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

[LifeRider]

This winter I may try purchasing a new head assembly for my 250 Hawk DLX and milling off .030 to raise the compression. Will also probably clean up the ports and polish the exhaust port. Has anyone out there tried this on the CG engine? Hoping to gain some incite from others who have tried this.

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

Examples:

2010 Dodge challenger purchased new (added): 6.1 Hemi, Kenne Bell supercharger, Meth injection, Corsa exhaust, custom interior and generates 650 HP with a 3:91 gear – 6 speed short throw Hurst shifter.

2016 Dodge challenger purchased new (added): Ray Barton built 392 HEMI Kenne Bell supercharger, Meth injection, 200 shot Nitrous, custom exhaust, Paramount transmission, 1500 hp drive shaft-axles and generates 1388 HP– 8-speed automatic. Worlds fastest Scat Pack record set in 2016. Car was in 4 magazines in 2017.

Road racing VW cabrio: won mid-west GP class 2016.

My list could go on but this is about the BIKE! Please help – Is it worth doing the head work on my Hawk?

[JerryHawk250]

We have a few that have done it. Me being one. Best mod ever. Megadan put all the information and links into one thread to make it easier to find. http://www.chinariders.net/showthread.php?t=23004

[alex_in_az]

is it possible to remove the cylinder head with the engine still in the frame?

[JerryHawk250]

Originally Posted by alex_in_az

is it possible to remove the cylinder head with the engine still in the frame?

On the Hawk you can for sure.

[Megadan]

Jerry beat me to it, but I can comment on the milling. I took off .039 (1mm) of a non stock head that had a smaller quench ring than the standard head and ended up at 10.3:1 static compression. If you do the standard head to .030 you should end up roughly around 9.8:1

Definitely invest in cleaning up the ports. Mostly cleaning up around the valve guides will make quite an improvement, especially on the exhaust side around the bowl and roof, and then smoothing all of the transitions to finish it off. Nothing fancy, but quite effective. The intake side needs very little in terms of material removal outside of opening up the port at the flange and smoothing that in, and obviously cleaning up around the guide again into the bowl.Pair it with a 30mm smooth bore carburetor and it takes the Hawk to quite a new level of performance. The PZ30 and VM26 clones are just too restrictive once you open up the breathing. Seeing as you have the EFI bike, it would depend on the size of the throttle body.

Is it worth doing? Absolutely. Will it give you the top end performance you are likely seeking. Yes, to a point. I have discovered the final limitation to top end performance to be the cam. Without changing the cam, what you end up with doing a ported/decked head with a larger carb like my PE30 or Jerry's PWK30 is a noticeable gain through he RPM range, but a big boost between around 4000-7000rpm. After that point the power starts to fall off due to the cam profile. What it does do is make the bike much stronger to pull taller gearing.

I am waiting on a new cam from Brazil as we speak to solve that last issue.

Like you, I don't tend to do stock very well lol.

Originally Posted by alex_in_az

is it possible to remove the cylinder head with the engine still in the frame?

Absolutely. I have a video where I did just that. No problem.

[JerryHawk250]

Liferider,
Do you know right off hand if the throttle body on the EFI is 28mm or 30mm? The ECU should adjust to the changes. 30mm throttle body would be perfect.

[Megadan]

Originally Posted by JerryHawk250

Liferider,
Do you know right off hand if the throttle body on the EFI is 28mm or 30mm? The ECU should adjust to the changes. 30mm throttle body would be perfect.

Depending on the style of throttle body it might be possible to find one that would bolt up. There is a seller on Aliexpress that sells the generic throttle bodies with options such as with or without the injector port, etc and offers a machining service to take the standard 28mm to 30.

That is one area where us carby heads are in the dark. We don't know enough about the DLX to offer much insight.

[alex_in_az]

Originally Posted by Megadan

Jerry beat me to it, but I can comment on the milling. I took off .039 (1mm) of a non stock head that had a smaller quench ring than the standard head and ended up at 10.3:1 static compression. If you do the standard head to .030 you should end up roughly around 9.8:1

Definitely invest in cleaning up the ports. Mostly cleaning up around the valve guides will make quite an improvement, especially on the exhaust side around the bowl and roof, and then smoothing all of the transitions to finish it off. Nothing fancy, but quite effective. The intake side needs very little in terms of material removal outside of opening up the port at the flange and smoothing that in, and obviously cleaning up around the guide again into the bowl.Pair it with a 30mm smooth bore carburetor and it takes the Hawk to quite a new level of performance. The PZ30 and VM26 clones are just too restrictive once you open up the breathing. Seeing as you have the EFI bike, it would depend on the size of the throttle body.

Is it worth doing? Absolutely. Will it give you the top end performance you are likely seeking. Yes, to a point. I have discovered the final limitation to top end performance to be the cam. Without changing the cam, what you end up with doing a ported/decked head with a larger carb like my PE30 or Jerry's PWK30 is a noticeable gain through he RPM range, but a big boost between around 4000-7000rpm. After that point the power starts to fall off due to the cam profile. What it does do is make the bike much stronger to pull taller gearing.

I am waiting on a new cam from Brazil as we speak to solve that last issue.

Like you, I don't tend to do stock very well lol.



Absolutely. I have a video where I did just that. No problem.

how were you able to order the cam from Brazil? I'm very interested in doing this myself.
I also don't do stock and am in the process of getting a webber DCOE45 dialed in on my '74 MG

[bogieboy]

Originally Posted by alex_in_az

how were you able to order the cam from Brazil? I'm very interested in doing this myself.
I also don't do stock and am in the process of getting a webber DCOE45 dialed in on my '74 MG

i would be interested in the cam ordering as well...LOL

[JerryHawk250]

Originally Posted by bogieboy

i would be interested in the cam ordering as well...LOL

The thing to do would be to have someone duplicate it here in the US.

[LifeRider]

Thank you everyone..... This has been very enlightening. It amazes me the amount of knowledge resource here. I will need to find more info on the throttle body.

This stuff is cheering me up on the winter project. Nasty weather ahead here in the midwest, so I need give my 2 wheeled summer babies some love.

[JerryHawk250]

The 28mm throttle body would probably be okay. The 30mm would flow much better.
I'm 61 myself. Just reading your first post I think we have the same sickness. lol Can't leave anything stock.
My last daily driver was a 6300 lb. 2000 3/4 ton long bed Chevy with Turbo charged 6.0L that was pushing just over 500hp That ran 13.90's at the track. I would have to leave the 5th wheel hitch in the back to help with traction. I've been involved in racing since the age of 13 with my older brother have a few race cars. Then in my early 20's was dating Leonard Hughes of Candies and Hughes race team' Daughter. Then at 30 I met my wife who's Uncle is the Late Paul Candies of Candies and Hughes. That was awkward. lol So yeah racing and modifying engine is in my blood too. lol Paul Candies two sons PB and Brett still race along with Brett's wife and son. Candies Family Motorsports.


You'll find the little CG engines are fun to fiddle around with.

[LifeRider]

Where do you suggest that I can purchase a spare head assembly and gaskets? Would like to get these on order.

[JerryHawk250]

Originally Posted by LifeRider

Where do you suggest that I can purchase a spare head assembly and gaskets? Would like to get these on order.

CSC. The TT250 head is a much better casting than the Hawk head. https://store.cscmotorcycles.com/TT2...ENTS-s/363.htm

[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. Valves needed to be readjusted. Head gasket was reusable. Porting tossed metal chips EVERYWHERE, head cleanup was a bitch so over to a bath in the ultrasonic tank.

If you are comfortable popping an engine head off and have basic hand tools be clean and methodical and you can do this too. Tho you’ll have to earn it - it’s one of the best mods you can do on a Hawk. I worked slowly and it was a 7 hour Sunday job start to finish. Decked & Ported.