Coupler Bolts

[Speakrdude]

Hey guys, (Gals), Is there a preference to the hardness of bolt the connects the coupler to engine? The thinking here is maybe the bolts would shear before the shaft or coupler did.

Grade 3, 5, stainless, Grade 8?

It looks to me like a 3/8" or 7/16" diameter x 1-1/2 long bolts.


(I just read an older post and Don mentioned Grade 8. I also found on Doug Russels site, the specs ressemble a bolt, 7/16 x 1-1/4. However, is this bolt without threads for the 1" through the coupler and 1/4" of threads at the end?)

Thanks

 

[greg82255]

Re: Coupler Bolts

I don't know what Mercruiser recommends, but considering those bolts are responsible for transferring power from the engine to the drive, and if they break you need to pull the engine, I'd be going with grade 8.. They only cost about $1 each.

As for the question about threads, what kind of drive are you working on? The couplers are different for alpha vs bravo.

 

[achris]

Re: Coupler Bolts

The bolt needs to be plain on the section that passes through the coupler and the flywheel, and only thread into the crankshaft. If you have sharp thread peaks in the flywheel holes or coupler holes, then they will cut in, especially the coupler and allow too much backlash in the setup, leading in turn to high stresses and eventual failure of the parts.... and yes, grade 8 steel bolts....

 

[Speakrdude]

Re: Coupler Bolts

I guess I was a little vauge, huh? The set up is an 88 Sea RAy 300 WE, MIE setup with straight through Inboard, Borg Warners, The couplers I am speaking of are external the transmission and connect to the prop shaft.

If you can read this (small) part # 10-11-12

 

[achris]

Re: Coupler Bolts

.... of bolt the connects the coupler to engine? ...

Nope, not vague at all.... I know exactly where that is...

I guess I was a little vauge, huh? The set up is an 88 Sea RAy 300 WE, MIE setup with straight through Inboard, Borg Warners, The couplers I am speaking of are external the transmission and connect to the prop shaft.

If you can read this (small) part # 10-11-12

Way too small to read. As I wrote before still applies. Plain bolt through the flanges, just enough thread to pick up and tighten down the nuts. Use grade 8 steel bolts with lock washers. Minimum of 3 threads exposed when the nuts are tight...

So if each flange is 1/2" and the nut is also about 1/2" thick, I'd use 2" bolts, that have 1" of unthreaded shaft.

HTH,

Chris...........

 

[Speakrdude]

Re: Coupler Bolts

Great. Thanks Chris.