Jump to content
Sign in to follow this  

Compression Release

Recommended Posts

I know this is off topic but I have a CR500 and really want to put a compression release valve on it. Anyone know where to get one? I already posted a thread in Honda Two Strokes but I know some of you guys are really knowledgeable so I thoght I'd put it here too.

Share this post


Link to post
Share on other sites

Compression release valves for 2 strokes were popular in the 60's and 70's. A second spark plug hole was machined in the head for the compression release. I doubt that is possible on a water cooled head. I don't know of any other way to add a compression release to your CR500. Why do you want one so bad?. Some OEMs put the release in the barrel but again water cooling will prevent that.

If you just want to reduce the compression that can be done by machining material out of the head.

Share this post


Link to post
Share on other sites
Compression release valves for 2 strokes were popular in the 60's and 70's. A second spark plug hole was machined in the head for the compression release. I doubt that is possible on a water cooled head. I don't know of any other way to add a compression release to your CR500. Why do you want one so bad?. Some OEMs put the release in the barrel but again water cooling will prevent that.

If you just want to reduce the compression that can be done by machining material out of the head.[/quote

On the Honda 2 Strokes site there are a ton of dudes that have installed them on the CR500 but no one mentioned where they got the valve from. I'm just trying to come accross someone that has done it before. Whether it can be done is not in question. I know what you mean about the water jacket, somehow they get around it. Maybe the jacket doesnt run through part of the top of the head I don't know.

Share this post


Link to post
Share on other sites

the hole still needs to be machined into the head. I've seen a valve recently, but since I don't ride a CR500... I don't remember where I saw it. The hole can be made by a competent home mechanic. (as I recall) you just drill, and tap near the spark plug.

If the guys in the Honda 2-stroke section can't help... it may not be made anymore. But, I would check in the Kawi 2-stroke section too.

OK... now for my vent...

It's a 2 stroke. Just kick it. I was riding open class SCORE when I was 14 years old. PE400, YZ460...ect. don't be a wuss... put on some boots, and kick it. (sorry, but it needed said)

Share this post


Link to post
Share on other sites

I don't think the compression release is for starting is it? 2 stroke releases in the head were for compression braking. Yamaha had a starting release in the barrel part way down the bore. Maybe this is a different style release than I have seen.

I would think a CR500 forum would be a better place to ask a CR500 specific question.

Share this post


Link to post
Share on other sites
the hole still needs to be machined into the head. I've seen a valve recently, but since I don't ride a CR500... I don't remember where I saw it. The hole can be made by a competent home mechanic. (as I recall) you just drill, and tap near the spark plug.

If the guys in the Honda 2-stroke section can't help... it may not be made anymore. But, I would check in the Kawi 2-stroke section too.

OK... now for my vent...

It's a 2 stroke. Just kick it. I was riding open class SCORE when I was 14 years old. PE400, YZ460...ect. don't be a wuss... put on some boots, and kick it. (sorry, but it needed said)

With all due respect you obviously don't ride a CR500... :banana:

Share this post


Link to post
Share on other sites
I don't think the compression release is for starting is it? 2 stroke releases in the head were for compression braking. Yamaha had a starting release in the barrel part way down the bore. Maybe this is a different style release than I have seen.

I would think a CR500 forum would be a better place to ask a CR500 specific question.

As I said I already did ask it there... Just trying to get a little more exposure and find someone who actually knows what I'm talking about and what a compression release is and is used for... :banana:

Share this post


Link to post
Share on other sites
the hole still needs to be machined into the head. I've seen a valve recently, but since I don't ride a CR500... I don't remember where I saw it. The hole can be made by a competent home mechanic. (as I recall) you just drill, and tap near the spark plug.

If the guys in the Honda 2-stroke section can't help... it may not be made anymore. But, I would check in the Kawi 2-stroke section too.

OK... now for my vent...

It's a 2 stroke. Just kick it. I was riding open class SCORE when I was 14 years old. PE400, YZ460...ect. don't be a wuss... put on some boots, and kick it. (sorry, but it needed said)

Maybe the two strokes were lower compression back then but the day I see a 14 year old kick over a cold 500cc single is a cold day in hell...

Share this post


Link to post
Share on other sites

I'm a lean 200 pounds in the gym nearly every day and the bottom of my foot has been bruised raw kickin this damn thing... Plus its my dads bike and he's coming up on 60, it'd be nice to see him not gettin so frustrated

Share this post


Link to post
Share on other sites
I'm a lean 200 pounds in the gym nearly every day and the bottom of my foot has been bruised raw kickin this damn thing... Plus its my dads bike and he's coming up on 60, it'd be nice to see him not gettin so frustrated

Maybe it's time for your dad to pick up a different bike? I had a KX500 for a while and I don't think I'd want it to be my main ride at 60 yrs old.

Share this post


Link to post
Share on other sites

you can buy a compression release that attaches to the spark plug. and with no clearance issues on a 2 stroke i wouldnt see why it couldnt work

Share this post


Link to post
Share on other sites

I had a compression release on a "71 " Yamaha DT250. I was told it was to "clean" off the plug, but what do I know, I was 12 at the time.

Share this post


Link to post
Share on other sites

nmccabe8686 OK I'm ready to learn. Explain to me how you use a compression release to add starting a CR500.

My 56 Norton 600 had a compression release, Various 2 strokes had a compression release. My SR500 has a compression release. My DRZ400 has a compression release. But never used a compression release to start a 2 stroke. Do you run it past TDC like a 4 stroke? or do you just release a little but keep the piston on the way up? Or is it just kind of a small leak that you leave open until it starts?

Share this post


Link to post
Share on other sites
nmccabe8686 OK I'm ready to learn. Explain to me how you use a compression release to add starting a CR500.

My 56 Norton 600 had a compression release, Various 2 strokes had a compression release. My SR500 has a compression release. My DRZ400 has a compression release. But never used a compression release to start a 2 stroke. Do you run it past TDC like a 4 stroke? or do you just release a little but keep the piston on the way up? Or is it just kind of a small leak that you leave open until it starts?

Its a valve that goes next to the spark plug in the head. You push a button on the valve or open it by a cable and there is now very little compression in the cylinder. You kick the bike and when it starts the increase in compression closes the valve and it is the bike operates as if there is nothing there. Check out the pic by "Old Timer" http://www.thumpertalk.com/forum/showthread.php?t=858245&page=2

Share this post


Link to post
Share on other sites

Interesting. So the motor will start with the compression release activated. Learned something new today. Do you happen to know what thread size needs to be machined in the head?

Share this post


Link to post
Share on other sites
Interesting. So the motor will start with the compression release activated. Learned something new today. Do you happen to know what thread size needs to be machined in the head?

It would depend on the size of that valve if I could only find one that I knew would work for sure. Not really an issue though with a tap set you could do it in your garage with ease. Just have to know the size of the valve obviously which I think varies. I've been hearing that you get these from Harley supply shops, apparently they are used frequently on the big twins. I would think the depth of the valve would be the most important to make sure you don't protrude into the cylinder where your piston could hit it. But I suppose the solution to that would be to put a couple washers on beforehand.

Share this post


Link to post
Share on other sites

i had a compression release on my 1975 suzuki 250 enduro. without question, the best thing i ever did to it. the controlled braking it enabled was simply stupendous. the confidence it inspired would have to be felt to be believed. the only reason i put one on was because one day while riding in the strip miles, i wrecked and the throttle stuck on and i went bananas trying to shut it off. trust me, the key was not able to be turned off. first and only time that happened.

Share this post


Link to post
Share on other sites
I'm a lean 200 pounds in the gym nearly every day and the bottom of my foot has been bruised raw kickin this damn thing... Plus its my dads bike and he's coming up on 60, it'd be nice to see him not gettin so frustrated

It's all in the technique not the force or weight. Don't slam the kick starter. Put your foot on it and push the engine just past TDC (so it has to go 300 degrees or so until next TDC). Give it a swift kick with authority starting with your foot ON the kickstarter with the starter at the very, very top of the stroke (obviously if you move it down once you get past TDC start over).

This technique lets you build some momentum in the flywheel/clutch and gets the kicker closer to horizontal where leverage is the greatest before you hit TDC. Only takes one or two revs to get it fired usually.

Share this post


Link to post
Share on other sites

I'm with PT Garcia... and I mean no disrespect on this... but yes... you father should find a new bike. The CR500 is heaver, and it's harder to start than most. Not to metion... you can pull more power out of an easy starting 250 than most people can handle.

But... also, as said above... it is in the technique. Push it past TDC, and have at it. That way you have almost one full cycle to build velocity.

Do I ride a CR500? No. Have I ?... heck yes. The bike has been mostly unchanged since the late 80's. It's not that hard to start. Sure... the big bikes I was running back in the day were air cooled, and they probably had less compression... but they were both big bikes, and took the right technique to get started. My dad couldn't get my PE400 race bike started... but I could do it in one or two kicks. And yes... I was 14. But in the late 80's... the liquid cooled bikes put out more power, and reved higher, so I changed over to 250's. (I could go faster)

But since I upset you... I'm sorry.

Share this post


Link to post
Share on other sites
I'm with PT Garcia... and I mean no disrespect on this... but yes... you father should find a new bike. The CR500 is heaver, and it's harder to start than most. Not to metion... you can pull more power out of an easy starting 250 than most people can handle.

But... also, as said above... it is in the technique. Push it past TDC, and have at it. That way you have almost one full cycle to build velocity.

Do I ride a CR500? No. Have I ?... heck yes. The bike has been mostly unchanged since the late 80's. It's not that hard to start. Sure... the big bikes I was running back in the day were air cooled, and they probably had less compression... but they were both big bikes, and took the right technique to get started. My dad couldn't get my PE400 race bike started... but I could do it in one or two kicks. And yes... I was 14. But in the late 80's... the liquid cooled bikes put out more power, and reved higher, so I changed over to 250's. (I could go faster)

But since I upset you... I'm sorry.

Haha I'm not upset sorry if it seemed that way. Maybe its just this 500, its now 23 years old. But there is a definite reason why almost all big thumpers have compression release now. I know how to start a bike and so does my dad. He was an AMA Pro roadracer in the 1980's. The bike is probably just temperamental from too much modding by the previous owner.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×