How thin can you go on triple clamps?

[tkent02]

Can I bore 35mm clamps to use 37mm fork tubes safely? How thin can you go without making it too weak?

 

[hampshirehog]

I've done it. I've no idea if it's safe but, to quote the Aussie politician, the front didn't fall off. It seems to me there's plenty of meat on there and it's only 1mm in radius.

 

[tkent02]

OK. That sounds right. There are four of them holding it together after all. They can't possibly all break at once. Can they? I'm sure Suzuki put at least an extra mm in there just for the what ifs. "What if some twatwaffle hits a lorry? Will the forks break if he hits a lorry?"

Have you taken more than 1mm off and had it not break?

Can any old machine shop do it?

 

[posplayr]

Can I bore 35mm clamps to use 37mm fork tubes safely? How thin can you go without making it too weak?

No simple answer. Assuming the did a decent job in the design to start with and there is no stress risers then compare the thinnest dimension score and after boring. The 35mm to 37mm bore is only 1mm off on any side so it is probably ok. In general I would not recommend it.

Unfortunately a failure could still mean they all go at once. If one (the weakest) goes suddenly three are now taking the load leading to the next weakest breaking then you are down to two for the same load. You see where I'm going. Under external load, If one goes expect them all to go.

 

[Steve]

I also find it interesting that you are willing to weaken one area just to make another one stronger. :-k

The larger forks would add to the strength and rigidity of the front end, but might also transmit a bit more shock load to the (now weaker) clamps.

So many of these bikes are still moving around (and quite well) on 35mm forks with no apparent problems. Unless you are setting one up for the extra loads of racing or off-roading, what do you really hope to gain with the larger forks? :-k

I am thinking it might be an exercise in futility.

.

 

[tkent02]

More room inside to convert it to a cartridge fork. Don't care how it moves, trying to get it to ride smoother.

 

[hardline_42]

What bike are the donor forks coming from? It seems like it would be much easier to swap over the entire front end, including the triples. GS850G forks are 37mm and so are GS500 forks. They should all use the same steering head bearings. I've got a 41mm SV650 front end in my garage waiting for a future swap onto my GS450.

 

[Guest]

Can I bore 35mm clamps to use 37mm fork tubes safely? How thin can you go without making it too weak?

Depends. How much material is there now with the 35mm forks?

OK. That sounds right. There are four of them holding it together after all. They can't possibly all break at once. Can they?

No, the first one would fail which would overload the next one in line which would fail, then the next and so on.

Can any old machine shop do it?

Most likely. You just need someone with the capacity to line bore both clamps together in one setup to ensure that they are a matched set. Will your pinch bolts clear the bigger fork tube?

What bike are the donor forks coming from? It seems like it would be much easier to swap over the entire front end, including the triples.

That sounds like a much better choice. OP, if you are looking at this to help with the cartridge conversion we discussed I would say that swapping to a complete front end with a modern fork that already has shim stack damping would be much easier. If you want to keep the classic GS look then this may be the better option.


Mark

 

[tkent02]

This is for my 550. Not interested in swapping forks on this bike. Got the single brake working well, want to keep it how it is. Don't really want to make a lot more work for myself. Considering swapping fork internals to make this fork into a cartridge fork. Going to 37mm would give a little more room inside for the cartridge. I have a set of 37mm forks from a GS1000 sitting here.

Could also swap steering heads, but I think all of the 37mm GS steering heads would put the fork tubes farther apart, again making more work for myself.

 

[hardline_42]

Could also swap steering heads, but I think all of the 37mm GS steering heads would put the fork tubes farther apart, again making more work for myself.

If that were the case, wouldn't it just require some spacers? If you're going to have machine work done anyway, I think machining spacers would be a safer route to take than boring the clamps.

 

[tkent02]

If that were the case, wouldn't it just require some spacers? If you're going to have machine work done anyway, I think machining spacers would be a safer route to take than boring the clamps.

Yeah, that's probaby a better plan.

 

[posplayr]

This is for my 550. Not interested in swapping forks on this bike. Got the single brake working well, want to keep it how it is. Don't really want to make a lot more work for myself. Considering swapping fork internals to make this fork into a cartridge fork. Going to 37mm would give a little more room inside for the cartridge. I have a set of 37mm forks from a GS1000 sitting here.

Could also swap steering heads, but I think all of the 37mm GS steering heads would put the fork tubes farther apart, again making more work for myself.

If you put a flat screw driver into the cut of the clamps, you might be able to open them the amount required to slip the 37mm ones in. When you tighten it down it, the aluminum will "conform" to the steel.

 

[tkent02]

If you put a flat screw driver into the cut of the clamps, you might be able to open them the amount required to slip the 37mm ones in. When you tighten it down it, the aluminum will "conform" to the steel.

Like that idea a lot better, it seems like it would be stronger, and safer unless something cracks. Any metals experts here? Is that safe to do as long as it doesn't crack? I need to go see how much it would need to be opened up. I have a bunch of spares to practice on.

Thanks for the idea.

 

[Agemax]

expanding cast aluminium by even that small amount will DRASTICALLY weaken it. That is if it doesn't snap or crack anyway before you manage to shoehorn the fork leg in.

 

[salty_monk]

Are you sure the 1000 triple clamps are wider? I would think that the centers are the same...

 

[posplayr]

expanding cast aluminium by even that small amount will DRASTICALLY weaken it. That is if it doesn't snap or crack anyway before you manage to shoehorn the fork leg in.

I have tweaked a set of welded triples clamps much more than I would have ever thought possible with no ill effects.

The clamps are made to flex, it has to to be able to implement a tightening bolt. So I suspect the metallurgy is substantially more flexible that a piece of simple brittle cast aluminum. Just think about the forces on the triple clamp transmitted from the road, through the tire/wheel and with the leverage it has through a RSU stanchion. The triple can not be inflexible and brittle.

 

[tkent02]

Are you sure the 1000 triple clamps are wider? I would think that the centers are the same...

Yes, something like 10mm wider. No big deal I guess.

 

[hampshirehog]

I don't think that forcing the clamps wider is a runner. The circumference would need to increase by 6 mm if I've done the maths correctly and I doubt the bolt holes would line up. When I did mine I just reckoned there was enough meat there to enlarge the holes.

As for can the work be done by your average machine shop, well I did the work myself using a plumbing reaming tool that my old chap had in his garage - no idea what it's called. I never measured how round the holes were and I may have only made them 36mm and a bit wide were, I just test fitted and they weren't far out and you certainly couldn't see air when they were clamped up.

 

[posplayr]

I don't think that forcing the clamps wider is a runner. The circumference would need to increase by 6 mm if I've done the maths correctly and I doubt the bolt holes would line up. When I did mine I just reckoned there was enough meat there to enlarge the holes.

As for can the work be done by your average machine shop, well I did the work myself using a plumbing reaming tool that my old chap had in his garage - no idea what it's called. I never measured how round the holes were and I may have only made them 36mm and a bit wide were, I just test fitted and they weren't far out and you certainly couldn't see air when they were clamped up.

yes there is a potential alignment issue that might require some adjustment.

Lets say that the diameter of the hole needs to be enlarged by 2 mm, that means that the clamp spacing (at the edge of the tube) needs to enlarge by approximately twice the increase in diameter of 4mm in this case.

Assuming the split was at the center of the clamp opening then you would have a 2 mm deflection on each side, granted that is more than the machine tolerance of the home, but certainly not that much compared to the total deflection you can put on the clamp to close the gap.

In the worst case, you could do something like split the difference, and increase the diameter by 1mm and spread the clamp by 2 mm (1mm per side) to achieve the desired result. I would much rather bend than remove material.

Thoise triples are much more resilient than you might imagine, but stiffness is proportional to the cub of distance so you loose a lot once you start milling.

 

[Jcgonzal]

expanding cast aluminium by even that small amount will DRASTICALLY weaken it. That is if it doesn't snap or crack anyway before you manage to shoehorn the fork leg in.

I'd have to agree with this. I tried it on a '77 XS750 back in the day, and sure enough I was able to snap the triple tree. It was in the middle of winter in a not so heated garage, which probably contributed to the brittle nature of the material, but nonetheless....