that will be soon.

Thanks Paul. I forgot that bit about Roger and email… It’s been a long time since I last talked with him.

Regards

Mike

[Zyx]

For what it is worth, years ago when racing hare and hound, we frequently encountered deep water. Deep enough to cover the transmission vent. To keep a suddenly chilled case from pulling in water, I used an additional vent. Turns out that the dipstick is the same size and thread as a spark plug. So I gutted a used spark plug, soldered into the top of the metal plug case a short length of metal tube, and used that instead of the dipstick. Attach a length of rubber tube to the stub soldered into the plug, run the tube up under the seat, use an inline fuel filter as a vent filter if worried about dust, and thereafter the transmission pressure is vented through the new vent, not the one on the top of the engine case. The one I made is still on the engine that I raced all those years ago (1973) with no issues, and it never pulled in any water, either.