A big thank you to everyone that helped me track down the necessary info. At least now we know what it is. Now comes the trick part. Tracking down the cover and rockers to get this head working again. Or detailed plans on how to make it myself, or have it made. Read on to hear the whole story ...

I have a cylinder head that was used in dirt track racers. I bought this in a lot of engine parts from someone that stopped riding yamaha 650 based side-car crossers. Online help allowed me to get more info on this unique piece, type coded OW72

The cover is missing. It looks a lot like a XS1 head, but it is in fact slightly smaller, and has different valve angle, bigger valves and a completely different combustion chamber. (sort of a heart shape) I need the top and the rockers , anybody got any ideas where I can find that, or can have it made at a reasonable price?

I managed to lend a XS1 top half and this is what it looks like. Notice not only the valve adjustment inspection covers don´t match up, but the rockers should be shorter as the valves have a steeper angle. The rocker centers are probably closer together too.

Got this reaction on this page from Jens Enno Born: (together with the pic below)

Also check out his site (only available in German), I listed it on the links page.

there were special cylinder-heads made by Yamaha for the dirt track bikes of Kenny Roberts. They were called OU heads. There´s a picture enclosed with this mail of such a head. When I compare it with your head, I think they´re different. So this information may help you to sort out what you have.

I got that picture from a internet-friend from the Uniteed States. He is in contact with the former mechanic of Kenny Roberts. This man is now over 90 years old and still engaged in XS tuning.

And Mike Konshak, the contact person Jens talks about, says:

The combustion chamber doesn´t look quite right for an OU. But the proof would be that the OU motors had aluminum combustion chambers with steel valve seats. All production models have a steel skull cap cast into the head with the valve seat ground directly into the skull cap. If the the valve angles are different than stock, then the top of the stem may be farther away from the cam which means the rocker arms would be a different length. I don´t know anymore, I haven´t been around that long and Shell does not have email. The combustion chamber shape looks stock to me. The OU has a perfect hemispherical shape.

And a reaction by Roger Bateson:

After spending 2 years working at Yamaha Australia I gained considerable knowledge and experience which I am happy to share.

In relation to your cylinder head rocker box the engine you are referring to is an OW-72 of which 25 were made in 1974 for flat track racing in the US. Sorry I can´t help you with parts. I have build number 21 fitted to my XS-2.

Marcel Keuch wrote, in reaction to my site I guess (return e-mail address was bogus)

Hallo Frank

Heb je het antwoord betreffende de speciale xs kop al gevonden ? Ik heb een keer in een Nederlands tijdschrift gelezen dat er ook in Nederland speciale
(USA) koppen gebruikt werden door zijspancrossers. Een naam die daar bij viel is die van Cor van den Biggelaar,ik heb geen idee waar deze te vinden
is.Ook schijnt hij bij xs koppen de klephoek veranderd te hebben, misschien kan hij je verder helpen. Succes Marcel

Dave wrote (off-list, several e-mails)

Hi,
My name is Dave, I posted asking about the parts for my bike the other
day. I will bring it in form the barn in the next week or so and take a
close look. I had a stock 650 for a long time and never looked very
close at it so making an identification from the pictures is impossible
for me but in a few weeks I´ll get it torn down and check it out. If I
learn anything useful I´ll drop you a note.
dc

Hi Frank,
I looked at the pictures on your web site of the OW72 head and if I
understand what it says, i.e. that only the OW72 heads have hard inserts
in an aluminum chamber and that the stock head had some sort of steel
cap which made the combustion chamber? I think I do have an OW72 head,
I´m sure the head on the bike was just like any other aluminum head I am
familiar with, with hardened seats in an aluminum casting. I brought it in from the barn this
evening and will get it up to the shop in the next day or so, I have
become very curious about just what it is. I´ll be in touch as I learn
more. Thanks for the information......
dc

I am getting several people involved in the search for
information on the Yamaha and will post what I learn in a couple of weeks after they all get
back to me. A couple of the guys know Don Vesco and they have promised they will talk to
him about it. I have known since the first time I started it that it was something kinda
special, I do love the sound. A couple of my old neighbors are racers and when I started it
for the first time every gearhead on the block turned up in my driveway within 10 minutes.
I did a quick run down the block and came back shaking, it was the quickest thing I had been
on and would lift the front wheel when it came on the cam at about 6k rpm in third gear.
Gotta go, later.....
dc

Bob Scogin wrote, in reply to a message from Dave

>they had to make the factory style race kit available
> to at least some privateers
Yamah developed quite a few special parts that differed from standard
production parts as part of the
OW72 racing program. One of those OW72 parts was a special head with altered
ports and a shallower valve angle to improve combustion chamber shape.
AMA Class C competition required that at least 200 of a certaimn model be
built in order to qualify as a "production" model and qualify for the class.
Most were retained by the factory team but some fell into the hands of
qualified privateers.

> and they were parts readily available from TRD. Toyata Racing Developments, or whatever that stands for. He gave me a list of
> part numbers and the local Toyota dealer had the valve on the shelf. Has
> anybody tried to put the kit together recently? I am going to restore my bike
> back to the state it was in when I first put it together in ´82

Interesting. I wasn´t aware that Toyota had anything to do with the program.
Perhaps there was some connection through the old Toyota 2000GT, which I
think used an engine designed by Yamaha. Is the engine installed in a
production XS frame? The OW72´s used a custom built flat track chassis and
was wondering if that´s what you have. Sounds like a nice project.
Bob Scogin
Slidell,La. USA

> and would like
> to put the pistons from the origional kit back in, melted one in ´84 and had to
> replace with a Wiesco set of rather lower compression ratio in the interest of
> being able to actually use the bike as commuter.
> At any rate anybody have the TRD part numbers? It is still one the the
> quickest bikes I have ever ridden and with all the interest in vintage racing
> I´d kinda like to get it out there. I would rate the performance just about
> equal to the Guzzi Centauro I ride today at least up to 110 or so which is
> where I run out of wrist anyway. The Centauro has about 95 hp at the rear
> wheel but carries almost 100 lbs more weight.
> Thanks for any help.....
> dc

Terry Gliddon wrote (in answer to dave´s questions on the special head he has)

I seem to recall reading somewhere, and if anyone remembers reading the same
article please correct me if I´m wrong, that Don Vesco used to sell some hot
up bits and pieces for the XS650´s back in the 70´s. These included 750 kits
and flowed heads fitted with Toyota valves.
I´m assuming that TRD stands for Toyota Racing Developments or something
similar and perhaps Toyota only supplied valves for the Vesco modified
heads.
The head in question may be one of these and not an OW72. If your head is a
genuine OW72 then you have really got yourself something worth keeping.
cheers
Terry Gliddon

I was contacted through mail by Willy and Frans, who are active in sidecar cross racing, and who have got 2 of these OW72 heads too.
This head is the spare head - you can see the combustion chamber is different from mine.

Problem with the spare head is that someone changed the exhaust ports - the angle to be exact - making it impossible to swap the head in use for this one, without substancial work changing the exhaust system.

This is a serious drawback - especially when something goes wrong during a race! I finally agreed to sell them mine. I was given a tour of their garage and I think they have the knowledge and the tools to make good use of my head!

They showed me the parts necessary to complete my head. The camshaft is unlike anything I have seen before. The rockers are shorter and look more fragile than original. This made me realise - even if I finally find the necessary parts - this is not suitable for everyday road use. (IMHO)

This is the sidecar outfit that holds the engine with the OW72 head. (WASP) It looks like new - but is well used. A real pleasure to see it in this state! The engine was unfortunately underneath a pile of other stuff, as they have got to make use of every bit of space in the workshop. I do hope they can make good use of this rare OW72 head.

Oh - and according to them - there are quite a bit of these heads that were used by sidecar crossers. They do not believe there can be only 25 of these heads.

I think this about wraps up the mystery of the special head I found in my spare parts. I am sad that I never had a chance to use it - on the other hand, I think I can safely say it is in good hands now, and will end up being used for what it was intended for.
I asked Willy and Frans to keep me informed about the progress, as there is a lot of work involved to make use of this head. They´ll probably have to match it to the head in use, so it can serve as a spare - allowing a straight swap in between races, if necessary.
A lot of thanks to all people who contacted me with information and tips about this.