Secrets of a CB750 early K

[Trigger]

This is getting interesting. PN 12238-300-300 was fitted to the late K1 and on.
I have done two sandcast heads that have the oil jet in but, on the third one it looked like Pete's and RGP's. I assumed on the third head that the oil jet had blocked, been drilled out, welded and a hole had been drilled.
It is strange that some sandcast/diecast heads have this jet and some don't, all I can put this down to is Honda had two suppliers of early heads but, that doesn't make sense.

[hairygit]

Or for whatever reason the bike had a replacement head fitted, either by a main dealer who would fit the later item, or by a previous owner who saw the later head looked similar and fitted okay, when it was just an "old" bike and nothing like as collectible as they are today!

[steff750]

  hi guys here is my take on these oil jets.
my frame number 1017*** diecast has the simple drilling my frame number 1031*** has the big oil jets(filter underneath) i have yet to strip a k1.but I've cannibalized loads of k2s k4s k6s and f1s and f2s and they all have long thin ones like in the parts manuel

[AshimotoK0]

covered here too  Hondaman may have a drawing

http://forums.sohc4.net/index.php/topic,154725.msg1770421.html#msg1770421


Here is mine.. Wonder what the PJ is?

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[AshimotoK0]

Here is my mate in York's early '71 K1 head. Not a good photo (not taken by me Trigger  ) Looks like O ring in the top of the oil jet.

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[Trigger]

That is PN 12238-300-300 jet Ash, that is the most common jet fitted from 1971 to the finish.

[steff750]

That is PN 12238-300-300 jet Ash, that is the most common jet fitted from 1971 to the finish.

good boy trigg
  we got a mate a rite know it all (we even call him the philosopher to this day) this was in the 70's he had a jock Kerr tuned f1 it was quick at the time but the top end run dry of oil,so he thought he would get more oil to the camshaft
anyways he decided to drill out the oil jets ,on restarting the rebuilt bike it lost the oil pressure to the mains and big ends and was junk ,after returning the bike too jock Kerr the guy went crackers and wiped the floor with him lol(the innocence of youth)

[UK Pete]

sounds and looks like the jets are quite finely tuned, but are so susceptible to blocking i wonder how they developed them to get the flow and balance right
pete

[Trigger]

 What I am always a little confuse with is that the engine evolved over the years and there is a provision in the moulding of the head head for oil jets to direct oil to number 1&4  but, were never drilled out and used.
The jets that I posted are pigs to get out as they are metal in a alloy head and if they have rusted up, then the only way to get them out is drill them.
Why the hell did they make a jet with a strainer on the back, which is very difficult to remove when the straight though hole that Pete and RGP has is so much easier?

[AshimotoK0]

Still confused Graham between the two part numbers circled in red below. What's the difference?

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[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]

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.

So what's the difference which part no is which?

[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.

So what's the difference which part no is which?

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