air cooled compression release

There's an adapter for Harleys that a 14mm spark plug thread x 3/8" long(threads). It has the 10mm threaded hole for the chainsaw compression release. The 14mm threaded adapter comes in different thread lengths. The 1/2" one is too long. The 3/8" one is perfect for this application. There on eBay. Just drill the head, counterbore or use a milling cutter or four flute drill then thread the 14mm hole.

If you dont already have an extra plug hole why use an adapter? Just drill and tap for the compression release.

The compression release should be in a smaller hole thru the adapter. This thru hole should be smaller than the valve on the compression release so if the shaft ever breaks in the compression release the broken part can't get into the engine.

You dont need to do that if you put it on the cylinder, drill the small through hole, drill the hole for where you will install the release only in the aluminum and you are done. No adapters needed, and the release functions better in the cylinder than in the head.

lets see a picture when its done

Ebay id #......?

Some pics in this old thread of mine I did a while back.

http://www.cafehusky.com/threads/new-project-82-500-cr.29316/page-3

86 400 xc how easy does it kick with the compression release?

like a weak 250

i think the biggest difference is that the engine turns over the 2nd time as you kick through . without de comp it moves over one revolution then doesnt go over the 2nd
i have one in the barrel of my 500 . starts 1st kick once warm . starts 1st kick cold too actually . couple priming kicks , push button . find tdc . kick it right through , engine runnning

my barrel had a 14 mm hole in it already so i made an adaptor myself . spark plug thread on one end . 10 x 1 thread in the other end for chainsaw decomp . the hole through the middle is 1 mm smaller than valve .

My 420 cylinder had the extra 14mm hole already in the head. I also have the older 14mm compression releases with the cable and lever that goes on the handle bar there brand new.

I'll look into installing the other compression releases in the cylinder.

Good point, something I hadn't considered. Compression release shaft breaking is probably unlikely but the damage that would occur from such an event would be expensive, especially on some vintage machines where parts are hard to find.

I've had a few reports of the barrel/cylinder decompressor being a better option than the head . Can anyone offer any tips before I tap into the back of the barrel of my 500?

I can't say based on personal experience because I've never added one but I do know that Husky considered a compression release as a standard item on the RT model in 1973. They changed their mind but not until the placement of the unit had been added to the RT's tooling. It appears that they thought the best place was in the barrel.

On my 500 ae, the decompressor is half way between top of exhaust and top of cylinder.
It is between 2 studs.
I have grinded one fin. Then send the cylinder to a specialist to make the hole.

Look awesome.

a mate of mine had a genuine husqvarna chainsaw de-compressor fitted to the head of a 500cc BSA motocross race engine, it blew the middle of the de-compressor out into his inner thigh, very bad bruise !