Topic: Weeping between the fins

[SohcCBs]

Oil coming from between the head and cylinder block (weeping).  Oil return only no compression leak, etc......is it these "O" type gasket marked "2" or "10" ?  The leak is just a trickel.  Been leaking a long time with no effect to running, but gets my left knee spattered with oil and keeps the engine a mess.

[DammitDan]

That's almost certainly an o-ring failure.  Gonna require a top end teardown to get to, too...

Good news is, as long as you can live with the leak, it won't really bother anything (right up until you finally lose compression on that outside cylinder, that is).

Though I don't definitely see the o-ring in question on that chart (it's probably #10 though)....

[Jonesy]

Looks like #10 are the O-rings that seal the pressurized oil.

Also, the rubber seal pucks under the cam towers can leak, too.

[SohcCBs]

There is no lack of oil preasure.  The bike operates normally at full power and duration......just makes a mess and I've got'a keep a minor eye on the oil level.  Yes I know I'll have to pull the engine.

[OldSchool_IsCool]

What engine?  A 550 can stay in the frame if it's just a top end rebuild.

[Terry in Australia]

I'm guessing it's a 750 and I'm thinking that it's just the pucks under the cam towers, the O rings won't make it leak between the fins, only along the head gasket joint. Don't crack the head gasket mate, just replace the pucks and you won't get any more hot oil spraying on yer left leg. Cheers, Terry.

[ofreen]

I'm guessing it's a 750 and I'm thinking that it's just the pucks under the cam towers, the O rings won't make it leak between the fins, only along the head gasket joint. Don't crack the head gasket mate, just replace the pucks and you won't get any more hot oil spraying on yer left leg. Cheers, Terry.

I agree.  And while you are in there, retorque the head.

[seaweb11]

...and if that doesn't work....wad up a tiny bit of cloth in to a ball and stick it between fins to collect oil

[Jonesy]

I had to do the puck replacement a year ago on another bike. I waffled back and forth over if I should just fix the offending parts, or go ahead and re-seal everything, as my luck after I did the pucks and refitted the motor, the o-rings would likely start to go and we'd be at it all over again...

[Blaize]

I used to ride a 550 years ago and it used to do the exact same thing if I sustained over 4.5k rpm for more than around 3-4 min. Had a pro look at it at the time and he told me it was in fact the orings you speak of. He said it didnt really hurt anything so I lived with it. Rode it for 2 more years and sold it and as far as I know it is still going strong and still leaking on the freeway. Don't worry too much about it.

[JohnG]

Assuming this is a 750, my experience with these is that it is the pucks between the cam towers and the top of the head. I have had good luck sealing everything else up but these are still a problem.

So if it is these, what is the optimal fix?  new pucks? new pucks and sealer?  If so what kind of sealer?
Are new pucks still available from Honda?

               john - MA

[kaysystems]

I just took my enging out for the very same reason. It turned out to be that oil was seeping through the bolt holes for the two small bolts next to the cam chain. The centre ones under the rubber pucks below the cam holders. It ran down the holes & onto the 3rd? fin down.
O rings were fine.

David

[Jonesy]

New pucks are available from Honda. I used a small amout of Permatex non-hardening sealer on the edges of them and so far, no problems.

[kaysystems]

New pucks are available from Honda. I used a small amout of Permatex non-hardening sealer on the edges of them and so far, no problems.

What I was meaning is the oil was leaking at the head gasket, from the centre, out to the bolt holes, then down to the fins.

David

[Raul CB750K1]

My spanish-made Sanglas has a common problem: oil weeps away from some o-rings for the rod's tunnels. Every Sanglas owner has the same problem and even when you replace the o-ring the leak will appear soon. The pressure and temperature of the head cause this, it's a design problem.

This head weeping problem was discussed even in the old Greenspun forums. I was not willing to open my engine in order to cure that small leak -though it is annoying-, so I tried to roll a piece of toilet tissue or paper napkin and pressure fit between the fins in both sides. So far no more dirty pants, the paper is hard to spot and you don't even have to remember to replace it; I do it generally when I remember it's there or when changing oil.

[OldSchool_IsCool]

I have the same weep.  In the picture, I cleaned the fins and sprayed athlete's foot powder spray on them to highlight the source of the leak.  I plan to re-gasket the top half of the engine this winter.

[SohcCBs]

I've been riding it ('76 750SS) with this leak for about three years, I'm sick of it....and would like to make sure of what I'm doing before taking the time and effort.....so it's either the pucks or the "O" rings(?).   I think I'll see if Mike Nixon might add to the info on this.....

[kaysystems]

I've been riding it ('76 750SS) with this leak for about three years, I'm sick of it....and would like to make sure of what I'm doing before taking the time and effort.....so it's either the pucks or the "O" rings(?).   I think I'll see if Mike Nixon might add to the info on this.....

Or the head gasket.

[mazingerzeca]

I've noticed it on my bike too. A cb 750 K8 with F2 engine. I hoped it was due to the high mileage of my bike.

I am having my engine restored this winter, by a mechanic, but if it happens on rebuilt engines, will I expect the same leaks, even changing o-rings, rubbers, gaskets, everything? Could it be due to the flatness of cylinder head bottom?

Anyone of this oil-leakers club experienced this on re-flatted cylinder heads?

[kaysystems]

Unfortunately even after having the head machined I still leak. But for me it seems to be a problem of the head gasket not sticking properly. It will this time. The head & cylinder surfaces have been roughened up. Need to make sure the surfaces are chemical & oil free,  and I'll use Hylomar in the appropriate places.

David

[eurban]

Having the surfaces cleaned, checked and machined flat is always a good idea.  One very worthwhile upgrade is to install heavy duty (chromoly) cylinder studs which allow just a bit more torque and do not stretch like the stock ones.  My 836 project (with heavy duty studs) is dry with 1K miles on the engine but of course it may be premature to celebrate. . . . .

[kaysystems]

Having the surfaces cleaned, checked and machined flat is always a good idea.  One very worthwhile upgrade is to install heavy duty (chromoly) cylinder studs which allow just a bit more torque and do not stretch like the stock ones.  My 836 project (with heavy duty studs) is dry with 1K miles on the engine but of course it may be premature to celebrate. . . . .

Talking about torque. What torque can be used? K0 manual says 13.7 - 15.2 ft/lbs. Didn't that value go up with later models?

David

[Terry in Australia]

Talking about torque. What torque can be used? K0 manual says 13.7 - 15.2 ft/lbs. Didn't that value go up with later models?

David

The stock cylinder studs are pretty weak, and the main reason for leaking head gaskets on the mighty CB750.

I just rebuilt the K2 engine in my K1 "Bitsa" as it was leaking from just about everywhere, so I replaced:

a. base gasket, 
b. head gasket,
c. O rings and rubber pucks under the cam towers, (with a little Threebond 1104 around the edges)
d. new cam cover gasket,
e. new sump pan (stripped sump plug thread) and gasket,
f.  kick starter shaft seal and gear lever shaft seal, and
g. RC Engineering cylinder stud kit.

Whereas the old studs in good condition can only be torqued to say 18 ft lbs (I know the book says less, but I always did and got away with it) the RC studs are good for 24+ ft lbs.

You can't buy an RC kit new anymore (to my knowledge) but you can buy a new APE stud kit, and I'd recommend it to anyone, my old studs were in pretty poor condition, there are two short studs that are exposed to the elements, and these were badly corroded, so probably would have stretched at a greater rate than the other spindly studs, causing uneven pressure at the gasket joint. My advice, (for what it's worth, of course) would be to replace all the gaskets and external seals, and the cylinder studs with HD items, and your engine can't leak. Cheers, Terry.

[mazingerzeca]

You can't buy an RC kit new anymore (to my knowledge) but you can buy a new APE stud kit, and I'd recommend it to anyone, my old studs were in pretty poor condition, there are two short studs that are exposed to the elements, and these were badly corroded, so probably would have stretched at a greater rate than the other spindly studs, causing uneven pressure at the gasket joint. My advice, (for what it's worth, of course) would be to replace all the gaskets and external seals, and the cylinder studs with HD items, and your engine can't leak. Cheers, Terry.

Hello. Where can I buy APE studs? Thank you

[Terry in Australia]

Hello. Where can I buy APE studs? Thank you

G'Day Mate, here's APE's site, Big Jay (the boss) is an occasional contributor here too. Cheers, Terry.

 http://www.aperaceparts.com/