Pretending it works on my P11

I have a modified 750 Norton engine that is a bit of work to get over TDC compression with the kick start. I'm not a 90lb weakling, but I'm not young anymore either. So I started telling myself I'll bet if I can get more air out of the crankcase on piston downstroke it should be easier to kick though TDC. Well dah. Hence I decided to take the plug cap off the hose barb fitting I installed in the drive side exhaust rocker cover during the last century and reconnect a hose to it. And Y that hose into the hose that vents to the oil tank from the cNw reed valve. Low and behold it does make kicking through TDC easier without stopping my kick entirely. I can still tell it has some compression, but it's a relief knowing I can kick right through it. What I don't know yet is if the reconnection of that hose will be detrimental to the power delivery at the top end since that hose out of the rocker cover does not have a reed valve on it to prevent it from sucking backward a little on upstroke. Hope to find out tomorrow.

I'm OK with butchering the rocker cover, because my '67 P11 is not a pristine high pipe restoration. If it was, I would have sold it 40 years ago and saved myself some dollars. ha

For those that don't already know there is quit a bit of air being pumped up through the pushrod tunnels on the pistons downstroke even when a reed valve is installed on the back of the timing case.

Anywho, ideally I would install one of the sump breathers to get air out of the crankcase. I think they probably work well, Unfortunately, my header pipes run right under the sump plug, and I like my funny looking exhaust. It both works and sounds impressive.

Schwany said:

For those that don't already know there is quit a bit of air being pumped up through the pushrod tunnels on the pistons downstroke even when a reed valve is installed on the back of the timing case.

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Not saying it ain't so, but how do you know that? It's not intuitive as the air has nowhere to go, other than increasing the pressure in the rocker chambers.

A simple test to see how much effect internal (crankcase pressure) has on kick starting is to simply remove the spark plugs and kick it over. Removing the spark plugs has zero impact on crank case pressure.

robs ss said:

Not saying it ain't so, but how do you know that? It's not intuitive as the air has nowhere to go, other than increasing the pressure in the rocker chambers.

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Right, but that seems like the answer to the question. Maybe I'm misreading it.

Easy to hear the air coming out of the fitting without a hose on it. Also easy to feel the air pressure with my finger on the end of the hose. It's only a 5/16" fitting, but I think it helps.

Do you mean how do I know it helps vacate the crank case and that the cNw reed valve is still working? That is a good question...

I have four 3/8" holes in the timing side case contrary to advice to plug holes on that side and do other things. Those holes let air out of the crank case and through the cNw reed valve. I'm fairly certain they are still functioning to get air out of the crankcase on piston downstroke. Although I have never actually put my finger on top of the cNw reed valve outlet while kicking the engine over and had the fitting open on the rocker cover.

Fast Eddie said:

A simple test to see how much effect internal (crankcase pressure) has on kick starting is to simply remove the spark plugs and kick it over. Removing the spark plugs has zero impact on crank case pressure.

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Done that test many times to ensure the valves weren't hitting the pistons making it hard to kick over TDC. Sure wish the engine was as easy to kick over with the plugs in as with them out.

To nobody in particular:
Venting the rocker covers was a common shade tree engineering modification in the olden days. I'm sure you guys have seen old worn out racey Nortons with a hose attached to one or the other rocker covers. If I had enough space under the tank I'd put a rubber bung in the rocker cover, push a PVC valve into it, and run a 3/8" hose to the oil tank froth tower. If you stand a high quality PVC valve straight up in a rocker or valve cover like they are in cars, they work as designed. Putting them in line horizontally doesn't work well.

What I did is easier than taking the head off and machining it for a compression release button, which by the way just seems like another failure point to me. Especially if I did the work. lol

What I should have done is bought a new PW3 cam with the machine work done to support a timed breather disc. My SS cam has no machine work done to it for a timed breather. I could still get the PW3 cam, but don't want to take the engine apart in 2026.

Edit: A compression release button into one of the combustion chambers would make the kicking much easier. What I did was only a minor improvement, not a real solution, but a pretend solution for a higher compression engine. One thing that did seem kind of real as a result of venting the rocker cover is the crank seems to spin up a little quicker. I hardy touch the throttle and it spins up to 3K RPM instantly. Haven't actually ridden it to determine if it makes any difference on the road. Enough of my nonsense. Stay frosty.

Schwany said:

I have four 3/8" holes in the timing side case contrary to advice to plug holes on that side and do other things. Those holes let air out of the crank case and through the cNw reed valve. I'm fairly certain they are still functioning to get air out of the crankcase on piston downstroke. Although I have never actually put my finger on top of the cNw reed valve outlet while kicking the engine over and had the fitting open on the rocker cover.

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Where exactly do you think the high pressure pulses are actually coming from?
They are caused by the pistons coming down.
If you have a functioning reed valve somewhere directly below the pistons then holes to the timing chest, in the rocker chambers and anywhere else will only make the situation worse.

robs ss said:

Where exactly do you think the high pressure pulses are actually coming from?
They are caused by the pistons coming down.
If you have a functioning reed valve somewhere directly below the pistons then holes to the timing chest, in the rocker chambers and anywhere else will only make the situation worse.

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I mentioned the crank case pressure is caused by "piston downstroke" in my initial paragraph. I guess I'm confusing you with the wording I'm using.

My reed valve is on the back of the timing chest where the magneto would go on a P11. The reed valve on the back of the timing chest isn't as effective as people may be led to believe on this site. It can use some help when mounted there. A reed valve would work much better on the back of the crank case or installed in the sump. I'm not going to explain why, it should be obvious.

What I'm doing is not making the situation worse. It is an improvement in my case. I have a small inline PVC valve in the line coming out of the rocker cover. Not sure it actually works that well though. It (the inline pcv valve) probably clogs up with froth after running the engine and stops pressure from coming out when it's cold more than anything else.