Mower head gasket - to seal or not to seal?

[YorkshireMidge]

Managed to strip the spark plug threads on my Mountfield mower. It's around 35 years old.

Got the cylinder head off and while I wait for a helicoil kit to arrive, does anyone have any thoughts on what to do with the head gasket? I was expecting some sort of composite gasket I would be replacing, but this is just flat machined steel and was obviously fitted dry originally as it came apart easily. Engine is a Tecumseh BVS153.

I was thinking I'd re-use it, and perhaps smear some Wellseal on it. Thoughts?

Thanks.

 

[Harry Bloomfield]

Managed to strip the spark plug threads on my Mountfield mower. It's around 35 years old.

Got the cylinder head off and while I wait for a helicoil kit to arrive, does anyone have any thoughts on what to do with the head gasket? I was expecting some sort of composite gasket I would expect to have to replace, but this is just flat machined steel and was obviously fitted dry originally as it came apart easily. Engine is a Tecumseh BVS153.

I was thinking I'd re-use it, and perhaps smear some Wellseal on it. Thoughts?

Thanks.

I have never taken an head off, where there is not some sort of gasket - perhaps someone has been in there before you?

For general purpose gaskets I make my own from brown paper, or corn flake boxes. A head gets hotter, so for that you need annealed copper sheet, cut to size with the appropiate holes cut in it, then annealed again. You can make a pattern using a 'brass rubbing' technique.

 

[YorkshireMidge]

Sorry if I wasn't clear Harry. There is a "gasket" but it is just flat machined steel as opposed to composite. i.e. it would never have compressed in any way. Have owned the mower since new and the head has never been off before.

 

[Harry Bloomfield]

Sorry if I wasn't clear Harry. There is a "gasket" but it is just flat machined steel as opposed to composite. i.e. it would never have compressed in any way. Have owned the mower since new and the head has never been off.

Likewise, I have never come across steel gaskets either. Usually the gasket is a softer material than the head or the block, to allow it to deform and seal. I wonder if annealing the steel gasket might work?

 

[Burnerman]

https://www.gardenhirespares.co.uk/2756-tecumseh-bv-bvl-bvs-lav40-50-cylinder-head-gasket.html
I think this is what you need....the original is composite aluminium with an asbestos sandwich in the middle.
John

 

[YorkshireMidge]

Likewise, I have never come across steel gaskets either. Usually the gasket is a softer material than the head or the block, to allow it to deform and seal. I wonder if annealing the steel gasket might work?

Those were my thoughts exactly, and it looks like I need to go to Specsavers Harry. I've cleaned it up and had the outer edges under a magnifier and that confirms it's not solid. It's just that the surface is dead flat and has picked up machining marks from the head and block.

Cheers.

 

[YorkshireMidge]

https://www.gardenhirespares.co.uk/2756-tecumseh-bv-bvl-bvs-lav40-50-cylinder-head-gasket.html
I think this is what you need....the original is composite aluminium with an asbestos sandwich in the middle.
John

Great - that looks like it will do the job. Cheers.

 

[Burnerman]

No problem - if the original gasket hasn't delaminated then usually they will work again......don't try to anneal composite gaskets though!
Wellseal is an excellent jointing compound.
John

 

[Keithmac]

I've built a few engines with no head gasket by design, all were 2 strokes.

Very odd but that's how they were made!.

 

[Nige F]

Did they have a raised flange on the block and a mating groove in the head ?

 

[Keithmac]

The barrels are flat, the PX has a raise sealing surface but the Zip just has a flat machined surface (no exhaust gasket either!).

 

[Burnerman]

Usually for high performance engines, maybe? The only one I've seen was on a racing JLO and that was ages ago......lapping the faces in with fine valve grinding compound was the order of the day.
John

 

[Keithmac]

I genuinely don't know why they chose not to use a head gasket, can't cost that much.

The PX 125/ 200 is quite a unique engine to be fair so probably did it just because they could!, that's Italians for you.

 

[Burnerman]

Just my own thoughts and based on no facts or research whatsoever.....
The head gasket is obviously the weakest part of cylinder head design and taking it out removes this item for failure. As high performance engines often run on a maximum ignition advance (and didn't used to be adjustable over a certain RPM) the inclination to 'pink' would put the gasket under even higher stress so leaving it out may improve reliability.
John

 

[Keithmac]

This is a PX, in all the high performance watercooled motorcycles I've worked on (200+ bhp per litre) they all have MLS headgaskets. I just think it's a quirk with some older designs.

Weirdly all the none head gasket engines all have base gaskets!.