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05-07 CR250 HEAD HANGER BRACKET

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So people are lowering their cylinder .030 and the cylinder head bracket bolts will still go through no problem. I wonder how low you can go with the cylinder till the bolt going through the hanger bolt begins to be a problem. i'm thinking of lowering my cylinder to over .030 maybe .040-0.050 but wonder if everything will still lign up if that much material is removed. Anyone want to be the ginea pig first who is thinking of sending their cylinder to be cut and lowered go to .050 ? this will further decrease crankcase volume since its like putting something in a full glass of water and the water spills out because your increasing surface area with the object in the cup. it's good to try it, if you have an extra cylinder around, see what affect it will have on the engine with benefits over cutting it to .030.

 

 

I have yet to do a port map on my 89' CR250, im curios because i know honda had it right back then and had many winning streaks.

 

 

So who wants to try to go to .050 first :thinking: then maybe the low end will be like :eek: then you can :moon: all your friends because your big bottom CR. honda was never a bottom engine. the manufacturers deside how they want the power to be, and they always focused on the mid and top. thankfully that can be changed so the power suites each individual to their likeing. i prefer mid and top but it wouldn't hurt to buy an extra cylinder and have it cut down to .050 and see what happens. also leave the extra compression that comes with cutting it that low. what would the compression ratio come out to be in PSI going to .050 ?

 

 

also i wonder if that negative taper in the head is bad and should be cut out or left there because it is an efficient combustion design.

Edited by Atieri

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i have never heard of any builder going beyond .030 I wouldnt be the first to try it,  And even if the hanger was a problem, its nothing a round file can't fix in a few minutes of oblonging the bracket hole. 

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Wouldn't you need a shorter rod? The cyl having super high compression is good for short rebuild intervals on top of lowered clearance would cause impact on plug I believe that's why the only go 030 super high comp engines don't last long plus race gas costs never running pump gas would be a pain

Edited by Crguy713

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I think the 05-07 base gasket is .010 so 5 stacked doesn't seem like much. compression wouldn't be super high, it'd be like 240-245 PSI. The problem is, if you wanted the head cut for pump gas, there would be way too much material to remove from the head. If it was super high compression, blowing the spark plug right out of the hole would not be uncommon. maybe .040 would be a better number to shoot for. I think .040 is totally doable. I see that Yamaha and maybe other manufacturers have a negative taper in the squish band also, so i guess it serves a purpose.

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I'm wondering how much more stress this would put on the top and bottom end bearings.

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PC has done the R&D work on this motor...

1.  0 shaved off the cyl.

2.  0 epoxy work

3.  0 work on the cases

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You seem enthusiastic about removing .030, but the way you talk about your bike, the motor is good all around but can get even more. there is good, better, and best. right now your @ good. I am curious if it can get better.

 

.030" is the magic number.

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Pro circuit isn't the same company they were in the mid 80's - early 90's. motocross isn't even the same anymore. everything is focusing on 4-strokes now. I would not send my 2-stroke to them for work. If it was 1988, i wouldn't hesitate for a minute to send it to them.

 

PC has done the R&D work on this motor...

1.  0 shaved off the cyl.

2.  0 epoxy work

3.  0 work on the cases

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Pro circuit isn't the same company they were in the mid 80's - early 90's. motocross isn't even the same anymore. everything is focusing on 4-strokes now. I would not send my 2-stroke to them for work. If it was 1988, i wouldn't hesitate for a minute to send it to them.

I agree about the game changing on the 2t's but PC did MC's 06 CR250r since Honda was no longer providing or devolping a Works 2t bike.   He got some hole shots & at a Anaheim race he placed fourth behind RC, JS & CR with Factory 450's if I remeber correctly.  I've got a case reed motor done by them so I'm speaking from experience & know how good the motor is.       

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You seem enthusiastic about removing .030, but the way you talk about your bike, the motor is good all around but can get even more. there is good, better, and best. right now your @ good. I am curious if it can get better.

 

 

I had my set-up dialed in over a year ago. I haven't felt the need to deviate from it since then, because the engine is the best 250cc 2-stroke I've ridden in the 35 years I've been racing motocross.

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What year and make are these other 250's you're comparing your engine to ?

 

How is your powervalve doing ? do you ever get on your bike and wonder if it's going to function properly or not ? have you ever replaced the electric motor that drives the powervalve ?

 

I am getting a back issue of Dirt Bike magazine where Honda master tech Eric Crippa discusses proper powervalve setup. supposedly better that the owners manual or shop manual explains the procedure. I want to get a clear cover for my power valve,

sometimes I find myself wondering if it's going to work right that day or not.

 

I took it out of that bogus internet adjustment of 12mm and set it to the shop manual and i instantly lost top end last time i took it out a week or so ago. i'd say my valve is a millemeter or 2 from opening all the way. it doesn't take much to throw off a 2-stroke.

 

I had my set-up dialed in over a year ago. I haven't felt the need to deviate from it since then, because the engine is the best 250cc 2-stroke I've ridden in the 35 years I've been racing motocross.

Edited by Atieri

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What year and make are these other 250's you're comparing your engine to ?

 

How is your powervalve doing ? do you ever get on your bike and wonder if it's going to function properly or not ? have you ever replaced the electric motor that drives the powervalve ?

 

I am getting a back issue of Dirt Bike magazine where Honda master tech Eric Crippa discusses proper powervalve setup. supposedly better that the owners manual or shop manual explains the procedure. I want to get a clear cover for my power valve,

sometimes I find myself wondering if it's going to work right that day or not.

 

I took it out of that bogus internet adjustment of 12mm and set it to the shop manual and i instantly lost top end last time i took it out a week or so ago. i'd say my valve is a millemeter or 2 from opening all the way. it doesn't take much to throw off a 2-stroke.

 

 

Sounds like the "bogus" internet adjustment wasn't so bogus after all. Maybe you should go back.

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It's bogus, all it does is put excessive tension on the cables making it harder for the electric motor to turn and thereby slowing down how fast it opens and changing the timing a little.

 

i knew mine had a little more slack than normal when i tinkered with it last time, but didnt feel like screwing with it any longer because I wanted to :ride: I instantly noticed the loss of top end though.

Sounds like the "bogus" internet adjustment wasn't so bogus after all. Maybe you should go back.

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What year and make are these other 250's you're comparing your engine to ?

 

How is your powervalve doing ? do you ever get on your bike and wonder if it's going to function properly or not ? have you ever replaced the electric motor that drives the powervalve ?

 

I am getting a back issue of Dirt Bike magazine where Honda master tech Eric Crippa discusses proper powervalve setup. supposedly better that the owners manual or shop manual explains the procedure. I want to get a clear cover for my power valve,

sometimes I find myself wondering if it's going to work right that day or not.

 

I took it out of that bogus internet adjustment of 12mm and set it to the shop manual and i instantly lost top end last time i took it out a week or so ago. i'd say my valve is a millemeter or 2 from opening all the way. it doesn't take much to throw off a 2-stroke.

 

My personal 250cc race bikes over the years.

 

1980 KX250

1982 KX250

1982 RM250

1984 CR250

1984 RM250

1985 KX250

1987 CR250

1989 KX250

1990 KX250

1993 KX250

1995 CR250

2001 250SX

2003 250SX

 

I also had the opportunity to ride/race several other makes over the years. I didn't like the stock 07 power delivery at all when it was stock. It was a one dimensional on/off switch. For very little money, I was able to turn it into the best I've ridden.

 

With regard to my 07 powervalve. It works properly. I just adjust it so that the front cable has all the slack out, without over-tightening it. It's the simplest powervalve system I've ever worked on.

Edited by CamP

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Did you just set your back cable to spec and make all future adjustments from the front spring loaded cable ?

 

My personal 250cc race bikes over the years.

 

1980 KX250

1982 KX250

1982 RM250

1984 CR250

1984 RM250

1985 KX250

1987 CR250

1989 KX250

1990 KX250

1993 KX250

1995 CR250

2001 250SX

2003 250SX

 

I also had the opportunity to ride/race several other makes over the years. I didn't like the stock 07 power delivery at all when it was stock. It was a one dimensional on/off switch. For very little money, I was able to turn it into the best I've ridden.

 

With regard to my 07 powervalve. It works properly. I just adjust it so that the front cable has all the slack out, without over-tightening it. It's the simplest powervalve system I've ever worked on.

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I found a 05-07 factory shop manual on eBay and used that to adjust my PV but the cables do seem much tighter than before pulling the cylinder. I did consider that maybe it was just to loose before, but not sure.

Any good rule of thumb on what's tight enough vs to tight?

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Did you just set your back cable to spec and make all future adjustments from the front spring loaded cable ?

 

 

Screw the back cable ferrule all the way in, then back out the front adjuster until the slack is removed. Don't over-tighten the cable. You just want to remove the slack.

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When I get this back issue of dirt bike magazine with eric crippa explaining this, i'll post up the info or the whole article on here.

 

it can't be adjusted in 5 minutes, you need to sit down with it and tinker at least a half hour to get it right.

I found a 05-07 factory shop manual on eBay and used that to adjust my PV but the cables do seem much tighter than before pulling the cylinder. I did consider that maybe it was just to loose before, but not sure.
Any good rule of thumb on what's tight enough vs to tight?

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it can't be adjusted in 5 minutes, you need to sit down with it and tinker at least a half hour to get it right.

 

 

I don't know about that. I've had my cylinder off 4 or 5 times and I've never spent more than about 60 seconds installing/adjusting the powervalve cables. 

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