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Goatse

Can anyone confirm if the piston height 'tool' from Beta is just a straight edge?

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I'm changing my 250 into a 300 (thanks GP!), and to get my piston height below the deck to the 0-0.1mm the service manual suggests, I have to use the thickest (0.6mm) base gasket.
 
But when I do that, my squish is in the 1.6mm range. Ideally I'd like to be in the 1.4-1.5 range, so it looks like the typical 0.4 and 0.5 base gaskets I see most guys using would get my squish numbers right, but the piston would be a touch over the deck at TDC.
 
So that leaves me wondering if there is a slight raise in the 300 side on the measuring tool. I know the 250 side is curved for the domed piston, but I'm also assuming the 300 side is a straight edge for the pre 18 flat top 300 pistons.

Also it might be worth noting that my 250 did have the 0.6mm base gasket in it from the factory.

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Thanks Steve. It looks like my RK insert won't be able to get here soon enough.

At least I'll be able to get all flavors of the 300. The mellow side, and then when the head shows up I think I might even squeak the 0.5mm base gasket in there. Awaken the beast.

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250 CDI. Easier to undo.

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250 CDI. Easier to undo.
Oh, I'll be playing around some. My whole goal here is learning/experiencing all the differences between the 250 and the 300.

I just better get it all sorted by the time racing starts back up in May.

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Last time I checked my 2017 RR300 squish band gap was close to 1.7 mm. 

This was done with a vernier caliper on the flat side of the head and measuring tin the beginning of the squish band slope (its not flat). A 2009 EXC 300 head I have lying around was 2.1 while the first dome of the S3 head I am using is around 1.45-1.5 (and the other 2 domes around 1.25 and 1.1 for the highest compression one). 

The reason to use the special tool is to compensate for small production variances between cylinders (and not alter port timing) and then take as a given the cyl head not to measure directly the squish band gap. 

 

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20 hours ago, Goatse said:

Thanks Steve. It looks like my RK insert won't be able to get here soon enough.

Can you order just the insert?

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Can you order just the insert?
Yes. Of course for that to work, you do need to already own an RK head.

We're lucky on the Betas (or me in this case). The outer shell is the same between the 250 and 300, whereas I guess the KTM is not.

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