Flange/coupler bolts

[John F.]

A transmission flange to coupler bolt sheared on Crows Nest. I’m guessing that the bolts have been on there at least 18 years and are pretty corroded. They’re not stainless. Can I use stainless and locknuts for replacements? Or are the bolts a specific hardness? Should I get them from my local prop/shaft shop or the hardware store? Any idea on proper torque? Crows Nest has 300 hp Detroit diesels. Thanks.

[Carl]

Use Grade 8- fine thread hardware for coupling bolts. Do not reduce the nominal size. A 7/16 hole in couplings should have 7/16-20 hardware, 1/2" hole, 1/2-20 hardware etc. I mention as fine thread hardware is not as readily available in hardware stores and some go , "eh, it's close enough".

Do not use Stainless steel hardware for the couplings.


Can be found at Quality hardware stores, and prop/marine machine shops. Or online - **McMaster Carr, Fastenal among others.

[John F.]

Thanks Carl. Just what I needed to know. I’ll just go to my prop/shaft guy and have him set me up.

[Rawleigh]

McMaster Carr will also have them.

[Marshall Mahoney]

Could have sworn mine bolts were metric. Inspect the gearbox coupling "centering ring??" prior to reassembly. When my bolts sheared, the centering ring got a small ding in it that prevented me from aligning the shaft. Took me forever to figure out the issue. Had to file the defect down.

[John F.]

I went to Kastel Brothers in St Michaels. They did the shaft/coupler work for me a few years ago on the port side. They miked up the bolt I brought with me, set me up, I bolted it back together, and ran her yesterday. She’s fine. Thanks for the help.