Topic: CB400F Head ?

[Ernest T]

What does nr. 3 do?  Its called a valve.  I've never seen anything like it in a cylinder before.

[grcamna2]

Isn't that the 6mm outside head bolt/screw w/ a cover on it ? I would think it would be on the cylinder head grid of the microfiche/parts breakdown.

I apologize Ernie T, I sure don't know what their function is.

[faux fiddy]

I guess it helps to regulate oil pressure to the head, and I assume it also functions to keep flow of oil to the head if a chunk of crap gets pumped up.  It sticks in one hole leaving the others flowing.

[Ernest T]

Isn't that the 6mm outside head bolt/screw w/ a cover on it ? I would think it would be on the cylinder head grid of the microfiche/parts breakdown.

I apologize Ernie T, I sure don't know what their function is.

No, it's not a bolt.  It's called a valve and it certainly loooks like a valve.  From the cylinder it connects to a passage that goes through the head and teminates in a casting next to the cam.  It is higher than the oil return so I don''t think that its an oil passage.  looks like it may equalize pressure within the engine.

[Bowswell]

It's oil jet, like carb jet.

[grcamna2]

Did you remove them to look inside ?

[Kanticoy]

^This

It increases the pressure to the oil tubes that lubricate the cam, etc. in the head.  Basically a nozzle.  And yes you can remove them to clean them.  The hole in the middle is much larger though.

[Ernest T]

Okay, then why go to the trouble to use valves instead of just casting the passage the size of the jets?  Do other SOHC cylinders have them?

[grcamna2]

Could they be one way "check valves" ? so the oil pressure to the cam box stays constant ?

[Kanticoy]

It isn't really a check valve, but it does accelerate pressure and prevent back flow.  They look a lot like a standard Keihin series pilot jet.  Like so:



They have an O-ring around them like the ones around the oil passage dowel pins.  Lots of head gasket leaks can be attributed to those o-rings going brittle.

[Ernest T]

They're aluminum instead of brass and look like emulsion tubes, complete with the holes along the sides.

[faux fiddy]

^This

 And yes you can remove them to clean them. 

+1

[Bodi]

Full oil pressure gets fed up through the barrels from the main oil gallery, to these "oil control orifice valves". Their purpose is to regulate the oil flow to the tubes that drip on the cam lobes. They have a bunch of little holes so that if something in the oil plugs one or two there's still flow. They also regulate flow to maintain oil pressure, without them in there your cam would get a helluva lot of oil but the system pressure would drop and the main bearings would not get enough oil.
The design around these things is a weak point on the 350/400. They are close to the edge of the head gasket and with full oil pressure below them and somewhat poor seals around them, the engines tend to weep oil from the ends of the cylinder/head joint.
Anyway, you absolutely need them. You will have main bearing failure without them. There are a bunch of ideas on sealing them to avoid the usual oil leak. Bon chance!

[Danno]

it is a drainback valve it regulates how much oil remains in the head for the cam in other words it slows down the speed at which the oil returns to the case

[strynboen]

it is a drainback valve it regulates how much oil remains in the head for the cam in other words it slows down the speed at which the oil returns to the case

no..not drain back  valvet..its pressure side under the valvet..and low pressure cam lubing over the valvet..there are not full presure of oil in the top..its flov free back in cam chain tunnel

[jessezm]

Anyway, you absolutely need them. You will have main bearing failure without them. There are a bunch of ideas on sealing them to avoid the usual oil leak. Bon chance!

Bodi, let's go over some of those ideas here for everyone's edification!  I'm about to reassemble...

[camelman]

My successful sealing goes like this:
1) clean head and lightly wet sand with 1500 grit to clean the head
2) replace all rubber seals
3) repeat...replace all rubber seals
4) reassemble

I've only had leaks come from the front corners from old rubber seals around the front outer cylinder studs. I've never had those oil orifices leak.

Camelman

[jessezm]

My last attempt failed terribly.  I'll try your approach.  No sealant or head gasket dressing at all?  I'm not too impressed with these ebay 466cc gaskets...  What do you think?

[heffay]

no sealant on head gaskets.  i really wish people would stop doing that.  i spent hours scraping that crap off a 650.

jesse, is your 400 a 466?  if not, that may be your problem.   

[jessezm]

Ha!  very funny.  It's a 466, yes.  I used copper gasket spray to dress the head gasket, but never any other sealant.  I think my problem was that last time I used some gray hondabond around the rubber seals, and that didn't allow them to compress properly, and they ended up getting squished between the head and cylinder block, preventing them from sealing.

This time around I have a few options.  Of course, I have new seals all around.  I was planning to use a copper head gasket that I have and use Hylomar spray made for these, but I am told that I'm asking for more trouble here, not less.  The other option is the gasket that came with the kit, with or without hylomar or copper spray.  Or I could have a better quality multi-layer gasket made by Ottoco or some other such company...

[gjunkie]

I was told that to fix this the actual Oil Orifice Valves had to be replaced. Is this not the case? Can this actually be fixed by properly sealing everything?

My understanding was that too much oil being pushed up was creating too much pressure, hence the leak... My oil leak is bad.. wondering what the best solution is....

Thanks!

[oldbob]

My 400 had the usual leak between head and cylinders. I replaced the head gasket and ALL of the o-ring/gaskets in that neighborhood with OEM parts. I scraped the gasket surfaces clean but did no other prep work. I reassembled it dry. So far (500 miles), no leak.

[gjunkie]

My 400 had the usual leak between head and cylinders. I replaced the head gasket and ALL of the o-ring/gaskets in that neighborhood with OEM parts. I scraped the gasket surfaces clean but did no other prep work. I reassembled it dry. So far (500 miles), no leak.

Hi Oldbob,

from what I see here: http://forums.sohc4.net/index.php?topic=111517.0 if you'd replaced the Oil Orifice Valves with proper, larger ones you should be fine, though that thread has a number of different methods to solve this... nothing seems to be the perfect solution as someone claimed that after 2000 miles the leaks returned.

Looks like another disassembly is in my near future.

[oldbob]

Hi Oldbob,

from what I see here: http://forums.sohc4.net/index.php?topic=111517.0 if you'd replaced the Oil Orifice Valves with proper, larger ones you should be fine, though that thread has a number of different methods to solve this... nothing seems to be the perfect solution as someone claimed that after 2000 miles the leaks returned.

Looks like another disassembly is in my near future.

To quote my late mother, "It's always something." If the leak returns, then I'll try a different approach.