Life expectancy of a 7hp Headgasket

[AlanBartlett]

This is probably sounds a silly topic but here goes. Is there a recommended life span of a Head gasket?

I think I've had to change the head gaskets on mine about once a year, I probably cover somewhere between 2000 - 3000 miles a year in the car. Through various shows and general weekend use. (Any excuse for a sunny day beach run!)

I've also found that one side seems to destroy the gasket when its on its way out, first of all youll get a squeak and blow out through the leak in in the gasket. Seemingly no loss of power just an annoyance of the noise. As we discovered at goodwood last year I was tightening down the head nuts in the right order, just not quite tight enough. On the side that went at goodwood this is still going strong. And then we went on to check the otherside. The (Drivers side) which is causing issues.

But what I haven't seen before is that it appears not to be leaking from the front of gasket (The side nearest the radiator) but it has pushed out the copper gasket partly. and is blowing from the rear (nearest the exhaust) This is happened before, and is usually my indicator that it is on its way out.

I think the solution would be to take the pots off and have them machined, but at present I'm reluctant to do this as the engine is running fairly well or has been running well for the past couple of years (touch wood apart from the headgasket) But I think it will be an option in the off season.

Hopefully two photos of the one of the gasket I changed last year on the same side, how it had been eaten away around the edges.


And one of the current gasket still in situ with the copper piece seemingly pushed out.

[David Kemp]

I don't know about vintage but Bradfords only leaked when heads or cylinders are not flush.
Check your heads before putting back on. Even though small the heads do warp.
Also check your water passages , if not perfectly clear the blocked passages can cause a hot spot.
Also you may need to remove the head studs & chamfer the stud holes , as over time the threads can pull above the cylinder deck, leading to head gasket failure.

[Forumadmin]

Posted from a sticky Cairns qsl.
Many things can cause repeated gasket failure. When tightening bolts you may notice uneven movement caused by stretching bolts or crankcase. My dry torque down method might work on your head. See Jav Jup section

[george garside]

I think that perhaps currently available gaskets may not be as as good as the originals. When running pre war (8) as everyday car I only once had to replace a gasket and that was due to a warped head . Otherwise I invariable reffited the same gasket after removal for valve grinding or decoke and certainly got 20,000 miles out of them. To remove gasket I always 'blew' them off with the starter i.e. slacken head nuts a few turns and press the starter and off they popped totally intact. I always refitted using hermatite red and torqued to I think 40 ft lb. checking again with torque wrench aafter about 30 miles running. Tighteniong the heads in the recommended order is also crucial.

David is spot on about checking both pots and heads for accumulated SHoneT and poking the water passages out with a suitable implement

george

[AlanBartlett]

Thanks for all the comments,

Looks like it will have to be a barrel off job soon then, When I take this one to change I'll have a good look around and see what could be causing it from the suggestions.

Interesting you say about using the red hermatite, I've used hylomar blue on the gasket before, and also grease. And have also fitted them dry. I know the current one on the passenger side is a dry fit of which I've had no issues with.

But I do think it is possibly due to un even surfaces, Definitely something to look at.

[ian Howell]

Top tip there from George - "I blew them off with the starter".

A blinding glimpse of the obvious that I have never seen or practiced before!

I guess there could be drawbacks - someone will know

[AlanBartlett]

Yeah, I've not heard of that before...

I usually use the spark plug, I think which is adviced in the manual just to wiggle it and get it moving off the barrel.

I shall have to try that one when I change it!

[george garside]

I have always used the starter to blow heads off on many different types and makes of engine. Why fart about when there is a wonderful supply of free compressed air in exactly the right place!

george

[ian Howell]

Precisely!

[AlanBartlett]

Well I've just taken off the head. And unfortunately the head was stuck fast, so George's trick wasn't very successful.

Now I think I have found the possible problem which would be.

The barrels appear to be earlier ones - or ones with less water ways, around the bottom instead of being four on the gasket and the head, there are two missing. Am I right in thinking later type ones had more water ways to allow for better flow? What I have is a late/more water way head with a gasket with more water ways on a cylinder with two less.

I think what is happening its heating up around the exhaust end where it leaks, cause it to blow the gasket where it does. Because there is not enough holes for the water to circulate, perhaps this is why what I think are later heads have more holes?

Can anyone think?

[Tony Fearn]

Here's a photo of two types of pre-war cylinder head which I think adds to the discussion.

Pre-war cylinder heads.jpg

Tony.

[AlanBartlett]

Hi Tony the pictures help.

Basically the actual cylinder head is "G" but the barrel is has the water ways of "F" I know they can be interchangeable but are they supposed to be?

[Tony Fearn]

Hello Alan.
I wonder if the 'F' cylinder casting will allow a couple of extra holes to be drilled in the face to give more access to water circulation.
There might be room behind the face into the water cavity.
May be someone knows, but I don't.
Of course if you do it and it's not right, you'll get choice words and a flea in your ear from George, and the cylinder will be ruined.
What do you think Ian/David?
Tony.

[k. rogers]

Alan, I'm a bit puzzled! Firstly, I thought you had 8hp barrels on your car (I must be wrong). Secondly, if these are earlier barrels, I didn't think they were interchangeable because of how they were bolted straight to the chassis. Perhaps George can enlighten us! Also, I don't think the problem would be this alone, after all, they must have been ok before the extra water channels were introduced. In my experience, all that happens by using the later heads is that you get a build up of crud at the redundant holes in the head. Does the burnt part of the gasket correspond to the exhaust side of the cylinder? If so, what are your valves like and is the valve clearance sufficient?

[AlanBartlett]

Ken,

I have the 7hp barrels on the engine (With the 7hp matching number casting), using std pistons from the 8hp(Which was the engine I had in there before I rebuilt the 7hp engine). Which is probably what your thinking.

Bolted straight to the chassis? These barrels have two front mounting studs which are mounted to a triangular bracket which is fixed to the hydraulic engine mountings. Do you mean the rubber chassis mounted type?

Oh so perhaps the later heads would be ok to use then? Well I've been using them up until now.

Yeah every time the gasket goes on this side it does go on the exhaust side. The top picture I posted is a bit back to front. Where it has been sort chewed away is on the exhaust side of the engine.