Crankcase venting ??

I don't doubt you at all. But I'm referring to constant vacuum in the crankcase versus PCV. Imagine hooking a shop vac up to the crankcase and running the engine at 8000 or more RPM. It's interesting to talk about, but very hard to implement. Time spent messing with this would most likely be better spent getting a good handle on kart setup.
 
Ksfastman said:
I just noticed your screen name...my first bike was a Combat Wombat. I had a bunch of Hodaka's
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Thank's for catching that and iv'e got to get off that subject or that's all that i will want to discuss HAAAA . Yes i understand your point but i was mearly making the point that the small negative pressure made by the piston returning to TDC should be of some benefit NOT as much as a constant vacuum system with a pump etc... I can't prove it but in my mind it's better than having the crankcase open to constant atmospheric pressure and yes i had a 75' Super Rat that embarrassed a few Elsinores....
 
meracer9 said:
I am building a mild open:

Dyno 98 cam
4.500 rod
.040 over bore
368 tillotson on methanol

I have a ARC billet dual outlet valve cover (breather) that was given to me which I'd like to use. My question is can it be used alone or should I still run a PCV valve off the front port of the side cover?

Thanks in advance
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I use all three...😉
 
Crank case breather and or vacuum systems on kart racing engines. A relevant fact about single cylinder 4 stroke engines is that they are unique in that the crankcase has a varying volume so trying to treat them like multi cylinder engines just wont work well, such as vacuum pumps or PCV valves you will still have an oscillating internal pressure, most devices used in kart racing only help keep the oil loss under control. PCV valves (Positive Crankcase Ventilation) need a vacuum source to operate properly, I have never seen this done on a kart mod engine, they are mostly used to restrict a large open passage in a breather hose to control oil losses. What I am getting at is let it breath, you need to move air in and out to get the most from your little 4 stroke. If a breather system is made properly, you can control the oil loss issue.
 
I had the same train of thought as this thread in the late '90's and put a power brake check valve in the vent line going to the puke tank.
This was a legal WKA stocker flat head. And well,, learned a valuable lesson.
So if you want to test this theory, just put a check valve in the vent line while your engine is on the dyno. It's easy to connect - disconnect
the check valve while the engine is running.

Best of luck, WP
 
WPaul said:
Destroyed the idea a single cylinder engine likes low vacuum in the crankcase.
Seems there's limit or say sweet spot to the amount of depression in the crankcase of a well sealed up single cylinder 4 stroke.

Best, WP
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Glad someone with a try or two chimed in. cause I have not but common sense tell me what R Bahnson claiming fact simply is.
 
You know what was interesting, whether the engine had the stock breather, a block off plate with a hose or the check valve, the net blow by was the same.
Now,, the procedure we used to measure net crank case blow by,, after many iterations the most consistent, was to measure the pressure in a small (let's call it) "puke tank" with calculated venting to the atmosphere. Once again,, a single cylinder engine has positive and negative oscillations or pressure spikes.
Best, WP
 
Ksfastman said:
I know the NHRA Pro Stock Bikes Love crankcase vacuum, but there in a point around 25-26 inches of mercury that some engines start having a wrist pin oiling problem. Active vacuum on our engines would work and make noticeable power gains, but implementing it is gonna' be a tough nut to crack.
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I ran an electric vacuum pump many years ago on the dyno and ran into all sorts of issues....

The constant changing volume of the crankcase on the single flattie created a high speed pulse from hell that remained constant with RPM... actually created ring seal issues which was what I was trying to improve it in the first place.. lol

One of the many things I tried that didn't really work.. lol

"Good" ventilation is as good or better than anything else I tried.
 
Ksfastman said:
I just noticed your screen name...my first bike was a Combat Wombat. I had a bunch of Hodaka's
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I had a Dirt Squirt and a Mud Puppy. :)

I had a basket case Bultaco I rebuilt but for the life of me I can't really remember much about it... seems like it was a 360 or 370cc.... some random displacement anyway, I remember that.

Even had a Maaco 504 eons ago.
 
White Feather said:
I had a Dirt Squirt and a Mud Puppy. :)

I had a basket case Bultaco I rebuilt but for the life of me I can't really remember much about it... seems like it was a 360 or 370cc.... some random displacement anyway, I remember that.

Even had a Maaco 504 eons ago.
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If Shell Oil Co did not try run a motorcycle company that Mud Puppy name would have been used LOL.. cause you know they made a 250 cc Thunderdog ...just would be a matter of time.
 
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