Intake crack

Engine, Transmission and related drivetrain.
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WxMan
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Intake crack

Post by WxMan » 08 Apr 2016 17:01

I have a Kyokuto intake for twin weber DCOE 40's that came with my car when I purchased it a few years ago. In the process of disassembling everything and cleaning it all up I noticed that a crack had developed in one of the threaded ports on top. As you'll see in the photo the crack is fairly substantial. The base of the crack is pretty much at the bottom of the plug threads. I'm no expert, but I do know that once cracks start they generally like to spread. Is there a practical way of fixing this thing? If possible I'd prefer to be able to salvage this intake as it is a bit shorter than the Cannon intake that would be the most likely replacement option. It also positions the carbs at a slight offset angle to each other which is a bit odd but gives things a slightly different look.

I did some searching and couldn't find much information about this intake online. It doesn't seem very common. I'm guessing it is very old. All I really came across was some six cylinder Z car versions. Also, and please forgive my ignorance, that port with the crack in it, what is it for exactly? Some intakes seem to have these and some don't.

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(old photo from before the great tear down started two and a half years ago...)
Russell

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okayfine
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Re: Intake crack

Post by okayfine » 08 Apr 2016 18:25

Sure, can easily fix it if you have access to a TIG welder, or know someone who does. Picture isn't that big, but if that crank only goes down towards the runner 1/8" or so as it seems, that could be welded up and the hole retapped, if you wanted to retain the ports.

Jason Grey's old site talks about branching the individual runners together via something like AN6 lines to smooth out the intake pulses. Not a huge deal, else all manifolds would be running them. I'm sure Vizard has some wisdom to share about that in one of his books.
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WxMan
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Re: Intake crack

Post by WxMan » 08 Apr 2016 19:19

Thanks Julien. I was hoping it was no big deal. Unfortunately I'm not a welder, nor am I well acquainted with one. I guess it's time to make some new friends. :)

I'll investigate further into the intake runner branching just because I'm curious about it. I have no doubt that you are correct that if it was really that beneficial all intakes would be set up similarly.
Russell

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Re: Intake crack

Post by greenthumb » 08 Apr 2016 19:41

Any idea if that threaded bung would have been bspt? Maybe someone put a standard pipe thread plug in there, hence the crack?

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WxMan
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Re: Intake crack

Post by WxMan » 08 Apr 2016 19:50

I'm not sure which type of thread it is, but I'm pretty sure it has a taper to it. Given that the walls of that hole are so thin it could have easily cracked if the plug was tightened just a bit too much.
Russell

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Re: Intake crack

Post by datzenmike » 08 Apr 2016 21:11

Remove plug and clean it and the threaded bung hole. Mix up and spread spread some JB weld on the threads. Tighten. Make sure the crack has some on it. About $8.
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WxMan
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Re: Intake crack

Post by WxMan » 08 Apr 2016 21:22

My first instinct was JB weld but I figured it wouldn't be good enough. I wasn't thinking about sealing up the bung permanently though. Thanks Mike.
Russell

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Re: Intake crack

Post by Byron510 » 08 Apr 2016 22:57

datzenmike wrote:Remove plug and clean it and the threaded bung hole. Mix up and spread spread some JB weld on the threads. Tighten. Make sure the crack has some on it. About $8.
Remove the plug and simply use some loctite thread sealer on the threads. Keep the repair simple. There's no sense in welding up the bung if you never need it, and it's only purpose is to seal the intake runner from a vacuum leak.

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WxMan
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Re: Intake crack

Post by WxMan » 08 Apr 2016 23:15

Hi Byron,

I will take a very close look and make sure the threads of the plug go down past the bottom of the crack. If they do then I will likely give your suggestion a try first. I'm sure I can rig up some sort of pressure test to be certain that it holds before I put it back in service. If it doesn't work then I'll take more drastic measures. Thanks for the input.
Russell

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Re: Intake crack

Post by Three B's Racing » 11 Apr 2016 07:20

okayfine wrote:Sure, can easily fix it if you have access to a TIG welder, or know someone who does. Picture isn't that big, but if that crank only goes down towards the runner 1/8" or so as it seems, that could be welded up and the hole retapped, if you wanted to retain the ports.

Jason Grey's old site talks about branching the individual runners together via something like AN6 lines to smooth out the intake pulses. Not a huge deal, else all manifolds would be running them. I'm sure Vizard has some wisdom to share about that in one of his books.
Julian is correct but a lot of dual carb manifolds are branched. Look at SU carb manifolds from the factory and a ton of Cannon/BRE dual Weber/Mikuni manifolds their branched. However, a lot of race motor manifolds are not branched because well, their running at full song pretty much all the time. Me, I'd branch them but first I noticed there is a support bridge between intake ports two and three, I'd have a look inside the ports to see if that support is branched.
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