Contemplating milling the CG head .030 to raise compression – Any input?

[Weldangrind]

Originally Posted by LifeRider

I seem to have a lifetime issue with stock performance, even at 60 years old. Need counseling, surely….

Most of us here require supervision.

[Megadan]

Originally Posted by Red Hawk

Things I noticed after .040 was nocked off and the ports were opened up. It finally kick started easily. The starter motor has a workout now as it passed the compression stroke at TDC. The exhaust note at idle and at RPM was cleaner you can really hear it breathing now and no crack/pop on idle. It also feels like it added 1/4 of the bikes HP range. And you WILL be rejetting for you carb guys.

Nail on the head. If you really focus on improving the exhaust port, which is by far the worst of the two, you will notice it at the muffler exit even at idle. The exhaust note is sharper - which is a good indication of increased exhaust gas pressure due to the increase in volume.

I still stand by what I say about where most of the improvement comes, which is the exhaust side.

The intake port is honestly not too terrible, mainly just needing some port matching and smoothing out with some material removed around the guide and a bit of blending here and there.

The increase in compression definitely can't hurt, but compression on it's own has never been a big factor in terms of power in my experience with engine building, and has often more been dictated by cam profile and maintaining a certain level of dynamic compression for proper ignition.

The exhaust side is what holds back these little motors the most. The bowl and the roof of the port around the guide is too low and forces the gas to make a very sharp turn right into a giant wall of excess material around said guide at a rather nasty choke point. if I had to guess, 70% of all of the material I removed came from those areas of the exhaust port.

My other suggestion, and one often left untouched by many, is to spend some time on the combustion chamber. At a minimum smooth out all of the sharp edges around the valves. I went a bit further and really blended all of the machinist ridges around the valves into the chamber itself to unshroud the valves as much as possible. This did increase my chamber volume a couple of CC's, but the benefit to flow past the valve into and out of the cylinder should not be under rated. This is how my chamber looked, almost all of this was done by hand except for the light polish job, which is kind of hard to see in the picture.




This is what I started with for a comparison.

[herbie]

I started working on my spare head and it looks similar to yours Dan. I tried to deck it thirty thousands off. I didn't do much to the combustion chamber other than buffing it out. I ported and polished the exhaust port and left the intake port alone. I may revisit the intake port if I don't like the performance but I'm thinking it will give me what I want the way it is now. Since this is a counterbalanced engine the one difference I found is in the head gasket. The oem one is thinner than the xmoto gasket I bought, so I ordered one from CSC. Mine also doesn't have the one O-ring on the stud like yours in your video.

[LifeRider]

I went to order the head from CSC and should not have mentioned the Hawk - My mistake now that cannot be undone. Here is what I requested.

Please quote the complete head assembly including head, valves, springs, rockers and gaskets for my Hawk CG 250.

I know dumb move.......

Their answer below.

James,

We do not sell Hawk parts, we only sell CSC TT250 engine parts. I cant tell you if the head for the TT250 is the same as the Hawk, they are different engines made from 2 different factories.

Here is a link to our parts for that engine, if you buy it for a hawk there is no return if it doesn’t fit.

Thanks

[JerryHawk250]

Don't worry it will fit. We have a few members that already installed them.

[NzBrakelathes]

Don’t worry they fit n better made etc
Old mate Motocheez has a head I dropped off but he’s not done it yet
You only need a head assembled you don’t need the top rockers etc
Valves in head and that’s enough
Head gasket n grab an extra cover gasket maybe exhaust gasket too.

[JerryHawk250]

If you haven't ordered it yet you can get it for much less at Brozz250.com. https://shop.brozz250.com/eshopprod_...r_Assembly.htm

[LifeRider]

I allready put in the order with CSC.

[LifeRider]

Originally Posted by JerryHawk250

If you haven't ordered it yet you can get it for much less at Brozz250.com. https://shop.brozz250.com/eshopprod_...r_Assembly.htm

CSC called and needed to back order some of my items. They where very good about letting me know - I give them credit for that and would purchase from them in the future. Allthough I canceled the order and ordered from Brozz250 and it was less than half the cost.

Thank You Jerry....

[Megadan]

Originally Posted by LifeRider

CSC called and needed to back order some of my items. They where very good about letting me know - I give them credit for that and would purchase from them in the future. Allthough I canceled the order and ordered from Brozz250 and it was less than half the cost.

Thank You Jerry....

Funny thing is, CSC is almost half the price of RPS parts through their dealers.

[JerryHawk250]

Originally Posted by LifeRider

CSC called and needed to back order some of my items. They where very good about letting me know - I give them credit for that and would purchase from them in the future. Allthough I canceled the order and ordered from Brozz250 and it was less than half the cost.

Thank You Jerry....

You will find that Jeff with Peace Sports Atlanta has a first class operation too. I don't know why I didn't send you to him first.

[Sochin]

I've had a TT250 head on for 2 years, works great.

[mixerdriver632]

can i buy a head for a borzz all ready done. mixerdriver 632

[JerryHawk250]

Originally Posted by mixerdriver632

can i buy a head for a borzz all ready done. mixerdriver 632

No, Not unless someone decides to start doing it. I would and have done a couple but I don't think you would want to pay the price. lol It takes a good bit of time to port and deck a head. If someone had a CNC machine that was programmed to do it then it might be doable at a reasonable rate. Porting is not hard, just time consuming.

[Megadan]

Originally Posted by mixerdriver632

can i buy a head for a borzz all ready done. mixerdriver 632

You are just buying a head in that instance. It would still need porting after purchasing. Now, if you can find somebody to port the head for you is a different question. I know Jerry has done a couple heads for other guys before, so you might want to contact him and see what he tells you.

EDIT: Nevermind, he beat me to the post by like 3 seconds.