Compression release

[mudmantra]

I'm trying to find more information on these compression release's. Who made them, and how they worked. I used to ride with a friend that had one on his old Yamaha 125. He used it for engine braking. And I remember one time he dumped his bike in the river and filled the engine with water. Then to restart his bike, he just pulled the compression release, hit the electric starter and pumped all the water out. Then the 125 started and we just kept riding. Those little 125's were tough! This is a picture of one on a Suzuki TM400. I also have one on my YZ465.

[AC Swank]

Google this: vintage japanese motorcycle compression release

There are several on Ebay.

[mudmantra]

Thanks. The kits also gave me a better idea of how to route a control cable. Now I've just been pressing down on the compression release, while kicking the motor over. A bit awkward on a tall machine. But it works anyway.

[AC Swank]

What year is your 125? I have a 1970 and a 1973 along with two 1970 175's.

[willis 2000]

A lot of us had those back in the 70s. If your bike's head came tapped for two spark plugs, it would screw right in. Otherwise, it took some machine work to install. The machined heads were prone to cracking between the plug holes.
It was also realized that these things let unfiltered air into the cylinder. Little engine braking occurred, but the sound was way cool.

[mudmantra]

Originally Posted by Armchair

What year is your 125? I have a 1970 and a 1973 along with two 1970 175's.

It was a friends bike. I think it was a 1972. It had 18 inch wheels front and rear. We lived were we could ride off road everyday, so our bike really took a beating. I know we all got new bikes in 1974. Mine had every part bent or broke with in a year. I only broke my arm. Still rigged the throttle, so I could ride. I don't know why the Doctor got mad when I brought my broken cast back for him to fix.

[mudmantra]

Originally Posted by willis 2000

A lot of us had those back in the 70s. If your bike's head came tapped for two spark plugs, it would screw right in. Otherwise, it took some machine work to install. The machined heads were prone to cracking between the plug holes.
It was also realized that these things let unfiltered air into the cylinder. Little engine braking occurred, but the sound was way cool.

Yeah I can't wait to get mine working from the handle bar. It well be a lot easier to start the YZ465. I agree, I think they sound cool too.

[motu]

Originally Posted by willis 2000

Little engine braking occurred, but the sound was way cool.

I found they gave too much engine braking. Deciding I was disadvantaged on the dirttrack with no engine braking, I fitted one to my TM400 - it just locked up the wheel and sent me off the track. Same on a trials bike, too much engine braking to be controllable on a steep decent.

[Strong Bad]

They work pretty well on a a 250cc and smaller 2 smoke at higher revs. Keep in mind that it is a direct pathway for unfiltered dirt to access you piston & bore. On a nice damp TT or Flat track they are bitchen, anywhere else you are asking for excessive wear.

[mudmantra]

Originally Posted by Strong Bad

They work pretty well on a a 250cc and smaller 2 smoke at higher revs. Keep in mind that it is a direct pathway for unfiltered dirt to access you piston & bore. On a nice damp TT or Flat track they are bitchen, anywhere else you are asking for excessive wear.

Good point, I don't want dirt inside the motor. Main use for the compression release, well be starting the motor when it's cold. That well reduce some wear and tear on the case and kick starter. I may have some machine work done on the cylinder head, to improve the combustion chamber too. The YZ465 is not most friendly bike to kick start. But If I get the jetting spot on, it should be better.... I hope.

[blaine.hale]

I use them in creek crossing on bikes with drum brakes. We all know drum brakes aren't as effective when wet, so the compression release is an excellent brake substitute.

[mudmantra]

Originally Posted by blaine.hale

I use them in creek crossing on bikes with drum brakes. We all know drum brakes aren't as effective when wet, so the compression release is an excellent brake substitute.

I better look at my brakes too. It stops good now, but they might be 1980 shoes. I've had old shoes come apart on me before.

[mudmantra]

This just came in. Old but new from ebay. The compression release is just like the one in my bike. Now I have a cable and lever too.

[mudmantra]

Looks like this place sells a compression release for 2 strokes too. looks like it should be a good item. I guess these are used a lot on the 2 stroke flat trackers.
http://www.omarsdtr.com/dtcomprel.html