GX500 build

Flyinhillbilly

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So I’ve decided that I needed something bigger than the 238cc small block that I’ve been running on my race kart, so I got a hold of a well used GX390 Honda that had driven a water pump on a farm, and then sat for a few months in a buddies yard.3A504E03-59D4-4914-B16D-E688B78F5023.jpeg
 

Flyinhillbilly

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The next problem is that this block doesn’t have a thick enough sleeve to bore to 96mm, so I called up my buddy at the local automotive machine shop and told him the measurements that I needed in a sleeve.

im officially to the point of using car parts at this point.9B126952-FFE7-453D-9234-ED457B8F947E.jpeg
 

Flyinhillbilly

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After boring all I’ve the old sleeve out, plus a fair amount of aluminum I was left with a gaping hole. It also has a few holes where the side cover bolts go.
As you can see, I left a shelf on the bottom for the new sleeve to sit on.3A04D184-42C3-4449-A25F-712DA4BFC830.jpeg
 

Flyinhillbilly

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The next hurdle was how to get the new sleeve inserted into the block since it’s .004” larger than the hole that it’s supposed to go into.
My solution is to pack the sleeve in a container with dry ice, and then add 91% isopropyl alcohol to create cryogenic alcohol that brings the temperature down to -130F.C8A58413-EFE7-4361-B972-79642360ABB7.jpeg
 

Flyinhillbilly

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After the hour was up, I dropped the sleeve into the block, and it fell right in with a solid “thunk” on the shelf while the alcohol sizzled and spit. I gave it a couple of good whacks with my 3lb deadblow hammer to make sure it was good and seated.00B237FA-D0E0-499A-AD9E-41DC33335966.jpeg
 

Flyinhillbilly

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Next, I bored it to .008” under where it needs to be for the finished product.
I’ll get my big drill from work tomorrow and chuck up the micrometer hone to finish it up. After that, I’m waiting on a set of adjustable reamers to come in so that I can increase the bore of the small end of the rod by .005” to fit the zongshen wristpin.

456F79C6-851A-400D-8448-067854FC86EE.jpeg
 

Denny

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Is there going to be enough meat left to keep from lifting the cylinder? Will you be able to flow enough to keep the cylinder filled and emptied?
All these questions will be answered! Tune in next week! Same Bat time! Same Bat Chanel!
 

Flyinhillbilly

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And just like that I have a 96mm bore GX390.
With the 69mm stroke crank it works out to be 500.13cc.
Now I’m just waiting on my new reamers to show up so that I can mock it all up with a stock rod so I can get an idea of what to order for rod length.5E61EB78-CCBE-4365-A8D7-0F1EE2411330.jpeg
 
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