Yamaha G1 engine rebuild

[YamiG1!]

Can someone give me the major do's and donts of a rebuild. Curious about what needs to be oiled and things of that nature. Any tips are greatly appreciated.

[sho305]

Most of the time you can bore the cylinder and put oversized piston in and it runs like new. Sometimes you have to get into the bottom end be careful about that. You can cut the head some to help compression, only so much or it gets into the chamber, to get more you have to mod the cylinder shorter iirc. 2 stroke is much simpler, just don't have any air leaks into the engine be careful about that.

[TheGDFP]

I like to be sure to add a little oil to the seal inner lip to avoid dry start wear, and to the bearings if they are cleaned and reused, or the replacements come dry.

Be sure to check the rod for up & down play. Some play side to side is normal.
New cranks are available, but are likely 3rd-world. Stocker can almost always be rebuilt better, for $50 or so less.

Cylinder sleeve is thick and can be bored quite a ways. Mine has a Yamaha Phazer piston for a 30cc up-size.

[DakotaEight]

What kind of rebuild are you referring to? Rebuilding the original engine or rebuilding the whole cart with a bigger clone engine?

[Scottvandenhout]

Originally Posted by TheGDFP

I like to be sure to add a little oil to the seal inner lip to avoid dry start wear, and to the bearings if they are cleaned and reused, or the replacements come dry.

Be sure to check the rod for up & down play. Some play side to side is normal.
New cranks are available, but are likely 3rd-world. Stocker can almost always be rebuilt better, for $50 or so less.

Cylinder sleeve is thick and can be bored quite a ways. Mine has a Yamaha Phazer piston for a 30cc up-size.

What part number for the phaser piston? What about shaving the head to bring up compression? Anyone port the jug? Not looking for high end power looking to be able to run 15-20 mph haul my tools and maybe small trailer now and then
Any ideas and tips would be appreciated

[Golf cart guy]

I wouldn't shave the head. The trick was to use the thinner Yamaha motor cycle gasket, this will raise compression. You don't want to get too much compression as then the starter will have a hard time turning the motor over. The other trick is to put on 2 base gaskets, this will change port timing. Its old school but works well.

[BrutalSoldier]

Originally Posted by DakotaEight

What kind of rebuild are you referring to? Rebuilding the original engine or rebuilding the whole cart with a bigger clone engine?

No Big Blocks for a G1 if ya still want reverse.

[mikeasis]

Originally Posted by BrutalSoldier

No Big Blocks for a G1 if ya still want reverse.

Don't forget the Yamaha Bravo 250cc snowmobile engine can be swapped and with the G1 electronics will still have reverse. Also doubling the HP

[sho305]

Originally Posted by mikeasis

Don't forget the Yamaha Bravo 250cc snowmobile engine can be swapped and with the G1 electronics will still have reverse. Also doubling the HP

If you mod the pipe to also fit. I always liked the 340 best, it sounded nastier. I have a 440 that could be used but no time for yet another project.

I had the head cut .030 I think and ported the exhaust up just a hair. If you run double gaskets under the cylinder you have to raise the compression somehow. Comp is really low not sure you could cut enough to make the starter not work. You can't cut the head much anyway due to the chamber shape. However advancing the timing and all that I was able to top 30mph with an otherwise stock cart. Was able to jump another G1, that was fun.

[mikeasis]

Originally Posted by sho305

If you mod the pipe to also fit. I always liked the 340 best, it sounded nastier. I have a 440 that could be used but no time for yet another project.

I had the head cut .030 I think and ported the exhaust up just a hair. If you run double gaskets under the cylinder you have to raise the compression somehow. Comp is really low not sure you could cut enough to make the starter not work. You can't cut the head much anyway due to the chamber shape. However advancing the timing and all that I was able to top 30mph with an otherwise stock cart. Was able to jump another G1, that was fun.

will the 340 run in reverse? does it do that stock or modified and if so has it been verified? I ask because I see a lot of post with engines people think can easily run in reverse but its not always that simple.