Topic: that oil jet port that isn't a port...

[grumpy]

OK, top side of a 750 head, under the cam towers.
Four holes w/ O rings.
Two hold the oil jets that feed the rockers.
Two hold... nothing.

WTH are those last two for?

I know the answer is here some place but what do I search for? "un-jet" "anti-jet" "vestigial port"

[Garage_guy_chris]

I read the other day that the drilled passages through the rocker towers is like a upside down "U" and feeds the journals and troughs under the lobes. The oil jet side feeds this "U" and the other side the o-ring just seals the U from uselessly bleeding off oil pressure.

[grumpy]

the o-ring just seals the U from uselessly bleeding off oil pressure.

yeah, that's what it appears do... but then why not plug the hole completely?
I'm guessing it's an artifact of when they drilled the journals. If it's not needed, and can lead to oil starvation if that O ring fails, then why not plug the thing?

[HondaMan]

the o-ring just seals the U from uselessly bleeding off oil pressure.

yeah, that's what it appears do... but then why not plug the hole completely?
I'm guessing it's an artifact of when they drilled the journals. If it's not needed, and can lead to oil starvation if that O ring fails, then why not plug the thing?

The early K0 cam bearings were exactly that, with just one inlet hole, causing them to be a Left and Right side type. That probably caused their techs to install them backward once in a while, with predictable results. The next versions that came out had holes on both sides, and slight mods to the outer ends, so they become universal. Or ambidextrous? Or hemaphroditic?

Anyway, now you can't install them backward.

[MCRider]

Wow HM, never thought of that.

[grumpy]

That makes sense; cut's production costs by 50% having to make only one part.

So can I plug it with Permatex #2?

[Mini Mo]

Ok, this brings up something I should have asked earlier. In putting together the top end to the K4 I'm working on I only saw 2 orings, the ones surrounding the oil jets. The Vesrah gasket kit had 6 of those orings included. I searched the fiche and my own photos to see if I was missing something. The fiche shows 2 only for my bike.

Should I have 4 of those orings somewhere under those cam holders?

[grumpy]

M.M. -

look under the cam towers. you should see 2 holes leading up into the journal.
one hole sits over the jet, the other sits over a blind hole in the head that's the same diameter as the jet port. the 2nd ring goes in there.
unless you've got something weird...

[flybox1]

o-rings in all four holes. 
(poorly) circled in blue

[iron_worker]

There's also the 4 to seal around the oil feed ports. 2 go between the cylinders and case and 2 between the head and cylinders on the inner most head studs on the intake side. These are of a larger size than the 4 smaller o-rings for around the oil jets and blank ports.

IW

[Mini Mo]

Someone got into this engine before me and did a couple of crazy things and it's been 30 years since I've been into a SOHC engine so I don't recall the oring arrangment.

When I disassembled the engine there were no other orings in the head or the cam holders. That's not to say there should be, but there were only 2. Looking at the fiche for that year, '74 Honda only shows the 2 for the jets, no other orings. The fiche showing the cam holders shows no orings at all.

I appreciate the help and I'm not doubting your knowledge, I just want to make sure before I have to pull this thing apart again.

There's also the 4 to seal around the oil feed ports. 2 go between the cylinders and case and 2 between the head and cylinders on the inner most head studs on the intake side. These are of a larger size than the 4 smaller o-rings for around the oil jets and blank ports.

IW

IW- Those I got and have been replaced. Thanks

[Mini Mo]

Fiche for the K4 from Honda-

[70CB750]

#17:

[Mini Mo]

Well there you go.

70CB750- Your fiche is different than the one I have for that year. They both have #17 but mine only shows 2 orings... until I looked at the quantity required - 4! Looks like for safety sake I'll be pulling this apart and installing the other 2. Couldn't hurt, right?

[70CB750]

The first fiche is 78F.  I would definitely make sure the o-ring is there - all four.

I believe they made a mistake, this is 73:



and this is 74:

[juliorice]

I never post here, but I will chime in with some experience.  I helped a kid put one together a while back.  He left one of the o-rings out on the outside.  Fired his bike up and took it for a spin.  When he didn't come back I went looking for him.  Guess why.

You need 2 o-rings under each tower.  4 total.  You will not maintain oil pressure for your cam and your ride will be short.  Good luck and take it easy.  Julio

[Mini Mo]

"I believe they made a mistake, this is 73:"

I think you may be right. Neither picture shows the second o-ring in place but it makes sense to have the second one to maintain pressure. Looks like it's coming apart again.

Thanks to the original OP for posting this and making me have a second look at mine!

[flybox1]

I never post here, but I will chime in with some experience.  I helped a kid put one together a while back.  He left one of the o-rings out on the outside.  Fired his bike up and took it for a spin.  When he didn't come back I went looking for him.  Guess why.

You need 2 o-rings under each tower.  4 total.  You will not maintain oil pressure for your cam and your ride will be short.  Good luck and take it easy.  Julio

+1
HM's book even list it as a necessity

[PeWe]

Back in the days we just placed the outer o-rings in the blind hole just before it should be there which was strange then. I did not think about the need of sealing the end of the oil channel and keep up the pressure. I'm really happy that I did not forget them.
I reused the outer ones in the blind hole with sealer, today new fresh of correct size, not to thick either.