BannedCR500Riders.com

ok, well now I know Adam has looked at this topic, but I couldn't find it, and I was not sure if he had measured the squish band dimensions angles, and volume, as well as bowl dimensions, in addition to the total head volume.



These dimensions were as close as I could tell with the tools I have.
I don't have a machine shop or engine building shop.

additionally I measured squish band angles, both were 17 degree's initial as close as i could tell with the tools I have.

I also had a pro x piston on hand.
From what i observed it has the identical 17 degree initial angle and a radius identical to the stoch squish band radius. So my old motor either had the angle cut wrong at my machine shop, or the wiseco i ran had a different dome radius.

I am not seeing any situation where and part of the charge would be trapped away from the bowl / spark plug

86 head pictures





01 head pictures




I will say this, this is the best low dollar mod i have ever done on a stock cr500 motor, .... I cut 1 mil or .040" off the head.... do not do this with pre 87 motors. The 87 and later heads had the piston to head clearance to get away with it. Should always check your P to H clearance before hand anyway.

I have been milling the heads on all my CR500's since 1987, trying to acheive .040 or more clearance, and best results with .050 on pump fuel.


any info to add, or questions are encouraged.

I also checked the prox piston for the exhaust port problem Adam brought up, and I found my new 89mm jug exhaust port was 1mm wider than the 91.5mm prox exhaust face.

That difference would be even more dramatic if comparing the 91.5 mm piston to a 91.5mm bore job, due to port taper.

Good point you brought up Adam.
Thanks!

so, on the HF is the margin .015 (1985) or .040 (1986)
the HF heads are the same chamber as the ML 87-88 heads, with 87 having a margin of .035 and the 88 at .040
later heads with the ML3N casting have a .070 margin and the ML3R is you checked is .080

the head gasket changed and changes the volumes aswell.

basically equals out the chamber volumes huh. gives you a chance to do some testing without cutting tho.

Thanks Adam,
More great info!

Roostius_Maximus wrote:so, on the HF is the margin .015 (1985) or .040 (1986)
the HF heads are the same chamber as the ML 87-88 heads, with 87 having a margin of .035 and the 88 at .040
later heads with the ML3N casting have a .070 margin and the ML3R is you checked is .080

This HF1 head I got from Seanmx has no margin at the edge of the piston, he said it came from an '86. It may have been cut.

The ML3R I have has .070" margin, I measured it at 1.75 mm.
My hand writing is messy I guess

I am away at work, but i will be sure to measure the total head volume the squish depth/margin is accountable for on the ML3R, so I can determine how many cc per .010" gasket fairly accurately.



that will be good info for calculating and adjusting compression ratios too!

I really kick myself for selling all my old 500 stuff!
I had 2 spare motors, manual, jets, enough gaskets and seals to rebuild both, spare heads, pistons, rings c clips, reeds, etc etc.... its becomeing very expensive to accumulate and more difficult to find good deals on the 500 stuff in these parts.

I should have never even tried the 4 stroke stuff... other than my KTM505, I was very dissapointed, and even that bike just didn't have the brutal hit I enjoy so much.

an excerpt from Eric Gor's Book....
I loaned mine to a friemd and never saw it again....

"Cylinder Head
Reshaping the transition between the combustion chamber and the squish band can be accomplished by turning the head on a lathe. Set the tool angle to 25 degrees and cut into the squish band starting 15mm from the edge of the chamber. Install a projected nose spark plug such as a NGK BP6ES."

"Cylinder
Raise the exhaust port 1.5mm and widen the two ports 4mm on each outer edge.
I have had the best luck running oversize Wiseco pistons, set to 0.004-inch piston to bore clearance. "
My clearence is/was 0.003752
This is what Trinity's 2stage porting did to mine expect the plug.
Shouldn't that be a BP 8 ES plug?

The old HF1 head has a squish band that is 15mm wide, the new heads have a squish band 19mm wide.
Both are ~17 degree radius squish angle.

He must mean cut the 25 degree angle 15mm from the outer edge of the bore/ squish band.
On the new heads that would be 4 mm off the edge of the bowl, and the old one wouldnt get cut.

otherwise a 4mm portion would be at 17 degree at the outer edge of the bore, then 25 degree from there will leave you with a massive bowl and near zero- only 4mm of squish band.
The MSV would be very slow... with no squish band, or one with 12 degree's more than the the piston dome....

I cut mine 4mm from the edge of the piston bore, outer edge of the squish band like he says, and it turned my bike into a dog. I hated it.
also it seemed to trap the charge in the 4mm area, my soldier was pinched down tightest at the edge of the new cut, it appeared like it would have affected the msv.
So am I missing something? cause it sure sucked for me.
I think it was a major cause of my detonation issues.

dubious01 wrote:ok, well now I know Adam has looked at this topic, but I couldn't find it, and I was not sure if he had measured the squish band dimensions angles, and volume, as well as bowl dimensions, in addition to the total head volume.



These dimensions were as close as I could tell with the tools I have.
I don't have a machine shop or engine building shop.

additionally I measured squish band angles, both were 17 degree's initial as close as i could tell with the tools I have.

I also had a pro x piston on hand.
From what i observed it has the identical 17 degree initial angle and a radius identical to the stoch squish band radius. So my old motor either had the angle cut wrong at my machine shop, or the wiseco i ran had a different dome radius.

I am not seeing any situation where and part of the charge would be trapped away from the bowl / spark plug

86 head pictures





01 head pictures




I will say this, this is the best low dollar mod i have ever done on a stock cr500 motor, .... I cut 1 mil or .040" off the head.... do not do this with pre 87 motors. The 87 and later heads had the piston to head clearance to get away with it. Should always check your P to H clearance before hand anyway.

I have been milling the heads on all my CR500's since 1987, trying to acheive .040 or more clearance, and best results with .050 on pump fuel.


any info to add, or questions are encouraged.

throw all them in the bush . contemplated posting this pic but if it can help someone then its all good . i feel its the best and proper way to correct a stock head.