Project Katmandu: GS rebuild

[flatdog]

Pete, excellent thread, thanks for showing.
Just a quick Q, by cutting to accomodate the tyre, is the mono lever strength compromised, if so then how are you going to reinforce the mono to accomodate the loss of material?

 

[pete.keys]

Pete, excellent thread, thanks for showing.
Just a quick Q, by cutting to accomodate the tyre, is the mono lever strength compromised, if so then how are you going to reinforce the mono to accomodate the loss of material?

Good question : I am not sure about compromising the strength - I suppose I must be, but i don't know how to work it out or therefore how to compensate for it .. have a spare one on hand just in case ???

 

[pete.keys]

monolever update

more metal has been cut away from the monolever to give clearance

And a plate made to fit over the top:

This now gives 5mm of clearance on the tyre with the 18" wheel rim (like my std g/s) and means that I don't have to offset the rim when it gets built if I only want to use a 130mm tyre. I might get it built with a slight offset for a 140mm.

I still need an 18" paralever front rim though ... hint hint hint

Next I'll have to fashion the lower shock mounting place which I reckon needs to be about here

 

[(RIP) Kaister]

Pete - As a qualified motorcycle engineer and ex-MOT tester, i'd be looking at that extension 'very' carefully.

to me, its not very aesthetically pleasing and looks la bit 'agricultural'
However after reading the thread i can see that it isn't that bad - but your average MOT tester won't know that.

You've put a flange at the shock mount ( point of max vertical reaction ), then cut a big slice off it and also cut away 1/3 of the tube halfway up the overall length- which will reduce your lateral and axial strength

You may want to get an engineers report - i can't see it being passed otherwise.

Just being frank

 

[(RIP) Kaister]

here's a warning

 

[pete.keys]

here's a warning

Blimey - that is a highly modified airhead

Now you have raised this issue I am thinking about how to calculate the effect of the changes that I have done - I have a degree in mechancal engineering, but I did it 25 years ago and fogotten most things since then!!

Some points to note:

The picture above is cast alloy. Failure mode typically quick fracture.

Monolever is extruded steel - failure mode would be more likely to bend and crumple.

The normal mod to do is to extend the swinging arm by inserting a butt welded tube

This is actually a really weak joint. Actually the joint itself is strong but the area either side of the joint is weak and is most likely to form a stress fracture. Interestingly this standard modification seams to be perfectly strong enough for "Dakar" use.

In terms of calculations for strength I think what I will do is work on the effective change of strength in the bending moment of a tube that has a flat put in on one side.

..no where I my old KA Stroud engineering mechanics book ....

 

[(RIP) Kaister]

I have a degree in mechancal engineering, but I did it 25 years ago and fogotten most things since then!!

well mine was only 15 years ago, but i've still forgotten it.

i think what i'm getting at is that the extension is very visible and likely to draw the eye of a tester, more than if it was a sleeve, ground and painted smooth so as no too look noticable.

I'm not saying its 'not' strong enough, just that it doesn't immediately look like it.

 

[pete.keys]

I'm not saying its 'not' strong enough, just that it doesn't immediately look like it.

No worries - I'm not offended - I have the same feeling myself!!

Rarely offended on this site - everyone chips in with their ideas - its a really good forum for that.

likely to draw the eye of a tester

Not sure where you are from - our testers in the UK I think are more relaxed than other countries. Non of that "has to be a TUV approved modification" here. Thats good and bad - but one of the reason people can build so many specials(and potential death traps) here.

Anyway I will think about the strength thing and work out how to do this. Ultimately I guess the only way one really knows it to destruction test it on a press but then I'd be back to square one

Keep your thoughts coming!

cheers

-Pete

 

[Padmei]

I love these mono extension threads. Very interesting reading for a would-be-if-I-could-be-engineer such as myself.

Have you read Stephen Botcher's thread. He has a great moving diagram on the positions of the GS vs G/S shock.

http://www.stephenbottcher.net/BMW/R100ST_2.htm#swingarm


If you did it again would you base your extension around the bottom position of the shock?

Keep up the good work & keep posting pics

 

[ChasF]

The normal mod to do is to extend the swinging arm by inserting a butt welded tube

I assumed that the HPN extension was a plug welded sleeve. I agree, if it is just butt welded mild steel extension, the steel either side of the weld will be brittle

 

[Shurv]

I have to say Pete, your swing arm is starting to concern me a bit,you've taken a lot of metal out of it, and I wonder if it still has the strength needed. You seem to be in a bit of a rush to get it finished,but why don't you hang on and get a proper Moorespeed one.I know he's busy but his work is of the highest standard.

 

[Kenny]

I have to say Pete, your swing arm is starting to concern me a bit,you've taken a lot of metal out of it, and I wonder if it still has the strength needed. You seem to be in a bit of a rush to get it finished,but why don't you hang on and get a proper Moorespeed one.I know he's busy but his work is of the highest standard.

+ 1

 

[carinatauk]

Sorry if this has been mentioned before however with the tight fit of the arm to the tyre, do you intend to run TKCs on your bike? It looks very tight

 

[Shurv]

my understanding is that the main issue is in trying to fit paralever hubs onto monolever swing arms.It's been tried before and it doesn't really work that well. A buddy of mine,Pete Richardson in Milton Keynes, tried it and gave up.I can understand why we want to use Paralever hubs, there is a greater number of tyre options with tubeless,but I don't know of anyone whose managed to crack this particular nut.

 

[pete.keys]

my understanding is that the main issue is in trying to fit paralever hubs onto monolever swing arms..

the issue is fitting a 4bolt monolever bevel drive with a usefull 33/11 ratio to a 3 bolt monlever. The real issue is that for some bloody stupid reason they never made a 4bolt spoke wheel for this config. They are all alloy - which doesn't work on a GS!

but I don't know of anyone whose managed to crack this particular nut.

I know its hard - I have even had people phone me up and tell me its impossible - red rag to a bull really

 

[richie moore]

not impossible i did it years ago just the end result is not good, devon rim built the wheel and even he said it was poor and not to give it any off road use. what is wrong with a 3 bolt with a 32/10 and plus 6% 5th or plus 10% if you really want a high gear.

 

[pete.keys]

not impossible i did it years ago just the end result is not good, devon rim built the wheel and even he said it was poor and not to give it any off road use. what is wrong with a 3 bolt with a 32/10 and plus 6% 5th or plus 10% if you really want a high gear.

nothing wrong with that ... I think that's the way I'll end up in the end

 

[pete.keys]

monolever progress

Not been out in my shed for a few days. Fitted iteration x on my monolever this morning and its looking good (ok barring everyones reservations on the strength aspect!)

This picture shows the issue with the 17" rim. I have the 18" rim on order and should get it this week to send off to the devon wheel company.

 

[pete.keys]

aaargg how do you get nipples out of a hub

Before sending the hub off to the devon wheel co I want to strip off the rim and get it powder coated.

Hacksawed off a spoke and throught the nipple would just punch out ? It won't shift!! Any suggestions on how to remove it? It won't turn with an alen key. I was wondering what size it is 5mm is snug but doesn't quite feel right.

 

[pete.keys]

Engine difference between say 76 R100 and 92 R100

I have been thinking of building up two engines. One high performance one for playing around the UK with assistance from Mr Moorspeed and a 2nd for Katmandu trip, less tuned and capable of running on poor quality fuel.

I have an option on a 1976 R100 engine. They appear to be pretty similar but what is the difference between the 76 R100 and a 92 R100GS engine? Looking at say the siebenrock kit it looks like different barrels... does this mean the crank is different?

Comments on the above greatly appreciated