Engine Mounting Bolt Dimensions

Bewarethemoon

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Can anybody help me with working out the lengths of various engine mounting bolts, predominately the bolts that locate through the frame and engine?

A7F10171-1ED5-4A08-AD43-6B69738EF3FE.png


Part #’s 19, 21, 22 & 24

Any help anyone can offer if always hugely appreciated!

Daniel.
 
On a regular or normal bolt, yes, but none of these are standard types. They're all flange head or dome head. You'll find no lengths indicated in the part numbers. I have a box full of spares I can pull out and measure, but I can't get to it until later, maybe not even until tomorrow (it is July 4th after all, lol). It's been something I've been meaning to do anyway.
 
On a regular or normal bolt, yes, but none of these are standard types. They're all flange head or dome head. You'll find no lengths indicated in the part numbers. I have a box full of spares I can pull out and measure, but I can't get to it until later, maybe not even until tomorrow (it is July 4th after all, lol). It's been something I've been meaning to do anyway.

I’d really appreciated it 5twins, this Titanium journey I’m in has got me deeply down the rabbit hole.

Enjoy your July 4th!
 
OK, finally got some numbers for you. #19, the front bolt through the engine, is an M10 x 100. #21, the long bottom bolt under the engine, is an M10 x 265. It's the longest of the motor bolts. #22, the rear lower, is an M10 x 127 or 128. It's an oddball for sure. There are 3 of the #24 (rear upper) and they're M10 x 70.

I spoke too soon about the lengths not showing in the part numbers. The shorter ones do (#9, 11, 13, and 24).
 
OK, finally got some numbers for you. #19, the front bolt through the engine, is an M10 x 100. #21, the long bottom bolt under the engine, is an M10 x 265. It's the longest of the motor bolts. #22, the rear lower, is an M10 x 127 or 128. It's an oddball for sure. There are 3 of the #24 (rear upper) and they're M10 x 70.

I spoke too soon about the lengths not showing in the part numbers. The shorter ones do (#9, 11, 13, and 24).

That’s great, you’re a legend 5twins! Thanks again for doing this!
 
OK, I found a nice, clear frame drawing in my parts manual collection and did it up, lol. As mentioned above, the shorter bolts do list the sizes in their part numbers .....

kCKlAAs.jpg


And here's another drawing that may be of interest, showing install sequence and torque values. Personally, I like the '77 values, they seem to make the most sense to me. I don't like the way Yamaha jacked the value for the long lower bolt like 25 pounds on the '78 Special. I think that's too much and won't use it .....

oM64GW9.jpg
 
OK, I found a nice, clear frame drawing in my parts manual collection and did it up, lol. As mentioned above, the shorter bolts do list the sizes in their part numbers .....

kCKlAAs.jpg


And here's another drawing that may be of interest, showing install sequence and torque values. Personally, I like the '77 values, they seem to make the most sense to me. I don't like the way Yamaha jacked the value for the long lower bolt like 25 pounds on the '78 Special. I think that's too much and won't use it .....

oM64GW9.jpg

Wow 5twins! You’ve created a really useful data sheet there! I think I’ll print and add it to my collection!

I wonder if I should I adjust the values for titanium? 6AL-4V has a slightly higher PSI rating than 8.8 grade steel?
 
I wonder if I should I adjust the values for titanium? 6AL-4V has a slightly higher PSI rating than 8.8 grade steel?
If you're using steel nuts, I'd stick with the original values. Torque is usually based on the lowest tensile strength of the individual parts... be it bolt, nut, casting, etc...
 
Something else I'll mention is that even though the original nuts are a locking type, they don't seem to grip as well after they've been on and off a few times. Because of that, I add regular split ring lock washers to them.
 
Something else I'll mention is that even though the original nuts are a locking type, they don't seem to grip as well after they've been on and off a few times. Because of that, I add regular split ring lock washers to them.

To all nuts used 5twins?
 
All the motor bolt locknuts, when possible. But there are a couple that won't allow it, they're a little too short. On my '78, those are the long bottom bolt and two of the three upper rear bolts (ones through the frame). If you're making them from scratch, you might consider making those a few MM longer to allow fitting a lock washer. If nothing else, I highly recommend fitting lock washers to the M8's in the top motor mount. You have to remove them quite often for head bolt re-torques.

I feel the motor mount bolts are something that needs to be checked from time to time, just like the head bolts. When I first got mine, I checked them. I found not one or a couple, but ALL the bolts loose, lol.
 
All the motor bolt locknuts, when possible. But there are a couple that won't allow it, they're a little too short. On my '78, those are the long bottom bolt and two of the three upper rear bolts (ones through the frame). If you're making them from scratch, you might consider making those a few MM longer to allow fitting a lock washer. If nothing else, I highly recommend fitting lock washers to the M8's in the top motor mount. You have to remove them quite often for head bolt re-torques.

I feel the motor mount bolts are something that needs to be checked from time to time, just like the head bolts. When I first got mine, I checked them. I found not one or a couple, but ALL the bolts loose, lol.

Thank you so much for taking the time to respond to this thread 5twins, I feel your advice is invaluable and therefore indescribably appreciated by myself.

With the help of this forum I’m going to build one hell of a XS650!

Daniel.
 
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