E: Engine Decompressors

[bmetcalf]

Forty years ago, I paid $25 to have a broken EZ-out EDM-ed from a Burman box, so I am very reluctant to use them!

 

[davidd]

Bill, I was going to get branded ones (like genuine Husqvarna) but thought I would get the cheapest first just literally to try them, then thought why not just build in a safety precaution. But I will probably buy a pair of branded ones anyway as they're not that expensive.

If it works, it is fine. The two stroke decompressors are different from the four stroke ones. A two stroke has to lower the compression prior to the piston riding by. The four stroke does not have the same problem. Sometimes the two stroke decompressor will allow to much compression lowering when used on a four stroke. The designs are quite different. However, if it works, you are good to go. Keep the part numbers of the ones that work!

David

 

[Sakura]

Forty years ago, I paid $25 to have a broken EZ-out EDM-ed from a Burman box, so I am very reluctant to use them!

EZ outs are about the worst tool available for this sort of job. There are many modern tools that are so much better.

 

[Bill Thomas]

If it works, it is fine. The two stroke decompressors are different from the four stroke ones. A two stroke has to lower the compression prior to the piston riding by. The four stroke does not have the same problem. Sometimes the two stroke decompressor will allow to much compression lowering when used on a four stroke. The designs are quite different. However, if it works, you are good to go. Keep the part numbers of the ones that work!
View attachment 31671
David

The thread is too short ?, For a standard plug hole, And the threads will soot up,
My ones do a proper job ! .

 

[Dave61]

If it works, it is fine. The two stroke decompressors are different from the four stroke ones. A two stroke has to lower the compression prior to the piston riding by. The four stroke does not have the same problem. Sometimes the two stroke decompressor will allow to much compression lowering when used on a four stroke. The designs are quite different. However, if it works, you are good to go. Keep the part numbers of the ones that work!
View attachment 31671
David

Hi David,
Who makes these ?
They look very interesting.
Cheers
Dave

 

[Chris Launders]

The adaptors I'm going to make will be full plug thread length, with shorter 10mm thread inside.

 

[davidd]

I did some research on decompressors years ago and the links I have no longer work. I thought it was an interesting idea. I did see a patent for one that had a hole drilled into a ring that the spark plug fit through and a high pressure tube coming out of the ring to connect a remote decompressor, so to speak. The ring designs below look more useful than the image I posted because presumably you can select a plug with a longer reach. There are two links below that work, but I did not go through them.

“EZ Release” Compression Release by Wimmer

Leave it to Wimmer to fabricate the easiest to install compression release ever. The idea is simple, a compression release installed on the rear cylinder retards the spark plug during ignit…

twistingthewick.wordpress.com

Kit for Decompression with straight Holder and Spark Plug, 64,50 &eur

Kit for Decompression with straight Holder and Spark Plug

motorbiker-shop.de

Adapters:

Compression Release Adapters — Alloy Art

designed to be used in twin plug heads Accept .650”/ 10mm x 1.0 compression release valves Sold each Made in the USA!

www.alloyart.com

David

 

[john998]

Fitted Enfield decompressors to my Rapide many years ago to get rid of the oil leak from the lifter mechanism. Ended up with two oil leaks in a worse place at the top of engine.
On the Enfield the head casting has a recess that takes what comes out of the decompressors to the exhaust pipe. John.

 

[vibrac]

Wouldn't the remote decompressing mentioned above reduce the compression ratio?

 

[erik]

As Chris writes,he is able to start the twin without desompressors.I can only start my comet without.I am 185cm tall and 120kg and can not start my twin without the decompressor! What is wrong?Erik