[Danny485]

Anyone know if all TRX, ATC, CT (70) heads are the same dimensions?? The head that’s on my trx is stamped EC-4, I’ve been informed the oem heads for trx70’s should be stamped HM-F4? I’m in the process of rebuilding the top end, not sure if I should look for a new head or not. I’ll take any help I can get!! Thank you.

 

[fatcaaat]

They are all interchangable but they are not all the same.

 

[kirrbby]

My guess is that you have the original, and correct head. Honda used different stamps on the same heads/castings. But trx70s are one year only bikes...86/87 but only produced for about a year, I think. There isn't much info out there about the specifics...such as head stamps.
And the engines...stators, and crank and such are one year oddball stuff too.
I'd plan to use the head that you have...buy a piston for a trx90. You just need the piston to match the head...matching dome to combustion chamber.
If you have the head off...and the new piston...show us some pics.

 

[Danny485]

Below are a few photos. I have a new piston, rings, gaskets and valves on the way. Just got the cylinder honed and everything is staying stock at 47mm.