Cracked head fixable?

[EFE 1230]

Scored a cheap Z900 head off evilbay, seller didn't mention the cracks in the combustion chambers, from the valve seat across to the end of the sparkplug thread, is this a fixable fault or is the head scrap?

Bought the head as a rebuilder and all the other faults were mentioned, worn guides/seats, brocken fin and needs exhaust stud threads repaired but no mention of the very noticeable cracks.


any opinions?

[Tony OW31]

Yes they are repairable, I have done quite a few in my time, not a quick or easy job though, you have to be careful to not get the head too hot as the alloy they are made of can lose its temper easily.
You will need to remove the seat, re-cut the seat bore and make an oversize seat to re-fit.

[EFE 1230]

Thanks, have you done bigger valves on a z9 before?

Just wondering what a good top end combo would be (cams/valve size/bore) to work with my 40mm dellorto carbs.

[Large]

prolly a suzuki head

Talk to Scotty Lynch in Brisbane. He is THE man for Kawasaki Z-series engines.

[Hagarr]

Hey Effie the cracks if not really large probably won't affect the seat at all as the seats are cast in to the head and unlike the new generation stuff the seat at the base of the head is actually bigger than the OD of the seat you see in the combustion chamber.

Photo?

biggest valve on a standard seat we used to fit 1000J valves which were 37mm OD you can go a whisker bigger but risk burning valves if you don't set the seat back towards the seat of the valve.

I have seen 40 mm but you have to unshroud the valve by cutting in to the chamber heaps which means you'll lose compression, if you don't the flow will be worse than a standard setup.

You can offset by using a piston with a larger dome but this also fucks up the flame front of the spark and you may have ignition issues.

If you go the dome pistons you really need to have the cylinder head fitted with another spark plug , improves torque immensely especially as you can use heaps more ignition advance.

I used to run 14 to 1 Methanol 1260 cc MTC forgies with Formula One cams and 2mm shaved off the head, if you gave it a big rev (Stop Lamp!) the rod would stretch and knock the spark plug gap down which was annoying but fixed with a washer under the plug.

The only problem you'll have then is spinning alternators and wearing out cam chain components quicker but when they go MAN they were good.

Good Luck. (P.S) Rode and fettled Z9 engines for 20+ years until I swapped to Gixxer engines and haven't looked back since.

Still miss my 'ol Zeds though. :(

[Tony OW31]

quote:Originally posted by Hagarr

Hey Effie the cracks if not really large probably won't affect the seat at all as the seats are cast in to the head and unlike the new generation stuff the seat at the base of the head is actually bigger than the OD of the seat you see in the combustion chamber.

:(


But to weld the crack up properly you need to remove the seat:)

[Tony OW31]

quote:Originally posted by EFE 1230

Thanks, have you done bigger valves on a z9 before?

Just wondering what a good top end combo would be (cams/valve size/bore) to work with my 40mm dellorto carbs.


Can't remember valve sizes, but I do seem to recall that in 900/1000cc form they didn't like anything bigger than 36mm carbs if you want it to ride nice.

[Hagarr]

Just leave the crack!

the only reason to fix the crack is the Aluminium expands quicker than the seat and the seat loses tension and will come loose and potentially fall out.

the Z9 seat will not come out as the base is larger than the area where the valve seats as they are cast in the head the section cast in the head which obviously you can't see is larger than the part you can see where the valve seats..

this all still depends on how bad the crack is [8D]

quite often if the crack is only minor you can peen the crack and blend in to the chamber but depends on how big the crack is.

If the crack is large enough then obviously removing the seat and welding is required then machine and fit new seat but many cracks in my experience are not sufficient to need to do this to.

[EFE 1230]

Thanks for the advice, 2 of the cracks are big enough to get your fingernail in.