Big Blockin a G1

[mikeasis]

FYI Dimensions are as follows. Pardon the bad pics its hard to do solo.

Brave case width flywheel side 12 inches
G1 case flywheel side 10 3/4 counting the little bolt hole tab left outside of case.

Across the case with exhaust facing you.
Bravo 7 inches
G1 6 3/4

Any questions please ask.
I have no timeline on this project. At this point im tinkering and still need to clean up the engine and install new crank seals. My ultimate goal is obviously more power but I want to be able to make a cradle that drops in and if need be pulls out and a stocker can be bolted in if the wife hates it.

[JRL]

Cannot add much, but if going with a Blaster expansion chamber, get the silencer with it. You'll need it. And if cutting to fit, don't take out sections. Try to slice and rotate...sorta snail it around keeping the chamber volume unaltered. It'll give you a lot more bottom end. It will function well no matter how twisted...mostly.
Watch the carb jetting initially. Changing pipes might lean it out. And might enrichen....I wouldn't depend on the oil injection system until you prove it works while running on premix.
Running without the silencer will cause bottom end power loss, hearing loss, and lean-out.

[mikeasis]

Originally Posted by JRL

Cannot add much, but if going with a Blaster expansion chamber, get the silencer with it. You'll need it. And if cutting to fit, don't take out sections. Try to slice and rotate...sorta snail it around keeping the chamber volume unaltered. It'll give you a lot more bottom end. It will function well no matter how twisted...mostly.
Watch the carb jetting initially. Changing pipes might lean it out. And might enrichen....I wouldn't depend on the oil injection system until you prove it works while running on premix.
Running without the silencer will cause bottom end power loss, hearing loss, and lean-out.

thanks for the information. I will most likely use the stock bravo exhaust system if at all possible. Is'nt the blaster engine a reed engine like the Enticer? If so I wonder how much of an effect that would make using that exhaust on a piston port engine. I think adding power down low would be ideal

[mikeasis]

looking at the right side of the bravo engine it looks like they intended to add an electric starter. Wondering if that happened later down the line for the bravos? Ehh after a quick search that looks like a no go. I wonder if this case was used for another engine?

Anyway back to tinkering. The first pic shows the stock G1 on an 82 engine stand (82 on is the same. the only difference I can see is the addition of the tension cable brackets and the updated belt tensioner still mounted in the photos) The second showing the Bravo engine and how it sits straight. From my generic measurements the G1 engine is tilted 18 degrees forward. The third pic is just a mock up of the bravo at about the same tilt. I don't yet know what this means with fitment for the exhaust or the intake but I can tell you I laid a starter generator in place and its going to be tight due to the increased size of the Bravos Fan case side a.k.a that spot that looks like it could hold a starter.

After looking at Enticer cases on ebay it looks like the exact same tilt with their case and I have no doubt the G1 is a debored and detuned sled engine. In all honesty the easy route here would be swapping the Entier engine or top end and modifying its exhaust pipe to fit and using its carb.

[JRL]

The original sled pipe will make considerably more low end torque than would a blaster pipe. Sled pipe will be easier to install too. A blaster pipe is a right good sized item.=
And yes, Blasters are reed valve intake.

[sho305]

Once there was talk of the G1 being based off the earlier yamaha sleds but I could never find info. That would be 70s sleds, I think they had a 400cc single at one time, but very hard to find stuff that old maybe early to mid 70s. IIRC the enticer 250 was late 70s early 80s. Some of the early sleds are GP model before the enticer/exciter models. Google 'yamaha GP sled engine' and hit images, the GP 292 was a single there are some pics of it.

You can't go crazy changing the pipe to a different rpm unless you change the porting too, they need to work together. In general a longer pipe is lower rpm, shorter is higher, especially the head pipe from cylinder to where it starts to get larger affects the rpm range a lot. The people I knew built pipes on race sleds they were short but they ran very high rpm maybe 8K or something, maybe 2'-2.5' long for the larger part and they got larger close to the cylinder. The size and contour of the larger diameter changes how hard and width of rpm range the pipe comes on at. Pipes that are thinner tend to be wider range such as a 2 stroke road bike, short and fat is a narrow range that hits harder like a MX bike. In case anyone wondered lol. I was told you could add a couple inches to the head pipe and knock rpm down slightly, but more changes you may need to change porting. Note the head pipe on a G1 is huge in length, though the chamber part is only seen if you cut the muffler apart. Someone has and posted photos on here someplace. Of course its a real mild pipe and low rpm, not typical on a 2 stroke.

[mikeasis]

here you go. The case parts numbers are the same for the 79-81 enticer and the early g1. The case part number changes for the G1 around 83, guessing for the additional port for the boost chamber added 83.

https://www.cmsnl.com/yamaha-et250c-...l#.XESKEvZFzug

https://www.cmsnl.com/yamaha-g1-a-g1...l#.XESKPPZFzug

Now here something interesting. the early enticer 77-78 case is different. Like the Bravo it also as what looks like a spot for an electric start, that or some type of PTO.

https://www.cmsnl.com/yamaha-et250a-...l#.XESLOPZFzug

[mikeasis]

Very loose mock up. the engine is just laying in there with the clutch lightly tapped on and the exhaust laying in the stock location. the exhaust needs to be flipped as the outlet is currently on the fuel tank side. im thinking Im going to make a stand for it and tilt the engine forward like the g1 engine as I think this will help with clearance for the carb and intake being close to the differential.

The last pic shows the 80 engine stand next to the 82 (the rusty one). The only things I see different is the starter gen mounting and belt adjustment. the starter gen on the early models had bushings installed on the bottom bolt holes and used a smaller diameter bolt. the belt tensioner on the early model was auto tensioning with the large spring and the later had a bracket with a slot in it. That and the addition of the engine limiter bracket on the later model (tension cable)

Im going to have to remove the bravo engine mount plate and start mocking up an adapter of sorts. I feel uneasy doing this as these bolts are what holds the case halves together but I think in order to replace the crank seals on this engine the case needs split but I am NOT yet %100 percent on that. check the lip on seal in the pic below. I really didn't want to disturb the engine gaskets.

[LittleEd26]

I've done a similar conversion on an early 80s G1. I ended up using a complete Enticer 250 top end on the G1 bottom end. That way I could maintain reverse with no other modifications. The cylinder, cylinder head, piston and rings were used. I eventually ditched the stock Enticer carb and installed a Mikuni slide carb which was a huge improvement once I got the jetting dialed in. I could never get it to run right with a modified Enticer exhaust. It ran much better with the stock G1 muffler. I also used a 94c duster clutch but I think the stock G1 clutch would work fine as long as the jetting and exhaust isn't choking it down. It's a nice improvement over stock if you can get the jetting and exhaust correct. The powerband is unstoppable.

[JRL]

The seal has locating tabs and it probably goes in from the inside. Add bearings too while you're in there.
Surprised it has a case gasket? Most (now) use Yamabond or 3 bond grey sealant for case halves. That said, if you see a gasket, it obviously has one, and it has to be in there for side to side crank bearing clearance. You might find that cylinder and head gaskets can be reused, if it has a cyl gasket. I don't know much about sled engines. Know Yamaha dirt scoots.
Don't recommend that, but, if clean, you'll probably be OK. Positively don't want any crankcase/cyl air leaks. If the crank seals are not seeping, you might want to complete the install and then determine what the engine needs.