Intake sump stud replacement

I am in the process of installing my Airflow Performance FM-150 fuel servo. Part of the installation requires the stock studs to be swapped out for longer ones. I was able to remove the stock studs without issue but the new ones thread all the way to the hilt (thread less area) with only finger pressure. The Lycoming SP-1776-5-6 manual says the minimum stud driving torque should be 25 in-lbs. I think this is to ensure there is adequate interference to prevent the stud from backing out when trying to remove a nut.

I have the specified sleeve retaining compound and activator ready to go but if I install the new studs with that, the thread lock will be the only thing preventing the stud from spinning out. The stock studs definitely have an interference fit that the new ones do not. As I said, I can thread the new ones all the way in with my fingers while I can?t get a complete turn on the stock studs. I?ve called around to several auto parts places but none of them seem to know anything about studs with tighter (oversized?) threads.

Have any of you run into similar issues? I?m not sure how to proceed at this point.

Oversized studs are widely available. Try a different auto parts store or industrial supply like Kerr Mc Masters.

You may already know this but thread size is different on each end, make sure you have the stud correctly oriented.

Thanks for the suggestions. The new studs are course on the base end and fine on top so no possibility of getting them in backwards. I?ll give Don a call Tuesday. Hopefully he?s seen this before. In the meantime I?ll keep looking for some oversized studs. So far, no luck. Thanks again!

TrueValue

Try Marys Peak or Robnett's True Value -- I had good luck finding studs at my local T.V. store.


Cheers

Stud interference fit

If you use a Lycoming/superior part # they have a interference built in to the thread cut, no need for oversized studs. If as you mention you want course thread/fine thread studs I would suggest using a Continental part # as that?s the style they use. Lycoming?s always use course thread on the end that goes into the case/sump (aluminum) side. You could always just switch to course thread nuts and eliminate the need for the course thread/fine thread studs. I would not use automotive studs in this application as most likely Chinese made of dubious quality and your not getting the engineered inference fit of the special thread cut on aircraft studs.

theduff said:

If you use a Lycoming/superior part # they have a interference built in to the thread cut, no need for oversized studs. If as you mention you want course thread/fine thread studs I would suggest using a Continental part # as that?s the style they use. Lycoming?s always use course thread on the end that goes into the case/sump (aluminum) side. You could always just switch to course thread nuts and eliminate the need for the course thread/fine thread studs. I would not use automotive studs in this application as most likely Chinese made of dubious quality and your not getting the engineered inference fit of the special thread cut on aircraft studs.

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Thanks, I?ll look into that!

bjdecker said:

Try Marys Peak or Robnett's True Value -- I had good luck finding studs at my local T.V. store.

Click to expand...

Thanks, Brian! I happen to know both stores have a large aviation department!

For closure to this thread...
I spoke to Don at Airflow Performance this morning and he said that the studs I have are the correct ones. He specifies Loctite 620 and activator and said ?you?ll need a torch to get them out.?