cylinder head differences By dryshave (Read 4,574 times)

[dryshave]

Have a CH250 motor and a CN250 motor. Noticed that the piston head was different as well as the cylinder head - the CH250 has an H-B stamp on the cylinder head and the collar around the firing chamber is wider (less cant?) whereas the CN250 has an H-A stamp on the cylinder head and the collar is narrower (more cant?). The pistons are significantly different whereas the CH250 has a recessed top, the CN250 has a slight domed top.
Apart from the visible differences, are the pistons interchangeable?
Does the piston shape account for any performance differences, I've heard the Helix motors were more powerful than the elite models (probably from having to haul all the extra weight - no offense).

I can add this next item to another thread if it's not the right place to discuss... but I've tried out the 13" front wheel with the disc brake on the CH250 front end and it all appears to fit... read a couple Yahoo Group threads about this, but it was inconclusive. I've noticed the'87 CH250 had a 10" disc brake, would it be better to go that route?

[JR]

Wow Dryshave! My heads a spinning! I've been doing some reading on the differences and the interchangable things on the CH250, CN250 and the CF250 and it appears there are some but how many is the guess.

For instance I've read the the CF250 uses 23 X 18 roller weights and the CN250 uses 24 X 18 but you can use the 23 X 18 in either?

I'll also holler a Cruiser he knows a lot of this and I'll see what I can find out too.

[dryshave]

Thanks, would be greatly appreciated. The question regarding the 13" or 10" tire would have to be, what would be the advantage one has over the other. The steam punk scoot is coming along nicely, I'm on holidays next week, so will be going hard on finishing the fiberglass (more pics soon)

[dryshave]

The 13" wheel and disc brake will not work from a Helix to a CH250 front end. The problem is with the support arms. They won't align correctly as the Elite 250 forks are narrower and won't allow the speedo module to mount, and any adjustment to the support arms would cause the wheel to ride 3/4" off centre. Could be done if I was stubborn enough... but I know when to drop the wrench.

[cruiser]

Jun 29, 2012 10:02:08 GMT -6 dryshave said:

Have a CH250 motor and a CN250 motor. Noticed that the piston head was different as well as the cylinder head - the CH250 has an H-B stamp on the cylinder head and the collar around the firing chamber is wider (less cant?) whereas the CN250 has an H-A stamp on the cylinder head and the collar is narrower (more cant?). The pistons are significantly different whereas the CH250 has a recessed top, the CN250 has a slight domed top.
Apart from the visible differences, are the pistons interchangeable?
Does the piston shape account for any performance differences, I've heard the Helix motors were more powerful than the elite models (probably from having to haul all the extra weight - no offense).

I can add this next item to another thread if it's not the right place to discuss... but I've tried out the 13" front wheel with the disc brake on the CH250 front end and it all appears to fit... read a couple Yahoo Group threads about this, but it was inconclusive. I've noticed the'87 CH250 had a 10" disc brake, would it be better to go that route?

Here's a little history on these engines that might help understand some of the differences. The CH250 was used on the Honda Elite. The CN250 was used on the Honda Helix which was a larger replacement for the Elite. The CF250 is a Chinese clone of the CN250 Honda engine. The cylinder heads of the CF250 and CN250 are supposed to be interchangeable which would probably mean that the pistons are also interchangeable.

The CN250 was updated from the CH250 with a domed piston which probably necessitated a different cylinder head to ensure valve to piston clearance. The domed piston most likely gave a higher compression ratio which equals more power. Trying to use the CN piston in a CH engine might result in the valves hitting the piston. Using the CH piston in the CN engine would probably result in a loss of power due to lower compression.

[dryshave]

I agree. I wasn't thinking that it was possible to swap them around, but trying to figure out if the domed piston was one of the reasons for the Helix's greater engine power. Have taken them in to be honed and valves re-set, expect them back by the weekend - engine's coming together. Just need the gasket kit and steam/punk will soon be ready for an engine test. Might be time to focus on the brakes.... Thanks for your info, it's learning something everyday.

[dryshave]

Have gone with the oversized CN250 head / new piston and oversized rings. I will have to check but I believe they were .005 but don't quote me. New valves and springs (am thinking about a loftier cam as well - but that's still just outside the radar for the time being
Engine is back together and lookin' purdy

[scootersonlyrepair]

I have an elite engine that my friend gave me for parts for my helix. So will the head work from the ch to the cn?my head is cracked from over tightening the exhaust. Anyone in Oakland or nearby please text 5108721104 anyone else who knows also text

[scootersonlyrepair]

Nov 28, 2016 14:38:43 GMT -6 scootersonlyrepair said:

I have an elite engine that my friend gave me for parts for my helix. So will the head work from the ch to the cn?my head is cracked from over tightening the exhaust. Anyone in Oakland or nearby please text 5108721104 anyone else who knows also text

,
Wooo 5 months and no answer. Thanks .

[cyborg]

I didn't eve the post,,,it's an antique thread,,,,no most internal parts don't match up,,,