2018 GP300 not starting / breaking kickstarters

[Neil E.]

Cylinder hole:
http://www.gasgasrider.org/forum/sho...8&postcount=14

http://www.gasgasrider.org/forum/sho...ight=bore+hole

http://www.gasgasrider.org/forum/sho...20&postcount=5

[Davehuge]

Originally Posted by Undertow

- After putting the plug back the engine gets hard to turn right away.

So based on that, the engine becomes very difficult to rotate as soon as you fit the spark plug...then it's pointing to high compression ratio.

As Neil E has suggested, it would be a good idea to measure your squish clearance, it's quite easy to do.

As I said before, if for some strange reason your compression ratio is very high/too high then I wouldn't run the engine as there's a risk of damaging your nice, shiny, new crank.

Good luck, Dave.

[RudolfHucker]

Have you checked the piston position at TDC? This is normally set by using different thicknesses of base gasket to adjust the cylinder height.

I would take the head off to check. It only takes a few minutes.

[Davehuge]

Originally Posted by RudolfHucker

Have you checked the piston position at TDC?

Similar to checking squish clearance... so we're starting to think the same, that maybe the compression ratio is too high.

[Davehuge]

By the way...is the compression vent hole only on later models? I don't remember seeing it when I fitted a new piston kit on my 2004 model.

14 years old and still going strong!

[Undertow]

I truly tried to kick with that old (fixed) lever and got up to 209 (14,4 bar). I guess this is as far it looks to go. I guess this is not hugely high? But just to be able to learn I?ll do the squish / head check. Unfortunately have to travel for the next two weeks so it?ll take some time to do it.

At the same time I can check the vent hole.

Thank?s for the help so far, we?ll get on top of this 👍

[Undertow]

So a short update...

Didn't go on the trip, don't ask

So had the time to do the bike

Did the squish. Seems to be around 1.5 mm. The measurement on the solder was 1.55 - 1.6 mm, but it was 1 mm line and had to twist it a couple of times. So I guess it may have some elasticity more than plain solder.

But anyway, not really bad squish I guess, and everything else seemed to be ok also. Without the head the engine turns nicely when pressing the kicker. Not binding anywhere.

And there was also the vent hole, a tiny hole in a nice new cylinder

And also swapped a new needle (NEDW), so had a productive weekend.

Well, guess what. After some kicks the new lever is giving signs of giving up! The reason? The bike kicks back twice as hard if it doesn't start.

Just came back from garage after having an idea of removing the spark plug cap and kicking the bike without it. And it doesn't kick back. So now I'm leaning towards ignition timing as Davehuge suggested. And this would make sense also from the running point of view. By this I mean that the engine is really happy to stall at low rpm and is still running kind of rough even with the new needle, which improved the situation anyway.

But how to check the timing? I'm an mechanical engineer, electricity is something of a mystery to me

[Jakobi]

Originally Posted by Undertow

Did the squish. Seems to be around 1.5 mm. The measurement on the solder was 1.55 - 1.6 mm, but it was 1 mm line and had to twist it a couple of times. So I guess it may have some elasticity more than plain solder.


But how to check the timing? I'm an mechanical engineer, electricity is something of a mystery to me

The squish is pretty tight for a stock setup.. thus compression ratio will probably be on the high side.

Ignition timing wise I'd start by pulling the flywheel cover, flywheel and making sure the woodruff key is still in place and not sheered off (or missing).

[Davehuge]

The flywheel is pushed onto the taper of the crank, then secured with a nut. it's position is set by the Woodruff Key to give the correct ignition timing.

If the Woodruff key has sheared or is missing, the flywheel could have rotated on the crank, giving the wrong ignition timing.

To remove the flywheel from the crank you'll need a flywheel puller/extractor, don't try and use anything else or you could damage the crank/flywheel.

Below is the part number for the genuine GasGas puller, but there's many aftermarket pullers available that will work fine, just make sure it's the correct thread, on the older GasGas EC300 it was a M27x1 Left Hand Thread, on the later models I think it's an M27x1 Right Hand Thread, can anyone confirm this is correct?

Key.JPG

Part number for Flywheel Puller/Extractor
Part Num.JPG

Flywheel Puller/Extractor
Puller.jpg

[Davehuge]

Here's a video showing a flywheel being removed, it's not a GasGas engine but the principal is just the same. On this engine the flywheel has a Left Hand Thread.

https://youtu.be/j_w8nlq0Vzg