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Head mods on KX 85/100: how much to take off?

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Just rebuilt our 02 KX 85. converted to a KX100. Compression is running about 148psi. I'd like to see it bumped to 175 but don't know how much to shave the head to accomplish this. Talked to 3 local shops who do work like this but they won't do it unless I tell them exactly how much to take off. One guy said start with .0020 and see how it goes...but he charges for each time we shave. Any guidelines of what to strart with would be great. We've noticed higher compression results in more bottom end which these bikes really want for.

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If you can't find your answer on the boards check out this web site. www.phatheadracing.com I bought the phat head from these guys for my KX125. It comes with a cool head and two different compression domes. The head and domes are sealed with O-rings instead of gaskets. They have about 10 different compression domes to choose from. Also I was able to save the stock head incase I wanted to put it back. Phat head should be able to help you out and the kit if I rememeber cost's about $200. It's not a bad price and the guess work is taken away. Besides if you cut the stock head and it's not enough or too much money is wasted. Check them out. :thumbsup:

I just looked at their web site and for the KX100 the head and domes run $149.00.

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Thanks for the response. If I can't figure out how much to shave off the stocker I'll probably just go with the Phathead setup. :thumbsup:

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I run the Phat head KO3 with a 94cc bbk and get about 180 psi comp.

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I run the Phat head KO3 with a 94cc bbk and get about 180 psi comp.

jbrun

Can you give some info on your 94 bbk and head? What kit did you use and do you remember how much it cost? What are the beggest improvements with the bbk ? I'm assumeing you did this for more bottom end? My son rides a KX 85 off-road and play MX - more bottom end would be great - the bike has plenty of power for him.

Is 180 psi a high comp head? What is stock? If you run 180 psi do you need to run race gas?

TX

dp :thumbsup:

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dp400 to get more bottom end off the 85 did you put a bigger rear sprocket? On my 125 it came with a 48 and I put a 51 on there and out of the hole or berms it pulls the front wheel in 3rd.

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Crusty, did you have any run time on the conversion before you took the compression reading? By going to a larger bore with the same head, your compression should have gone up as you are trying to squeeze a larger amount of air/fuel into the same head volume. Tdub

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jbrun

Can you give some info on your 94 bbk and head? What kit did you use and do you remember how much it cost? What are the beggest improvements with the bbk ? I'm assumeing you did this for more bottom end? My son rides a KX 85 off-road and play MX - more bottom end would be great - the bike has plenty of power for him.

Is 180 psi a high comp head? What is stock? If you run 180 psi do you need to run race gas?

TX

dp :thumbsup:

I did the BBK for the all out desert. I run VP U2pro race gas. There is no way I could run pump gas on that engine. The BBK gave the bike more power so I could go to taller gears.

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With the head and all the macine work it cost me around 400.00

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With the head and all the macine work it cost me around 400.00

Thanks for the info :thumbsup:

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dp400 to get more bottom end off the 85 did you put a bigger rear sprocket? On my 125 it came with a 48 and I put a 51 on there and out of the hole or berms it pulls the front wheel in 3rd.

Yes I've geared it down 3-4 teeth from stock. I also put a torque spacer in and a flywheel weight. :thumbsup:

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Had about 10-15 hours on the bike of trail riding when I took the reading. I put a KX100 head on afte the conversion because if I used he 85 head I'd most likely see the piston doing it's own maching job :applause::ride: Just a guess. Could I really put a 99cc piston in and stil use the 85 head? Never crossed my mind. Well hopefully this tread is done being hijacked and I can get some good responses to this query :thumbsup:

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Thanks for the response. If I can't figure out how much to shave off the stocker I'll probably just go with the Phathead setup. :thumbsup:

You might simply be able to get a thinner head gasket from Kawasaki. I know on my 500 there are 3 different thickness head gaskets available. 1.0 mm, .4 mm (standard), and .2 mm. I run the thinnest .2 mm (I run uncut Cam II race fuel). Don't get into shaving heads and thinner gaskets unless you are willing to commit to running race fuel.

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Unless you want to spend $5+ a gallon for race gas I wouldn't shave the head. Having the cylinder ported/polished and matched to the cases would be money better spent.

That being said, about .025 to .028" between the top of the piston and the squish band at the cylinder wall (measured at TDC) worked very well on 125cc kart engines, but WILL require race gas, 102 octane minimum.

If you see any pitting on the top of the piston after making modifications you have detonation and need higher octane or more head clearance.

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I have a kx100 and i just installed a phat head with the 5.6 cc dome. I check the compression and its at 300psi. I know that when the powervalve opens the compression drops but that still sounds high. What do you guys think? I've only installed a vfroce 3 reed and the phat head, other than that its stock. What jets should i start with?

Thanks guys

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