compression relief valves, to allow easier kicking?

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Dances with Shrapnel said:
Can you share some pictures of these compression release valves installed on the combustion chamber side?

compression relief valves, to allow easier kicking?


compression relief valves, to allow easier kicking?
Click to expand...

"Dances with Shrapnel", I can't share pictures of the valves installed on the combustion side as those two pictures is all I had filed. However the only visible difference is a 2,5mm little hole from the face of the hemisphere to the threaded cavity of the valve.

Constant Trossèl
http://www.hollandnortonworks.eu
 
These valves when used in 2 stroke chainsaws do not close until the engine fires, they are connected to the combustion chamber by a small hole which partially insulates the valve from the compression in the chamber so it only blows on firing instead of just full compression and also stops the valve head of the decompressor if it drops off from entering the chamber and causing damage.

Briggs and Stratton have a ramp on their inlet cam with a bob weight pressing a ramp out so that at starting revs the compression is reduced until the revs pick up, then the bob weight stops pressing on the ramp and the compression is restored. You can see it close to the camwheel in this pic.

compression relief valves, to allow easier kicking?


The spark plug versions use a long long reach plug with a reach of 26.5mm, they use this extra 7.5mm to add in access to a release valve.

compression relief valves, to allow easier kicking?
 
What am missing here?

The way I see it, no matter how long the spark plug is, the thread into the head will still be 'filled' by the thread of the plug.

I realise it will not be fully sealed if the sealing washer is not tight. But I can't really imagine enough gas escaping past the plug threads to make that much difference to the starting.

Or, as I say, am I missing something ?
 
They either drill a hole down the side of insulator with a cross hole to enter the sleeve on the 7.5mm extension or they mill a groove in the spark plug thread to give a route up, the downside of the groove is the contamination from carbon which will wear out the thread in the head everytime you unscrew the plug. They all come with modified sparkplugs as far as I can tell, but they start with a std 26.5mm plug, I found out by looking at the patents. Patents are good for giving you details of mods and patents only protect commercial use, not private use only copies.
 
Very interesting!

Thanks for digging that up and sharing.

Now... who's gonna try some first...?

Could be just the ticket for my 920...!
 
Try this, simple really.

compression relief valves, to allow easier kicking?


The hole down the side of the thread will be the most difficult, I have some old plugs I can try it out on an a Bridgeport mill to do the drilling on.


compression relief valves, to allow easier kicking?


The photos never show the holes.
 
jimbo said:
In the past on several different makes (and in the present) ,there were/are cable operated systems that kept the exhaust valve open with a mechanical stop acting upon the spring collar. However that's a big engineering hill to climb for our bikes.
Click to expand...

Been done. Unfortunately no pics from the inside. Bike is fitted with an Alton electric starter.

compression relief valves, to allow easier kicking?


compression relief valves, to allow easier kicking?
 
slimslowslider said:
jimbo said:
In the past on several different makes (and in the present) ,there were/are cable operated systems that kept the exhaust valve open with a mechanical stop acting upon the spring collar. However that's a big engineering hill to climb for our bikes.
Click to expand...

Been done. Unfortunately no pics from the inside. Bike is fitted with an Alton electric starter.
Click to expand...

wow! there you go, so where do people line up for that setup? :shock:

....... I know ,its a one off :(
 
Don't some of the big American muscle cars prop open the exhaust valves, crank the engine, hack the ignition and dump the valves back on the cam ? Drag cars maybe?
 
slimslowslider said:
jimbo said:
In the past on several different makes (and in the present) ,there were/are cable operated systems that kept the exhaust valve open with a mechanical stop acting upon the spring collar. However that's a big engineering hill to climb for our bikes.
Click to expand...

Been done. Unfortunately no pics from the inside. Bike is fitted with an Alton electric starter.

compression relief valves, to allow easier kicking?


That looks great. I am guessing its a one off and a lot of work was involved. I thought that something like that maybe possible (but in no way could i make it look that good with things i have available) but i was worried about the cover retaining screws/studs not being strong enough, is that an issue??

compression relief valves, to allow easier kicking?
Click to expand...
 
One of the things I like about my Joe Hunt maggie is it throws out such a big spark it fires up on 1/2 a swing on the kick start every time, I also have the T160 longer kick start lever which also helps with easier kicking, my Norton is a one kick start every time whether cold or hot, but I have been kicking it for over 40 years now, I was a skinny 17 year old when I brought it new, I soon learned quickly how to start it, I can also sit on the seat to fire it up.

Ashley
 
Holland Norton Works said:
Dances with Shrapnel said:
Can you share some pictures of these compression release valves installed on the combustion chamber side?
Click to expand...

"Dances with Shrapnel", I can't share pictures of the valves installed on the combustion side as those two pictures is all I had filed. However the only visible difference is a 2,5mm little hole from the face of the hemisphere to the threaded cavity of the valve.

Constant Trossèl
http://www.hollandnortonworks.eu
Click to expand...

Thanks Constant. What you describe is not what I expected and seems to be rather unobtrusive. Sounds like a rather tidy alternative. Well done.
 
I had a 1950 BSA B33 and it had a compression release on the handle bar. I never found it very useful. Like others said, you still have to get it over compression during a firing stroke to start it. About all I found it good for was to get it over that first compression so you could get some inertia during starting. I not very strong in the legs and I have to stand on the pegs to get my Norton started, but I still do the same I did with the BSA, just get it over compression by slow force, reset the start lever and then give it both barrels with my weight to get it through the next compression, and if it's tuned right it almost always starts. If it takes more than 2 tries, there's something wrong. I never was able to start the bike sitting on it or off to the side, unless it was completely warmed up. Switching to syn 20W40 helps too.
 
The B33 and other exhaust valve lifters release all the compression when they are opened, so they are to be used to get the piston over TDC before kicking, they are not designed to be operated during the starting kick. The chainsaw release valves are designed to release some of the compression leaving enough to allow the engine to fire and rotate enough to get over the next TDC, under the increased first firing compression they then close so full compression is achieved at this next TDC and all subsequent TDC'c.
 
Just fit the long kickstarter as supplied by RGM, it's a version of the folding one as fitted to T160s, costs around £100 and makes starting so much easier
 
The longer the kick start lever the more it's going to hurt when it does bite back. The classic single cylinder racers way of getting the piston in the correct place for bump starting is, put it in gear let the clutch out and pull the bike backwards until the compression stops it.
 
gripper said:
The longer the kick start lever the more it's going to hurt when it does bite back. The classic single cylinder racers way of getting the piston in the correct place for bump starting is, put it in gear let the clutch out and pull the bike backwards until the compression stops it.
Click to expand...

Always worked pretty well on a Commando twin too. I sometimes do it before wheeling my bike back onto the rollers these days, it is not essential, and really I do it as a check the bike is properly in gear, but it seems to help a bit when cold.
 
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