02 RM125 cylinder head/squish question

Headling
Profile picture for user Headling
Posts
336
Joined
3/13/2017
Location
GB
Headling
Edited Date/Time 3/5/2019 11:03am
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??

|
brody
Profile picture for user brody
Posts
419
Joined
11/26/2018
Location
GA US
brody 3/1/2019 11:47am
3/1/2019 11:47am
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
1
Headling
Profile picture for user Headling
Posts
336
Joined
3/13/2017
Location
GB
Headling 3/1/2019 12:28pm
3/1/2019 12:28pm
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
Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 3/1/2019 2:23pm
3/1/2019 2:23pm
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
Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 3/1/2019 2:26pm
3/1/2019 2:26pm
Comedic used to sell 0.3mm and 0.5mm base gaskets for rm125.... 0.5 is stock

The Shop

See All »
Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 3/1/2019 2:27pm
3/1/2019 2:27pm
I take it the machinist will weld it up and re cut?
Headling
Profile picture for user Headling
Posts
336
Joined
3/13/2017
Location
GB
Headling 3/2/2019 1:49am
3/2/2019 1:49am
Thanks for the info Bruce, will show this to the machinest for guidance
mrg172
Profile picture for user mrg172
Posts
109
Joined
11/30/2015
Location
Gilbert, AZ US
Fantasy
451st
mrg172 3/5/2019 8:12am
3/5/2019 8:12am
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.
Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 3/5/2019 11:03am
3/5/2019 11:03am
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...
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

Post a reply to: 02 RM125 cylinder head/squish question