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405 head - What size thread is this?

jamesinc

jamesinc

WD-40 Enthusiast
Joined
Dec 28, 2010
Location
Sydney, Australia
54f3SUPl.jpg


I guess it was originally for the EGR or something? I need to buy a plug bolt to block it but I don't know what thread it is.

I'm also looking for the thread size of the flywheel diagnostic hole on the block.
 
Try a pipe plug, some of the holes on my 160 head were standard pipe thread, or alternatively you could tap out to the next bigger pipe thread size and use that size plug.
 
On my formerly KJet USA '81 244, it was 3/8" NPT, and held the thermal time switch, or whatever they call it. I purchased a 3/8" -> 1/4" NPT adapter, then drilled out the center and tapped to M12x1.5 so that the coolant temp sensor would fit during an LH2.2 conversion.

Edit: Turns out I had a 160 head. Info isn't correct for a 405.
 
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Kestrel said:
On my formerly KJet USA '81 244, it was 3/8" NPT, and held the thermal time switch, or whatever they call it. I purchased a 3/8" -> 1/4" NPT adapter, then drilled out the center and tapped to M12x1.5 so that the coolant temp sensor would fit during an LH2.2 conversion.
Click to expand...

the hole you speak of is betw #3&4 port, this is betw 2&3 and is different cant recall but there was a thread recently about that hole, egr related.
 
vvpete said:
the hole you speak of is betw #3&4 port, this is betw 2&3 and is different cant recall but there was a thread recently about that hole, egr related.
Click to expand...

That's what I thought too, til I got in there. There is indeed a switch between the 3/4 runners, but there's also some kjet related switch/sensor in the 2/3 spot that was 3/8" NPT tapped. May not be the thermal time switch, but... It was something KJet.

Sadly, my car has been taken by another family member, otherwise I'd go take a photo right now and stick it up here, adapter and all. But I assure you, it is most certainly a 3/8" NPT tapped hole leading to a coolant passage.

Edit: Turns out I had a 160 head. Info isn't correct for a 405.
 
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The temp sensor with the yellow wire is 3/8 npt but the other holes in my 405 head were 14mm x 1.5. I used allen head bolts and for the one on the very back cylinder I made a plug out of the allen bolt by cutting the head off. Then I used red loctite on the threads. This way it fit under the intake manifold flange. I cut a slot in it so I can unscrew if I ever need to remove it.
 
Made a mistake! I could have sworn I had a 405 head, but it turns out I've actually got a 160 on my B21. So please disregard my previous posts. I suspect much of it is the same, but who knows whether they moved the placement around or not. The rest of the adapter info and so on is of course going to be good, given the right application. Just may require a different placement...
 
This chart from the greenbook shows what goes in which hole. The hole in question (#2) is for a thermal vacuum switch which is 3/8"-18 NPT.

SensorChart.jpg



The temp sensor with the yellow wire (#3) is 5/8"-18, not 3/8"-18 NPT. The ecu temp sensor is 12mm-1.5.

B234FSenders.jpg
 
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