86 ATC 250r Build

**CodyRosa** · 07-14-2015, 07:17 PM

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Ok guys.. it's been a very long 5+ months waiting for this motor.. it isn't here yet but it's finished and looks awesome! It's ported and polished, 265cc and it's coming with a 38mm carb. Other than that it's all stock.

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**yaegerb** · 07-14-2015, 07:21 PM

Originally Posted by CodyRosa

Ok guys.. it's been a very long 5+ months waiting for this motor.. it isn't here yet but it's finished and looks awesome! It's ported and polished, 260cc and it's coming with a 38mm carb. Other than that it's all stock.

Whew, very nice. Hold on cause it's gonna rip. Did Rob do anything for porting or did he change the compression with a cr gasket?

**CodyRosa** · 07-14-2015, 07:40 PM

Thank you! For the head we went with an O ring instead of a gasket so I'm not sure if that'll bump up the compression or not? For porting it was a $300 port job.. that's all I know to be honest haha. I have a few pics of the cylinder.

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**yaegerb** · 07-14-2015, 10:48 PM

o-rings won't bump compression. Just an advanced way to seal the head. Looks great!

**barnett468** · 07-15-2015, 12:56 AM

Originally Posted by CodyRosa

Thank you! For the head we went with an O ring instead of a gasket so I'm not sure if that'll bump up the compression or not? For porting it was a $300 port job.. that's all I know to be honest haha. I have a few pics of the cylinder.

Depending on how the system is set up and installed, in many instances, if you used a 2 O ring system similar to the one below, and it no longer has the standard head gasket which is around .028” thick if I remember correctly, AND the head you are running is orig or has the same or less volume as the orig, you raised the compression by at least .5 [1/2 a point] . . Also, unless it has a recessed squish band the piston will likely be too close to the head at tdc especially when it’s running.

If your exhaust port was raised when it was ported, this will reduce the compression, therefore if the O rings increased the compression and the exhaust port was raised which will reduce the compression the two mods will cancel each other out to some degree.

The most important thing you can measure is static compression . . If it is less than around 140, it is pretty wimpy for high perf apps . . If it is around 170 or higher, it is very good.

**82 250r** · 07-15-2015, 02:13 AM

Motor looks great!
What color/paint did you use for the motor?

**atc300r** · 07-15-2015, 07:28 AM

Looking great.Im thinking of having my motor done by bdt with a 68 mill piston and port .

**CodyRosa** · 07-15-2015, 08:00 AM

Thanks guys! I still havent got the color name haha.. Barnett that was a nice little bit of info so thanks! I was told it will bump it up just a tad like you said. So what is static compression?

atc300r.. I highly recommend it! You definitely wont be disappointed.

**CodyRosa** · 07-21-2015, 03:31 PM

Well i got the motor finally!! and got it all put together to find out she has 230 psi when I'm only running pump gas. I'll be overnighting the head and hopefully it'll be back before the weekend which was my deadline for this wheeler lol.. so i'm cutting things very close here.

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**barnett468** · 07-21-2015, 04:32 PM

Originally Posted by CodyRosa

Barnett that was a nice little bit of info so thanks! I was told it will bump it up just a tad like you said.

no prob, you're welcome . . yeah, changing the distance from the piston to the head more than .010" in any vehicle will make a measurable change . . Changes of .040" or more can be felt.

Originally Posted by CodyRosa

So what is static compression?

it is the amount of compression an engine has when just being turned over by the electric starter or kick starter.

the test should be done with the throttle at least 1/2 open . . it is also called uncorrected compression.

the compression while it is running is called corrected or dynamic compression . . dynamic is the most common term.

the compression will vary slightly with engine rpm which is why its referred to dynamic . . dynamic basically means moving or changing.

**barnett468** · 07-21-2015, 04:34 PM

.

Originally Posted by CodyRosa

Well i got the motor finally!! and got it all put together to find out she has 230 psi when I'm only running pump gas.

that's perfect....if you are using 130 octane, lol.

fyi - cheap compression gauges can be off by up to 20 lbs.

**CodyRosa** · 07-21-2015, 05:42 PM

haha yea no i'm sending the head out to get worked on.. 230 would be awesome but no thank you.. i want pump gas

**barnett468** · 07-21-2015, 08:01 PM

Originally Posted by CodyRosa

haha yea no i'm sending the head out to get worked on.. 230 would be awesome but no thank you.. i want pump gas

i would shoot for around 170 - 180 then.

**CodyRosa** · 07-23-2015, 08:55 AM

Yea I told him I only want to run 91.. thats the only thing I can get around here.. no 93 or 94 anywhere that I know of!

**yaegerb** · 07-23-2015, 12:35 PM

Originally Posted by CodyRosa

Yea I told him I only want to run 91.. thats the only thing I can get around here.. no 93 or 94 anywhere that I know of!

230 PSI is redic. That head sounds like its had some work done to it or the cylinder has been milled down. Who are you sending it back to? Rob?

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