It works! Low compression?

[Noobi06]

Hello, I am back!
I finally got the gasgas together and it works! Im super happy and special thanks to everyone that helped, especially Anders, Zman, F5 and 5valve!
As you may have read from one of my threads, I screwed my old cylinder and piston which I had insane compression on! It was kind of tough to even kick it with my foot, and its a 125cc!
After screwing the cylinder, I took a cylinder and a piston from my other gasgas 125cc, which the cylinder and piston is basically brand new.
Now the bike works but im not happy with the compression.
Its really easy to turn over with your foot, and tough with the hand, but considering that there was a lot of resistance with foot before, im not really happy.
Is it normal, or is it because the cylinder is almost new and maybe needs to get ridden a bit?
Thanks in advance and thanks for the help from everyone! You made a 15 year old go from no knowledge to now being able to fix a whole ass bike!

[Zman]

Very glad to hear you got it back together!

Did you put the old head on the new cylinder or vice versa? I believe some of the early GG125 years had a domed piston and maybe the newer later years had a flat top piston. Putting a flat top piston under a head intended for a domed piston will result in poor squish and compression similar to what you are describing. Also putting the flat top head over a domed piston will yield high compression and make it hard to start and detonate.

There was a MX version of the 125 engine and a EC enduro version.

Which year and model head did you use and which cylinder did you use?

Can you get a compression tester and run a test to see where you are now.

[(F5)]

Hadn't ridden a 125 for ages but did last month. Was quite easy to kick over. But yeah as above. Compression testers are a very blunt tool, many people put way too much trust in them
-but if you have circa 170psi or so you should eliminate a massive mismatch of parts.
Borrow one with right thread for your plug. Not push in type. Throttle wide open. 10 quick kicks.


We tested a mates 125 Aprilia Road bike on Sunday. About 30psi. Had stopped running suddenly. Yep. That'll do it. Stuck ring for sure

[Noobi06]

Thanks guys. Ill get a tester.
Zman, the cylinder also came from a gasgas ec 125 2005. I own 2 identical ones so I don't think the cylinder, head or piston should be a problem.
Ill see if I get my hands on a tester though, maybe it's not even bad, but having the compression I had before, awhh man that was really nice.

[Zman]

Great points on the compression test.

Did you use the piston that came with the cylinder or did you buy a new one? Does it have a dome or is it a flat top?

[Noobi06]

Is dome when it has like 2 weird holes on the top?
Either way, I took both the cylinder, top and piston. The top of the piston is flat, I don't know what a domed pistol is but it is flat.
Piston head is the same type as my other cylinder which had awesome compression. Therefore I assume that it is correct.

[Zman]

A domed piston has a slightly rounded top. A flat top piston is flat.

If you have two cylinder heads, they can be different and change your compression even if they look very similar. It is hard to see less than 1mm difference between two heads but it can make a big change in compression.

The new cylinder can also be slightly taller which will also change your compression ratio.

If you used the thicker base gasket under the cylinder it can change your compression ratio.

How does it run?

[Anders]

As you are in Sweden, try to contact
https://www.blixtensracing.se/nikasi...ndruro/gasgas/

Sent fra min YAL-L21 via Tapatalk

[Zman]

It is not the end of the world but you will also need a new piston kit.

[Noobi06]

Ah well. Thats not so fun. Either way. I will be sending both my cylinders (i got 2 gasgas now) for replating and welding.
I found a company in Sweden that does the job and gives me a kit (piston, ring, bearing, etc) for only 4300 SEK (400USD).
Also, I wasnt the smartest and didnt replace my bearings inside the engine even though they had metal shavings in them, so I will be opening it again and replacing them.
Also, one question. I want to wash the engine components when it is in pieces. Can I wash it or will I damage stuff? My dad told me we should wash it with diesel fuel so im asking you guys if thats a good thing to do or if we should avoid it or use another liquid.
Also is it bad to use water to wash? Is there anything I can't wash? Like the crank or the clutch plates?
Thanks guys