Z1OwnersClub GB

Does this indicate a bathtub Unitrak cylinder head. Engine is a 83 KZ1100LTD.

An "A" stamped in the inlet indicates a Uni head which were also supposedly factory ported .
Don't know about the 5 but some 83 - 85 Z1100 ltd/spectres also had the same bathtub head but ran milder cams and 29mm shim on top instead of the Uni's shim under.
A view of the piston crowns using a boro scope down the plug hole would tell you what you have without pulling the head.

As above. The US spec D model Spectre came with the unitrak motor but de-tuned a little and perhaps for the first year only. My cylinder head was from a breakers and is a unitrak head, and was complete and un-molested with Unitrak full lift original cams, shim under etc. and was painted gold from the factory. Its from a US market Spectre. Mine have the capital letter 'A' stamped into the ports. That 5 looks like its cast in. The letter 'A' is in the six o'clock position and a little further in, up the port than that 5 at the seven o'clock position as it appears in youre picture. Guessing the 5 was obliterated by the porting process and a letter 'A' stamped in manually afterwards to denote the additional work.

One difference between them and the standard J model heads is the different valve angle as you know. If you take the cam cover off, you can see a small, but measureable difference between the position of the valve gear wells for inlet and exhaust when you look at their proximity to the cam covers' seating surface for example. Its small but it is there.
Take a look at the head side on. You may see a difference between the angle of the casting of the 'wells' from inlet to exhaust as they appear above the combustion chambers of each cylinder.

https://www.motorcyclespecs.co.za/model ... a%2082.htm
AL

I suspect that's a manufacturing location mould mark showing it was position five on the casting mould.
Once cleaned of the casting mould webs if a head was found to be deffective or a mould fault was evident the number would tell them where on the mould the fault was evident.
It's common practice in manufacturing to maximise the number of units per "pour" so as to minimise cost.
I suspect that six or eight heads per casting mould would have made up one "pour" mould.
This would indicate there should be other heads that have different numbers to indicate where on the casting mould their position was.

zed1015 wrote:An "A" stamped in the inlet indicates a Uni head which were also supposedly factory ported .
Don't know about the 5 but some 83 - 85 Z1100 ltd/spectres also had the same bathtub head but ran milder cams and 29mm shim on top instead of the Uni's shim under.
A view of the piston crowns using a boro scope down the plug hole would tell you what you have without pulling the head.

Thankyou Zed i borrowed an endoskope and can confirm that this just normal J type cylinder head.
I have 2 spectres the later one has the bathtub head with shim over. I have never had the carburetors off so cannot confirm any "A" inlet markings.

Al wrote:As above. The US spec D model Spectre came with the unitrak motor but de-tuned a little and perhaps for the first year only. My cylinder head was from a breakers and is a unitrak head, and was complete and un-molested with Unitrak full lift original cams, shim under etc. and was painted gold from the factory. Its from a US market Spectre. Mine have the capital letter 'A' stamped into the ports. That 5 looks like its cast in. The letter 'A' is in the six o'clock position and a little further in, up the port than that 5 at the seven o'clock position as it appears in youre picture. Guessing the 5 was obliterated by the porting process and a letter 'A' stamped in manually afterwards to denote the additional work.

One difference between them and the standard J model heads is the different valve angle as you know. If you take the cam cover off, you can see a small, but measureable difference between the position of the valve gear wells for inlet and exhaust when you look at their proximity to the cam covers' seating surface for example. Its small but it is there.
Take a look at the head side on. You may see a difference between the angle of the casting of the 'wells' from inlet to exhaust as they appear above the combustion chambers of each cylinder.

https://www.motorcyclespecs.co.za/model ... a%2082.htm
AL

Thanks AL for my sins i alao have 2 Spectre the later one has the unitrak bathtub head. The other 83 is a normal J type. No inlet numbers Externally there does appear to be a difference between the two. I had not noticed before.
But all that Gold what were they thinking of.

Gold head - Liberace was still alive so the Yanks were still game for anything then.