Squish Clearance on 2001 CR250


14 replies to this topic
  • bhaugeberg

Posted 17 July 2013 - 11:49 AM

#1

What is the proper squish band clearance for a 2001 CR250? The head is stock and I run 50/50 VP110 with pump gas. The cylinder is a warmed over 2000 piece with the Eric Gorr Mo-Betta porting if that makes a difference. Top-end is new with 2000 PWK A/S carb. If I was to guess, I would say about 0.045" would be good, but would like to here from others with similar set-ups. I am hoping to have this complete bike rebuild done in a few weeks, we shall see.

I seem to find lots of info on the 02-07 engine regarding this but less on the 92-01 engine. Apparently some of the 02-07 engines had problems with this.

Thanks.

Bryan

  • hawaiidirtrider

Posted 17 July 2013 - 01:27 PM

#2

why don't you call eric gorr? You have his motor setup.. might as well go all the way.

  • bhaugeberg

Posted 17 July 2013 - 05:40 PM

#3

I though somebody might ask if I had called EG. That part of the plan, but does anybody else have any worthwhile input or experience with this subject? EG is good, no doubt, but he's not the only 2-stroke builder out there with any experience with the 92-01 CR 250 engine. Someone may have a slightly different recommendation than EG because of a specific effect on the power that they were looking for or a different parts combination. I looking for the experiece of others besides EG. Don't worry, I am more than capable of filtering the information as to whether or not it will apply to my part combination or not.

Thanks again.

  • hawaiidirtrider

Posted 17 July 2013 - 06:34 PM

#4

I though somebody might ask if I had called EG. That part of the plan, but does anybody else have any worthwhile input or experience with this subject? EG is good, no doubt, but he's not the only 2-stroke builder out there with any experience with the 92-01 CR 250 engine. Someone may have a slightly different recommendation than EG because of a specific effect on the power that they were looking for or a different parts combination. I looking for the experiece of others besides EG. Don't worry, I am more than capable of filtering the information as to whether or not it will apply to my part combination or not.

Thanks again.


What's wrong with stock? I've not heard of anyone fooling with the head for an 01. The 02 and above have issues that guys want to address...but not for an 01. Again why not just call EG. You have an eric gorr ported motor it doesn't make sense to go get info from someone else to me. You could also go another way and just get a phathead cool head and change domes if you want. I did but just went to closest to stock dome and left it. One of these days I might put the higher comp. dome just to fool around.

http://phatheadracing.com/cr250.html

or check here..

http://www.eddie-san...tegory_s/24.htm

http://www.prodesign..._cool_heads.htm

Edited by hawaiidirtrider, 17 July 2013 - 06:38 PM.


  • bhaugeberg

Posted 17 July 2013 - 08:34 PM

#5

What's wrong with stock? I've not heard of anyone fooling with the head for an 01. The 02 and above have issues that guys want to address...but not for an 01. Again why not just call EG. You have an eric gorr ported motor it doesn't make sense to go get info from someone else to me. You could also go another way and just get a phathead cool head and change domes if you want. I did but just went to closest to stock dome and left it. One of these days I might put the higher comp. dome just to fool around.

http://phatheadracing.com/cr250.html

or check here..

http://www.eddie-san...tegory_s/24.htm

http://www.prodesign..._cool_heads.htm


Nothing may be wrong with stock. The head looked stock as well. The real question is "What is the stock squish clearance supposed to be. I have only one engine in front of me and the parts will stack up in some manner and give me a squish clearance. Problem for me is that is a sample size of one (1) and statistcally that's not enough to be a representative sample of what stock should be. I have blueprinted many automobile engines and worked with a few other motorcycle engines as well and there is usually a specification given somewhere for bearing clearances, valve clearances, etc. But the Honda manuals don't give this number that I am aware of.

Anyway thanks for the information and I will get a hold of EG for his opinion on this build as well. Doesn't mean I will use it exactly, I sometimes get a case of tinkeritis and do things a bit different, provided I can keep myself out of too much trouble. Other people's opinions are on this subject are welcome.

Thanks.

  • highmarker

Posted 17 July 2013 - 08:54 PM

#6

1mm is considered tight enough to pinch the end gasses off the surfaces so they don't remain to pollute the next charge. So .040 is a a good target.

But anytime your talking squish clearance it should be considered in light of all the other factors that are used to compute squish velocity. Compression, squish band width and angle etc etc. In general the narrower the squish band width the tighter you can set the squish without trouble.

Since mass manufacturing makes it hard to set precise clearances they tend to design wider safer squish clearances, combined with wider squish bands. Usually leaving a little room for the careful builder to tighten it up a little.

  • bhaugeberg

Posted 18 July 2013 - 05:26 PM

#7

1mm is considered tight enough to pinch the end gasses off the surfaces so they don't remain to pollute the next charge. So .040 is a a good target.

But anytime your talking squish clearance it should be considered in light of all the other factors that are used to compute squish velocity. Compression, squish band width and angle etc etc. In general the narrower the squish band width the tighter you can set the squish without trouble.

Since mass manufacturing makes it hard to set precise clearances they tend to design wider safer squish clearances, combined with wider squish bands. Usually leaving a little room for the careful builder to tighten it up a little.

Thanks for your input. Anybody else have any input or experience.

  • adam8781

Posted 18 July 2013 - 11:39 PM

#8

.040-.045 (1-1.1mm) is what i would shoot for.

  • frdbtr

Posted 19 July 2013 - 12:23 AM

#9

If you have an Eric Gorr ported motor, the head would have been worked by him as well. He would have set the compression and squish band for the type of fuel you want to run and the altitude you are running at.

  • bhaugeberg

Posted 19 July 2013 - 04:44 AM

#10

If you have an Eric Gorr ported motor, the head would have been worked by him as well. He would have set the compression and squish band for the type of fuel you want to run and the altitude you are running at.

It does not look like he machined the head at all in this case. Given the information I gave him, he must have felt it was fine the way it was. The cylinder base was not machined either, at least that I could tell. I will be contacting EG today to get his opinion on this. Thanks

  • Bentbars

Posted 19 July 2013 - 05:48 AM

#11

go check out RB Designs website. He's done a few head for me over the years. The only way to know what you have for sure is to do a squish test
with it solder.
EC dosn't even turn the head with a 2mm over bore (265 kit) i know i had him do 3 265 kits. 1-01 & 2-02. I sent the head to Ron after re-assembly and solder test. ended up with .42-43 on non e super. no race fuel for me.

  • bhaugeberg

Posted 19 July 2013 - 11:31 AM

#12

go check out RB Designs website. He's done a few head for me over the years. The only way to know what you have for sure is to do a squish test
with it solder.
EC dosn't even turn the head with a 2mm over bore (265 kit) i know i had him do 3 265 kits. 1-01 & 2-02. I sent the head to Ron after re-assembly and solder test. ended up with .42-43 on non e super. no race fuel for me.

Thanks for the info. I agree with and will be using the solder method to check the squish clearance, probably will use an air gun pellet as it is a bit softer than solder and I have a ton of them around. It not as easy as the typical V-8 auto engines that I am used to doing. There I just use a depth mic with the piston at TDC and add the compressed gasket thickness. The info on compressed gasket thickness doesn't seem to be readily available from every source for gasket for a CR250.

  • Bentbars

Posted 20 July 2013 - 05:19 AM

#13

thats why you should bolt it all together, and just pop the head on and off for each solder smash. you need to get a good clean square edge on the solder so it can be right against the cylinder wall.
do about three of them. you can use the same new head gasket even when your finish it will be fine. i bought 3 different sizes as i wasn't sure of much
room i had in there to begin with. to small and you won't get a good test. to thick and it's too hard smash. bring the piston up close to tdc fit the solder, across the wrist pin then bolt the head down and put it in gear and rotate the wheel by hand to bring the piston up to and passed TDC.

pretty easy stuff.

  • hallsy

Posted 20 July 2013 - 05:14 PM

#14

Don't know if this helps... when I pulled my 01' apart to replace the top end I didn't see any signs of it being worked on. I checked the squish distance with solder and found it to be .048". The previous owner never mentioned any cylinder or head work so I can't say for sure that the .048'' was stock. I had read lots of threads about squish correction on the YZ forum and they were suggesting @ .045" for the YZ 250. I figured I was close enough that it didn't need to be done but spoke to a local builder about it since it was apart. He recommended we set the squish distance to .035"! From what I remember he cut @ .020" off the head then re-cut the squish band parallel to the stock piston to get to .035". The stock piston is a flat top piston so I think he changed the angle but don't know anything about the width. There was no work done to the dome to bring the volume (compression) back to stock. He assured me that at our elevation (5000'-10,000') I would be able to continue to run on pump premium without any trouble. That was 5 years ago and so far all is well. However we spend most of our time riding in the woods and very little at the track, also I'm more of a lugger than a rever but have screamed it's guts out a few times.

  • bhaugeberg

Posted 21 July 2013 - 07:37 AM

#15

Don't know if this helps... when I pulled my 01' apart to replace the top end I didn't see any signs of it being worked on. I checked the squish distance with solder and found it to be .048". The previous owner never mentioned any cylinder or head work so I can't say for sure that the .048'' was stock. I had read lots of threads about squish correction on the YZ forum and they were suggesting @ .045" for the YZ 250. I figured I was close enough that it didn't need to be done but spoke to a local builder about it since it was apart. He recommended we set the squish distance to .035"! From what I remember he cut @ .020" off the head then re-cut the squish band parallel to the stock piston to get to .035". The stock piston is a flat top piston so I think he changed the angle but don't know anything about the width. There was no work done to the dome to bring the volume (compression) back to stock. He assured me that at our elevation (5000'-10,000') I would be able to continue to run on pump premium without any trouble. That was 5 years ago and so far all is well. However we spend most of our time riding in the woods and very little at the track, also I'm more of a lugger than a rever but have screamed it's guts out a few times.

Thanks for the information. Especially what you found with your stock '01.





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