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View Full Version : 50cc 4-stroke head milling advice



airmobile101
08-27-2008, 03:10 PM
I need some advice from any 4-stroke 50-90 tuner. I was planning on milling my sons head before the next harescramble series kicks off in Oct. Well, I called a few places(machine shops) and they said ,"no problem". Well, I called one guy and he threw me a curve. He claims if I mill the head, it will retard or advance the timing(depending on which way the engine rotates). Im thinking, "ahhh, ok". Then claims with me doing that,the cam chain would have no tension. Now I thinking,"wouldn't a cam chain tensioner pick up the slack?". Anyways, I was only wanting to mill 15-20 thousands off. Its current stock compression is low. 10:1:? . Something in that range.

Anyways, I can adjust the timing,but will the cam chain be an issue? Or, is it worth even doing?

Only reason I thought of this is because he has to run his quad in the 51-70 modified class(they don't have a production 50 class). Not exactly easy when your running against a DRX 70. But, with that said, he still catches up to a few stock TRX90 riders.

Its an 07 Kawasaki(kymco) 50

LT80
08-28-2008, 07:59 AM
I've not heard ofanyone milling the head on a 4 stroke. I'm sure it has been done but with attention to the above stated problems.
Comp is usually raised with a aftermarket piston.
Try that nice lady at Poweroll (SP). :)

silicaman
10-03-2008, 10:18 AM
You should consult the pit bike guys and get their opinion on that. I know that there is high compresion piston mods that do not afect the cc requirement.

airmobile101
10-10-2008, 01:59 AM
I just went ahead and dropped him down a tooth on the front sprocket. That seemed to help him out alot.

airmobile101
10-15-2008, 12:48 PM
Well, it seems I could never leave anything alone. I yanked my sons engine yesterday to do a ring job on it and to do a valve adjust. Let me tell you this, you knock off .0200 of that head, your gonna notice an improvement. To make a long story short, instead of installing the cylinder gasket, I slapped some blue Permatex gasket RTV on there instead. The stock gasket measure out at .0200(I calipered it). It really woke up his cam up, Zero flat spots in the entire RPM range. This with me riding it. So, I had him ride it after he go home from school for some hard numbers. I got a 100ft drag setup for him to run in front of the house. I use this to determine if a mod works or not by timing him. In a 100ft, he was averaging 6.03-6.18 seconds before the gasket removal. Now he is nailing 5.82-5.89 without the gasket. Not too bad for a 4 stroker. The funny thing is that little quad has some torque now. My son laid into the throttle and the front wheels damn near came off the ground:D I give my props to Kymco/Kawasaki. So I would say its safe to mill the head at .0200 or just remove the base cylinder gasket and slap some Permatex on it. Im satisfied with the power now, so its time to work on his suspension.

LT80
10-15-2008, 01:03 PM
Cool! :)

jplltz50
02-21-2009, 08:08 AM
two years ago i yanked my sons 2006 ltz 50 head had .025 taken off and the results were amazing.......these motors dont have an overhead cam so you dont have to worry about cam tension etc....just readjust pushrods.

i probably could have gone maybe .030 but went on the conservative side

desratt
02-22-2009, 05:40 PM
you use the same dyno as we do....

keep me up on any kawi50 upgrades

airmobile101
02-22-2009, 08:13 PM
Originally posted by jplltz50
two years ago i yanked my sons 2006 ltz 50 head had .025 taken off and the results were amazing.......these motors dont have an overhead cam so you dont have to worry about cam tension etc....just readjust pushrods.

i probably could have gone maybe .030 but went on the conservative side

Ours is an SOHC, So I didn't want to take a chance of slapping the valve. .20 is a safe bet with the Kymco's.

desratt
02-23-2009, 11:57 AM
anyone have a lead on aftermarket pistons???

airmobile101
02-23-2009, 02:40 PM
Well, from what I can gather and I could be wrong , its the same piston as a CRF50(my KFX50). Powroll makes a HC piston. But Im already running 155 psi at the head, so I don't think that would help much. The head would probably blow up with that piston on my sons bike! FYI, the bike ran like sh*t until I ran 75% 110 octane mixed with 25% 93 octane.