850 commando crankshaft studs

Hi All, can anybody tell me why I have 2 studs longer than the others & why there are normal length nuts & long ones. The c/shaft was balanced before I bought it, if I change the studs should it be rebalanced?
Thanks in advance for your replies, Paul.

hayabusaman0 said:

Hi All, can anybody tell me why I have 2 studs longer than the others & why there are normal length nuts & long ones. The c/shaft was balanced before I bought it, if I change the studs should it be rebalanced?
Thanks in advance for your replies, Paul.

Click to expand...

The 2 longer studs with 4 longer nuts should be in top of the crankshaft and yes if you change these your crankshaft will be rebalanced but only to an amount you won't notice!

hayabusaman0 said:

Hi All, can anybody tell me why I have 2 studs longer than the others & why there are normal length nuts & long ones.

Click to expand...

Apparently, those two long studs with longer nuts are there to make it easier to fit a spanner on them (according to Mick Hemmings) as they are both close to the big ends.
(see section C27 of the factory '70-'73 manual for stud/nut positions)

Yes, I took apart my 69 750 crank the other day and the top two bolts were longer with long nuts on them, the next two were bolts with shorter nuts on them and the bottom 2 were double studs with nuts on each side and a tab washer on each side also with the short nuts. I think the 850 is a bit different, but I don't know how. OldBrits seems to have the correct ones, but I found Mick Hemmings has them at quite a bit less, but different configuration. I'm calling him tomorrow.

Dave
69S

...and so are these tab washers to be properly bent over? :shock:

The lock plate ain't to lock nuts only pure torque, staking and belief in heated red stud loctite does that, its just to hold dowel in. Soft steel so tends to crush down loosing clamp force and is not supposed to bend over the nuts, so leave flat if used.

hobot said:

The lock plate ain't to lock nuts only pure torque, staking and belief in heated red stud loctite does that, its just to hold dowel in. Soft steel so tends to crush down loosing clamp force and is not supposed to bend over the nuts, so leave flat if used.

Click to expand...

That's what I figured/hoped...

Interestingly, the factory service manuals tell you to fold over the locking tabs after assembly. The manuals mention that the nuts are staked with a punch at the factory, and will be difficult to turn, but do not direct you to stake the new ones after assembly, only to use the locking tabs.

When I started racing with 750 Commandos in the '70s, I rebuilt several crankshafts by re-using the original nuts, studs, and lock tabs, and never had a problem with them. I usually had the studs and nuts magnafluxed along with the crank parts every time an engine was apart. I used red Locktite and never had a nut come loose. In fact, you could tell that the Locktite was still holding strong by the effort it took to take the crank apart next time. I don't believe the crankshaft ever gets anywhere near hot enough to affect the Locktite bond.

Ken