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IO-320 crankcase bolt

1bigdog

Well Known Member
Top of the IO-320-D1A are 1/4" crankcase bolts. I need to get a few longer ones but can't seem to find a part number.
The parts catalogue seems to show an image of the correct part with a "U" hoist point associated but no number assigned:

figure 1-1 crankcase assembly - right side of image, left of part #15

https://www.lycoming.com/sites/default/files/O-IO-LIO-320 Parts Catalog PC-103.pdf

Any idea what these bolts are or what their equivalent is?

Thanks for the guidance.
 
Top of the IO-320-D1A are 1/4" crankcase bolts. I need to get a few longer ones but can't seem to find a part number.
The parts catalogue seems to show an image of the correct part with a "U" hoist point associated but no number assigned:

figure 1-1 crankcase assembly - right side of image, left of part #15

https://www.lycoming.com/sites/default/files/O-IO-LIO-320 Parts Catalog PC-103.pdf

Any idea what these bolts are or what their equivalent is?

Thanks for the guidance.

Look 6 pages further at figure 1-5, crankcase attaching parts. There they specify what is used which is 1/4-20 by X length.
 
Last edited:
Look for ms equivalents, more reasonable.

MS90725 Grade 5

MS90728 Grade 8
 
Last edited:
Which grade ?

Look for ms equivalents, more reasonable.

MS90725 Grade 5

MS90728 Grade 8


I appreciate the addntl reference. There seems to be some debate about what grade those bolts are. I don't think that was ever resolved.
 
From what I've researched the lycoming bolts are 123000 tensile strength, C26 Rockwell hardness minimum, C32 max.

Grade 5 have 120000 tensile strength, C25 min, C34 max.

Choose enough for me to hold the case halves together.
 
Is there a downside to grade 8

From what I've researched the lycoming bolts are 123000 tensile strength, C26 Rockwell hardness minimum, C32 max.

Grade 5 have 120000 tensile strength, C25 min, C34 max.

Choose enough for me to hold the case halves together.

I'm assuming you meant "close enough". No argument from me. Let me ask a more basic question. Given the superior qualities of grade 8 (the NAS equivalent) is there a downside to using MS90728 for this application?

Thanks
 
yes i meant close enough lol

The grade 8 ms bolts are zinc coated not cadmium like the 5's. besides cost I don't see a downside, but I'm not an expert lol
 
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