Crack near sparkplug, does this happen to bathtub head?

Hello everybody,

I just gave away my bathtub head to weld up a cracked thread from the cylinder head cover, nothing bad but ugly and a pil leak...

Right next to it I have seen two, I think kz heads with cracks between sparkplug tread and exhaust valve seat.
So I discussed a prevention of such a a crack on my head, which will get bigger valves and new seats and also some boost pressure * yes I said "Turbo" here* .
Our conclusion was to weld up the original spark plug thread and put a 10mm sparkplug at the same spot, so 2mm less in radius and therefore more meat on both sides.

So now the question to the common knowledge of the community:

Would that be overkill or some well spend money?

Those cracks are more common than not and are usually just surface expansion fissures which won't do any harm..
Our KZ1000 Turbo drag bike which runs 250bhp at 30psi on  VP C16 race fuel has those cracks with no issues.
The drag bike runs an earlier KZ900/1000 head on which the cracks are more likely than the later heads.
I have several J and GPZ  heads and non have the cracks.
If your head has no cracks then just use it as it is.
Welding up the plug hole etc to reduce the likely hood of cracks developing is a waste of time,  won't make a difference and the welding is likely to cause more issues than you think you can prevent.



 

Thank you for sharing your experience!

Did you try dual sparkplugs on a Turbo application?
I thought it may be useful to prevent knock due to a retarded ignition time?

I have dual plugs on both my Supercharged Yoshimura and Racecrafters bikes but the Turbo can only run 4 plugs due to the Bill Hahn HEI boost retard distributor ignition that is fitted
The boost pressure activated ignition timing retard is what helps combat detonation..