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Loctite for SDS Fuel Injector Bosses

TASEsq

TASEsq

Well Known Member
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Just completed an engine build (angle valve 360) and we went to install the injector bosses into the cylinders.

The SDS manual calls for the use of Loctite 246 on the threads - however this is unobtanium here.

For reference the 246 is pretty specialised - it’s blue medium strength, but unlike the normal one is useable to 450F. Normal blue loctite 243 is only good to 360F (so not useable for the cylinder heads).

Anyone have any other suggestions on what to use?

Ross is adamant that i need some form of thread locking on these bosses. The threads are 1/8-27 NPT as far as I can work out - so normal practice for a NPT fitting would be some thread sealer (such as 567), however I see nothing in the Lycoming overhaul manual about sealant - found a few references to using a dab of anti-seize. So sure why Loctite 246 Is called out. I’ve asked the question.
 

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This does not directly answer your question, but here are a couple of data points.

My neighbor has an SDS equipped angle valve 540 in his Glasair. He found several loose injectors. He switched to the newly recommended Loctite and he hasn’t mentioned anything about them coming loose. He races Sport Class so his engine sees a bit tougher life than average. He mentioned another racer that also has SDS and found loose injectors.

On his recommendation, I checked my PV 540 during the last CI. I found two injectors loose. I switched to the new Loctite and will check later this month when the CI is again due.
 
N10KE said:
This does not directly answer your question, but here are a couple of data points.

My neighbor has an SDS equipped angle valve 540 in his Glasair. He found several loose injectors. He switched to the newly recommended Loctite and he hasn’t mentioned anything about them coming loose. He races Sport Class so his engine sees a bit tougher life than average. He mentioned another racer that also has SDS and found loose injectors.

On his recommendation, I checked my PV 540 during the last CI. I found two injectors loose. I switched to the new Loctite and will check later this month when the CI is again due.
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That’s a great data point, thank you.

I’m trying to track down some locally - it’s not sold here for some reason. Barry has kindly offered to send me a bottle - so we may have to wait for that to get here. Shouldn’t stop us running it on the truck without it Loctite’d I don’t think.
 
you can try the std loctite hi temp red. I believe it is good into the low to mid 400's. Pretty sure they say the parts must be heated to 500 for removal. If you haven't used this stuff before, DO NOT try to remove those bosses without applying heat via propane torch first. Otherwise could damage things on the AL head. don't believe there are thread serts on those.
 
lr172 said:
you can try the std loctite red. I believe it is good into the mid to upper 400's. Pretty sure they say the parts must be heated to 500 for removal. If you haven't used this stuff before, DO NOT try to remove those bosses without applying heat via propane torch first. Otherwise could damage things on the AL head.
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That area of the head (intake plenum area) is nowhere near the temps deep in the chamber portion of the head where your sensor is, so 400* rated stuff will hold just fine. that area sees constant cool air from the servo internally as well as beieng thin with good cooling air flow externally.
 
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lr172 said:
That area of the head (intake plenum area) is nowhere near the temps deep in the chamber portion of the head where your sensor is, so 400* rated stuff will hold just fine. that area sees constant cool air from the servo internally as well as beieng thin with good cooling air flow externally.
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Thanks. I don’t think I want to go with the red - too hard in case I have to remove it. If I can’t get the high temp 246 then the normal temp 243 (good to 180c / 360f) would be better than nothing i suppose (I would check with Ross first).
 
I'm not a big fan of the red, like previously stated heat releases it but I would go with the common blue stuff if you can't find the recommended version. It's much cooler where you will be applying it (as stated above)
 
Trent,

I have some Loctite 246 down in Hobart, had to import it 12 months ago when I had to re-fit an SDS boss. Happy to mail it over so you can use a few drops....
 
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