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ltn6a

Active Member
Can any of you help,I have an IO-320B1A and im trying to sort out which size prop bolts i have they are marked A988 3 LFC .Any one know what size these are.I have measured the Plain shank which is about .4" the thread is abaout .430" but the internal of the prop flange is about .375 that is inside of the protruding sleve which is about .6" outside dia.I am about to order my Prop so don`t want to get the wrong one.
 
In the certified world....

The brand new prop comes with the appropriate bolts that are for the approved installation. Most prop bolts are the same as AN bolts but usually have an extended thread length. This is so they don't bottom in the flange nut in the crankshaft. The thread length is a little longer in the nut than a regular tension nut.

The first place you should try is the manufacturer of the prop. If it is Sensenich, they usually supply the proper bolts if they have all the pertinent information.

That would be the ideal scenario, its not always that easy.
I would check with whoever is selling the prop, they are hopefully already prepared to meet your reasonable request.

Best Wishes!
 
Hi GAHco

Thanks for the reply,I am going to buy my prop from Vans but i am not sure if the crank flange has 3/8 or 7/16 bolts given the dimensions from my previous post.

Mark
 
Fit test

An easy, no questions approach would be to buy a 7/16"-20tpi and 1/2"-20tpi bolt from your local Lowes or Home Depot aviation supply store and see which one fits!:D You can then answer with certainty which thread your engine crank has.
 
ltn6a said:
Can any of you help,I have an IO-320B1A and im trying to sort out which size prop bolts i have they are marked A988 3 LFC .Any one know what size these are.I have measured the Plain shank which is about .4" the thread is abaout .430" but the internal of the prop flange is about .375 that is inside of the protruding sleve which is about .6" outside dia.I am about to order my Prop so don`t want to get the wrong one.
Click to expand...

Based on the dimensions that you've given, your crank appears to be bushed for 7/16 bolts. The bolt size is the nominal outside diameter of the male (external) thread, also known as "major diameter". For 7/16 that's 0.4375", which roughly corresponds to the "about 0.430" " that you measured on your existing bolts. The "minor diameter" is the outside diameter of the thread root or "groove". For 7/16 UNF, that's theoretically 0.3762". The i.d. of the "nut" or threaded bushings in the crankshaft approximately correspond to the minor diameter of the thread specification for 7/16 (usually the measurement is slightly greater), since the overall ID of a female thread is designed to engage the root or groove of the male thread.

Skylor
 
Hi Guys

Thanks for the posts had another measure to be sure and orderd the prop,Another step closer to what must be the slowest 6a build

Thanks
Mark
 
caryr said:
normally a O-320 is bushed for 7/16 bolts
and a O-360 uses 1/2" bolts
Click to expand...

O-320 can be either 3/8" or 7/16" bolts.
Typically the low compression, 150 hp engines used 3/8", but I have seen 3/8" on some 160 hp engines as well.
 
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