Engine builders, how does this head measure up?

nytsmaC
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nytsmaC
Edited Date/Time 2/10/2015 5:54am
Bike is a 2014 TM 144MX. I'm putting in a new piston and rings. I did not take stock measurements prior to teardown.

I decided to try a 0.1mm thinner base gasket, as I know they are a bit conservative with the heads on these bikes and I run full race gas. I just hope it won't cost me too much top end.

Squish is now 1.05mm, which is what I was looking for. I know I can go with less and still be safe, I had 0.85mm on my Husky but 1.1mm was recommended to me.

Head volume is 11.1cc, which I'm not sure of. I was told that 12.8cc is optimal on this bike. Would a 0.1mm thinner base gasket put my measurements off by that much? Or is 11.1cc fine?

I measured by finding TDC and filling with oil through the spark plug hole until the oil reached the bottom of the threads. I did not fill to the top of the threads as I figured I was doing it correctly.

I'm using Renegade SX2, which is 104 octane and 5.6% oxygenated. From time to time I will run VP C12 mixed 50/50 with non ethanol pump, also. I'm ok with it if I can't mix anymore.
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Jakes Dad
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Jakes Dad 2/8/2015 12:33pm
2/8/2015 12:33pm
I am not a builder but a critical area you didn't mention was the squish band ratio. Using a wider gap your MSV will drop unless you go with a little wider band width. Our old RM 150 ran .82 with a 55% band ratio, worked well in Schoolboy 2 and especially softer tracks. Ran U4.4 to race and 100ll when practicing.
markit
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markit 2/8/2015 12:36pm
2/8/2015 12:36pm
I have always used solder, search setting squash
nytsmaC
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nytsmaC 2/8/2015 12:44pm
2/8/2015 12:44pm
I did use solder to check the squish gap. How do I measure the squish band ratio?

I did another head volume check, this time filling to the top of the spark plug hole and I got 13cc, which seems more along the lines of what I've been told I should be aiming for. I guess this must be the normal measurement used.

I mistyped about my base gasket change, it is 0.1mm thinner, not 0.01mm as I stated in the original post. Still a very minor change but I wanted to be technically accurate.
Jakes Dad
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Jakes Dad 2/8/2015 12:56pm
2/8/2015 12:56pm
My experience is wider squish gives it a more abrupt hit, less linear. Keep a few different base gaskets around to help dial it in to your preference. Cosmetic makes quite a few different sizes with other makes, not sure for yours.

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markit
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markit 2/8/2015 12:58pm
2/8/2015 12:58pm
Wate for pp, I've never messed with the volume.
slipdog
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slipdog 2/8/2015 1:14pm
2/8/2015 1:14pm
If I did my math correct, your .1mm gasket would only change .26cc
nytsmaC
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nytsmaC 2/8/2015 2:52pm
2/8/2015 2:52pm
Thanks, it's making sense now. So how do I measure the squish band ratio? Can I use the piece of sodder that I used for the squish test?
Jakes Dad
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Jakes Dad 2/8/2015 4:32pm
2/8/2015 4:32pm
You should get a good impression on the solder. The width going around the circumference is what you are trying to measure 55% (as in what I ran on the 150) meant the band width took up 55% of the bore area, think of it as one dimensional like drawing it on a piece of paper. By the way remove 1.8cc to account for the volume of the spark plug hole.

You're not going too far off course with the squish, not a big worry.

Jakes Dad
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Jakes Dad 2/8/2015 4:41pm
2/8/2015 4:41pm
The biggest problem I encountered was a buddies motor done by a well known motor and suspension guy. Felt bad it went through 3 pistons in about 10 minutes of total run time. Builder put a stroker crank in the 144 making it a true 150 (Ktm) to account for piston clearing the head he stacked base gaskets not paying attention to the squish. Large squish gap led to hot gases finding there way around the perimeter leading to high temps and detno very quickly. In a matter of a couple minutes there was aluminum stuck to the cylinder wall and melted o-ring sealing the head. That (proper) gap traps unburnt fuel creating a cooling ring plus forcing the hot air back into the center of chamber for a better burn.

Strictly my uneducated way of explaining this.
Bruce372
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Bruce372 2/9/2015 4:05pm
2/9/2015 4:05pm Edited Date/Time 2/9/2015 4:09pm
nytsmaC wrote:
I did use solder to check the squish gap. How do I measure the squish band ratio? I did another head volume check, this time filling...
I did use solder to check the squish gap. How do I measure the squish band ratio?

I did another head volume check, this time filling to the top of the spark plug hole and I got 13cc, which seems more along the lines of what I've been told I should be aiming for. I guess this must be the normal measurement used.

I mistyped about my base gasket change, it is 0.1mm thinner, not 0.01mm as I stated in the original post. Still a very minor change but I wanted to be technically accurate.
Remember back in school where they taught area of a circle and you thought I'll never need to use this ever in real life??? Smile

You have two circles, one is the bore, 58mm?? Pi r squared. The squish area is the total area minus the area of the smaller circle, then you can do the percentage calculation
Bruce372
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Bruce372 2/9/2015 4:08pm
2/9/2015 4:08pm
And if you are at 1.05mm squish, I would leave it since taking the head down 0.1mm isn't easy.

When I get home, I will post a pic of the tool I used to measure volume with the head removed, really easy with a flat top piston
CamP
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CamP 2/10/2015 5:54am
2/10/2015 5:54am
Run it. It will be fine.

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