exhaust valves stem size the same as intake

I got this mystery head that had a mark on the combustion chamber that indicated something blew up in the bottom end. Cleaned up the mark. Now there's also one exhaust valve spring seat that obviously has been busted up. Problem is, it's not stock inner diameter. Exhaust valves on this head have a stem that's as thick as intakes. Any idea who made those? I just need ONE top spring retainer to make this otherwise good head work. Thanks in advance!

I might assume the head has been modified for reliability. Did you remove the head? Check the valve face for markings? Ask the PO what motor work was done and/or where?

I got this mystery head that had a mark on the combustion chamber that indicated something blew up in the bottom end. Cleaned up the mark. Now there's also one exhaust valve spring seat that obviously has been busted up. Problem is, it's not stock inner diameter. Exhaust valves on this head have a stem that's as thick as intakes. Any idea who made those? I just need ONE top spring retainer to make this otherwise good head work. Thanks in advance!

 

You didnt say what year the bike is or what year cyl head your looking at is but up through 07 the int and exh valve stems were the same size-5mm.

 

In 08 for the 250R the exh valve stem size changed to 4.5mm but the int stem size didnt change. If you look at a parts diagram and compare you'll see some of the other exh valve components were changed also, make sure to get the correct parts and dont get them mixed up with the other size. Hope that helps.

Edited by TDW

All I was told is that it got rebuilt together with the bottom end and the bottom end wasn't assembled right, threw a rod almost immediately. From the shape of the ports it's definitely not an 04-05 and likely not an 08, so most probably 06-07. Intakes look very similar to an '08 and exhausts are a bit different. One intake valve was slightly bent so replaced that, exhaust valves and combustion chamber have almost no carbon buildup so I believe in the story.

Thanks for the tip on 08 head! I actually have an 08 head sitting here too. Exhaust valve stems on the "mystery head" are .5mm thicker than 08, 5mm. It also has a funky dual spring deal for valve springs.

Edited by dakh

So yea, thank you -- looks like I just need a retainer from pre-08 head. Cool!

If it uses dual springs it could likely be using a kibblewhite spring kit which would require the correct retainer, not a honda retainer.  

 

Are all four of the springs double springs?

 

Would be a good idea to figure out exactly what parts the mystery head has installed to get the right replacement parts. 

I decided not to play any games and just get stock springs/valves/retainers, to eliminate any guessing games. Not that expensive on the exhaust side so it's all good. Thanks again for your help!

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