Yz250 head question

RK Tek

https://www.2strokeheads.com/index.php/gas-gas-oem-head-reshape

I've used RB Designs multiple times in the past and currently am running an RK Tek head (RK did not require a solder test for my Rieju 300). I have also used a local dealer that has a multi decade engine guy who specializes in Yamahas and Kawasakis.  He's been an AMA pro in MX, flattrack, and road racing. His work for me has been excellent and he has enough experience with YZs an KXs to not necessarily need the solder test (Yam and Kaw motors are consistent enough to have known tolerances). Contact Vickery Motorsports Service Department and ask if Bruce Sass is available to cut your head (he's semi-retired but still does motor work). 303-755-4387

Solder samples tell them exactly how much squish clearance there is, so they can remove the correct amount. Without those, they're just guessing. The YZ250 has a significantly oversized squish, and I recall it being not-so consistent  bike to bike (could be wrong, it's been a long time). Solder samples fix that unknown.

If it were me, I'd trust the guy asking for solder samples over the guy who doesn't. It's a simple process and removes uncertainty.

I'm not disputing that and I am not trying to be an @$$ but it's a "correctly performed solder sample" and not just a "solder sample". Ron from RB Designs as mentioned by the original poster had a whole procedure on his website on how to perform the solder sample and what kind of solder to use (it matters).  Ron required 4 or 5 separate samples (yes, insert solder, put the head back on, and repeat 4 or 5 times). I talked to Ron about this process for each of the heads I sent to him about 15 or so years ago for an original GasGas 300 and 250 as he said he needed multiple tests as folks typically were not able to accurately and reliably get the sample.  He told me my samples were not exactly what he wanted but he knew how to work with them (I believe he said he had to interpolate the outer edges). He stopped asking for samples years ago and does not request one for the KDX heads he still modifies to this day. 

When I asked RK Tek about the solder tests for a head I ordered, they told me it was not required as they were too unreliable (I assumed he meant the "retail public's solder test").  I copied in their technical article below on how to measure piston deck height and how it relates to head modifications.  They even mention using an "offset factor" (or interpolation) being required for domed pistons (I believe a YZ piston is a dome shape) as their preferred method of measurement is too difficult to get an accurate reading. In summary, they assert that "measurements matter" but my takeaway is that they really want the whole motor to ensure an accurate test is performed for both porting and head mods.  Barring that, they told me a solder sample was not desired.

https://www.2strokeheads.com/index.php/site-map/articles/80-technical/9…

just go to Apex Innovations.......awesome company and great product.  They can either sell you a new head with adjusted squish or adjust your current head.  Talk to them but they are pretty awesome.

APEX RACING OFFICIAL Yamaha Racing Products — Apex Technical Innovations (atinno.com)

Sure, it obviously needs to be a correctly done solder sample, but they're not too difficult to do. Without it, they're guessing. It's an educated guess, but a guess nonetheless. And they're going to guess small (of a cut) to be on the safe side, and you'll be leaving performance on the table. Even if it's done wrong, they can extrapolate the width at the edge of the cylinder to get the data they need and be better informed of how to cut the head than they would be without it. Regardless, you can do whatever you want, just giving my perspective! 

I'm with Billy on this. I think solder is simply the best way to get an accurate head cut. Even if it's not done perfectly, it's normally better than a measurement. As long as you don't try to check a .080" squish with .125" solder, the odds of getting decent solder test are better than getting an accurate measurement. And if the person cutting the head says they don't need solder, or a measurement then you're getting a guesstimated cut and generic performance. They're also probably going to tell you a lot of other bull, too. If you have someone just cut .010" of your stock head, you're going to typically end up about .068" +/- a couple and not even reduce the volume by half a CC. 

Dude, you are using imperial and metric in the same sentence, lol... what the hell is wrong with you. ? 😀

What is the actual measurement of stock squish gap? I think my 2001 yz250 was over 2mm?

I am all about doing things right and precise, but I've never been able to nail a squish gap within a 0.1 to 0.2mm target plus or minus.  On a 250, if you are getting close to 1.2mm. to 1.50mm I think it will be good...  maybe a little but lower also. So many little things add up to error like gasket thickness and engine wear.  Of course, if you are taking metal from the head sealing surface,  some will need to come out of the bowl to correct for compression. 

I would look at apex heads, very good feedback. I just bought a 150sx dome from them and it's right on the money with optimized squish gap and width

Imperial and metric in the same sentence? Where? You mean inches and CC's? That's the way I roll. 

The current stock head (which is the same as your '01) is about .080" or 2mm on a stock engine with OEM parts. 

1.5mm is .060", which I consider to be too much. 1.2mm is .047" which is toward the top of my normal spec. 

I'd be disappointed if I was .004" (0.1mm) off on a cut, if I had the engine in hand. Not so much on a ship in - ship out, where I didn't have total control, but I still expect better of myself.

In addition to the solder samples, RB would also measure the volume of the stock dome, so he could machine it back to the original volume after the head was cut.  I used to go to his shop a lot when I lived around Portland trying to learn stuff.  Bummed to hear he's no longer doing it, but good on him for retiring.