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Hey Scirocco. Love that bike! So you mean you went with outside lines because too much off the block to accommodate o-rings? My ZRX has external lines, Oil by the studs was not the greatest idea,. especially after mods. Best method,, like most engines, separate oil galley through the block to the head.

This is a very popular engine mod to secure a stable oil flow to the cylinder head.




I will do this on my project bike this winter with a big bore kit.

So have you seen any real examples of oversize studs reducing oil flow enough to hurt the top end? Most folks say it's not enough to hurt anything, including APE. Possibly even a benefit with the obstruction forcing more oil to the bottom end in performance applications. I've already calculated the amount to drill out the outer stud holes in the block and head to maintain OEM oil flow with oversized studs.

The big issue is in the head, not the block, since the head holes are significantly less ID than the block. So that's where any significant oil flow reduction would take place,

PS: You're bikes are killing me! Reminds me of Bull Dock in Japan...

oversize studs reducing oil flow? Yes, and rises the oil pressure in the oil flow system.
Liquids can not compressed like air. This let the oil pump do a lot of stress by blow by oil and a loss of engine power.
Thats the physics of liquids in a close system.

I fully understand hydraulics. Don't you think increasing the stud hole ID equally to the oversized stud OD will accomplish the same as external lines? And again, have you ever seen evidence of oversized studs in OEM block and head causing any top end damage?

VTEC wrote

I fully understand hydraulics. Don't you think increasing the stud hole ID equally to the oversized stud OD will accomplish the same as external lines? And again, have you ever seen evidence of oversized studs in OEM block and head causing any top end damage?

No i have not seen an evidence of oversized studs in OEM block and head causing any top end damage and will not.
But if some little piece of what ever stuck in this little passage (after some head work)and block the oil flow you will notice a
top end damage.
Increasing the stud hole ID equally to the oversized stud OD will do the same as external lines.
But it can be a source for oil leaks between the cylinder block and head.

The restriction issue would be in the head since the hole IDs are smaller than the block. My calculations, given to me by a mechanical engineer, gives me drilling out the head holes to 11.8mm. This would still be less than the block OD. This means the o-ring mating surface top and bottom would be near equal and would not cause an oil leak (also going to use the 0-ring spring washers used on P bikes). At the same time, as suggested by another member, when drilling the head drill upward and stop after passing the horizontal oil galleys. This will maintain the sealing surface of the top sealing washers.

I know I'm a pain, but really appreciate all the knowledge from you experienced KZ guys.

PS: Thank you, who ever fixed the site page-load issue.

Yea, the site loading times are a lot faster, thumbs up to the admins

I received the o-rings, and I have the top end all reassembled. The stockers were malformed so I really did need new ones. All new gaskets and o-rings from the base cylinder up. Monday looks like a full days work so I should be able to get the Dyna coils and plug wires installed with the Wired George mod, the carbs and all the cables back on it.
PS- Apologies for hijacking the thread. 8-)

There's no such thing as good 30 year (or even 10) year old rubber.. I do 10-15 year old rear main seals on a regular basis. Leaking like hell and brittle like hard plastic when I pull them out. And that's under much lower temperatures than an air cooled head.

True enough. I was quite surprised their shape was distorted.

Installed the new Dyna coils and spark plug wires. Added the Wired George mod as I had 12.3V on the battery and only 10.1V at the coils. Installed the carbs, addressed a bind in the throttle sleeve and bar end plug. Installed a new speedo cable as the prior one had broken off the tips at the drive end. Blew out the broken tips with compressed air. Installed the exhaust. I should be able to add some fluids, install the tank and fire her up today. I'll repost pics once completed.