Inlet rocker cover breather modification advice sought

mikechelsea · Feb 16, 2016

Morning lads,

I have a 71 Commando that has had the inlet rocker cover mod-ed with a breather. I've found that at high revs, and on trips, etc. it absolutely pukes oil. I've tried relocating the breather hose to different areas of the bike, with the result of coating said areas in oil, or having it spew over my mates following in behind (sorry Steve). The volume it loses is pretty serious, so a bottle is out of the question as it would fill up pretty quickly. Currently, I've plugged it off, with no ill effects as of yet, but as it's there, I'd like to put it back into use as a breather.

So, in chatting with other Norton folks, I thinking of adding a T junction on the engine breather line, with the straight part of the fitting in this line, and the T coming in from my inlet cover breather.

My questions are, can anyone suggest why I wouldn't want to do this - what could I be screwing up, and how catastrophically I might be doing so by doing this - you think this is a jolly good idea, you have another solution, or I should just leave it plugged up?

Cheers for you thoughts!
Mike

1up3down · Feb 16, 2016

Hi Mike,

I have never understood the why, the benefit, of putting a hole in the rocker inlet cover with an exit hose, can you explain?

Is there some excess pressure in the head that this mod is supposed to relieve and if so then why are almost all of us not aware of and applying this modification?

chris plant · Feb 16, 2016

mike,i don't think the problem is with the breather on the inlet cover, it used to be a common mod on triumphs and bsa,inlet and exausts,i think theres too much oil in the head,check the drain hole under the right hand side inlet valve chris

mschmitz57 · Feb 16, 2016

chris plant said:
i think theres too much oil in the head,check the drain hole under the right hand side inlet valve chris

Speaking of oil drain holes, my Atlas cylinder had a plugged drain hole. It was packed solid with oil soaked glass beads from the dreaded previous owner. Should be easy enough to test by squirting some oil near the hole in the intake rocker box and verifying that it drains.

Inlet rocker cover breather modification advice sought

comnoz · Feb 16, 2016

Any air that would be evacuated through a vent in the valve cover would need to come from the crankcase and travel up the pushrod tubes and oil drainback holes. When air is going up the drainback provisions then the oil has a difficult time going down and a flooded cylinder head is the normal result.
I would suggest plugging the hole in the valve cover. Jim

Reggie · Feb 17, 2016

mikechelsea said;

Currently, I've plugged it off, with no ill effects as of yet,

or I should just leave it plugged up?

It wasn't an original feature on a Commando engine, and is not required as long as the original breather still is operational. The original breather will be at one of three places.
1. End of the camshaft, coming out on the left crankcase just below the barrel and above the primary case.
2.The bottom of the crankcase at the rear of the engine.
3. The rear face of the timing chest behind the engine.

I'd leave it blocked off if it was mine.

concours · Feb 17, 2016

OP, to summarize, everyone pretty much accepts the rocker cover vent was a misguided attempt by owners/mechs to solve oil leakage, and it should be plugged. Also, the original crankcase vent should be upgraded to the check valve type, Comnoz breather , XS650 or the like, and oil leaks will be reduced/eliminated.

cash · Feb 19, 2016

I'm not wanting to get into any argument over the pros and cons of this breather mod.

In the early days of fitting crankcase breather check valves to the Commando my good mate Trevor fitted a second small dia breather and check valve set for inlet only to the exhaust rocker cover. His idea was that crankcase vacuum would create a flow of cool air through the head removing excess oil at the same time. He was very happy with it too.

Dave

Bernhard · Feb 19, 2016

mikechelsea said:
Morning lads,

I have a 71 Commando that has had the inlet rocker cover mod-ed with a breather. I've found that at high revs, and on trips, etc. it absolutely pukes oil. I've tried relocating the breather hose to different areas of the bike, with the result of coating said areas in oil, or having it spew over my mates following in behind (sorry Steve). The volume it loses is pretty serious, so a bottle is out of the question as it would fill up pretty quickly. Currently, I've plugged it off, with no ill effects as of yet, but as it's there, I'd like to put it back into use as a breather.
So, in chatting with other Norton folks, I thinking of adding a T junction on the engine breather line, with the straight part of the fitting in this line, and the T coming in from my inlet cover breather.
My questions are, can anyone suggest why I wouldn't want to do this - what could I be screwing up, and how catastrophically I might be doing so by doing this - you think this is a jolly good idea, you have another solution, or I should just leave it plugged up?Cheers for you thoughts!
Mike

I feel you need to do a check on the oil feed components to the rocker box.
Start with the banjo bolts at the oil pump pipe on the bottom crankcase, following the other two on the top of the cylinder head. The oil hole on these banjo bolts should be smallest as they act as a restrictor, if these are OK then one or more of your rocker spindles has been refitted the wrong way, as the oil holes in these should be 180 degrees to the oil hole in each rocker.
if these oil holes on the rocker shafts line up with the oil holes on the rockers, the cylinder head will flood with oil :!:

mschmitz57 · Feb 19, 2016

cash said:
I'm not wanting to get into any argument over the pros and cons of this breather mod.

Dave

LOL! Good Luck with that one! There's no shortage of complex answers to simple questions here.
Didn't they explain this to you at the door?

cjandme · Feb 19, 2016

Bernhard said:
......the banjo bolts at the oil pump pipe on the bottom crankcase, following the other two on the top of the cylinder head. The oil hole on these banjo bolts should be smallest as they act as a restrictor, if these are OK then one or more of your rocker spindles has been refitted the wrong way, as the oil holes in these should be 180 degrees to the oil hole in each rocker.

I wouldn't have thought of that right away, just another reason I love this forum

mikechelsea · Feb 21, 2016

Thanks for all the responses folks! Lots of interesting stuff there, for sure.

I think comnoz nailed it, though. I have the breather blocked off now, and will make it permanent. There wasn't an oil issue so much as when riding long distances at high revs, oil would puke out of the 'non-stock' breather (a breather was added to the inlet rocker cover at some point), and I wondered whether to either plug it, or plumb it into the engine breather and have the oil returned to the tank. I mostly wasn't sure whether it was a good idea/actually accomplished anything, or if plumbing it into the engine breather might cause other issues. Anyway, all good.

Slight off topic, but I was having seeping from one of my rocker spindle covers, and installed some of the one-piece versions from Rock Point Cycle, and man, do they work a treat. Look cool too.

Cheers!
Mike

1up3down · Feb 21, 2016

There's no shortage of complex answers to simple questions here.
Didn't they explain this to you at the door?

fiatfan · Feb 21, 2016

mschmitz57 said:
cash said:

I'm not wanting to get into any argument over the pros and cons of this breather mod.

Dave

Click to expand...

LOL! Good Luck with that one! There's no shortage of complex answers to simple questions here.
Didn't they explain this to you at the door?

Haha, +1 there Mark spot on! :lol:
Tommy

Inlet rocker cover breather modification advice sought

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