CB750 K3 Oil leak

[sim2011]

Hi Seamus
You are both wright and wrong , the eraly K3 had this set and the later ones Dowels with rubber seals, my bike is a very early K3 produced December 1972 for Jan 73 launch.
My engine has never been apart and I took plenty of photos when stripping it down.
Thanks
Simon

[Seamus]

Typical Honda, a new model definition, but still using the older stuff in it. I have the same with a K2 that seems to have a lot of K1 parts fitted.

It was worth a thought, although I had not realised that your motor had never been apart.

Be interested in the final diagnosis though.

Good luck

Seamus

[Bryanj]

That "O" ring is part number 91309-035-000 and is 11 x 2.5

[sim2011]

Hi
The Genuine Honda Head Gasket turned up Pt No 12251 - 300 - 307
This measures 1.15 (pattern measured 1.16) so it aint that
The new  O rings measure 2.44 the new old ones measured 2.36 after being torqued down.
The only thing I can assume is that the Genuine Honda gasket might squash down more when its been torqued down ?

The New Head gasket does not have any sealant on it at all ( unlike the F2 one )
This leaves with a bit of a headache
Do I use Silicone sparingly on the O rings ?
Do I use sealant around the cam chain and oil feed holes on the Graphite gasket ?
If So what does anyone recomend ?
Answers on a post card to mr confused

[UK Pete]

I have made the decision to use blue hylomar on my head gasket to help seal it when i rebuild my top end and i am going to seal the o rings, rubber pucks and anything else with threebond 1194.
Before you reassemble your engine place your head on the barrel dry with no gaskets but with all the dowels and check that there is nothing preventing the two from fitting  together properly, its got to worth a try as something is not right to leak so much oil out
good luck
Pete

[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 )

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

[Yoshi823]

I seem to remember that the 750F2 cylinder head had a modified part to the oil drain at the front of the head, so that not only would oil drain down via the cam chain tunnel but also via the head studs. I think that there were two holes per side, as in down the stud holes between 1 & 2 cylinders and 3 & 4 cylinders. On the F2 head there was only the one drain hole. What i'm getting at is, maybe it's not the oil supply to the head, but the drain of the oil back to the crankcase, that's causing the problem.

I also seem to remember, & it has been a few years now, that there were some recesses in the top of the barrel that had places for dowels & the tall sleeve rubber seals, but the engine came without them. I filled these recesses with dowels & their relevant sleeve seals, & never had a problem.

This is the fiche for the 750K3...
http://www.cmsnl.com/honda-cb750-four-k3-us_model481/partslist/E++05.html

and this is the one for the F2...
http://www.cmsnl.com/honda-cb750f2-supersport-england_model14689/partslist/E03.html

Parts 2 & 3 arn't shown on the K3 fiche, & it was these parts that I added extras to on my F2. There's also a seal at the base of the cylinder stud that used to compress with the barrel being bolted down...part 22 on this fiche...
http://www.cmsnl.com/honda-cb750f2-supersport-england_model14689/partslist/E14.html

[K2-K6]

Assuming that all discussed is mechanically ok and as you've stated that cam discs were not leaking but definitely coming from gasket joint, then I'd be looking at the pressure side for the cause.

I was considering the blocked cam feed bit that Bryan has posed, but would have thought that the relief valve on the pump would stop that and guessing that it was ok before stripping.

About the function of the O-rings, I'd say that to work properly that they would have to have "traction" on the mating face to the casting so that when subjected to internal pressure that the ring could not slip over the surface to be deformed by the pressure into leaking oil. If they are assembled with ANY lubricant (from workshop handling or release agent from manufacture) I'd guess at a lowered pressure capability.

With that statement, I'd say that through using Hylomar on the gasket that I may have been inadvertantly catching a leak with what is a secondary gasket from the point of design intent.

If it were mine I would build it now by degreasing completely all the mating surfaces plus O-rings, hands / fingers etc  and coating both sides of the head gasket with Blue Hylomar (anybody would think I owned the company) let it dry, then assembling otherwise dry and torqueing to spec.

Then hopefully enjoy some sunshine on it.

[Bryanj]

Can you clarify for me exactly where the oil was comming from as if it was the end at LH side that would mean if the "O" ring leaked the oil found its way from the middle stud to the end without leaking out anywhere else which although not impossible is rather improbable

[sim2011]

Hi Brian

The whole head gasket was dripping with oil almost like that both o rings were not sealing  i have checked that the head mates with the cylinder with both dowels in and everything is fine.
Look at the pic below

[rigwit]

a skewed in dowell or a bit of muck under one  will cause a gap for oil to gush out     and blue Hylomar is not a silicone type of sealant, i,l be useing either the blue or golden to seal c/cases once ready to build up,  blue  never let me down in over 40 odd years in engine work..