J

JimWoo50

Well Known Member
Just getting ready to put together an order to aircraft spruce and No time to drive to airport to check bolt sizes for alternator tension arm. I know the case bolt is an-5 by three quarters coarse thread but what size is the bolt for the tension arm into the alternator and what type thread? Thanks a bunch. Jim. Hope to start the engine real soon.
 
That depends on your alternator Jim - if it is one of the ND automotives, it is likely to be metric - I want to say 10 mm, but not sure.
 
Ironflight said:
That depends on your alternator Jim - if it is one of the ND automotives, it is likely to be metric - I want to say 10 mm, but not sure.
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If it is a "standard" Lycoming type alternator, the parts manual has both bolts the same at a STD-1817 which is a -5 coarse thread and 3/4 inch long.
 
automotive alt

Its a automotive type alternator originally for a subaru samurai i think the model number was 1487. Thanks for the replies I never even thought it would be metric.
 
I have an auto alternator, it's a ND for a Honda. I can say with certainty that mine is NOT 5/16-18 (coarse) or AN5 fine thread, because I have tried both. They both seem a little on the large side, although the fine thread bolt does thread in about 3/4 of a turn before stopping (by hand only, of course). AN4 will definitely be too small though. I'll try 10 and 8mm next, but guessiing that it's 8mm.
 
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Metric

JimWoo50 said:
Its a automotive type alternator originally for a subaru samurai i think the model number was 1487. Thanks for the replies I never even thought it would be metric.
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Almost everything automotive, US included, is now metric.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
krw5927 said:
I have an auto alternator, it's a ND for a Honda. I can say with certainty that mine is NOT 5/16-18 (coarse) or AN5 fine thread, because I have tried both. They both seem a little on the large side, although the fine thread bolt does thread in about 3/4 of a turn before stopping (by hand only, of course). AN4 will definitely be too small though. I'll try 10 and 8mm next, but guessiing that it's 8mm.
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That would make it a M8 Fine with a 1 mm thread pitch.

Your 5/16-24 bolt has a 1.06 mm thread pitch, so it almost worked...:)
 
az_gila said:
That would make it a M8 Fine with a 1 mm thread pitch.

Your 5/16-24 bolt has a 1.06 mm thread pitch, so it almost worked...:)
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Went to the aviation aisle at my local home improvement store and bought some M8x1.0 fine thread and some M8x1.25 coarse thread bolts. The M8x1.25 were perfect (but a little short). Now to find some cad plated ones that will be aluminum friendly. Unfortunately after an extensive online search I found no mil spec aerospace fasteners with metric threads (imagine that). Guess I'll have to settle for Grade 10.9 yellow zinc plating from Fastenal.

Wonder if I can pick up some cad plated metric bolts when I'm in Germany later this year....
 
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