Very interesting to see these comparison photos Paul. I'd say it proves the piston pins are located the same in both.
Do you have Prussian Blue? I't get a tube (cheap) and apply some on the valves, and the bevel of the pistons. Drop the head again (no bolting it down of course), and turn the crank a couple times. That will perfectly show if there is any contact.
The pistons are in a radically different shape, but imagining the volume, perhaps the combustion chamber volume wouldn't change? Of course that's just a speculation.
I haven't read anything about interchanging the pistons between KZ and ZN. And I'm glad to hear the seller is fine with taking them back. I am confused though with them coming from a KZ story. Perhaps he got things mixed up unknowingly and doesn't really know the difference. Or perhaps they did come from a KZ? That would be something I haven't read about. Perhaps it could work? Except I am wondering about the for valve spaces in the pistons. Are the ZN and KZ valves the same size? Perhaps KZ has smaller valves, they would fit snug into those spaces. On the other hand, would leave a lot of room around fitted with the ZN pistons. I'm not sure if that would be desirable as aerodynamically it wouldn't be as smooth and no gas flow restricting like if fitted with the KZ.
There are many people here with waay more history with these 1300 bikes than me. I hope someone could shed a light on this. I'd imagine it has been already considered long time ago!
Didn't they make the Z1300's up the 89 model year (in Europe ?) Wouldn't be weird for different pistons to be used as the model aged especially if compression ratio's changed (seems to me the later models were lower compression but maybe I have that backwards as they had more HP)
The 10 hole oil way was the z1300 carb model and was the first of the piston design, this was why the z1300 used oil, they made sure we had plenty of top end lubricant.
The 20 hole is the DFI, they have a high profile, do not use these on the carb bike unless you have the head, cams and valves to the head. these are different to the carb models.
Hope that helps
So I guess I'll just put back the original ten-hole versions and keep an eye out for oil consumption... nothing that my Z1000 doesn't do anyway!
Later addition to this post: this morning I spoke to the guy who did my cylinder head and he was questioning the role of the extra holes in reducing oil consumption. He states that oil consumption happens when the rings don't fit properly and oil goes 'upwards' past the rings and into the combustion chamber. The extra 10 holes being underneath the oil rings, they would only help lubricate the cylinder walls....
Anyone any thoughts on this?
He is also quite happy to drill extra holes into the pistons if I want... but I'll bring him both sets to see and discuss and will await any comments from anyone on KZ1300.com on his view before I decide.
This is one of those moment when I wish I could a some spare cash in the back pocket, haha I am itchy to buy a ZN head as well as other few crucial components from different years and models and directly compare. I've been going back and forth checking compatibility on Partzilla and it can be confusing. It also makes me wonder if what they offer in the list is 100% complete, or just partial, being very detailed at it. For example, a starter reduction gear for an early model will show compatible with a specific ZN, but looking at that ZN it want show backward compatibility.
From what I see, the early piston doesn't have those holes, has a slight bevel, but doesn't have that distinct grove area machined above it. The other piston has extra holes, a bevel, and a machined grove. The holes open directly into the crank case and are partially in the grove, partially right on the bevel.
My 'bird brain' tells me that if whatever this does helping lubrication, it also removes oil more efficiently. Perhaps oil from the crank case splashes and gets into those holes giving improved lubrication, but also any extra oil has a place to collect (in that grove), and the bevel directs it to the holes and through the holes out - instead of being trapped (restricted passage) making it's way to the combustion chamber and disappear.
I think the key point here is the machined grove and holes drilled ON the bevel.
From what I gather reading and listening, I think the most common complain I've heard is oil consumption of these machines, not poor lubrication. Trouble with poor lubrication is secondary - due to low oil levels when people fail to check them.
I don't think the 20 hole design has anything to do with DFI or high profile. My A4 1982 carburetor model came with low profile 20 hole pistons. I think they already started implementing it earlier. For example, the 81 model shows two different pistons compatible. One 'STD', which I think would be standard, and the other 'L O/S' - I don't know what it stands for, but my feeling is this is the 20 hole piston.
I think if your machinist is willing to drill those holes that awesome, but I think he should also machine that grove. I have no idea how the engine would behave having holes and no grove.
Had an interesting conversation with an automotive machine shop that specializes in race engines (Competition Engines in Markham Ontario). I was telling him about the oil consumption issues with our bikes and he suggested that he checks his oil rings after fitting by installing the oil rings on the pistons and no other rings, then installing the pistons in the cylinders, then attaching a tension force gauge ( fish scale for lack of a better description) to the connecting rod and does a pull test to determine what force it takes to move the piston in the bore. He stated that at a minimum he would like to see 20 lbs force. He has seen 11 lbs force and the end result was oil consumption. He feels that oil scraper ring pressure is paramount to successful oil control.
Just thought I would share this info.
While I was there, they were setting up a 1969 426 Hemi on the Dino and following that engine will be a 256 Ferrari engine they just finished working on.