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ET: Engine (Twin) Oil Leak

nigsey

Well Known and Active Website User
VOC Member
I appear to have an oil leak in the crankcase of my C twin which I think may have been caused by the main drive chain rubbing on the casing probably due to a slack chain. If that if the case I’m gutted because I’ve only had the bike a short while. Anyone else had experience of this and the problems associated with repairing it please?
 

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vibrac

Well Known and Active Website User
VOC Member
If youb fit a D cap I always found you should pop a plug in the original breather and fit a small PCV valve in the up pipe from the cap
 

Cyborg

Well Known and Active Website User
VOC Member
Personally I wouldn’t fit a D cap on the front head and block off the timed breather until I knew for sure what the front head looked like. Without removing the front exhaust rocker, you don’t know what sort of restriction is between the head and rocker bearing. It’s a bit of a convoluted path for pressure to get from the crankcase to the inspection cap to start with, so could make things worse without some minor surgery.
 

Bill Thomas

Well Known and Active Website User
VOC Member
You have lost me again Cy',
Who the hell is Hugh Latimer,
I have this on both my Twins for years, Some don't like the look but I have always done things different.
 

Cyborg

Well Known and Active Website User
VOC Member
He was burned at the stake for wandering off the beaten path... similar to you and your modifications. If the rivet counters do burn you at the stake... being the owner of a Vincent powered Honda, they probably use me and my blasphemous abomination as kindling.
 

oexing

Well Known and Active Website User
VOC Member
Compliments, Norman, for remembering my idea, I drilled from chain case into the gearbox filler tube, just to ventilate the primary case via the gearbox vent. It should do I hope, without filling up the gearbox with primary oil, maybe I fit sort of shield around that drilling, but I will try without this first. Certainly you´d have to get the engine breathing right before thinking about that idea of chain case venting. For this I packed a real seal between the drive side main bearings, no scroll any more. A steel ball type one way valve seems too massive to me for engine breather, better get a reed type valve - but check it for minimal contacts around the reed else it will stick a lot with any oil film in there. I did some with a feeler gauge blade and placed at the end of a hose high up like under the seat. So any minmal oil up there will drain down before exiting to free air through the breather - worked on a few bikes like this without oil mess and catch canister. The last idea was to do a phenolic paper one way valve screwed onto a valve spring cap to breathe into the oil tank (UFM ) . As said, you´d look for an engine without lots of air leaks so there is not a lot of air that has to exit via the breather, just a bit from blow-by from pistons.

Vic
P1060966.JPG


P1060970.JPG


Reed/disc valve onto valve spring cap:
P1080155.JPG


P1080150.JPG

hose end reed valve:
P1060385.JPG


P1060370.JPG
 

Cyborg

Well Known and Active Website User
VOC Member
Further to fitting the D breather on the front spring cap. The first photo shows a C front head and it has both the crescent shaped reliefs top and bottom. The second photo shows a head that came out of the factory quite late. It doesn’t have the relief on the bottom so more restrictive if used with a D breather cap. Not much air gets past the top relief because it is almost sealed off by the rocker bearing. Without the relief on the bottom, it severely limits the ability of air getting through the two drain grooves, so more air would be forced through between the rocker bearing and rocker arm. It would be interesting to see a photo of a known original D front head. Was the bottom relief left out intentionally or was someone asleep at the switch.....26EF5A2B-2F66-4F2E-BBD0-4021BC51C6C8.jpegB503C3E8-14C1-4A1A-81C5-A960B8FB439B.jpeg
 

oexing

Well Known and Active Website User
VOC Member
In an engine in good condition there is not sooo much air coming out of the breather - basically. So some groove on the rocker bearing should do to pass air .

Vic
 

vibrac

Well Known and Active Website User
VOC Member
With a small tubular PCV valve there is no flow of air once pressures have equalized the french letter test proved that years ago
Remember on the Egli racer we had one valve on front exhaust cap and one on rear inlet up through the pipe via the PCV valve and down to a single catch tank (ACU size 500cc) total oil for season I desert spoon full.
90 % of breather oil output is because of engine condition
 

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