GX390 Build

Flyinhillbilly

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When I converted the cam to a straight cut gear I slotted the bolt holes which makes the gear adjustable.

Under the button head bolts in this pic the holes are slotted which allows the gear to be advanced or retarded.

When you get a non adjustable cam from the factory your stuck with whatever timing the cam was manufactured with, which can very.



That’s why I run the billet tool steel cams. They’re a snap to degree, rather than having to twist the crank gear you just pick the set of holes you need to get it where you want it.
 

Mammoth

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Just took a look at those cams and that looks like a good option. Really light weight as well.

Ground off these bumps that just restrict air flow.




Made a plate that blocks the starter hole from venting air thats supposed to go across the cylinder fins.



Took some pics of the head breather holes I'd filed bigger allowing heat to ventilate faster.





Tried to make sense of the ignition system. Looks like this kit is designed more for a briggs or Tecumseh.

 

Mammoth

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Had to make a bracket that holds the trigger pickup right next to the flywheel. Not sure if this will work, or if its in the right spot.




Made a top plate that holds the coil and the hall effect controller. Left all the wires long for now.

Jetted the carb and found a velocity tube that fits.

Still a long way to go, but its starting to take shape.



 

anickode

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It's a fantastic build to be sure. Your machining skills are excellent, but those welds on the head are, unfortunately, crap. I don't mean to be rude, but I don't understand putting this much time and money into almost every aspect of the build, only to cut corners on others. :huh:
 

Mammoth

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If I could have welded on this type of aluminum better I would have. My experience on a tig welder is slim to none.

When I raised the ports I ground through the walls, so it required some welding. I welded it up and was happy with the numbers on the flow bench.

I know looking good is what most people care about, but thats the least important thing to me. I'm building this engine to run the best I can get to, and thats what really matters to me.

It was quite the experience to take my race kart with hand built body work to the track with all the other karts that had the same factory body work. Some people may have thought I was an idiot. Most didn't know what to make of it, and very few realized what I had done.

I built the most streamlined kart that track ever seen with a skid pan that made more down force than three of there karts combined.
In the end it didn't matter what it looked like it was about performance.
 

anickode

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I totally get the function over form approach. What I am saying is that porosity in a weld is not just a superficial defect. It could cause you some serious and expensive mechanical problems, which is money down the toilet. Carbon accumulation, hot spots, cracks that you can't see, etc.

If you opened up a brand new engine from the factory and found casting defects in the cylinder head, would you go ahead and do a high performance build with it, or would you get a new head from Honda?

If you are putting all that time and money into it, and you're admittedly not a good Tig welder, why not pay a few bucks to have it done well? I get that there's pride in DIY but there's no shame in getting help where it's needed, because nobody is an expert at everything.

I am excited to see it run. We don't see a lot of fully built big blocks. It would just be an awful shame if it went boom over something easily avoidable.
 

Mammoth

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Mammoth

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Kinda strange how things work out sometimes.

Ive always had to use a friends tig welder which limits my time and experience with them.

About a month ago I shot a guy an offer through craigslist on a welder he had. He declined my offer which was 300 less than the asking price saying "he can't go any lower because its worth twice as much".

Yesterday he emailed me and said its got to go so I picked this up today.



Story is its an ex Lawrence Livermore Lab unit that was purchased new in 1990 and serviced every six months. The seller worked there and used it until they replaced it with new models. He liked it enough to purchase the unit, but its only sat in his garage since.

I talked to an ace welder that recommended this model to me saying it will do everything you need and parts are much easier and cheeper to replace than the new ones.

Took about 10 months to get ahold of one. Total price was $1000

Its super clean inside and out and has the optional pulser and water cooler. I think I found the right one for me.

Now I can spend the time to raise the ports on a 390 to the heights Ive always wanted to. This is going to be cool.
 

Flyinhillbilly

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Kinda strange how things work out sometimes.

Ive always had to use a friends tig welder which limits my time and experience with them.

About a month ago I shot a guy an offer through craigslist on a welder he had. He declined my offer which was 300 less than the asking price saying "he can't go any lower because its worth twice as much".

Yesterday he emailed me and said its got to go so I picked this up today.



Story is its an ex Lawrence Livermore Lab unit that was purchased new in 1990 and serviced every six months. The seller worked their and used it until they replaced it with new models. He liked it enough to purchase the unit, but its only sat in his garage since.

I talked to an ace welder that recommended this model to me saying it will do everything you need and parts are much easier and cheeper to replace than the new ones.

Took me about 10 months to get ahold of one. Total price was $1000

Its super clean inside and out and has the optional pulser and water cooler. I think I found the right one for me.

Now I can spend the time to raise the ports on a 390 to the heights Ive always wanted to. This is going to be cool.
Like this whole build, that’s awesome. I have a crappy DCEN tig, I’d love to land a deal like that.
 

Mammoth

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The shrouds ducting design on these only works so good especially when running a smaller flywheel.

One way to get these flywheels throwing air is to make a shroud as close to the fins as possible without hitting.

I made one piece at a time until it worked.











You wouldn't even know its in there and this cooling system should really work now.



I couldn't find a bottom shroud online, so I made one.

 

Mammoth

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Been getting whooped by another project I got going on. Literally digging dirt and rocks by hand for six days straight nine hours a day. So I haven't had much time to do any work on it.

I will have some free time this weekend.

The temperature range I'm shooting for is between 300* and 400*. Anything past 400 and things start slowing down.

It may seem like I went over board on the cooling, but it makes a difference.

One bike came into my friends shop that was slowing down 1200 rpm by the end of each race. The only thing we did was work on making it run cooler, and it ended up gaining 500 rpm.
Right about 3/4 of the race like clockwork all the other bikes would start slowing down and this bike would slowly move up until it was in first. It won many races this way.

I've herd many stories about people using this to there advantage so I focus on it a little bit.
 

Whitetrashrocker

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We put frozen water bottles on the drag car engine and blow fans on it to bring the temps down between passes. We even have tried blowing air IN the block to help get rid of heat.
Back in the gas days before the blown alky we had a fuel line coil in an insulated can we packed with ice.
Try everything.
 

Mammoth

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Finally able to make some progress.

The top cooling shroud was raised too far off the cooling fins for my liking, and it partially blocked the compression release so I built another one thats formed around the fins.







Shortened all the wiring to length. Mounted the on/off switch along with a fuel pump and silicone fuel hoses.



[img]https://i.imgur.com/X1cfbd9.jpg[/IMG]


Mounted a one way check valve to suck air out of the crankcase which will be plumed into the exhaust. When the piston goes down it will push air out of the valve and when the exhaust pressure goes negative it will pull air out of the crankcases.
Reducing crankcase pressure will free up more power.

I put a oil splash guard on the inside so oil doesn't get sucked into the exhaust.



I'm deciding what battery to use on this. It just has to complete the circuit of the electronics and run a bilge pump. A lightweight 12 volt lithium of some type.
Anybody have any recommendations?


.
 

Mammoth

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Just about complete.

I tested for spark by giving it a few pulls with no results so I thought to hook up a battery. Gave it another pull and it through a huge spark.

Had to machine the camshaft end down to 15mm diameter because the stock 16mm ID bearing is hard to find in ceramic.

Made the stepped exhaust out of stainless and gave it a polish. The steppes should widen out the power band.

It took me a while to get all the parts for the tig welder, but its up and running now. The exhaust is the first real weld I've ever done with a tig.
I've melted aluminum on heads, but never fused pieces together.

Coated the heat shrouds with heat dissipating ceramic.

Waiting on a battery coming in the mail then i can get it on the dyno for firing and tuning.

[url=https://imgur.com/Z6xTRys][img]http://i.imgur.com/Z6xTRys.jpg[/url][/IMG]

[url=https://imgur.com/xNhCWEl][img]http://i.imgur.com/xNhCWEl.jpg[/url][/IMG]

[url=https://imgur.com/FsFmyEn][img]http://i.imgur.com/FsFmyEn.jpg[/url][/IMG]

[url=https://imgur.com/fZ38zB5][img]http://i.imgur.com/fZ38zB5.jpg[/url][/IMG]

[url=https://imgur.com/FjobcXM][img]http://i.imgur.com/FjobcXM.jpg?1[/url][/IMG]
 

.Chris.

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Great thread Mammoth!

I'm also changing my gears to straight cut gears b/c I'm facing a lot of side load (it's a 74mmx95mm engine) with the heavier springs (80lb).

May I ask you what material and treatment you used when building the gears? I'm thinking of using 8420 (or 4320) and cementation/temper, which is basically what is done for transmission gears, but sounds like an overkill sometimes.
 
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