Sealing off Half Compression Valves

[piscisteve]

Even after a full rebuild, the half compression valves leak, spewing oil all over the place and I am sure that I will be loosing power.

I have seen them blanked off on many occasions, do we really need them? because I am thinking of blanking off mine.

I do not want to remove the exsisting valves and just blank off with a plug or bolt. Is there any way that I can blank them off and leave the valve insitu or seal the valves airtight shut?

If I have to use a plug, what thread and size is it? I thought it was 14mm, but I am wrong.

Regards Stephen

[Erik]

Hi Steve,

So far I see no need to use them with Scotts being relatively low
compression anyway. On my Flyer the valves are sealed with a large bolt. See pic. This works fine.

On my two speeder the valves are in place but there is no lever attached.

Sealing them with the valves in place seems rather difficult. I have not had a look at such a valve yet but could not you grind them in to get them tight again?

Cheers,
Erik

[piscisteve]

Thanks Erik for your kind reply.

The valves are 3/4″ outside diameter. The castleated boss that holds them in looks cycle thread 26tpi. What size and thread are the bolts you have used?

If I turn down a thin copper blank about 20 thou thick and place it between the valve, up against the cylinder wall, tighten down as tight as I can, as far as I can see I will make the valve inoperative and should have an gastight seal. Am I right or have I overlooked something?

My professional background is nursing and I am afraid that my engineering skills are in there infancy.

Cheers lads

[Erik]

Hi Steve,

To be honest, I would not know the thread/bolt size. My Scott came with this bolts. I will measure one for you this weekend.

Your solution with the copper blank should work I think.

And I am no engineer too, my work is in Business Intelligence/Information management…

Cheers,
Erik

[Erik]

Hi Steve,

I just checked the bolts. The tread is exactly the same as on the valves, some fine 26tpi thread type. The bolts are 23,27 accross the flats, my 1/2 W spanner was a bit on the large side.
To be honest, looking at the bolts (also being hollowed out at the ends for some reason) I think someone made them from scrap.

Cheers,
Erik

[piscisteve]

Hi Erik

The thread inside the exhaust ports is 24tpi!!!, I have never come across this before. Out of pure interest, does anyone know of this thread?

Please do not tell H.R.H. but I have taken out the valves and rubbed 2 pre 1985 pennies (copper) on wet and dry untill smooth. I then inserted them into the ports to cover up the hole in the cylinder wall. Hopefully this will seal the ports and cure my oily valve leak.

I will let you know following a run this weekend.

Regards Stephen

[piscisteve]

Success……….We completed 30 miles today. No misfiring, no boiling, valves sealed and hardly an oil leak…………wipee

My thanks to everyone for all help

Regards

Stephen

[Author]

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