Blown Head Cover Gasket

[tomoco]

The siren was going off, so I removed the lower unit to look at the water pump. It looked fine. Then I removed the Cylinder Head Cover (not the cylinder head) to see if I could find Junk in the cooling passages. I found a hole in the gasket I could put my thumb through. But no Junk. (see photos)
I am figuring that a new gasket will solve my problem, but still, how could such a hole have happened? Might there be similar holes elsewhere?
How can I test if water is flowing as it should?
1972 65 hp

 

[F_R]

Re: Blown Head Cover Gasket

Nah, the hole has nothing to do with it. They really only need gasket where it is pinched between to metal parts. The rest is only there for manufacturing convenience.

 

[wbeaton]

Re: Blown Head Cover Gasket

Water + 35 years = deteriorated gaskets. At least is didn't effect anything. I'm not familiar with that model, but I'd check the regular things first. You've done the impeller and the head cover. Did you also check the intake screen (if it has one). Did you try blowing water or air through the cooling passages?

 

[tomoco]

Re: Blown Head Cover Gasket

Actually, it is a completely rebuilt power head about ten years old. I still have the corpse I replaced. It has a very solid looking gasket! The newer, blown one looks a little thinner.
I put in the old, intact gasket, removed the thermostat and attached the garden hose to the water tube. I did not seal the gasket for this test, so water squirts out everywhere, but I get little or none coming out through the vent holes.

It looks to me like the water flows up to the thermostat on the inside of the gasket and down on the outside. The hole is at the bottom where the water comes in. So it is sort of like a short circuit.

I wish i knew more about the water path.
Does all the cooling water flow thru the thermostat? When tstat is closed, does pressure build, or is there an alternate path?

 

[F_R]

Re: Blown Head Cover Gasket

I think you are incorrect in your accessment of how the water flow. However, I don't have the parts in hand to argue the point.

But I can say that there are two paths. One is through the thermostat and the other is the pressure relief valve. That is the plastic valve and spring there beside the thermostat. Normal water pressure should open that valve anytime the 'stat is closed.

 

[offshore100]

Re: Blown Head Cover Gasket

It looks to me like the water flows up to the thermostat on the inside of the gasket and down on the outside. The hole is at the bottom where the water comes in. So it is sort of like a short circuit.

I wish i knew more about the water path.
Does all the cooling water flow thru the thermostat? When tstat is closed, does pressure build, or is there an alternate path?

Of course there's an alternate path, your pee tube should always work regardless of whether the t-stat is activated or not.
As I understand it, water always flows around cyl. heads; until 1: engine temp opens t-stat or, 2: engine speed (incresed water pressure) opens pressure relief function of t-stat if temp hasn't been reached........

at which point cooling water is then also directed deeper into the motor, around cylinder walls.
Please correct me if I'm wrong>

 

[wbeaton]

Re: Blown Head Cover Gasket

Did you torque the cover properly for your test? Since you've just re-used a gasket I'd expect it to leak, but I would think that water squirting everywhere would denote a blockage or restriction. At least, that's been my experience.

 

[tomoco]

Re: Blown Head Cover Gasket

Guys.
Thanks for the info. I didn't understand how the Pressure Relief worked. I see now.

I had another look.
I'm pretty sure about the flow. Except, it's up to the thermostat on the outside of the gasket through Tstat/PRs and down on the inside. Direction is clear because of the direction of the PR valves.

Water inlet and outlet are on the bottom near the gasket hole. Tstat is at the top (see photo). On the top of the way up it hits the Tstat & PR valves, which are right next to each other. If they are both closed it is a dead end. When they open the water is free to travel down the inside.

Except in mine there is a shorter path through that thumb-sized hole right near the inlet/outlet. This has to reduce the water flow past the Temp Tensor, which s just downstream from Tstat & PRs.

The PR Valves probably do not open. Tstat probably does open. The temp sensor goes off because of slower flow past it.

I'd like to know whether water going around the Cyl Head Cover is going to, or coming from other engine areas, like cylinders or exhaust manifold. I think it might split paths as it leaves the cover.

But I'm feeling more & more that a new gasket will fix me up!

Now all I have to deal with is the Stupid Electric Shift!!

 

[tomoco]

Re: Blown Head Cover Gasket

Did you torque the cover properly for your test? Since you've just re-used a gasket I'd expect it to leak, but I would think that water squirting everywhere would denote a blockage or restriction. At least, that's been my experience.

I "sort of" torqued it. But the Tstat Gasket is damaged and I hadn't cleaned the metal surfaces properly. I think I am going to cut my own Tstat cover gasket, goop up the Head cover gasket with two coats and try again.
If f it seems OK, I'll try it in the water.

PS: I lived in Hamilton for 14 years ending in 1981. Visited up there last year. No boat tho, those were canoe days!

 

[wbeaton]

Re: Blown Head Cover Gasket

Small world! I've only been here 5 years. And I'm glad my canoe days are over, too!