Is there a difference between the conrod in the newer GO engines compared to the
older GX-5R. I put a new rod in mine not long back & can use a Novarossi R7 rod also, but was interested to know if the newer GO rods had changed in size, they would most likely be stronger.

No difference between the GX Series and the 5RHO or new GX II Plus rods.
Same part number GO 21-0600.

Running these shims in my gen 5 GO 5 port with 25% gen 2 Byron's fuel.
The motor isn't quite run in yet there is still metal pinch and I think it needs another half galon of fuel.... My question is... Can I remove one of these shims when the motor is fully run in??
Thanks
Rob

Does Gx2plus crank shaft fit part 21-0907T1 fit underdog project 4port? Is it worth the upgrade, rear ceramic bearing s well.

Hi Rob,

When run in the stock head shimming for that motor would be .5 mm
That should include 1 x alloy .3 mm shim, and either 1 x .2 mm copper shim - or 2 x very thin copper .1 mm shims, depending on the year of manufacture.
That is the factory shim stack, and is good for up to 30% fuel.

Cranks and rods for those motors have different part numbers - so no, I dont think that would work.
The UDP was a long stroke 4 port.
I'm not 100% sure, hopefully someone else will know for definite.
Ceramic main is always a good upgrade, as long as its a reputable good quality bearing.

Thanks grizz

Think I'm running two .1mm copper shims there. There's no alloy shim. Where can I find a .3mm ?
Thank mate
Rob

I've always thought that .5mm stack is good for break-in, but once break-in is over you want to remove the 0.2mm shim and run with the 0.3mm shim only.

Do I have it all wrong?

I've always used the .5mm for the first couple gallons on a new engine.
Once broken in I drop to .4mm.
I have run engines that have NO pinch at operating temp as low as .3mm with no ill effect.
This is at 30% nitro. I am at 1300 ft. above sea level. (the air is less dense at higher altitudes)
Always consider altitude when adjusting shim total. (combustion chamber volume/compression pressure)

Guess factory come with .5shim + 1 break in .1shim for break in. So after run in. .5 is perfect

The GO engines by their design are fairly low compression, so there is a bit of leeway.
As Matt said, you can run .4 to .3 mm and get away with it - but the facrory "safe zone" shim stack for the old pro series, gx-r series and gxII- 5rho motors was .5 mm.
if you drop to .4 or .3 on 30% fuel, just be aware of plug heat range and watch out for signs of detonation.
If you start blowing plugs, then put some shims back in.
If your not a "confident" tuner - just run the factory shims.

Rich - The new gxII plus is possibly different due to a new head button design. I cant recall shim stack off the top of my head, and I'm away overseas at present so cant check a new motor to confirm. My memory tells me there may be less shim stack height on the new motor. ?

Thanks Grizz, I thought they would of been changed when they made the new Plus engine, thats alright, atleast I know I can still get them if needed.

The 21-0600 rod is pretty stout.
Crankcase, crank and rod from the GXII-5RHO were carried over into the new GXII Plus.

so how did the Cera run? specs look good and so does the pictures. Might be a deal at the cost this engine is selling for.

Very smooth engine but how much power is unknown as here raining season now. Cant get to track to do further testing