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JD 318 w/ B43
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304 Posts
Discussion Starter #1
Just thought I would post this to help others and get some feedback if there are better ways to do this. I had the infamous Onan surge. I'm in the middle of a restoration, so I decided to reseal the intake before painting the intake. I also have a carb kit to redo the carb. Anyway, this was intended to give some guidance on how to re-seal the intake manifold on the 318 Onan 20 HP. Mine is a B43G. As you may know, the original intake manifold is riveted.
1) Therefore it has to come off the motor to remove rivet since the center of the rivet cant be seen from the top of the manifold.
2) Center punch each rivet from the underside of the intake.
3) Drill each rivet w/ a 7/64" drill bit. Its a little smaller than needed for now.
4) After all rivets are drilled, gently pry the 2 halves of the intake apart. Dont pry too much in one place. Aluminum is weak and easily bent / warped. Gasket surfaces have a small raised edge all the way around the manifold. Use a small flat tip on the rivet extensions ONLY. DO NOT PRY ON THE GASKET AREA OF INTAKE. See pictures below. Once each and every rivet extension budges a little bit, use 2 small flat tips to go around and gently pry apart little by little. You dont want to damage the raised aluminum edge on the flat gasket area or you might have a worse leak when your finished. See below to note what the gasket surface looks like before you pry:
ImageUploadedByMyTractorForum Free App1428095881.774832.jpg
See below 2 pics for how to pry:
View attachment 1217337
View attachment 1217345
5) Once the intake is apart, gently pry out any remaining aluminum rivet material, since ur drilled hole will likely not be exactly in the center of the rivet.
6) After all rivet material is removed, this will allow you to find the original center of the hole better. Now drill it out again w/ 9/64" drill bit one at a time.
7) After each new hole is drilled, insert and tighten a #6 x 5/8" long machine screw to keep everything clamped as you drill the remaining holes (tightening a screw in each one as you go). This will keep holes aligned as you drill each one. If you cant find 5/8" long, use 3/4" long screw (Its only about 1/8" longer than needed).
8) Disassemble and clean gasket surfaces very good w/ tiny flat head in grooves. I also cleaned the inside for smoother flows.
9) I used fine sandpaper sanding parallel to gasket direction to smooth any burrs on gasket surfaces
10) There is NO gasket for the intake halves. Use Permatex Moto Seal 1 Ultimate Gasket Maker Grey.
11) Assemble intake halves using the #6 screws. I used a flat washer and lock washer on both sides of each screw. Flat washer will spread screw force a little better. Lock washer will prevent screws and nuts from unscrewing and creating another future air leak.
NOTE: if any drilled holes ended up too close to intake sidewall, you may have to grind the edge off of that flat washer. See picture below to show what I mean:
ImageUploadedByMyTractorForum Free App1428095728.940090.jpg
ImageUploadedByMyTractorForum Free App1428095759.859068.jpg
This is what the inserted screw looks like w/ 3/4" long screw:
ImageUploadedByMyTractorForum Free App1428095809.244557.jpg
12) Let it dry and Good Luck w/ the carb kit if needed!
 

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Premium Member
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2,224 Posts
smithly
if you have a B 43G you have 18 HP.
also, i have NOS intake manifolds ava for 18.00 plus ship.
thank you. boomer ( the used onan engine parts guy, also NOS and new. )
 

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JD 318 w/ B43
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304 Posts
Discussion Starter #3
Thanks for catching my mistake on 18 HP. Don't know what I was thinking about.

I'll take it! I didn't think they made a gasket for it. I could just use the gasket maker material, but for as much problem as these Onan's have w/ surge, $18 is a decent price for an insurance policy. But I didn't see the intake gasket that goes between the (2) halves on your website. Do you have a link to it so I can order from website over the weekend?
 

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JD 318 w/ B43
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304 Posts
Discussion Starter #5
Oh Ok. I didn't read that close enough. Thanks, but this one is still in really good condition. I don't see any advantage to replacing it unless there is something I am now aware of. Plus I like the ability to take it apart if needed for troubleshooting. Thanks, but I think I'll stick w/ this one and go with the gasket maker. But that is a really good price for an intake!! I did get the carb kit from you already. Will B43 intakes fit a P218? Just curious.
 

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JD 318 w/ B43
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304 Posts
Discussion Starter #6
I posted this b/c when I went to repair it, I couldn't find any info on what size drill bits and screws to use. Just curious if anyone has used any bigger screws?
This was the biggest screw I could find that the flat washer fit against the side of the intake.
 

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Premium Member
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2,224 Posts
smithly
the B43G intakes were used on the P series,
spec A and B, with the carb adapter.
on spec. C and later the carb bolted directly to the manifold.
thank you boomer
 

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Three of my friends
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8,785 Posts
Boomer,will the later intake physically fit the B43/P218 motors?
 

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JD 318 w/ B43
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304 Posts
Discussion Starter #9
Cleaned the intake up slicker than an eel!! You can see the raised sealing surfaces better here. And you can see what a prying flat head does to the raised edges, which is why it is important not to pry on the sealing surface and only pry on the rivet extensions...
ImageUploadedByMyTractorForum Free App1428283162.302239.jpg
ImageUploadedByMyTractorForum Free App1428283176.117603.jpg
ImageUploadedByMyTractorForum Free App1428283195.530870.jpg
ImageUploadedByMyTractorForum Free App1428283207.246689.jpg
 

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Three of my friends
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8,785 Posts
Looks great,a helping hint I got on here is,put the Moto Seal on and leave it set for 5 min,gives it time to kinda set up before squishing the 2 pieces together.Kinda makes the sealer more stable.
 

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61 Posts
Sorry for bringing this back. This is a great write up and thank you. I will be performing this very soon. I do have one question for the op. With the "polishing" you performed on the inside of the manifold I am curious to know how the unit ran after reassembly. Did it require a little more fuel? The reason for my question is most intakes need a semi rough manifold surface to enhance the atomization of the fuel in the air. Sometimes the fuel can form droplets and effect the running of the engine. Usually the exhaust ports are typically the polished side to move the gases quickly.

Thank you,
 

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JD 318 w/ B43
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304 Posts
Discussion Starter #13
Purrs like a Harley. Love the sound of the Onan! Idles perfect and runs great at full throttle. Smooth all the way through. I don't have any attachments yet besides the mowing deck. Doesn't bog down at all
 

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61 Posts
Purrs like a Harley. Love the sound of the Onan! Idles perfect and runs great at full throttle. Smooth all the way through. I don't have any attachments yet besides the mowing deck. Doesn't bog down at all
Outstanding. I just finished and letting it cure overnight then a shot of paint. I have a few days before mowing again with all this rain. :thThumbsU
 

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JD 318 w/ B43
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304 Posts
Discussion Starter #15
Not sure why previous owner choose bumble bee scheme, but it kinda had a unique appeal, so I stuck with it. It is definitely unique! Maybe the yellow intake will help troubleshoot any possible future air leaks??? I really liked the yellow flywheel
 

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Registered
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61 Posts
Not sure why previous owner choose bumble bee scheme, but it kinda had a unique appeal, so I stuck with it. It is definitely unique! Maybe the yellow intake will help troubleshoot any possible future air leaks??? I really liked the yellow flywheel
Wow that looks very nice! Mine is a red Gravely. Don't kick me out for not being a JD! I really like this onan engine. Very unique and timeless.
 

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JD 318 w/ B43
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304 Posts
Discussion Starter #20
Still have to paint the air cleaner too... but you can see the color contrast here. Not for every old fashion JD fan, but it kinda grew on me, so I went back with what the previous owner had done....
 

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