2006 YZ250 Cylinder Head Squish Band Rework for C12

WileCyot
Profile picture for user WileCyot
Posts
459
Joined
9/23/2014
Location
Katy, TX US
WileCyot
Edited Date/Time 5/17/2015 11:52am
Ok guys, I'm about to pull the head off my YZ250 tonight to inspect the cylinder and remove the Namura piston that the PO installed before it has a chance to grenade on me.

1. Can I use the Namura piston to measure the squish band tonight or should I wait on the new Wiseco that I'll be ordering to replace the Namura to do the squish measuring?

2. Who are some reputable shops that can set the squish band for C12? I'm running stock porting to my knowledge and at this time it's fine for my purposes but I wouldn't mind getting a little power all throughout. Suggestions and reasoning as to why I should go with them please.

Obligatory pictures of bike below....

|
Jakes Dad
Profile picture for user Jakes Dad
Posts
1865
Joined
6/22/2009
Location
Brooksville, FL US
Jakes Dad 5/13/2015 4:24pm
5/13/2015 4:24pm Edited Date/Time 5/13/2015 4:32pm
My opinion you don't need to go to 110 octane, 100 is fine and much much cheaper at the end of the year. I'd wait on new piston, another factor most don't take into consideration is "piston rock" from piston to wall clearance. This needs to be factored in when doing squish adjustments.

www.tdc2strokeperformance
Jake #719 2006 YZ250 450 C Fl. Winter Am's at Gatorback.
All cad designed with rider factors considered for proper setup.
Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 5/13/2015 7:12pm
5/13/2015 7:12pm
Measure the squish side to side instead of front to back.
keeptwostrokesalive 5/14/2015 5:44am
5/14/2015 5:44am
I sent my 2006 yz250 cylinder head to powerseal USA to have them set the squish, I just had them set it up to 93 octane and I have not had a SINGLE problem so far. In fact my bike has been bullet proof, and the cylinder head has not experienced any pinging whatsoever
Paw Paw 271
Profile picture for user Paw Paw 271
Posts
3640
Joined
4/3/2013
Location
Benton, LA US
Paw Paw 271 5/14/2015 6:17am
5/14/2015 6:17am
In stock form these heads have a squish pattern that leads to detonation. You can have it fixed as stated above for premium 92 octane fuel.
Remember, octane does not add power, but rather slows down the burn to help with detonation. This engine will run better and last longer if set up for pump fuel.

Paw Paw

The Shop

See All »
WileCyot
Profile picture for user WileCyot
Posts
459
Joined
9/23/2014
Location
Katy, TX US
WileCyot 5/14/2015 9:30am
5/14/2015 9:30am
While Premium alone would be more than plenty for me, finding it without ethanol is proving to be difficult. I'm able to get the following fuels easily:

100LL (Avgas) - $3.99 / gal
Sunoco 260 GT Plus (104 Octane unleaded) - $10 / gal (Highly oxygenated producing more power)
Sunoco Standard (110 Octane) - $10 / gal
Sunoco Supreme (112 Octane) - $10.50 / gal
Sunoco Maximal (116 Octane) - $12 / gal
VP C12 - ~$13 / gal (5 gal pail)
CP U4.4 - ~16 / gal (5 gal pail) for fuel injected 4 strokes so it's out.

I was running 100LL without any issues until I discovered the dealership next to my house had C12. I like the smell of race gas and I'm able to afford to pony up a little bit so I bought 10 gallons. Today I found out I have Bumbera's Performance next to me that will sell me the Sunoco fuels at the prices listed above. Instead of C12 I'll swap over to any of the others as it'll end up being cheaper. I now have the two 5 gallon pails to store it in and mix my oil which will be handy.

If 100LL is sufficient I'll run it. The added lead pleases me as well as the cost. Much cheaper than C12 or Sunoco Standard. From what I'm reading the GT Plus may also be a contender if I remove it from my carb after every ride (not a huge deal) but will it, with proper porting and head rework, make more power than 93 pump?

Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 5/14/2015 9:41am
5/14/2015 9:41am
I would stay away from the Sunoco GT plus, it used to be really, really good (MTBE based), but now all the oxygen comes in the form of ethanol and causes all sorts of issues.

I blew up a RM144 running it, its a silent detonator and burnt through the top of the cylinder until the o-ring was compromised.

The Sunoco supreme is a really good choice, its 112 octane and runs very similar to VP C12; compared to the other 110 leaded fuels, it has a much more superior distillation curve and the extra 50 cents a gallon is totally worth it.

Bottom line, the best place for ethanol is in your cocktail, not your dirtbike fuel tank!

Lots of people run Avgas, but the compromise is that it is designed to be operated thousands of feet in the air, so the physical properties are different than surface fuels.
Matt Fisher
Profile picture for user Matt Fisher
Posts
3947
Joined
4/1/2008
Location
Visalia, CA US
Fantasy
1117th
Matt Fisher 5/14/2015 9:53am
5/14/2015 9:53am
The Avgas is great stuff, particularly for the money. If you aren't racing at the top level, the potential power increases from some of the race fuels is tough to justify for the price.

I drain the tank and carb back in to a metal container if the bike isn't going to be ridden the next day. By doing so, the fuel will last for months and there's no chance the carb will get gummed up.
BAMX
Profile picture for user BAMX
Posts
2841
Joined
1/22/2012
Location
Fallbrook, CA US
BAMX 5/14/2015 12:47pm
5/14/2015 12:47pm
Bruce372 wrote:
Measure the squish side to side instead of front to back.
I have always been told to do it parallel with the pin and both sides.
WileCyot
Profile picture for user WileCyot
Posts
459
Joined
9/23/2014
Location
Katy, TX US
WileCyot 5/14/2015 12:51pm
5/14/2015 12:51pm
Bruce372 wrote:
I would stay away from the Sunoco GT plus, it used to be really, really good (MTBE based), but now all the oxygen comes in the...
I would stay away from the Sunoco GT plus, it used to be really, really good (MTBE based), but now all the oxygen comes in the form of ethanol and causes all sorts of issues.

I blew up a RM144 running it, its a silent detonator and burnt through the top of the cylinder until the o-ring was compromised.

The Sunoco supreme is a really good choice, its 112 octane and runs very similar to VP C12; compared to the other 110 leaded fuels, it has a much more superior distillation curve and the extra 50 cents a gallon is totally worth it.

Bottom line, the best place for ethanol is in your cocktail, not your dirtbike fuel tank!

Lots of people run Avgas, but the compromise is that it is designed to be operated thousands of feet in the air, so the physical properties are different than surface fuels.
Everyone says this but the greatest load these engines see is during takeoff.... which isn't thousands of feet in the air.... So I can't buy into that.
Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 5/14/2015 12:57pm
5/14/2015 12:57pm
Bruce372 wrote:
I would stay away from the Sunoco GT plus, it used to be really, really good (MTBE based), but now all the oxygen comes in the...
I would stay away from the Sunoco GT plus, it used to be really, really good (MTBE based), but now all the oxygen comes in the form of ethanol and causes all sorts of issues.

I blew up a RM144 running it, its a silent detonator and burnt through the top of the cylinder until the o-ring was compromised.

The Sunoco supreme is a really good choice, its 112 octane and runs very similar to VP C12; compared to the other 110 leaded fuels, it has a much more superior distillation curve and the extra 50 cents a gallon is totally worth it.

Bottom line, the best place for ethanol is in your cocktail, not your dirtbike fuel tank!

Lots of people run Avgas, but the compromise is that it is designed to be operated thousands of feet in the air, so the physical properties are different than surface fuels.
WileCyot wrote:
Everyone says this but the greatest load these engines see is during takeoff.... which isn't thousands of feet in the air.... So I can't buy into...
Everyone says this but the greatest load these engines see is during takeoff.... which isn't thousands of feet in the air.... So I can't buy into that.
its not about the load, its about the distillation curve. As you go up from sea level, the outside pressure is reduced, so the boiling point of any liquid is lowered.

but at the end of the day, if its leaded and ethanol free, just go ahead and run it- nothing bad will happen.
Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 5/14/2015 12:58pm
5/14/2015 12:58pm
Bruce372 wrote:
Measure the squish side to side instead of front to back.
BAMX wrote:
I have always been told to do it parallel with the pin and both sides.
that's what I was trying to say, but maybe it was clear as mud, LOL
WileCyot
Profile picture for user WileCyot
Posts
459
Joined
9/23/2014
Location
Katy, TX US
WileCyot 5/14/2015 2:33pm
5/14/2015 2:33pm
Bruce372 wrote:
Measure the squish side to side instead of front to back.
BAMX wrote:
I have always been told to do it parallel with the pin and both sides.
Bruce372 wrote:
that's what I was trying to say, but maybe it was clear as mud, LOL
Ah that makes sense. It will be consisted of heavier components than say a fuel designed for use at sea level as the pressure is higher and less likely to see evaporation.

I'll probably end up running the Supreme after I use all this C12. I bought that built motor CRF to flip and need the fuel for it anyway.
BAMX
Profile picture for user BAMX
Posts
2841
Joined
1/22/2012
Location
Fallbrook, CA US
BAMX 5/14/2015 5:38pm
5/14/2015 5:38pm
Bruce372 wrote:
Measure the squish side to side instead of front to back.
BAMX wrote:
I have always been told to do it parallel with the pin and both sides.
Bruce372 wrote:
that's what I was trying to say, but maybe it was clear as mud, LOL
I got it but was adding the use of two pieces of solder. I have seen people do it with one but it isn't right.
WileCyot
Profile picture for user WileCyot
Posts
459
Joined
9/23/2014
Location
Katy, TX US
WileCyot 5/14/2015 6:46pm
5/14/2015 6:46pm
BAMX wrote:
I have always been told to do it parallel with the pin and both sides.
Bruce372 wrote:
that's what I was trying to say, but maybe it was clear as mud, LOL
BAMX wrote:
I got it but was adding the use of two pieces of solder. I have seen people do it with one but it isn't right.
Can you explain the pin method? I'm assuming you mean run two pieces of bent solder on either side of where the pin would be inside of the piston? If that's the case how will you be able to distinguish the radial measurement of the squish band this way without also knowing the exact placement of the two solders?
Sixeightone
Profile picture for user Sixeightone
Posts
363
Joined
3/8/2014
Location
Central, CT US
Sixeightone 5/15/2015 12:35pm
5/15/2015 12:35pm
You use one piece of solder bent in the middle, you measure squish on the sides of the cylinder not in the middle. But here is the thing you don't need to set your squish because you will be wasting your time. Those Yamaha's are junk motors to begin with. So just put it back to stock, ditch the junk wiseco piston you bought. Buy a vertex piston, run all the stock gaskets and run 100 octane av gas in the thing and that's how it will last the longest. I've rebuilt about 10 of those yz 250s now, all of which have blown up cause by detonation! Don't increase your compression. If you want to go faster take riding lessons! Engine Longevity is key! Just my $.02

Johnboy



southwick_mx 5/15/2015 2:25pm
5/15/2015 2:25pm Edited Date/Time 5/15/2015 2:29pm
Sixeightone wrote:
You use one piece of solder bent in the middle, you measure squish on the sides of the cylinder not in the middle. But here is...
You use one piece of solder bent in the middle, you measure squish on the sides of the cylinder not in the middle. But here is the thing you don't need to set your squish because you will be wasting your time. Those Yamaha's are junk motors to begin with. So just put it back to stock, ditch the junk wiseco piston you bought. Buy a vertex piston, run all the stock gaskets and run 100 octane av gas in the thing and that's how it will last the longest. I've rebuilt about 10 of those yz 250s now, all of which have blown up cause by detonation! Don't increase your compression. If you want to go faster take riding lessons! Engine Longevity is key! Just my $.02

Johnboy



This is crazy talk. Read up on the function of a squish band type cylinder head before you rant. Compression can be increased, but in many cases you choose not to, all depending on what type of fuel will be used. A correct set squish clearance (which is very simply put the smallest possible clearance not causing the piston to hit the head under any circumstance) is a very good insurance against detonation.

Any knowledgeable tuner knows to make the combustion chamber bowl deeper to compensate for the cc:s lost when tightening up the squish clearance.

And no tuner worth his salt would rework a cylinder head without access to accurate squish measurements from the engine to be tuned. Variations in manufacturing means there are no two identical engines, even in 2015.

/Lasse
BAMX
Profile picture for user BAMX
Posts
2841
Joined
1/22/2012
Location
Fallbrook, CA US
BAMX 5/15/2015 2:45pm
5/15/2015 2:45pm
Bruce372 wrote:
that's what I was trying to say, but maybe it was clear as mud, LOL
BAMX wrote:
I got it but was adding the use of two pieces of solder. I have seen people do it with one but it isn't right.
WileCyot wrote:
Can you explain the pin method? I'm assuming you mean run two pieces of bent solder on either side of where the pin would be inside...
Can you explain the pin method? I'm assuming you mean run two pieces of bent solder on either side of where the pin would be inside of the piston? If that's the case how will you be able to distinguish the radial measurement of the squish band this way without also knowing the exact placement of the two solders?
I just mean to place the solder like the above picture. The reasoning is that parallel to the pin and going all the way across will eliminate the rocking of the piston. If you want some insight into detonation, read the below article. Klemm knows 2 strokes.

http://www.klemmvintage.com/deto.htm
Sixeightone
Profile picture for user Sixeightone
Posts
363
Joined
3/8/2014
Location
Central, CT US
Sixeightone 5/16/2015 6:08am
5/16/2015 6:08am
southwick_mx wrote:
This is crazy talk. Read up on the function of a squish band type cylinder head before you rant. Compression can be increased, but in many...
This is crazy talk. Read up on the function of a squish band type cylinder head before you rant. Compression can be increased, but in many cases you choose not to, all depending on what type of fuel will be used. A correct set squish clearance (which is very simply put the smallest possible clearance not causing the piston to hit the head under any circumstance) is a very good insurance against detonation.

Any knowledgeable tuner knows to make the combustion chamber bowl deeper to compensate for the cc:s lost when tightening up the squish clearance.

And no tuner worth his salt would rework a cylinder head without access to accurate squish measurements from the engine to be tuned. Variations in manufacturing means there are no two identical engines, even in 2015.

/Lasse
Maybe I wasn't clear enough.. Obviously any tuner knows he needs to compensate for lost cc's when machining a head. But What I was saying is that these Yamaha two strokes are a poor design to begin with..

I was telling the OP that he would be wasting his time and money to try and get any more power out of a motor that is going to grenade regardless of whatever you do to it. My solution to the problem was to get a Vertex piston with the stock squish setting which I believe Yamaha calls for right around 1.2mm?!

With the forged vertex piston, and I recommend vertex because of the inconsistency at wiseco, run 100 octane fuel and this will give you the most longevity. 25 hours MAX on a top end!! I've seen these yamahas do some weird stuff. Skirts breaking off the back of the piston, holes in the middle of the piston!! I've seen brand new 2014 yamahas come with missing stator plate bolts (only one bolt installed from factory) and on that same bike the clutch basket was cracked on 3 of the fingers and the bike only had 3 hours on it!! They are just not the fit and finish of any other manufacturer's 250 two strokes.. It amazes me because the same basic motor has been in the works for 10+ years! And it still sucks!!!!!!

So to the original poster, save your money! Save your time and frustration! Don't get crazy inside your motor!

Pit Row

See All »
WileCyot
Profile picture for user WileCyot
Posts
459
Joined
9/23/2014
Location
Katy, TX US
WileCyot 5/16/2015 6:44am
5/16/2015 6:44am
Sixeightone wrote:
Maybe I wasn't clear enough.. Obviously any tuner knows he needs to compensate for lost cc's when machining a head. But What I was saying is...
Maybe I wasn't clear enough.. Obviously any tuner knows he needs to compensate for lost cc's when machining a head. But What I was saying is that these Yamaha two strokes are a poor design to begin with..

I was telling the OP that he would be wasting his time and money to try and get any more power out of a motor that is going to grenade regardless of whatever you do to it. My solution to the problem was to get a Vertex piston with the stock squish setting which I believe Yamaha calls for right around 1.2mm?!

With the forged vertex piston, and I recommend vertex because of the inconsistency at wiseco, run 100 octane fuel and this will give you the most longevity. 25 hours MAX on a top end!! I've seen these yamahas do some weird stuff. Skirts breaking off the back of the piston, holes in the middle of the piston!! I've seen brand new 2014 yamahas come with missing stator plate bolts (only one bolt installed from factory) and on that same bike the clutch basket was cracked on 3 of the fingers and the bike only had 3 hours on it!! They are just not the fit and finish of any other manufacturer's 250 two strokes.. It amazes me because the same basic motor has been in the works for 10+ years! And it still sucks!!!!!!

So to the original poster, save your money! Save your time and frustration! Don't get crazy inside your motor!
Someone sounds a bit jaded regarding the YZ250. I've heard nothing but good things about them and definitely haven't heard the horror stories you're discussing.

Would you say that a vertex piston is more consistent than a wiseco or OEM?
yamahuh
Profile picture for user yamahuh
Posts
79
Joined
4/1/2008
Location
US
yamahuh 5/16/2015 10:21am
5/16/2015 10:21am
The YZ's (125 & 250) IMO both need race fuel; as stock they are borderline with pump fuel. I have used C12 for a long time and never had any issues. Also...OEM pistons in both, again no issues.
That pic looks like from Rio..
southwick_mx 5/16/2015 11:17am
5/16/2015 11:17am
I know for a fact there are many YZ250 engines coming stock with squish clearance way off, 1.9-2.0 mm not uncommon. This will make any 2 stroke engine very prone to detonation, which is why I'm advising every 2 stroke guy out there (not just YZ250 owners) to take a squish measurement and have the head modified.

The engine will become more responsive, easier to jet properly, less prone to detonate and have a better gas mileage. As a bonus, you can pick and choose a compression ratio to suit the kind of fuel you'll be using.

If Yamaha has been delivering bikes with quality issues, well that's bad on their part, but don't write off the YZ250 engine as a bad design because of it. In my view it's an amazing power source.

By the way, I have never used a piston in a 250 for more than 20 hours. Read the manual, follow the service intervals, and in many cases avoid stuff like broken skirts and so on.

Stretching the service life of a two stroke piston is just not very smart, performance will suffer and sooner or later so will your bank account.

/Lasse
slipdog
Profile picture for user slipdog
Posts
10044
Joined
7/25/2009
Location
Nor Cal, CA US
slipdog 5/16/2015 8:08pm
5/16/2015 8:08pm
Vertex pistons are cast not forged.
Harry Backmon 5/17/2015 5:45am
5/17/2015 5:45am
Sixeightone wrote:
Maybe I wasn't clear enough.. Obviously any tuner knows he needs to compensate for lost cc's when machining a head. But What I was saying is...
Maybe I wasn't clear enough.. Obviously any tuner knows he needs to compensate for lost cc's when machining a head. But What I was saying is that these Yamaha two strokes are a poor design to begin with..

I was telling the OP that he would be wasting his time and money to try and get any more power out of a motor that is going to grenade regardless of whatever you do to it. My solution to the problem was to get a Vertex piston with the stock squish setting which I believe Yamaha calls for right around 1.2mm?!

With the forged vertex piston, and I recommend vertex because of the inconsistency at wiseco, run 100 octane fuel and this will give you the most longevity. 25 hours MAX on a top end!! I've seen these yamahas do some weird stuff. Skirts breaking off the back of the piston, holes in the middle of the piston!! I've seen brand new 2014 yamahas come with missing stator plate bolts (only one bolt installed from factory) and on that same bike the clutch basket was cracked on 3 of the fingers and the bike only had 3 hours on it!! They are just not the fit and finish of any other manufacturer's 250 two strokes.. It amazes me because the same basic motor has been in the works for 10+ years! And it still sucks!!!!!!

So to the original poster, save your money! Save your time and frustration! Don't get crazy inside your motor!
I'm not going to make any grandiose claims regarding Yamaha's "legendary reliability" with the YZ250 engine, but I've never had any trouble with my top end. I ran the original stock piston almost 50 hours with no trouble. When I tore it down, the pin holding the top ring in place had broken off and made a tiny hole in the top of the piston where it came through and ejected itself out of the exhaust. It still ran fine.

However, I am currently having my transmission gone through for the second time. Third gear went out AGAIN. So, yeah, I'm a little disappointed with Yamaha. Next new bike I buy will be a KTM 250 smoker.
quicken
Profile picture for user quicken
Posts
243
Joined
3/17/2013
Location
Rhinelander, WI US
quicken 5/17/2015 11:52am
5/17/2015 11:52am
You are doing the right thing by getting the cyl head set up for your bike....listen to what southwick_mx has to say.

Send the head to RB Designs. Last cyl head I had done, total turn around time was one week using Priority Mail.

http://rb-designs.com/rb_designs_llc_025.htm

Measure the squish with the piston and base gasket you plan on using and try stick with them for consistency.


Post a reply to: 2006 YZ250 Cylinder Head Squish Band Rework for C12