Correct material for shaft coupling bolts

[merjan]

I am replacing the old bolts on a split shaft coupling - both those four that squeeze the coupling around the shaft and those that fix the coupling to the gearbox flange. I am wondering what sort of steel is the correct material to use here. I suspect A4 stainless steel wouldn't be the best as they might shear. The engine is a 1GM10 and the shaft diameter is 1". Any advice would be much appreciated!

 

[jwfrary]

In my experience this sort of thing would be a 12.8 steel bolt, but best to refer to the manufacturer if possible!

If it's the yanmar coupling, then it's common practice to fit a grub screw as they have a habit of coming adrift. The same coupling is used with the 26hp engines so I suspect a high grade stainless bolt will be adequate and save you a lot of time if you have to remove it again!

 

[andsarkit]

The Yanmar coupling uses cap head bolts and the R&D version uses hex head bolts. Which one do you have?

You could check with the manufacturer but I would expect that any good quality 8.8 bolt would be OK.

 

[vyv_cox]

Allen bolts suitable for the application, or hex head if more convenient, in 8.8 would be perfectly satisfactory.

 

[Poignard]

The Yanmar coupling uses cap head bolts and the R&D version uses hex head bolts. Which one do you have?
View attachment 150253 View attachment 150254
You could check with the manufacturer but I would expect that any good quality 8.8 bolt would be OK.
View attachment 150255

I wouldn't be happy using those flanged bolts in the first picture.

The diameter of the flange is so large that its inner edge appears to be bearing on the rounded 'fillet', preventing it making full contact.

I would use standard hex head bolts with a plain washer under the head.

 

[merjan]

The Yanmar coupling uses cap head bolts and the R&D version uses hex head bolts. Which one do you have?
View attachment 150253 View attachment 150254
You could check with the manufacturer but I would expect that any good quality 8.8 bolt would be OK.
View attachment 150255

I have the one on the left (I guess that's the Yanmar one?): cap heads to squeeze the shaft and hex bolts to connect the coupling to the gearbox.. I was considering getting Bumax 109 (1000 MPa TS) for both the but it looks like 8.8 or 12.8 would be ok, too.

Does anyone by any chance know if the Yanmar coupling uses metric or imperial threads?

 

[penfold]

It's not very clear from the picture but the casting is relieved for clearance around the flanges.

I wouldn't be happy using those flanged bolts in the first picture.

The diameter of the flange is so large that its inner edge appears to be bearing on the rounded 'fillet', preventing it making full contact.

I would use standard hex head bolts with a plain washer under the head.

 

[emmalina]

My little 120hp perkins has four M10 304 Bolts never been a problem

 

[Poignard]

It's not very clear from the picture but the casting is relieved for clearance around the flanges.

You are right

 

[Tranona]

I have the one on the left (I guess that's the Yanmar one?): cap heads to squeeze the shaft and hex bolts to connect the coupling to the gearbox.. I was considering getting Bumax 109 (1000 MPa TS) for both the but it looks like 8.8 or 12.8 would be ok, too.

Does anyone by any chance know if the Yanmar coupling uses metric or imperial threads?

Metric.

 

[bikedaft]

Metric.















I used stainless 316 about 10 years ago, no problems. Nylock nuts.

 

[PaulRainbow]

I wouldn't be happy using those flanged bolts in the first picture.

The diameter of the flange is so large that its inner edge appears to be bearing on the rounded 'fillet', preventing it making full contact.

I would use standard hex head bolts with a plain washer under the head.

If you look closer at the picture you will see that the surface where the bolt head makes contact has been machine flat.

EDIT Already said.

 

[Poignard]

If you look closer at the picture you will see that the surface where the bolt head makes contact has been machine flat.

EDIT Already said.

Your young eyes are better than mine! I couldn't see it on my mobile's screen until I found a photo of the coupling without bolts. Which I ought to have done earlier.

I plead the lateness of the hour and an excess of strong cocoa.

Can you find it in your heart to forgive me?

 

[PaulRainbow]

Your young eyes are better than mine! I couldn't see it on my mobile's screen until I found a photo of the coupling without bolts. Which I ought to have done earlier.

I plead the lateness of the hour and an excess of strong cocoa.

Can you find it in your heart to forgive me?

My eyes are unlikely to be any better than yours, i just zoomed the picture, on a 40" screen

 

[vyv_cox]

In my experience this sort of thing would be a 12.8 steel bolt, but best to refer to the manufacturer if possible!

If it's the yanmar coupling, then it's common practice to fit a grub screw as they have a habit of coming adrift. The same coupling is used with the 26hp engines so I suspect a high grade stainless bolt will be adequate and save you a lot of time if you have to remove it again!

Does 12.8 exist? I think that achieving such high strength increases brittleness considerably, thus 12.9 is the one I am most familiar with. I think this is unnecessarily strong for the application.

 

[merjan]

I assumed 12.8 was a typo and jwfrary meant 12.9.
Thank you everybody for informative responses!

 

[burgundyben]

Does 12.8 exist? I think that achieving such high strength increases brittleness considerably, thus 12.9 is the one I am most familiar with. I think this is unnecessarily strong for the application.

I thought that too, andsarkit posted a table showing the same.

Curious.