Mix and matched engine parts? Need help with ID!

[dpow]

Just picked this up. Title says it's an 81 xs400. PO did some top end work, and it came with two different cyl heads. The exhaust pipes/flanges don't fit to the head I got running on it. I need to get new pipes and/or flanges, but don't know which head this is! It's not rounded like the 81 xs400 heritage specials I've seen. Thanks!

 

[bcware]

My 1978 has a square head like that; the exhaust pipes DO fit differently on the head compared to the later rounded heads. I had issues installing my mac 2-1 exhaust; I had to install longer studs.

The collars on that style head go the other way; you have it on backwards in the photo on the far pipe; and there should be two flanges inside the collar. The later rounded heads should have the collar on the way it is shown in your photo.

 

[xschris]

Make sure the rocker box and the head are a matched set. There are a set of numbers stamped on the intake side of them. Some have used un-matched one and said they had no issue but they may have just gotten lucky. I also notice your missing the top engine mount. You may want to find one of them.

 

[bcware]

Oh good call Chris; that's right. I wonder if the "bearing" would be mismatched/uneven if they are different beyond just being potentially leaky.

 

[dpow]

They are not a matching set. One is stamped 3317, the other 4L6.

I put the two together, and sealed with Permatex, after setting cam timing. I finally started the bike for the first time last night after buying it (the top end was disassembled when I got it) - no leaks from that top. Was very excited just to get it started.

So far I've:
- set cam timing
- adjusted valve clearances
- thoroughly cleaned carbs/new gaskets

...and she finally ran! (jumped bad battery from my truck.)

Should I continue with this rebuild or locate a matching head set? Thanks for the help!

 

[rshutchinson]

If it works and doesn't leak, go for it.

 

[bcware]

I say run it too. If something goes wrong you'll have to replace the entire top end with a new matching set so get some miles out of this one. The swap can be done with the engine in the frame too.