It works! Low compression?

[Noobi06]

Exactly. As my squish is 0.8, raising the cylinder like 0.1cm would be perfect

[Zman]

Yes raising the cylinder with a thicker base gasket will make it better but you still dont know your overall compression.

[Noobi06]

How much squish should I aim for? Before you guys told me 0.8 but now that im there, you say it's too low. 0.9 maybe?
No, i do not know my overall compression but I am getting a new piston so I will be measuring piston clearance and then buy one. I also have a new piston ring.
How much piston clearance should I have? (mm between piston and cylinder wall)

[(F5)]

Sorry if I confused you. I said 0.8 was ideal, but that's from an engineering point of view. It can't be taken in isolation. You get some movement in a running engine. If you set to 0.6 you would likely get the piston smacking the head which would be bad.

Whenever a tuner works an engine he sets the squish and then measures the volume at top dead centre (tdc). Then adjusts the headshape and volume to where he wants it.

There will be variation in engine to engine so you have to measure if you are seeking optimum. 2mm would likely be safe if you don't want to measure.

What we were trying to find out was if there was a dreadful mismatch of parts so like if you had 4mm squish or something completely wrong.

Maybe just maybe someone has machined the head before, but I wouldn't count on it. Thinking back, both my 200 and 300 had a black coating on the surfaces. Does yours? Is there evidence of some of it being machined off?

Perhaps the 125 is different.

I rode a 125 GasGas yesterday as it happens and it was very easy to kick over. But not the same engine as this was a Trials bike!

[(F5)]

For giggles if you have time here is an old thread of mine explaining the process of head mods.

http://gasgasrider.org/forum/showthr...highlight=Head

[Zman]

The last 125 head I cut to bring the squish to 1mm, then I had to cut more material from the dome of the head to increase the volume to compensate the compression for pump gas.

[Noobi06]

You guys recommend I have around 1mm squish? I can fix that no problem, just increase the base gasket a tiny bit. Also my squish test was very quick, I can probably do it better and get a slightly different reading.
However when I google, my results say 0.8mm is ideal for a 125.
Edit: after some more googling, it looks like ideal is 1mm for road riding. If you want more performence like on tracks where you don't expect it to last, 0.8mm is ideal.
My engine needs rebuilding either way, so I will be doing that. After that I will be trying the same base gasket and I will do a real proper squish test. If its under 1mm, I will up the gasket till it is 1mm.
I will update you guys from there.

[Noobi06]

One more thing. I got some issues and now my piston has a ton of vertical lines, however none of them can be felt by the finger nail. Is it a worry? It is a lot of lines but cant be felt.
Also if its no problem, will that piston last the same as a regular? around 100h ish.
I know you cant never know but still

[Zman]

Please post photos of the head and piston. Can you feel a ridge at TDC (the top of the cylinder where the piston stops and changes direction)?

It is not uncomon to have some wear small scratches on the cylinder. It can mean that your air filter is letting debris and dirt past it.

[Noobi06]

Ok, I will post photos once I get home. Im home at Thursday.
Reason why it has lines was because my bearings failed. Learned from my mistake once again, I tried to avoid changing the bearings even though I knew they had metal shavings in them. Literally after a minute of being started, once I took the engine out to do it properly, I noticed it already damaged.
Either way, Ill see how deep it is etc.
I will send photos and stuff