Topic: Why did Honda create the "adjusting bolt"?

[Hush]

OK I'm working on a 1991 L model CBR400RR, neat bike, nice to be working on a Honda again.
It's all going together fine but something puzzles me, the rear upper engine mounting bolt which passes right through from one side of the frame to the other, normal in every way but one....Honda fitted a big fat oversized threaded adjusting bolt which requires a "peg spanner" to remove and refit it.
What is it?
Why is it?
Is it important or did Honda just have a brain fart, why not just stick a normal nut and washer on it?
Anyone??

[dave500]

to stop tampering?does it have to clear the frame with suspension action?

[Hush]

Bike has monoshock Dave, the bolt (axle) that goes from one side of the frame to the other is about half a metre long.
There are two 5 centimetre spacers between frame rails and rear engine mount so it's quite a long section to be playing with.
I just don't see the justification for having such a gee-whizz nut/bolt type thing on the end, why not just a nut?
They also used one of these on the swing arm pivot axle, maybe they just had a few million spare floating around the factory and thought " lets get rid of these and look cool in doing it"!

[dave500]

got a photo for us?

[Hush]

First photo is where it goes in from the side of the bike, next is a photo of it removed where you can see the large thread that screws it into the frame rail, it has a hex key end too. Next shot is to show it's mate lower down which the swing arm pivots on, last shot is looking down onto the long axle bolt that runs from one side of the frame rails to the other, the tube things are spacers which it also runs through.
It's got me stumped why Honda would do this and Google hasn't helped, it's my son's bike which he will be going very fast on so I'm just being a bit anal about everything I do to it. I'd love to know how vital to the bike's handling these things are?

[simon#42]

its done so that the swing arm is an exact fit in the frame and there is no need to mess with shims etc .on the race bikes there is a torque setting for the inner part . the tool for the lock nut is only cheap and makes the job much easier . on the other hand and if your a cynic , its done because honda cant make a swing arm that fits the frame .
and oh yes it is important to the handling

[Hush]

Thanks Simon, I can understand the use of this strange device for the swing arm, as you say it allows for adjusting the play in the arm but the upper adjusting bolt still has me bemused. It's only possible use would be (to my mind) to wind in the flex of the allow frame rails but in this it fails as once it makes contact with the spacer tubes it cannot do any more, plus the whole front of the frame is one piece solid welded alloy.
Guess I'll never know.

[w1sa]

I think they are designed that way to spread the torque/load of the steel bolts/nuts/pivots onto the alloy frame/fixing points.....to eliminate excess stress and wear, of the alloy frame.  Cheers..     

[Hush]

Yeah the more I look at it, they seem to be a fancy way to take the adjustment out of the frame mounts.
I guess I'll screw it in until it hits the spacer then lock it with the locking ring and then throw the end nut on.

[754]

 I dont think its a fancy way..if the frame cant close up, which it looks like it cant, then other means must be used..

[Hush]

So you think it's because of the welded alloy frame then 754, yeah I guess on our older bikes there is some give in the mounts when we put a motor in then bolt it up.

[754]

I think it does away with shims, and is a quicker way to set it up

[robvangulik]

Can't be true, for the CBR1000F I use for transport for the last 25 years has a steel frame, and the same adjustable bolt with nut in the upper engine mount.
In my experience it makes putting the engine in the frame a lot easier.....

[Hush]

Yeah got it now, easy way to take the play/slack from the engine mounts, just wind it in until it puts pressure on the spacers and then lock it up with the castle type lock nut then put the actual engine bolt nut on.