Mod head test.....Squish band stuff....

[RCannon]

I installed the head tonite. I played it slightly conservative and ended up at close to .050 to .053 for a squish measurement. Total cost was 40 bucks. This was on my ebay 2001 head that was quite different from our current 06 heads.

It would have been almost worthless on the bike in stock condition. I had nothing to lose. 2001 head compression read 180psi. This is with a super-trick Wiseco piston, ti nitride ring, and broken in.

This was with my DEP pipe, pc long silencer, and the jd jetting kit.

result 1......Upper midrange that is strong..really strong.

result 2......Bike was lean. How could I tell? The plug was no longer BLACK. It finally changed colors.

result 3.......Throttle response was .....silly. The stock bike is something, this is at a whole new level.

Was I impressed?

Let me put it this way. I ran in the house and instantly ordered another stock 06 head. This might be nice to have around as I have my oem 06 head cut.

WHAT THE HELL???? WHY???

Because Lord-Faded..(pause for an honorary moment of silence) said the result would be better. Good enough for me. If he tells me to chop a finger off, i will do that as well.

Anyone can mill .030 off of a head. hell, we could probably do it in my garage while spinning it in my Icee machine. Thats not the idea.

I needed more combustion pressure due to Utah being void of air. Well, 4500 ft of elevation puts hurt on power and pressure. My work was no big deal. Despite removing .030 in, I had the pressure raised only 25psi. (185 before...210 now).

For people with pressures at 210 already, this mod is still desirable. The head can be cut, but the combustion chamber can have material removed as well. You keep the same pressure, but put the squish band in the proper place.

I would love to let faded go after my car.....

All and all i am more than thrilled with the improvement. This 40-50 spent here gave me far more than my pipe collection.

I will let you know how I like my 06 headmod, pt 2 in later chapters.

Sorry about my 3rd grade style of describing this. I understand enough to make me dangerous. There are pages and pages of this info on the net. Dont be afraid to search and decide on your own spec.

In the meantime, buy any used yz head off of ebay you can find...you wont be sorry.

I found this site very helpful in measuring the squish band. http://www.rb-designs.com/

Go there, click on head mods, then click on Gas-Gas head mods. Incredible instructions that are easy to understand.

If you dont get these measurements close, you might be in for a nightmare.

One other thing from the sick mind of Roland.

I pushed the clearance fairly close. My bike is damn near new and is owned by a 41 year old rider who likes fast bikes. I ride like James Stewarts grandma. I am not sure I would get too creative on a 10 year old bike with a worn crank.

Things need to be in good condition before you can go nuts in this area.

One other small detail....3rd gear under quite a load........severe uphill with a sand surface....week old pump premium with yamalube r, 32:1...no pinging. motor actually much more quiet than before.

A 5 gallon can a race gas costs more than this entire mod.......well, other than the o ring rape I receive from the Yamaha dealer.

[Markopolo400]

Sounds awesome RC.

[kx_rider53]

Sounds awesome RC.

I second that motion.

[NYMXer]

Roland, when your all done, post a step by step for us simpletons please........

and yes, Faded knows what he is talking about and you'd be wise to listen to his advice.

[RCannon]

I cannot thin of a better step-by-step than this link http://www.rb-designs.com/.

Click on "head mods"

then click on "Gas-Gas head mods"

This will show you how to measure where your at now.

I would never in a million years be able to tell someone how much to cut. The guys like Faded have done this hundreds of times. This is my first.

Its not hard, but screwing up on a measurement could be very costly.

[RCannon]

I tested thsi again last night. At first I had thought that the extra combustion pressure has made the top end run flat. It was not like I regretted the decision. The low and midrange gains more than made up for it.

The conditions last night were different. The temp had dropped from 90 to the 65-70 region.

I had forgotten how this bike likes the correct main jet. After trying a few different things I found the right combo. I did not lose any top end...none at all.

So far this has been excellent. Very little cash outlay and improved performance. Thanks to Faded and Skipn8r. These guys really know their stuff.

I am busy trying to talk Faded into moving into my neighborhood. He would be an excellent neighbor.

[wrenchbender]

Roland- do you know if there is a big difference between an 03 head & an 06 head? I'm gonna check & do my 03 but if the 06 head is a lot better I will get one of those.

[RCannon]

The 03 and 06 use the IDENTICAL head.

The older heads were 1/2cc smaller. My 01 head also had a larger squish measurement when mounted on the 06.

I also like that one now that is is modified. It is a little smoother down low.

This winter we should be able to pick up extra YZ heads for next to nothing. I still have a few things I would like to try....well, Ideas stolen from Faded and skipn8r........

[Pincushion]

Roland,

did you take the measurements exactly as that website illustrates (remove the head) or did you stick solder through the spark plug hole like the kid in the Honda forum did?

And did you did you speak to Faded about optimal clearance for the YZ's? Is .050 a good compromise between optimal combustion and wear tolerance for the big end bearing?

I think I'm going to perform this myself. I dont have detonation issues, but this will certainly help throttle response and jetting for me at 1500ft.

[RCannon]

I pretty much followed the web page instructions.

I tried the soldier through the hole and it worked, but it was difficult to feel exactly where the soldier should end up. Follow his instructions on soldier type. Dont get solid core anything. Rosin core, or like I did.

I raided my dads toolbox and found some of the old and good "lead" solder. I will use this on plumbing if I get a chance as well.

You will waste a set of head gasket o rings doing this. For some reason the Yamaha gaskets Grow as soon as heat hits them. They wont go back into the slot after this happens.

The feeling I had was that .050 was somewhat of a maximum they liked to see. Both of the guys talked about .035-050 .

I went to .050 on the old 01 head and .045 on the 06 head. Both are really good. The 06 head just feels a little better down low. Both are improvements over stock.

This will work well for me. I can run pump gas here in Utah. Should I ever go to a sea level track I can steal some race gas. I say steal because my local shop just raised their price to 9.50 per gallon......for last years stuff!

I wonder if anyone has ever done the "dine and dash" while buying race gas?

[Nitroused383]

Sometimes raising the compression will cause a slight loss in top end power, probably not even noticable. There is a pumping affect in the cylinder and at higher rpms there is more resistance for the engine to squish all the air/fuel mixture into the head. It's probably not even noticable, but if you want the bike to feel like it has more top end, try lowering your compression.

[RCannon]

Thats exactly what they told me. So far I really like the increased lower hit. I will use that a thousand times more than a little more upper end. Still, it would be easy to do.

Maybe I will mod the spare head for extra top end...

[Nitroused383]

I don't know if this is possibly but I think you should try it. My bike around 1500' puts down around 235 psi with the stock compression. Since you're at a much higher elevation could they raise the compression up enough to be around 240 psi or so?

[RCannon]

Thats exactly what my compression turned out at....240 psi on possibly the worst compression tester ever made. The Harbour freight model. This is with the mod 06 head.

I have no ides what the mod 01 head turned out at. The hose for the tester crapped itself the next test.

[Pincushion]

I don't know if this is possibly but I think you should try it. My bike around 1500' puts down around 235 psi with the stock compression. Since you're at a much higher elevation could they raise the compression up enough to be around 240 psi or so?

What advantage would proper squish clearance have in our situation? I also ride at 1500ft.

If milling the head raises compression would I have to run race fuel at our elevation?

[Faded]

What advantage would proper squish clearance have in our situation? I also ride at 1500ft.

RCannon said it:

result 1......Upper midrange that is strong..really strong.

result 2......Bike was lean. How could I tell? The plug was no longer BLACK. It finally changed colors. (Cleaner jetting)

result 3.......Throttle response was .....silly. The stock bike is something, this is at a whole new level.

One other small detail....3rd gear under quite a load........severe uphill with a sand surface....week old pump premium with yamalube r, 32:1...no pinging. motor actually much more quiet than before.

[Pincushion]

And no need for race fuel at lower elevations?

If so, I'm sold and will be cutting that sucker quick time.

[RCannon]

So far, so good on the race gas thing. The race gas was reasonably priced a few weeks ago. Most local places raised it to 9.50 per gallon! It will not take long to pay off head mods at that rate.

[Faded]

And no need for race fuel at lower elevations?

As long as the head volume is kept the same you're not changing the compression ratio and it'll run fine on 95 octane (RON) fuel as suggested by the manual...that's 91 octane (R+M/2) for us in the US.

You machine the gasket surface of the head to get to your target squish clearance. By doing that you also reduce the head volume and up the compression ratio. This can be corrected by re-machining the 'bowl' deeper or at more of an angle into the head to get some volume back. Just make sure you don't narrow the width of the squish band unless that is your intention. You should CC the head before and after to so you know what you're dealing with.

A competent machinist will understand and shouldn't have a problem performing these tasks.

[2strok4fun]

And no need for race fuel at lower elevations?

If so, I'm sold and will be cutting that sucker quick time.

Taking a guess, cutting the same ammount on a head for sea-level to 1500 asl would be needing race gas or some race gas even with the improved combustion efficiency that the tighter squish nets. That is unless you have someone good to cut and reshape the dome to take out some cc's of material to have closer to stock compression ratio and improved squish. But then it is a more complex mod then simply cutting the head base.

Dont want to confuse the issue, but want you to be safe as well.