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CB750 K3 Oil leak

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K2-K6:
I've Never used silicone on these engines, I think it's really good stuff in the right application but have taken too many things apart to find silicone bits all over the place and have a huge fear of getting any of it into small oil ways.

As Pete says, it may be good to check if the head is going clear down onto the barrels with no gasket first to see if you can spot anything.

I doubt if the gasket itself squashes to any degree, not at the torque used with flat surfaces. The design arrangement is almost perfect in that the head and the barrels are compressed buy the studs so you don't get any local distortion as you can with a stud screwed directly into the block (as on many cars).

Also check that the barrels have been seated completely before you place the head on as any binding here can the show at the head gasket when compression is applied during start-up.

I presume your torque pattern is as per book?

The suggestion for using blue hylomar is just the smallest amount spread as thin as poss both sides but to cover the whole area minus barrel rings as they should compress. The aim being to have ZERO loss of hylomar once clamped up.

I've never used increased torque as the studs are designed to be pulled into their elastic tolerance BUT NOt past it into stretch.

K2-K6:
Just a quick question

Are there any dowels between the head and barrels at all on your engine?

sim2011:
Hi
Yes 2 sets of 2
2 at the bottom of the barrells and 2 between barrels and head and they are the same height,
I have checked that these dont interfere with anything
I still think its got something to do with gasket and o ring thickness
Thanks
Simon

K2-K6:
It seems there is something odd happening, It's always a concern if you can't identify what is really wrong and keep taking pot shots at it as you don't know if you've really fixed the problem.

Could be focusing on the wrong angle for a reason why, may be worth describing the logic to see if anyone can spot a prob in it.

If the cam cradle plugs are not leaking (they go into clear air and not the gasket anyway, don't they) the only scource of pressurized oil is from the O-rings protecting oil supply to the cam area, so the oil must be coming from them as a primary fault, right or wrong?

The head gasket is primarily there to seal the barrel to combustion chamber area and the rest is to take up any minor variation in the machined faces, if it was the original intention to stop pressured oil it would probably have had something like the barrel rings in copper around oil ways. Back to the O-rings?

Why don't they seal? If the O-rings were too big (total volume) they would hit the capacity of the counterbore and possibly prevent the head properly compressing the barrel rings, so leaking compression?

When the O-rings have been in a long time they look square is section showing that they've been squashed and seal against the casting.

Soooo the problem appears to be that the rings are not sealing against top / bottom faces, Why? (sounds like a corporate problem statement!! bit of blue sky, out of the box thinking there ;D)

What affects that:-

Dimension, is it correct?
Material, some rings are noticeably harder that other (pattern? some applications would have a different material spec to this one, think it's called Sure rating) and would affect the physical sealing to the faces.

Clamping, assuming this is correct, but are you sure of your torque wrench accuracy. I've always used a small scale one for this 0-40lbs as it gives good seperation of scale and more accurate actuation at light loads. Have you got any genuine new Honda O-rings to use?

Hope this is of some use, any comments welcome.

Bryanj:

Firstly oil leaking from anywhere tends to appear as if its comming from the head gasket area

Secondly only reason for a new gasket and "O" rings to leak immediately is damage to or not flat condition of barrel/head joint surface.

There are several known causes of oil in the head gasket area.

(1) Most obvious is the oil feed O rings in the gasket but this is only after time

(2) The rubber seals under the cam bearings not sealing due to damage or lack of clamping between bearings and head

(3) oil leaking down the threads of the bearing retaining studs/bolts as the holes go right through, this is more common if the threads in the head have been repaired with helicoils as oil has two threads to work down.----Normally this can be curred by using Hylomar on the threads JUST NOT GREAT GOBS OF IT TO BLOCK OILWAYS. A better form of thread repair in this area is a "Keensert" fitted with a sealing compound on its outer thread

(4) oilways to cam blocked causing overpressure at the joint although the cam normally seizes before the O ring blows.

Lets assume (always dangerous) that the engine did not leak like the Torrey Canyon before stripdown,
the most common cause would then be  (2) then (3) or damage during stripdown.

The other assumption here is that the head nuts run free and all washers are in place.

I hope this helps and you sort the problem, as to gaskets back in the 70's we rarely used genuine sets due to cost and mostly Noboru with not a problem to my knowledge

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