XS250 to XS400 rocker cover question

[Bellerophon]

Hello All,

Thanks for accepting me onto the forum.

A while back I purchased an XS250 engine with a the parts to covert it to a 400 for a bit of fun.

This afternoon I was cleaning and building the XS400 rocker cover the when I found that I was missing a rocker shaft. So rather than rush out onto eBay and buy a shaft I took the top off the XS250 and low and behold it looked identical!

I am now wondering whether I can use the 250 rocker cover as it seems to be in much better condition - I have read on here that, although seemingly identical, you should try and keep the two rocker covers and heads as a set as they have matching numbers (indeed the two sets have corresponding numbers between their covers and heads). Can anyone elaborate on this?

Also, if you look at the rockers, the tappet adjuster is less worn on the 250 but the rocker face is less worn on the 400. They also have different numbers cast into the sides (see pic) - anyone know what they mean?

So I am left wondering whether I can strip both rocker covers and take the best bits out of each and reassemble - any advice would be greatly appreciated.

Pictures:
Rocker covers - 250 on left, 400 on right (after cleaning!)
Rockers - 250 on bottom, 400 on top

 

[NewHavenMike]

In general, I think its a bad idea to mix up engine parts that wear together. Lobes and lifters wear together and if you mix up two different wear patterns then you might accelerate wear. If the camshaft looks absolutely spotless, you could probably get away with it.

I bought a used camshaft on this site to swap into my 360 to see if theres any performance benefit. I actually bought a GoPro to record my findings and post it here if the cam swapped over and worked without an interference. I still havent done it yet because im worried about mashing two different wear profiles. I may have the cam polished/refinished..

Also, my Brother insists that I use zinc additive and kind of freaked out when I told him that I only use regular modern motorcycle oil. He specifically noted the flat tappet cam but Im pretty sure theres some zinc in Castrol. Ive been fine over the last 4000 miles since rebuild.

 

[xschris]

You need to use a matched rocker box and head as they are line bored to fit. There are numbers stamped into the carb side of them where they meet. As for the internals if they are in spec you should be ok. If you have to use used parts then go for it but new is always best. That's getting very hard to do with these bikes.

 

[Bellerophon]

Thanks for the replies. It's a fair point about mixing up used parts that haven't been "wearing on each other" as such. As far as the cam goes, I have two replacement cams in the job lot I bought, but from inspecting them they look no different to each other or the one in the 200, so I suppose there's another conundrum on which one to pick.
Yup, the numbers on the casings match so I will keep it that way - bit of a pain in the bum as the tachometer gear is broken in the 400 one so will need to swap that out too.
I don't think they're beyond use so don't really want to purchase new ones, especially as I'm trying to keep the costs low where I can - I am buying all new rings, gaskets and seals however.