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Secrets of a CB750 early K
Trigger:
I know what is the difference in the oil jets as I have both types in stock. What I am confused with is this engine was to evolve but, to put a jet in to a head that blocks is going backwards.
AshimotoK0:
--- Quote from: Trigger on June 10, 2016, 08:16:44 AM ---I know what is the difference in the oil jets as I have both types in stock. What I am confused with is this engine was to evolve but, to put a jet in to a head that blocks is going backwards.
--- End quote ---
So what's the difference which part no is which?
Trigger:
--- Quote from: AshimotoK0 on June 10, 2016, 08:25:03 AM ---
--- Quote from: Trigger on June 10, 2016, 08:16:44 AM ---I know what is the difference in the oil jets as I have both types in stock. What I am confused with is this engine was to evolve but, to put a jet in to a head that blocks is going backwards.
--- End quote ---
So what's the difference which part no is which?
--- End quote ---
12238-300-010 is the later type used on the K1 onwards .
K2-K6:
Trigger, as you and hairygit point out, they are restricting the oil flow\pressure to the head.
So they must have been after oil supply for the crank mains and big ends I'd guess and as steff has two examples of close numbers but different configs it looks like their R+D was already changing the spec maybe before the very first run assembly had even started as you see the modded heads come into the production flow during that initial run so testing and approval must have happened prior to any production machines with a sign off for the mod going through after the very first heads had left casting and machine shop operations.
As to the reason, again I'd have a guess at something like endurance running, probably on a dyno, would have given them concern that under high heat and load the log of oil pressure would have shown they where too close to their own tolerance of low oil feed in the main gallery and possibly a power loss with increased friction in those circumstances to force a contingency.
The requirements of lubrication in the head are largely low/no pressure as it's more or less an oil bath system and as long as it doesn't run away too quick then it's job done form a design print of view.
But, if you need greater feed at the crank you've really got two choices, increase oil pump output or reduce leakage somewhere. If they felt they had excess which was doing nothing in the head it would at that late stage of development seem logical to restrict one to help the other area and jets seem a good solution as you could also then trim them if required without any real costs or production hold up once the casting could accommodate just a switch of a small component.
The strainer on the back of the earlier jets shows a nervousness of the jet becoming blocked and\or maybe experience from their 60's race bikes possibly.
AshimotoK0:
http://www.bkperformance.com.au/product_info.php?products_id=22179
Probably don't have any stock but interestingly described as 11 mm type so must be type with strainer underneath ;)
PN 12238-300-300
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