alternator tension arm bolts ?

JimWoo50 · #1 06-23-2011, 09:23 AM

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.

Ironflight · #2 06-23-2011, 10:34 AM

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.

az_gila · #3 06-23-2011, 10:58 AM

Quote:

Originally Posted by Ironflight

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.

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.

JimWoo50 · #4 06-23-2011, 11:02 AM

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.

krw5927 · #5 06-23-2011, 02:38 PM

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.

John Clark · #6 06-23-2011, 07:24 PM

Quote:

Originally Posted by JimWoo50

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.

Almost everything automotive, US included, is now metric.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

az_gila · #7 06-23-2011, 10:09 PM

Quote:

Originally Posted by krw5927

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.

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...

krw5927 · #8 06-24-2011, 06:13 AM

Quote:

Originally Posted by az_gila

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...

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....