Athena cylinder head kit.

[FFRacing11x]

Andrew, did I pass??

[Faded]

Originally Posted by FFRacing11x

Andrew, did I pass??

With flying colors! It's about time we had some more 'technical' discussions around here, I always enjoy hearing what you and Andy have to say.

[ossagp1]

Well you could go on about how an engine which has a lower adjusted compression ratio can actually have higher upper rpm compression than an engine which has a higher adjusted compression ratio when it winds to the same rpm. Wait,,I confused myself.

[YZ125motoracer]

i checked the UPS site and the cylinder should be here by wed, or thursday

[MotoMcGee]

Where'd you buy your kit?

[YZ125motoracer]

i ordered it from worldofpowersports.com for $500. i get better deal than most other people because im registered as a dealer.

[YZ125motoracer]

i put the cylinder on last night nd tomorrow im going to walden NY to ride. i ran it for a little while last night and it sounds like a 250 (o yea i ran a compression test and it came up as 138psi!!!) i cant wait to tomorrow!

[Faded]

Originally Posted by YZ125motoracer

(o yea i ran a compression test and it came up as 138psi!!!)

FWIW, 138psi is weak, really weak. . . I thought the CR on this thing was 14.8:1; should it be more like 217psi???

[Racer#857]

i replace my piston on my kx125 (stock cylinder) when it gets below 180 psi. It normally peaks around 220 with a new piston in it

[YZ125motoracer]

i did the compression test befor ever starting the bike, could the compression be lower because the engine wasnt broken in?

[Florida 393]

I taught Physics and Chemistry for three years and did Boyle's Law and other compression/detonation discussions and I never stated things as clearly as your guys just did. I repeat my request that a header be placed in both the 2T and 4T forums that if Faded, OSSAGP1 and Tryce post you must listen (read) carefully and write everything down. When these guys post please listen to what they share you will learn something and it will be for your benefit.

My one day with Tryce at Tunica was a graduate course in bike preparation and set up. I'd love to spend several weks with all three of these men to learn some real tuning and mechanics .

Bill

[FFRacing11x]

Bill, just don't tell anyone about the starter nut incident We had a blast that weekend! Tdub

[ossagp1]

If you came in the summer you might have to listen to me while we caught salmon.

There could be lots of reasons why it is reading 138. on a reeded bike I take the reading without the carburetor, and with the power valve linkage disconnect and the valve bottomed. On the older models that was less important.

[Michael Parker]

Originally Posted by ossagp1

LOL, I wouldnt worry about that 14.8 number. Not to wind anyone up again, but Racer,,just consider it somewhere in the
9's. If you really did have a compression ratio that high on a twostroke, I would bet it won't live a moto, and maybe not a full minute on gasosline you can buy. Anyone curious as to why using a compression gauge won't work to figure your compression ratio (I had a science teacher that thought it should too) should read ALL of Boyle's Law first. Then they should get closer to how an engine works and how inertia affects air flow. Finally, they should compare the reading given on one revolution to the one they get on "several kicks", or just have an actual knowledge about what is happening and how the gauge works.
Then a good pinch of reality (make sure you are awake if anything)should be administered; as you wonder why the factories and the engine builders go to all the trouble to CC or pour a head and cylinder to determine it rather than to just "use a compression gauge".
Or just don't worry about 14.8 to 1 LOL

im just wondering if there is something that makes you doubt everything i tell anyone?

[ossagp1]

I dont doubt that you got a reading of 215 on a compression gauge. I also dont doubt that you don't realize how a compression ratio is measured. That simple enough for you parker?

[Michael Parker]

yes i know that a compression gage uses the buit up preasure from several kicks rather that one upward stroke, therefor not reliable.
i just dont have the equipment to measure comp. on the bottom of the piston

[ossagp1]

The reason you get an inflated reading is as much from heat as it is from the "builtup" pressure. The gauge traps a tiny amount which reacts faster to the heat buildup in some cases, and the entire volume warms up considerably in just a few kicks. Tuners would love to be able to use a gauge rather than a a burett to figure it with I am sure.

If you keep your procedure as close to identical each time you take a compression reading, you will at least have something to check your engine condition with. That will include ambient temp and humidity as well as your own technique and gauge. That is all a compression test was intended for. Now that you have a fourstroke, you may wish to build something like the pressure tester that Faded posted the instructions for a year or so back. Cheap to do, and you can do your own bleed down tests to check conditions. If you can hear better than me you can even get an audible reading as to where leakdown is occuring.

I think I mentioned that when I was way younger a science teacher told me that you could indeed figure what your compression ratio was from a compression test. In theory you can, if you do it the way I mentioned earlier assuming you could get close to a total seal and then figure for the heat rise. In his case, he was not at all familiar with the actual tool and procedure or the other things such as were mentioned by Tryce earlier.

[Michael Parker]

Originally Posted by ossagp1

The reason you get an inflated reading is as much from heat as it is from the "builtup" pressure. The gauge traps a tiny amount which reacts faster to the heat buildup in some cases, and the entire volume warms up considerably in just a few kicks. Tuners would love to be able to use a gauge rather than a a burett to figure it with I am sure.
If you keep your procedure as close to identical each time you take a compression reading, you will at least have something to check your engine condition with. That will include ambient temp and humidity as well as your own technique and gauge. That is all a compression test was intended for. Now that you have a fourstroke, you may wish to build something like the pressure tester that Faded posted the instructions for a year or so back. Cheap to do, and you can do your own bleed down tests to check conditions. If you can hear better than me you can even get an audible reading as to where leakdown is occuring.
I think I mentioned that when I was way younger a science teacher told me that you could indeed figure what your compression ratio was from a compression test. In theory you can, if you do it the way I mentioned earlier assuming you could get close to a total seal and then figure for the heat rise. In his case, he was not at all familiar with the actual tool and procedure or the other things such as were mentioned by Tryce earlier.

this i learned something from, but can you repost the instructions for that thing you talked about?