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06 CR 250 Head Questions

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This past spring I sent my cylinder and head out to Eric Gorr for him to shave the base of the cylinder and recut the head for pump gas. Before I sent it out my squish band was .084 just like everyone else's 05-07 250. I asked him to take .030 off the cylinder. Anyways I have been experimenting around lately and was tinkering with the idea of getting another stock head and just running race fuel. Reason being is I'm having a hard time getting the bike jetted just right and seem to have a small bit of knocking at certain times. I have tried to jet this out but haven't had much luck. The plug always comes out black and yet the motor seems a bit lean. Anyways I decided to take the head off and remeasure the squish to see where I was at before buying a new head. I know I should have done this before assembling everything the first time but I didn't. I took three measurements and got .0685- .069 on all of them. I'm using a cheapo micrometer so that may just be an error with it. I'm kind of a little bummed because I figured I'd be down around .050- .055 after the cylinder and head work. I noticed it looks like Eric cut some more material out of the squish band and then cut an angle up in the done to get me back on pump fuel. Now my question is can I simply take my head to a local machinist and have him take .019 off the bottom of the head? That would put my squish down around .050 which is about ideal I hear. I don't know what this would do to the dome in reference to compression, but I don't mind having to mix race fuel or go straight race fuel although ideally I'd still like to not HAVE to. I've posted up a few pictures of the head and I'm hoping some of you experts here can lead me in the right direction. Am I better off buying a new head and sending it out to RB Designs to have him cut the dome for pump fuel? It now makes sense that I can't get my jetting perfect with this large of a squish band. Thanks for all the help!

24752C57-7DC5-4762-A273-DC43536A638B-878

6DCB31E8-EF60-4982-A447-33CDD09DC2C4-878

EE7FF0F4-C517-4AE7-BA58-8D952EC9C341-878

Oh and one more thing I forgot to add is that I forgot to measure the depth of the squish band on the head, but did compare it with that of a quarter and it is almost exactly as deep as a quarter. I will try to get an exact measurement tomorrow night but there definitely is enough material there for .019 to be removed. The outer edge of the piston just ever so slightly protrudes about the top of the cylinder. I'm thinking that however much Eric took off the bottom of the cylinder he put almost that much again back into the squish band on the head. I wrote all the details out for him on the paper, but I honestly don't think he read them because just by glancing at the cylinder bottom it looks like he took a good bit more than .030 off the bottom. I have not measured that either though to confirm. Just looked like quite a bit with the naked eye. Maybe he was concerned by taking that much off that he needed to make up some of the difference again in the head. Wow I'm sorry for rambling on, but I want to give as many details as possible.

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gorr sets pretty large squish on his work, i have no idea why.

 

You can go either route, if the head you have now is set for pump fuel, than yes absolutely machine it down to .050inch and run at least 100 octane.  Or call rb designs and tell him what you told us here. if there is still enough material left in the head he can mill it down to proper squish and open the head back up for pump fuel.

 

or a new stock head set to .045-.050 and what ever fuel you like. Again go with rb, his quality is as good as it gets.

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Adam thank you for your reply. That's what I wanted to hear. I'm not trying to knock his work because the bike does run great aside from the jetting issue which could be completely my fault. I do wish though that he would have used my measurements and tailored everything accordingly. There is for sure enough material left on the bottom to get the squish set up right, but as far as the dome for pump fuel again that I don't know. But you do suspect that if I do have this head cut down that even with the angle in the dome that Eric cut I will still be forced to run high octane? I know the stock heads don't have this angle cut in them and they also don't have this deep of a squish area either and others report only needing 100 octane. I guess the only way to know for sure would be to have the head cut and then measure the dome which I have never done before nor do I know how to. I hate to have to spend the extra money to have rb do all this, but looks like if I want to run pump fuel my only options are to send the head out. Thanks again for your advise

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I have previously had head work performed on the same engine by Gorr, Pro Circuit, and RB Designs.

Of the three, the best performing head was the RB.

RB will not work on a previously modified head, insisting on OEM spec parts only.

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If it were me I would call Eric Gorr and tell him that you are having some pinging with your head and ask him if he would check it for you, I would mail the squish test solders that you made the other day with your stuff and that would tell him exactly what it was doing.  By the way, RB designs won't touch a modded head so you would have to buy a new head and send it to them in order to get them to work on your stuff.

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If it were me I would call Eric Gorr and tell him that you are having some pinging with your head and ask him if he would check it for you, I would mail the squish test solders that you made the other day with your stuff and that would tell him exactly what it was doing. By the way, RB designs won't touch a modded head so you would have to buy a new head and send it to them in order to get them to work on your stuff.

I know that you recently had your cylinder and head cut by Eric. Did you by chance perform another squish test when you got your parts back? Does your head appear to be cut the same way as mine? I'm just curious since I wrote down pretty much exactly what you did aside from the high altitude part. Looks like I will probably be taking my head down to my local shop and have him shave it down and go from there.

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I know that you recently had your cylinder and head cut by Eric. Did you by chance perform another squish test when you got your parts back? Does your head appear to be cut the same way as mine? I'm just curious since I wrote down pretty much exactly what you did aside from the high altitude part. Looks like I will probably be taking my head down to my local shop and have him shave it down and go from there.

 

I didn't do another squish test.  Mine isn't pinging at all, sounds perfect.  If it were pinging, I would do another squish test and call EG to have him back up his work.  I did a squish test and sent him the solder with my cylinder and head though.  My head (as far as the way he shaped the combustion chamber) looks exactly like yours.

Edited by frdbtr

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It's weird because I don't know if I can classify the noise as actual pinging or not. The weird thing is that it seems to happen with a 48 pilot and not with the 45. I was going to mix up a 50/50 mix of race fuel and see if that made any difference but then id have to probably mess with my jetting again. I just went through the carb again and found that the float height was a little bit off so that may have been a contributing factor. I almost wish I wouldn't have even checked the squish because now I don't think I can put it back together without trying to "fix" that first. I guess I should just call Eric but its been 4-5 months since the work was done so I wouldn't expect him to do anything at this point. Just a bit frustrating since I did all that measuring to get it perfect and its pretty far from it. The bike does run good though aside from my jetting frustrations.

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It's weird because I don't know if I can classify the noise as actual pinging or not. The weird thing is that it seems to happen with a 48 pilot and not with the 45. I was going to mix up a 50/50 mix of race fuel and see if that made any difference but then id have to probably mess with my jetting again. I just went through the carb again and found that the float height was a little bit off so that may have been a contributing factor. I almost wish I wouldn't have even checked the squish because now I don't think I can put it back together without trying to "fix" that first. I guess I should just call Eric but its been 4-5 months since the work was done so I wouldn't expect him to do anything at this point. Just a bit frustrating since I did all that measuring to get it perfect and its pretty far from it. The bike does run good though aside from my jetting frustrations.

He will re port your cylinder for free for the first year after he does the work. At least that is what he used to do before millenium bought him out. I would call him and talk. It couldn't hurt. He has always been helpful with me when I called him.

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I didn't have any port work done, well aside from having the cylinder lowered. Just asked him to lower the cylinder by .030 which by the naked eye looks like more than that and to have the head reshaped to run pump fuel again. I think Eric does beautiful work and is a master of his craft, but him being so busy I don't think he has time to custom tailor every cylinder or engine he gets in. Seems like its more of a one size fits all type thing. The only complaint I have is the head being cut to deep and other than that everything is great. Not trying to bash the guy, but now I know. Will let you know how everything turns out once I figure out which direction I want to go.

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What carb are you running? Maybe the right side main is leaky and you are sucking some gear oil. My motor is stock and I run 100 ll avgas. It just ran like shit on Cali pump. Good fuel will get you to a baseline on how to jet it.

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I'm running a pwk from an 02 yz. Whole bike is completely new. Replaced every bearing and seal in the entire engine and chassis less than 8 hours ago. Float height was a little high so I lowered it down. I put everything back together to test it out before I get the head cut. There isn't a lot of riding season left around here so I'm going to try and run it till winter then get the head issue corrected.

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