XS650: XS1 Heads   Leave a comment

Kind of strange how you can do a job dozens of times and one day discover you’ve been missing the art. Blindly bypassing the finer details not directly pertinent to what you’re doing.

I pulled an old NOS XS1 head out of the mothballs the other day. Pretty clean. Next to it sat a used XS1 head. Well used. Started to clean it down. Slowly I became aware of differences. Mostly minor. But functional.


1 .. S650-0148## on the left ... NOS to the left

S650-0148## on the left … NOS to the left


I found 8 or so differences on the outside alone.

  • thicker, differently formed and more cleanly cast mounts and supports, front and rear on the used head
  • thicker tappet adjustment cover mounting face flange on the used head
  • artful blitz moulded into the unused head where the oil feed pipe passes
  • round cam sprocket tunnel on the used head, blocky cast on the unused head


2 .. inside the rocker cover

inside the rocker cover


Multiple casting marks on the unused cover. Rougher casting quality too. What are the other differences?

  • cast ridge inside each tappet adjustment cover opening, used head
  • cast ridge between the bearing supports and the oil inlet cast, directly over the cam, used head
  • round brace for each of the inner stud holes on the used head are replaced on the unused head

They appear inside the cover only. Later models have a thicker wedge shaped form sitting over the cam. I assume these are for better splashed oil control. Seems the ridges above the adjustment openings would reduce oil draining onto the inside of the adjustment cover,lower leak risk. Those above the cam would allow oil to concentate and drip directly onto the cam/rocker mating surfaces.

I’ve seen the blitz on some early models and the blocky sprocket tunnel cast is standard so I assume the unused head is early but later than the used head. Why they were experimenting with lighter top mounts and relaxed oil control I have no idea.


3 .. XS1 head

XS1 head


Later models differ too.


4 .. a later head

a later head


  • Thick wedge above the cam
  • oil inlet node different
  • adjustment opening ridges intact
  • this later head has the 4 bolt front left cover


5 .. and outside

and outside


  • no blitz, but definite casting mark
  • adjustment cover flange thicker than the unused head
  • has the rectangular casting on the cam sprocket tunnel and the heavier front/rear mounts-cant see here

All the heads have the walling before the inlet valves-presumably to pool oil to the front so it has to drain past the exhaust valves into the cam chain tunnel. As they all have the feed channel to the exhaust valves. The bleeding holes from the breather box are also the same.

I guess there are other differences and other heads.

Apart from these differences the unused head seems to be useable. Wonder how critical those ridges are. Guess if the covers leak and I mark cam lobe surfaces I’ll know.

Posted June 3, 2011 by xscafe in Motor - Head, Motor - Oil

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