02 RM125 cylinder head/squish question

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3/1/2019 10:59 AM

Hi Guys, my RM125 02 model has been running great (bought it as a project but hadn’t opened the engine up has had a fairly new piston in it when I bought it)

Opened it up today to check the piston size so I can order a new top end and the cylinder head seems to have seen a bit of action!!

The barrel/piston etc are all spot on and the bike has been running wel but obviously need to sort this problem out

I’ve spoken to a guy I used to race with who builds road racing 2 strokes and he can machine the head

He has asked what squish the RM125 normally run?

Think he needs this info so he can adjust barrel with different thickness gaskets (I’m on 98octane pun fuel btw)

Any ideas Guys?? Photo
Photo

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3/1/2019 11:47 AM

i wouldent trust a guy who does not have squish specs, I would get a phat heads head and, run that.

.030 is for 100 or better

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3/1/2019 12:28 PM

The guys a trusted guy who used to build my TZR250 engines but he doesn’t do mx questions hence he wanted some guidance on what to aim for

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3/1/2019 2:23 PM

1.0 to 1.3mm is fine on a rm125 imo.

From memory (and unless the cylinder base hasn't been cut), the deck height is 0.5mm and the recess in the head should be 0.5 to 0.8mm... cant remember the squish angle, nut it might be on Eric gorrs website

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3/1/2019 2:26 PM

Comedic used to sell 0.3mm and 0.5mm base gaskets for rm125.... 0.5 is stock

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3/1/2019 2:27 PM

I take it the machinist will weld it up and re cut?

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3/2/2019 1:49 AM

Thanks for the info Bruce, will show this to the machinest for guidance

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3/5/2019 8:12 AM

Bruce372 wrote:

Comedic used to sell 0.3mm and 0.5mm base gaskets for rm125.... 0.5 is stock

Any feedback on going to the .3mm base gasket over the stock .5mm. How did the powerband change? I’ve got an 03 that I’m debating trying the base gasket or cutting the head for 1mm squish. already running 110 mixed 50/50 with 91. Bike rips, just looking for a tad bit more oomph.

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3/5/2019 11:03 AM

Bruce372 wrote:

Comedic used to sell 0.3mm and 0.5mm base gaskets for rm125.... 0.5 is stock

mrg172 wrote:

Any feedback on going to the .3mm base gasket over the stock .5mm. How did the powerband change? I’ve got an 03 that I’m debating trying the base gasket or cutting the head for 1mm squish. already running 110 mixed 50/50 with 91. Bike rips, just looking for a tad bit more oomph.

To be fair, you probably wont notice a lot of difference. Good idea running leaded duel though.

Bottom line, if you have a 15 to 20 year old 125 that started out around 30hp, I would just focus on reliability, if you are looking for dramatic power increase then just buy a new bike or a bigger bike

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