• Husqvarna Motorcycles Made In Sweden - About 1988 and older

  • Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

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Installing a chainsaw compression release?

Bigbill

Bigbill

Husqvarna
Pro Class
I'm installing a push button compression realise in a left side kick air cooled engine. Where do you guys put these in the head or on the top edge of the cylinder? I need to drill and counter bore threw the upper cylinder or head on the rib then drill and tap a 10mm hole for the compression release assembly. Now should I put 1/8" hole through the cylinder sleeve then stay shallow with the 10mm tap drill so there is a smaller 1/8" hole in the cylinder?

I'm thinking if the compression release ever breaks the parts can't get into the cylinder.
 
Use the 1/8 as a pilot slam that puppy straight through, measure depth them go with 10mm to half deotg then tap the chainsaw comp thread, done.
 
Thx.
That looked lika a bit of a pain in the but to make, and im not so found of drilling thru the water jacket.
I have seen some Honda Cr500 heads with a Decompressin valve, but they just drill a smal hole in the head.

I have to do some research on it.
 
$T2eC16FHJGQFFh+8K+)mBSDUkvk2OQ~~60_57.JPG


Maybe it's possible to drill a smal hole next to one of the headbolts.
 
Possible im no genius but how would you do the head bolt up or the decomp valve that close to one another.
I looked and spitablled a few ideas around a few racers n good head workers and this was the overuling outcome.
I would as stated in the thread make the slug bigger for a 14mm autodecomp. With a shoulder to reduce exposed hole to combustion chamber.
 
ngrdd3.jpg

I mean that I would make the hole from the side of the head, not from the top.

Maybe weld a bung on it so the thread from the Decompvalve will fit "outside" of the head and only have a smal chanel to the chamber.
 
Yup that should be fine, told you im no genius. You may have to surface grind the head as distortion could occur that close to the face.
Keep us posted on how it goes.
 
All the older air cooled Maico's had them installed in the cylinder just about a 1/4" below the rings when the piston is at top dead center. Like the picture shown. It works better in the cylinder once the engine is lit. The hole only needs to be about 1/8" to 3/16" in the liner. A compression release in the combustion chamber of the cylinder head is for down hill braking old school style. Old school head mounted ones were'nt used for starting or aiding in starting, If it's cable operated, It releases a bit too much compression to let the engine start up properly IMO. Push type ones like the ones commonly used on big Cube V-Twins would work fine in the head though.
 
Hmm.
Then I have to go back to the drawing board again.
I wonder how I would make it without getting water in the engine.

You can buy a Honda cr500 and Kx500 head with decomp valve in it.
 
I drilled a hole in a aluminum piece of round stock in a lathe. I drilled a hole opposite the water pipe between the spark plug hole and the head bolt in the dome of the chamber. I chamfered the round stock and the head so I got more filler material in the weld joints. Then I used the through hole as a guide to setup the head on a angle fixture on the milling machine to drill and tap it for the c- release. Sorry you weld in the combustion chamber and the outside around the sleeve so the coolant won't leak. I made the chamfer deep enough to over lap two passes with the TIG welder.

I put the sleeve between the spark plug hole and the smaller head bolt hole not the long rod head bolt. Lucky I can machine and weld at the time.

Stupid me I did all this work on my 400 wrx and sold it. Liquid cooled sorry.

My next c-r will be in my air cooled.
 
Pictures would be excellent as im just seeing what ive done to my head as the same location to what you did BigBill.
 
Here's how I did mine
With a lot of help from the great people from this site, Havn't been able to fit it yet. There are also some drawings/pics for the side mounted version, I think that calls for some extra metal to be added alongside one of the head bolt castings.
After welding I put the head on a piece of glass with some lapping paste and there was no distortion from the welding at all.
http://www.cafehusky.com/threads/88-xc430-de-comp-mod.41593/
 
Cool.
I think I'm going to try the side mount version.

Can keep you guys updated if you like?
 
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