250x head on 350x

[lndy650]

anyone ever try this? the 250x has smaller valves but it has a roller bearing cam... i have a TC 250x head i want to put on my 350x big bore until i port the 350x head. i know they bolt up the same i just havent checked if the cam chain is the same length. also my big bore is on a 250x and i have a TC Supertrapp exhaust for the single outlet on the 250x head.

[lndy650]

top sprockets are 38. anyone have a spare 350x cam chain to count the links? 250x is 110. i think the 350x is 112 but the cylinder is taller...might just have to try it.

[HondaHarry]

that would make the bottom sprocket 19 tooth.
all cams rotate at half crank speed.

not sure if the cam chain is the same length though. HH

[lndy650]

guess i should have thought of that lol makes sense

[racerxxx]

top sprockets are 38. anyone have a spare 350x cam chain to count the links? 250x is 110. i think the 350x is 112 but the cylinder is taller...might just have to try it.


350X Chain:

CHAIN (75-010M-114)------One would assume the the 114 is the links
14401-HA7-671 (honda part#)


250X Chain:

CHAIN, CAM (110L) ------ One would assume the the 110 is the links
14401-HC0-003 (honda part#)

I'd measure everything, or take the time to port the 350X head

[Mosh]

What about the single exhaust port on the 250X head?
You gonna make a pipe for that?

Also is the valve spacing different between the 2 heads for the piston reliefs?
What about the compression dome? Is it sized for the 350X head gasket to seal properly? I wonder if a 250X head gasket wont be big enough in diamter to fit the 350x sleeve for a proper seal.

What about the cam lifts between the 2 heads?
Will the 250 valves hit the 350 piston due to longer duration or higher lift?

[Preddy05]

250x valves don't hold up in a stock 250... so putting that head on a 350 sounds like a bad idea.

[lndy650]

its acually a 452 big bore. the 250x engine i have was built by Tom Carlson for Nac's in 1998 and is a 350 89mm piston my 350x has a 92mm piston.
i want the single pipe because my bigbore is in my Nac's 250x chassis. the dome is ok i just have to check if the valves are going to hit.
this is just an idea as the 250x cam setup is far superior to the 350x

[lndy650]

my TC engine has a bad crank thats why im considering this until i get the crank rebuilt then the 350 is going back in. that 350 is insane it would beat my yfz.

[Dirtcrasher]

I would think you'd have to recut the dome and check the squish.....

There isn't any issue with the 3509X head, just people running low on oil, not changing oil and the inability to install an oil filter correctly :D

[lndy650]

well it may become an issue with mine when because its a 92mm bore advanced timing ect ect... ive never had a problem but i dont like the setup. my engine gets very very hot in a 250x chassis and because of the thin cylinder walls from the BB.

[Mosh]

I think, GT Thunder or someone will line bore those 350X heads and fit them with a Ball bearing camshaft..At least that is what I heard a few years ago.

[lndy650]

that would be nice....

[SWIGIN]

I think, GT Thunder or someone will line bore those 350X heads and fit them with a Ball bearing camshaft..At least that is what I heard a few years ago.

megacycle cams has done this for years and are the only place i know that does this.


from what i remeber from back in the late 80s early 90s the heads do not swap as far as a bolt on deal.

[The Goat]

amp up the cooling with a proper oil cooler...

[lndy650]

i have 2 oil coolers on it already.the stock one with a 400ex cooler and the one you can get off ebay