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B Rapide venting oil mist at hi speed

craig

Well Known and Active Forum Website User
VOC Member
I have a B Rapide that is venting oil out the cap hole at hi speeds, 70+mph.Is this common?
I have only the standard, timed case vent with the rubber vent tube tucked in the right stand plate.
This standard vent seems to work well with no or little oil drip.
I have seen a oil neck baffle plate fitted to Cary's early B Rapide.
What is the experience of this group?
Thanks Craig
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stumpy lord

Well Known and Active Forum Website User
VOC Member
This is a well known fault if you are running a two speed oil pump, the answer is to either change to a single speed pump, or fit a deflection plate in the filler neck.

stumpy lord
 

davidd

Well Known and Active Forum Website User
VOC Member
OilSplashguard03.JPG


Don Alexander used to tell the story of his first race on a Parkin. On the first lap he tucked in for the straight putting his chin on the tank and a great spurt of oil came from the oil cap vent hole. He had to continue the entire race with blurred vision.

It is difficult to lose the one I made and it will not fall in the tank like the first one I used.

David
 

A_HRD

Well Known and Active Forum Website User
VOC Member
Craig,

On the std timed breather, check your breather tube is not blocked or even partially blocked for some reason. This will cause all manner of oil pressurising symptoms - including oil-loss through the cap when riding hot and fast. Are you sure its properly timed?

Peter B
Bristol, UK.
WANTED: Series 'A' Front Frame.
 

greg brillus

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VOC Member
They will also do this at elevated speeds if the tank/chain oiler is blanked off. The tiny hole in the oil tank cap is too small to vent the amount of return oil/air volume. If it is a genuine B UFM then just rout the tank/chain breather outlet near the rear axle with a piece of 3/8 diameter flexible hose. Cheers.......Greg.
 

craig

Well Known and Active Forum Website User
VOC Member
Thanks to all on this, Stumpy it is a stock oil pump, David your photo is golden thank you, Merc I don't know where the screw would go, Peter the standard breather tube is working fine, Greg the chain oiler tube is plugged off at tank 1/4 bsp.
I rubber banded a folded paper towel over the cap and at speed the venting was much less........so I think it is combination of too much oil in the neck from pump splashing at the cap, and a low pressure outside caused by 70+ speed.
I thought about a motocross type tubing vent added to cap and tubed elsewhere. But if you look at David's photo....it all becomes clear.
I am pretty sure a "C" oil pump/tank will do same at high speeds.
Thanks to all, you are all a treasure.
Cheers
Craig
 

davidd

Well Known and Active Forum Website User
VOC Member
I think, as you do, that there is just too much oil splashing around the cap vent at the higher revs. I use a standard oil pump, but I believe there is a point where the sluggish oil stream becomes a jet, well, relatively speaking, and much of the oil is splashing upwards. I wanted it to flow down as much as possible.

David
 

greg brillus

Well Known and Active Forum Website User
VOC Member
Craig you said your chain oiler is blocked off.....in this condition the only way the tank can breath is via the tiny hole in the cap. Some will disagree, but that hole will struggle at elevated speeds to vent the tank properly, causing other oil leakage issues else ware. Take my advice and vent it to the rear axle area where any lost oil will do no harm...you can even put a "T" piece in and plumb it neatly into your engine breather, so as only one line is out the back.....use a minimum of 3/8 or 10 mm bore hose from the "T" to the rear. Try this.....put the cap chrome side to your lips and try blowing through it.....You will see my point, so the engine/tank has far more capacity returning to the tank than you can blow through......think about what is going on.. Cheers ...Greg.
 
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