It works! Low compression?

[swazi_matt]

There are a few posts on how to do a squish test. Maybe try that and report back on findings
As you are wanting to ride on the road it may be a good idea to do this anyway and possibly get the head shaped correctly for squish

 

[(F5)]

Std bikes (only measured my 200 and 300) are often about 2.5mm gap so don't be surprised if on the first try you need to double over solder..

 

[Noobi06]

this shit looks complex asf. is there an easier way? I thoguht it would be ring end gap or too small of a piston

 

[Noobi06]

I did actually notice the previous owner had 2 gaskets, while I only had 1. Maybe I add the other one back?

 

[(F5)]

What's complex about shoving some solder down the plug hole?

 

[fred99999au]

Not experienced with the GG engines, but I find that odd. Most of my other 2 bangers have the piston reach very close to the top of the cylinder and the compression space is in the cylinder head.

Hence the difference in head shape and CR etc.

What has changed in the bottom end? It is either going to be cylinder height or crank throw that makes a difference.

What base gaskets have you used?

 

[Noobi06]

The previous owned had 2 base gaskets. I only use one now.
Before that I had another cylinder that had really high compression. I guess I will just do the solder thing

 

[Noobi06]

if the squish is too bad, do i need to cut the bottom of the cylinder? Thats not something I can do myself either way

 

[(F5)]

Just make sure it is as good as stock and nothing is wrong or mismatched.

Yes, ideally on a 125 0.8mm would be a better number. 1mm on a bigger engine. You'd skim the head to reduce the gap. But most often closing the gap up will make the compression ratio too high and detonation will occur. Unless you make the chamber of the head bigger.

Let's not get into that, our lad here is trying to get the bike running best it should for an affordable price.

Btw both my 200 and 300 had two base gaskets std. I took one out on the 200. Lower barrel will typically give a little more low end. That is broadly speaking, very generalized.

 

[Zman]

If the squish is too large, you can either reduce the base gasket thickness, cut the cylinder base so the overall height is shorter or cut the head mating surface in a lathe so the head protrusion goes deeper into the cylinder.

 

[Noobi06]

If I understand this correctly. The cheapest and easiest way for a 16 yo to do this is to:
Measure the squish, should be around 0.8. Im doing this on Saturday or Sunday
If the squish is larger than 0.8, I should get a thinner base gasket or cut some of the base of the cylinder
If the squish is too small, Ill get a thicker base gasket
Is this right?
2. If squish is lets say 0.1 too big. Should I use a gasket that is 0.1 thinner? Or cut 0.1?

 

[Noobi06]

I just read about timings. I watched this video. https://www.youtube.com/watch?v=_uBPDfL8KQc&ab_channel=RockyMountainATVMC
I learned that I need to use that tool and when the piston touches it, the marks on the flywheel should line up. I have definately not done this.
Does anyone know where I can buy the tool?
If I get my hands on that, the rest is easy. I fix the solder thing, and after I just time it and i should be good to go, right?

 

[(F5)]

Ok, we're getting off track.

Don't cut anything off the base. It will affect the port timing which is important. Keep it somewhere near std.

If the flywheel is fitted with woodruff key and the stator backing plate is fitted in std place (they have a special washer to limit where it goes, then the ignition timing will be right. You Don't need to do anything else.

Don't try to optimise the squish clearance to 0.8. It is ideal BUT it will make the volume above the Piston too small. You would need to machine metal out to compensate. Standard they run fine. Maybe one day but not now.

Measure the squish. If it is not more than say 2.5mm. you will be right. If the shape of the squish is parallel that is good.

Let's see if it is all as expected. Then let's try work out if the compression is OK. If it starts easily enough it should be.

 

[Noobi06]

I removed spark plug and took a piece of solder. I kicked the piston over and my squish measures out to 0.8mm. Im super happy.
This means it can only be 2 things right? Either one:
Piston ring needs to be replaced (either worn or end gap)
If not that, the piston is too small

 

[Zman]

I agree with your analysis.

 

[(F5)]

I agree. Apart from the bit about being happy with a o.8mm squish.

I have never ever seen a bike with ideal squish that has had a low enough compression RATIO. You usually (always) have to rake some meat out of the dome if they get that close.

Or run 130 octane gas.

 

[Anders]

Yes.
On my '15 200, I had to remove quite a bit after setting the squish. According to my notes, I removed approx. 2cc. It took a few iterations of
"lathe work, measure volume, repeat..."

 

[Zman]

I also agree with the need to compensate for the volume. I have never seen a stock GG 125 with a squish measurement that low. If all goes well the person that cut the head also corrected the volume for compression. That being said, this bike seems to have some serious leakdown.

Were you able to do a compression test?

Did the cylinder have a ridge at the top that you could feel with your finger?

 

[Noobi06]

Can I not add a thicker base gasket? This way I get smaller squish
No, I have not done a compression test since it is super low either way. In approx a week, I will be inspecting the ring, and changing it. I will also be measuring the piston and cylinder diameter to see if piston clearance is too big, resulting in bad compression.

 

[blitz11]

Thicker base gasket RAISES the cylinder, reduces squish/compression.