What's the correct type of bolt for the starter?

Hi guys.

I need to buy another bolt for the starter. It's the fwd left bolt I need.
Anyone know the correct tread, size etc so I can order one? I guess ACS has them?

Thanks!

Lycoming manual states 5/16-18, but no specific length. Lycoming PN is LW-31-0-.94 (so I guess it's .94" long).

Edit - Also, a 5/16" internal tooth lock washer is needed.

bolt

The Lycoming hardware is typically available from companys such as aeroinstock.com, Dart Aircraft in Waco TX etc. Nothing wrong with using a hardware store bolt for starter.

jrs14855 said:

...... Nothing wrong with using a hardware store bolt for starter.

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As long as it is a Grade 5 bolt or bettter, and not one of those soft ones with no marks on the head...

I know this is an old post, but thank you for the info, as mine has fallen out and I didnt know what size it was also.
+1 to VAF once again.

az_gila said:

As long as it is a Grade 5 bolt or bettter, and not one of those soft ones with no marks on the head...

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Second this. Gr 5 or 8, 5/16" coarse thread I believe (can get these at hardware stores around here). Length - try probing the hole and measuring. You want as much thread engagement as you can in that casting attachment.

But whatever length you end up with, make sure it will freely engage the case threads over the full length until tight. If the hole in your case isn't threaded fully, you have something blocking the engagement of the bolt, or the bolt is too long - you might damage the case (very, very bad...). And watch your torque. Did I say it would be bad to damage the casting?

And even with a lock washer, I use thread lock compound since it's coarse into cast aluminum. Just my 2 cents.

...I thought I was replying to the Alf not knowing much about starter attachment. Oh well. Same applies to all.

Although it would probably work fine in this case, I would avoid using grade 8 bolts on aircraft. They tend to be brittle and don't tolerate vibration well.

Is this really a place for a bolt???

Other two visible corners have studs in them.

Mel said:

Although it would probably work fine in this case, I would avoid using grade 8 bolts on aircraft. They tend to be brittle and don't tolerate vibration well.

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I believe I'd have to disagree with you Mel. Properly torqued, they are better able to handle all loads - shear, tensile - than Gr 5 or less. Equally good in fatigue. I have been wrong - someone offer me details or reference.

Yes, Mike. There's a cap screw in the one hole.

Note - theses comments are not intended to imply that anything other than designer specified fasteners should be used in critical load applications. In the case of attaching the starter, the Gr 8, 5 or similar are perfectly suitable.

I used a MS20074-05-06 bolt here. It's 5/16-18, cad plated, was the correct length for my application (Skytec NL starter) and has a drilled head for safety wire. The only downside is they're kind of expensive, but I had a few extra lying around. Some vendors here on VAF have them.

I do agree that a grade 5, 5/16-18 bolt would be just dandy in this application. The local Tractor Supply sells cad (maybe yellow zinc?) plated bolts by the pound.