Victoria! Zeke's CB175 Build
- Thread starter Texasstar
- Start date
crazypj
Split personality, I fake being smart
Never bothered with it.
I found it's just as effective and less work to fit a non-return valve in breather.
You have to fit a non-return valve anyway
You don't have big pistons moving a lot of air, plus you have a relatively large volume in crankcase/transmission compared to a car engine (particularly high rpm V-8)
It may give a few tenths of HP but I don't see you getting dramatic increases
I found it's just as effective and less work to fit a non-return valve in breather.
You have to fit a non-return valve anyway
You don't have big pistons moving a lot of air, plus you have a relatively large volume in crankcase/transmission compared to a car engine (particularly high rpm V-8)
It may give a few tenths of HP but I don't see you getting dramatic increases
I figure it will aid in cooling...I bought a bung for the exhaust 
Texasstar
Can't is a four letter dirty word
Agree or disagree?
"The timed breather employed on the Gold Star, A10 and early Commandos probably produces the opposite effect to Charles' ideal breather. If it's working properly, there is a partial vacuum on the upward piston stroke, and on the downward stroke this is cancelled out by blow-by, so that there is atmospheric pressure on the downward stroke, or even positive pressure if the breather outlet is too small and the gas can't escape fast enough. I think we've been through all this on brit-iron before, but the ideal practical solution is to use the escaping exhaust gasses to scavenge the crankcase and produce negative crankcase pressure throughout the cycle. However this is difficult to achieve, and involves unsightly plumbing to the exhaust system, so the next best alternative is to do what most classic racers do and fit a very large open breather pipe, and let the piston suck in and blow out air as it pleases. There is no power loss with this system as long as the breather is of a sufficiently large diameter, so that no significant pressure difference builds up between the crankcase and the atmosphere. The problem with many old Brit bikes is that the breather is much too small. On the early Norton Commando, the crankcase has to breath through four tiny 1/8" diameter holes in the camshaft, equivalent in area to one 1/4" hole. At 6,000 rpm the engine has 5 milliseconds to pump 750cc of air through a 1/4" hole. Someone on brit-iron suggested the following experiment. Try sucking and blowing through an empty ball-pen tube, then try the same thing with the tube from the centre of a toilet roll. I think you'll find it's much easier in the second case. There was an article in Classic Bike a few years ago about a vintage racing Gold Star. The only significant power gain they were able to achieve was by modifying the breather to the large open pipe type. If I remember correctly, this gave a 3 bhp increase in peak power, and lowered the piston crown temperature (I don't know how they measured this) enabling a main jet two sizes smaller to be used. I don't know to what extent the power gain came from the improved breathing versus the fact that they nolonger had to run an over-rich mixture to keep the engine cool."
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"The timed breather employed on the Gold Star, A10 and early Commandos probably produces the opposite effect to Charles' ideal breather. If it's working properly, there is a partial vacuum on the upward piston stroke, and on the downward stroke this is cancelled out by blow-by, so that there is atmospheric pressure on the downward stroke, or even positive pressure if the breather outlet is too small and the gas can't escape fast enough. I think we've been through all this on brit-iron before, but the ideal practical solution is to use the escaping exhaust gasses to scavenge the crankcase and produce negative crankcase pressure throughout the cycle. However this is difficult to achieve, and involves unsightly plumbing to the exhaust system, so the next best alternative is to do what most classic racers do and fit a very large open breather pipe, and let the piston suck in and blow out air as it pleases. There is no power loss with this system as long as the breather is of a sufficiently large diameter, so that no significant pressure difference builds up between the crankcase and the atmosphere. The problem with many old Brit bikes is that the breather is much too small. On the early Norton Commando, the crankcase has to breath through four tiny 1/8" diameter holes in the camshaft, equivalent in area to one 1/4" hole. At 6,000 rpm the engine has 5 milliseconds to pump 750cc of air through a 1/4" hole. Someone on brit-iron suggested the following experiment. Try sucking and blowing through an empty ball-pen tube, then try the same thing with the tube from the centre of a toilet roll. I think you'll find it's much easier in the second case. There was an article in Classic Bike a few years ago about a vintage racing Gold Star. The only significant power gain they were able to achieve was by modifying the breather to the large open pipe type. If I remember correctly, this gave a 3 bhp increase in peak power, and lowered the piston crown temperature (I don't know how they measured this) enabling a main jet two sizes smaller to be used. I don't know to what extent the power gain came from the improved breathing versus the fact that they nolonger had to run an over-rich mixture to keep the engine cool."
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crazypj
Split personality, I fake being smart
Late model CX500 uses breather in inspection cover for setting cam chain tensioner. Pretty sure it's same thread as rocker cap?
Kawasaki EGR reed valves are pretty easy to come by, you can bolt them to almost any flat surface.
I've seen the info on single large breather before, 3bhp increase on a Gold Star is impressive as it was pretty well sorted over many years. The factory was getting about 50bhp in the 1950's (100bhp/liter)
Kawasaki EGR reed valves are pretty easy to come by, you can bolt them to almost any flat surface.
I've seen the info on single large breather before, 3bhp increase on a Gold Star is impressive as it was pretty well sorted over many years. The factory was getting about 50bhp in the 1950's (100bhp/liter)
the cx one is a windage vent that was added to the later gl650s to stop them from throwing gaskets it was done as a warranty thing as well
it is the same size as a valve adjuster cap but it has no oil baffling so if you put it in the head i think you would loose a lot of oil thru it
it is the same size as a valve adjuster cap but it has no oil baffling so if you put it in the head i think you would loose a lot of oil thru it
