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Old 06-23-2012, 06:27 AM   #1
mudmantra OP
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Compression release

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.
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Old 06-23-2012, 06:52 AM   #2
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Google this: vintage japanese motorcycle compression release

There are several on Ebay.
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Old 06-23-2012, 09:02 PM   #3
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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.
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Old 06-23-2012, 10:56 PM   #4
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What year is your 125? I have a 1970 and a 1973 along with two 1970 175's.
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Old 06-24-2012, 12:24 AM   #5
willis 2000
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old school for sure

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.
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Old 06-25-2012, 09:48 PM   #6
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Quote:
Originally Posted by Armchair View Post
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.
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Old 06-25-2012, 09:52 PM   #7
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Originally Posted by willis 2000 View Post
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.
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Old 06-26-2012, 04:29 AM   #8
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Originally Posted by willis 2000 View Post
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.
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Old 06-26-2012, 03:14 PM   #9
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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.
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Old 06-27-2012, 06:00 AM   #10
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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.
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Old 06-27-2012, 07:30 AM   #11
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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.
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Old 06-29-2012, 05:35 AM   #12
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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.
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Old 07-01-2012, 08:48 PM   #13
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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.
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Old 07-01-2012, 08:54 PM   #14
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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
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