Cam Advance MC Mod. - Page 2 - Kawasaki KLR 650 Forum
2008+ KLR650 Wrenching & Mod Questions For repair, maintaining or modifying discussions related to the newly updated 2008 and beyond, Generation 2 KLR650 Motorcycle.

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post #11 of 95 Old 05-07-2015, 12:17 PM Thread Starter
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I can see how the pcv could cause better ring seating and braking with the engine because the vacuum created by the pcv, better gas mileage and less oil burning...seems it would be the opposite making the engine work harder and pulling more oil up on the cylinder wall. Maybe the valve timing is enough to to eliminate the vacuum created, if so that would end the better ring sealing which was the purpose of the mod to start with. After seeing that small hole in the airbox where the vent hose is connected caused me to rethink this mod and the reason Kaw did it this way. Maybe it works for some oil burning engines? Give it a try tell us how it works for your bike.

Some things you do not question. How long before i get banned here?
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post #12 of 95 Old 05-07-2015, 12:51 PM
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Originally Posted by Drifter. View Post
I can see how the pcv could cause better ring seating and braking with the engine because the vacuum created by the pcv, better gas mileage and less oil burning...seems it would be the opposite making the engine work harder and pulling more oil up on the cylinder wall. Maybe the valve timing is enough to to eliminate the vacuum created, if so that would end the better ring sealing which was the purpose of the mod to start with. After seeing that small hole in the airbox where the vent hose is connected caused me to rethink this mod and the reason Kaw did it this way. Maybe it works for some oil burning engines? Give it a try tell us how it works for your bike.

Some things you do not question. How long before i get banned here?
Actually, Drifter, in actual tests, no vacuum has ever been measured in the crankcase of a KLR650 engine with PCV Mod installed; whether spring-and-ball valve or vane-type, no vacuum. Rather, an over-pressure (compared to atmospheric) exists in the running engine's crankcase . . .

Nevertheless, the operational enhancements mentioned (i.e., more power, better fuel mileage, lower oil consumption, improved engine compression braking, enhanced ring sealing) have been reported by users firmly convinced of these benefits.

I think the reasons Kawasaki "did it this way" (i.e., valveless vent hose to atmospheric pressure side of air box) was: 1. Engine as-built passes current emission standards, and 2. Intake backfire dynamics adequately managed by baffle arrangement (a major function of a "real" PCV valve in an automobile is preventing intake backfire flame from entering crankcase, where combustible mixture may exist). DISCLAIMER: Conjecture on my part; don't know why Kawasaki, "did it this way!"

Fear not banning for expressing your opinions, generally, on this website; or . . . even for questioning concepts . . . depending somewhat, perhaps, on the mood/attitude of the moderator poised over the banning button!
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post #13 of 95 Old 05-07-2015, 12:53 PM
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...Some things you do not question. How long before i get banned here?
Yer gonna have to try real hard to get banned here.

Generally we just love a good discussion.

Some of us will question everything that doesn't have a logical explanation, doesn't pass the sniff test, or will, at the very least, make for a good argument. Some of us want to understand 'how' and 'why'. 'It just works' is fine, but what do you learn if you can't understand the how and the why?

The sort of conversations that you'll find here are the sort of conversations you'd find around a friendly campfire. Anything and everything is fair game for discussion as long as it stays the way you'd do it in meat-space. If you think that something you'd say in meat-space would get your ass kicked there, it'll happen here. If not, not.

Aside from spammers and porners, I think we've banned mebbe three or four people in the past few years. That says a lot about the caliber of people on this forum. Gentlemen and scholars, all.

Tom

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post #14 of 95 Old 05-07-2015, 02:08 PM
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Damocles,
I dis-agree about the crankcase venting the "the atmospheric side of the air box".

The atmospheric side is the Dirty side!

I'll suggest there is a 'slight' vacuum in the clean side of the air box when ever the engine is running.

I thought we had discussed it to end over here, http://www.klrforum.com/klr-other-mo...ntilation.html

pdwestman
Modify at "YOUR OWN RISK"!

Still riding my 1987 KL650-A1. 85,000+ miles & counting

Last edited by pdwestman; 05-07-2015 at 02:31 PM. Reason: Added link
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post #15 of 95 Old 05-07-2015, 05:26 PM
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Originally Posted by pdwestman View Post
Damocles,
I dis-agree about the crankcase venting the "the atmospheric side of the air box".

The atmospheric side is the Dirty side!

I'll suggest there is a 'slight' vacuum in the clean side of the air box when ever the engine is running.

I thought we had discussed it to end over here, http://www.klrforum.com/klr-other-mo...ntilation.html
Would it be fair to say, "vented to essentially atmospheric pressure in the air box?"

The point; NOT vented to manifold vacuum, as with a "true" positive crankcase ventilation system, as found on automobiles.

(We'll discuss the metering system used by automobile PCV setups on another thread! )
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post #16 of 95 Old 05-07-2015, 05:36 PM
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Originally Posted by Damocles View Post
Would it be fair to say, "vented to essentially atmospheric pressure in the air box?"

The point; NOT vented to manifold vacuum, as with a "true" positive crankcase ventilation system, as found on automobiles.

(We'll discuss the metering system used by automobile PCV setups on another thread! )
Sounds appropriately correct.

pdwestman
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post #17 of 95 Old 05-08-2015, 06:58 AM Thread Starter
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I do not understand how a vacuum is not created on the upstroke of the piston if the ring blow by and downward movement of the piston creates pressure?

If the vent is open in stock configuration, i think 14.7 lbs of pressure is a constant in the box i can see how that might eliminate the vacuum, with a pcv there would be no pressure to equalize the crankcase? What fills that empty sealed space?

Use a small fish tank pump as an example, each cycle one side sucks air the other blows air. For every action there is an opposite and equal reaction.

I think Tom is referring to you guys, i do not fit his description.....
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post #18 of 95 Old 05-08-2015, 09:14 AM
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Hypothetically speaking, say you had an engine without a vented crankcase and the combustion chamber was open to the atmosphere. If you spun the crankshaft the pressure in the case would rise when the piston went down and drop almost equally when it went up. Leakage past the rings would cause the case pressure to be less than what the swept volume of piston would calculate to. But because the leakage would be equal in both directions (combustion chamber open to the atmosphere for discussion sake) there would be no vacuum or pressure gain in the case.

A running engine without a case vent will build pressure in it's case because the pressure of the power stroke will force more leakage past the rings into the case than the lower case pressure can force back on the down stroke of the intake stroke.

The KLR's small vent orifice relieves enough of that pressure to prevent problems but is not really big enough to vent the case. (Ever wonder why the oil gets so dirty so fast?)

Last edited by twinjet; 05-08-2015 at 09:16 AM.
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post #19 of 95 Old 05-08-2015, 07:51 PM
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Originally Posted by Drifter. View Post
I do not understand how a vacuum is not created on the upstroke of the piston if the ring blow by and downward movement of the piston creates pressure?
The "vacuum" may be immediately negated by the pressure of the downward piston stroke . . . and further compromised by piston blow-by . . . were there vacuum to be retained, the PCV valve would have to open and close at TWICE the rate of the engine valves, perhaps a daunting mechanical task for a passive PCV or check valve, even a vane-type . . . regardless, as previously mentioned, in actual tests, no durable "vacuum" has ever been recorded in the crankcase of a running KLR650 engine, even with the PCV Valve Mod, even with a VANE-TYPE check-valve installed.

Said tests were reported on .net; instrumentation consisted of a manifold vacuum/fuel pump pressure gauge teed into the crankcase vent line. With no durable static vacuum measured (except during extreme and brief deceleration), hard to account for all the claimed advantages of the PCV Valve Mod, IMHO. Durable crankcase vacuum doesn't appear to be available, thus hardly responsible for the improvements.

Regardless, more power to those who enjoy the PCV Valve Mod's benefits.

Last edited by Damocles; 05-08-2015 at 07:54 PM.
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post #20 of 95 Old 05-09-2015, 03:40 AM
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Talking Not going back to stock timing

Mean while back to the subject of MC mod. I hold tec days in Arizona and assist at other tec days in Flagstaff. The Flagstaff TD we have Eagle Mike and his bag of tricks, Dooheckys, KLX needles, Thermobobs and all the rest.

We do valve adjust and MC mods. I have done MC mods on a dozen or more 1st and 2nd Gen bike. So far no one has changed back to stock timing. That's the great thing about this mod. If for some reason you don't like more low end torque and power. You can change it back with no harm.

Eagle Mike has done the dyno testing. He was going to market a cam advance gear. Found that your not going to do much better then the 7.5 degrees jump of one tooth on the exhaust. So he past this on as free power. The problem with this is people screw it up. They advance one tooth on the crank, giving a 15 degree advance on both cams. Retard instead of advancing. There's a lot of room for error.

All I can say is try it. It's not that much work. If your savvy enough to do your own valve adjustment. You should be able to turn the exhaust cam one tooth counter clock wise. I know I'm not going back to stock timing on my 2013.

You may now go back to the previous off topic descussion.
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