E: Engine PCV Valve
- Thread starter Chris Launders
- Start date
I don't run any PCV valve or similar on my 665 race single........all you have to do is keep the breather outlet away from any oil spray and you are done. Thing to remember in a Vincent is the timing chest is one giant oil pump.......Its where most seem to like running breathers from.......I did the same, only I've put a big cylindrical shield around the outlet pipe to keep oil away from it. Since i did that, no oil collects in the breather tank anymore........Simples.
That is very sensible thinking my handsome.
I had something very similar on my "A" Rap with a big box over the coffin plate and a discharge hose from a washing machine to the back of the bike from the bottom of the box was a mango bolt and lead down to the engine plate with a loop around that to create a trap then into the sump, never had any trace of oil at the rear of the tube with a trip across America R 66 in 2016 then four lengths of Tasmania 2017 and twice Rond NZ in 2018. then I gave it to my daughter
I had something very similar on my "A" Rap with a big box over the coffin plate and a discharge hose from a washing machine to the back of the bike from the bottom of the box was a mango bolt and lead down to the engine plate with a loop around that to create a trap then into the sump, never had any trace of oil at the rear of the tube with a trip across America R 66 in 2016 then four lengths of Tasmania 2017 and twice Rond NZ in 2018. then I gave it to my daughter
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I've ordered a couple from Ben.If they run in the Goodwood twin for a season with no oil in the catch tank who could want more?
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Q. is it possible to ware out a photo by posting ita lot?
The one that's given up the ghost is on my Norton, straight off the rear rocker cover, I haven't checked the one on my Norvin yet, that's off the front cylinder tappet cap.
The thing about breather valves is, they get a bit of oil mist so all sealing contacts inside have to be very narrow, else oil will lead to sticky valves on their seat. I do my reed type valves but dremel all seats for small contact, no troubles from them ever.
Yes, having the breather start at the timing cover is no brilliant idea, with all that oil inside there. Valve spring caps appear a lot more logical I´d think.
Vic
Yes, having the breather start at the timing cover is no brilliant idea, with all that oil inside there. Valve spring caps appear a lot more logical I´d think.
Vic
If the breather tube is long enough the resistance of the tube for the gasflow is like a valve. This system I have on my twin. The twin tube exits the engine on the exhaust valve cap of the rear cylinder and the inlet valve cap of the frontcylinder and syameses then leading to a stainless steelel tube towards the rear axle. Erik
when talking about flow of air/oil in breather pipe with an PCV valve remember that the flow stops or at most oscillates slightly once the internal engine pressure is established (say 60 seconds after start up)
But remember leaking valve guides or piston blow by and all bets are off, let the oil flow!
But remember leaking valve guides or piston blow by and all bets are off, let the oil flow!
That would be why comparing a breather system on a properly maintained and monitored (leak down etc) race bike to a street bike might not be fair. Once internal pressure is established….. what is the pressure reading…. it would be interesting to know. I think it’s safe to assume that to some degree lower pressure is better. Early on in the drag racing world, folks needed a way to keep oil, gaskets and oil seals where they are supposed to be. Venting the engine into the exhaust headers would create a lower crankcase pressure and they discovered that it also gave them an increase in horsepower. When noise bylaws mandated the use of mufflers at some tracks, they lost the necessary vacuum supply and they started adding vacuum pumps to the engines. I recall seeing at least one Vincent racing twin with a vacuum pump installed, but I would think that with old British iron that is dependent on splash feed , you wouldn’t want to suck too much oil mist out of the engine. If slightly lower crankcase pressure in a Vincent does make some sort of gain in hp, then it would be advantageous to run a PCV or better yet a reed valve on a race engine. I’m pretty sure a valve will get lower crankcase pressure. Only one way to find out.
I think the main problem with the timed breather on the Vincent twins and singles is the timing is wrong. I time my breather so that the center of it's opening period is approximately when the piston or pistons are at bottom dead center. (on a twin one piston will be at 25 degrees before bdc and one 25 degrees after bdc) I think someone at the works had the wrong idea. In Richardsons and also some original factory documents the instructions say to time the breather so it would close right at BDC but that is exactly when it really needs to be open. Someone was thinking the breather was like a pump for liquid, but it is gas in the crankcase. If you time the breather right it will work more like a PCV valve. The breather needs to open when the crankcase volume is minimum. It doesn't make any difference if the pistons are going up or down. This timing works, my twin, and several other people I know time them this way as well. My bike has negligible consumption and few leaks. It is likely that if the breather is timed right the pressure in the crankcase can average below atmospheric pressure. Nigel