So I'm working on the motor for the air gas hybrid build I've been posting up. I tried today to test the motor to verify that it is indeed working properly, and while the side of the motor I have modified works great, I'm having issues with the other side. Basically, if I turn the motor by hand, the valves don't seem to be sealing properly. During the intake stroke, the motor will suck in air, but during compression, air is being forced back out through the intake port. I've checked valve clearance and ensure that when sealed, there is a slight amount of clearance between the cam and the shim, so it's not being held open in that manner. I have even changed valves out with the valves I removed from the other side of the motor and lapped them in case the issue was with the valves themselves. Motor still behaves identically. The exhaust side of the motor seems to do the same. While turning the motor over by hand, it'll actually suck air in through the exhaust port, then expel it out again.

Just to reiterate, I've checked and verified clearance, I've tried switching and lapping valves, and I've reset cam timing about 5 times to ensure it's accurate.

I have also verified on the motor on my bike that it operates as expected, so I can confirm it does infact only suck through the intake port and blow out through the exhaust.

Any thoughts? Thanks

for what you're looking todo, I believe what is required are "reed valves" that permit air to flow in a single direction only.


http://www.autoblog.com/2008/04/19/scuderi-split-cycle-engine-almost-ready-for-sale-to-automakers/

I'm not having issues with the side I'm trying to behave as I wish(which has reed valves installed). I'm having problems with the stock side

do you have an something for illistration purposes. being that i'm not a physics major, or mechanical engineer, its hard for me to visualize what you're building right now.

Do you feel resistance when on the compression stroke and hear a hissing noise, when you turn it over by hand?

If so, that's normal.

thats valve overlap, its designed into the cams. a high revving engine requires alot of overlap to effectively move at high engine speeds. try retarding the cam timing, this will open the valves later and reduce the overlap, it will hurt high rpm performance but will help low rpm performance.

It's not an issue of overlap. It's an issue of the valves not sealing. During the compression stroke, when the motor is turned by hand(or via the starter), air is escaping past the valves. The motor on my bike does not do this when it is turned by hand or via the starter. What I can't figure out is why. The motor on the bike works as expected... crank over the motor and it sucks air in through the intake port on the intake stroke and pushes air out through the exhaust port during the exhaust stroke. The motor on the benchtop sucks motor in through the intake during intake, expels it past the valves during compression, sucks more in during the combustion stroke, then expels it out on the exhaust stroke.

This problem is unrelated to the air gas hybrid aspect of my project. That side of the motor works as designed. The side not working has not been modified in anyway. If you're looking for more information regarding that, I have a build thread going on here or go to crecca.wordpress.com for my blog on the subject.

did u lap your valves when you reinstalled them?

valves never seal properly, but have you done a leakdown test... ngrclown?

Quote from: joshr08 on May 11, 2010, 04:17:54 PM
did u lap your valves when you reinstalled them?

yes


junkie: I'm not expecting a 100% seal. A little air getting past is one thing. This will completely empty the cylinder of air on the compression stroke.

stuck shim bucket?  whats your clearance on your shims?

Quote from: joshr08 on May 11, 2010, 04:46:58 PM
stuck shim bucket?  whats your clearance on your shims?

shim buckets are moving properly. This was my first thought, and I have verified that there is indeed clearance between the cams and the buckets when they're not engaged.

I don't know much of anything about anything, but...

When you lapped the valves did you test the seals by inverting the chamber and pouring a bit of gas over the valves?

Quote from: romulux on May 11, 2010, 08:14:56 PM
I don't know much of anything about anything, but...

When you lapped the valves did you test the seals by inverting the chamber and pouring a bit of gas over the valves?

I did flip the cylinder and fill the combustion chamber to verify that it wasn't leaking.

Quote from: saxman on May 11, 2010, 08:18:16 PM
I did flip the cylinder and fill the combustion chamber to verify that it wasn't leaking.

Again, I'm pretty ignorant about internals...

Is there any way to assemble it so ex/in are reversed?  Swapping or reversing cams somehow so exhaust is now intake and intake is now exhausting?

Quote from: romulux on May 11, 2010, 08:25:50 PM

Quote from: saxman on May 11, 2010, 08:18:16 PM
I did flip the cylinder and fill the combustion chamber to verify that it wasn't leaking.

Again, I'm pretty ignorant about internals...

Is there any way to assemble it so ex/in are reversed?  Swapping or reversing cams somehow so exhaust is now intake and intake is now exhausting?

I've pulled the cam and reset the cam timing at least half a dozen times, with people verifying my every step.

Anyone else have any brilliant ideas? I am stumped.

did you disassemble the valve springs, guides and such. maybe the springs were switched intake instead of exhaust. or could the springs be out of spec?

I disassembled the whole assembly, however, I did each valve one at a time. They couldn't have been switched but may be out of spec. I will verify this afternoon.

I hope you get it figured out, this is a cool project.