Help a DIY newbie - is it safe to spread the forks?

Greedings to all!!

Although new to ES forums I read articles here for a month or so...

I am in the prosess of making my first DIY project for my girlfriend and I just found a bargain used dahon d3 curve...

I was planning to use the cute x85 or something motor that BMS battery makes as it is the narrower motor I could find at 83mm....

Before buying it I called the local dahon dealer to find out the fork dropout and material of the D3 curve, to see if I can fit the motor on it...

I was not so happy to hear that D3 curve's fork was only 74mm wide, but thankfully I was informed that it was made of cromolly not alloy as I first thougt..
I heard that a lot of people spread their forks even more than 1cm to fit their motors in cromoly forks, so I thought it was ok...

The dealer though, told me -as soon as I told him that I would spread the forks 9mm (possibly up to 11mm to fit the nuts and bolts needed)- that it will not be safe to do this as it will affect the welds and therefore risk a crack!!

So I am asking, what do you think is the case?

1) does dahon welds and materials so inferior to bromptons that will indeed be a problem?
(I am saying this because a co-forumer from pedelecs.uk forum already did this with the same motor succesfully on his brompton which has a 75mm fork)

2) It has to do with the fact that the fork is too short given the 16in wheels? Because As he stated all 16/20in dahons has 74mm forks and I think I have seen a lot of front mount dahon conversions in the past... Is there somewere a smaller motor or the did it the same way as I was planning?

3) Dealers ignorance and/or repulsion for electric bikes (that are not the dahon boost they sale at a ridiculusly high price) was the reason for discourage me from that project...

I want to believe that the right answer is number 3, but I need to know and you know, you are the experts!
I am running out of time here, tommorow I sould decide whether to buy the D3 or not and I dont want to buy a bike I will not be able to convert to electric...

Cheers to all in the community, you do a great job here!

John

Not forks but information on spreading frames here:
http://www.sheldonbrown.com/frame-spacing.html

Before you do anything make sure the forks aren't aluminum, simple magnet test will do.

If you are careful and take it slow I don't see an issue spreading the front forks 5mm per side. The welds should be as strong or stronger than the forks themselves. If not, the welder didn't do his job right.

I have spread STEEL front and rear suspension forks using either AllThread and nuts.washers or a jack for years now on many bikes. I even got my LBS to do a front fork for my wife's Bike-e. I have spread some over an inch with no problems except to re-align the dropouts with a big taped crescent wrench. I thought there were some Bafangs and Cutes maade specifically for 70-75 mm front dropouts for those folding bikes? Gaerlan in California has really good information and smarts for folder people. You might want to call him.
otherDoc

Many thanks for the quick replies! Fist of all I don't know the difference between cromoly steel and simple steel. A magnet affects cromoly the same way as steel?

Contacting ecitypower(cute motors manyfacturers) retailers, BMS battery, I found out tha 83mm is the narrower motor I can find..

tsakis said:

Many thanks for the quick replies! Fist of all I don't know the difference between cromoly steel and simple steel. A magnet affects cromoly the same way as steel?

Contacting ecitypower(cute motors manyfacturers) retailers, BMS battery, I found out tha 83mm is the narrower motor I can find..

Click to expand...

Wikipedia said:

41xx steel is a family of steel grades, as specified by the Society of Automotive Engineers (SAE). Alloying elements include chromium and molybdenum, and as a result these materials are often referred to as chromoly steel or CRMO. They have an excellent strength to weight ratio, are easily welded and are considerably stronger and harder than standard 1020 steel.

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So a magnet will still stick to cromoly steel, its just a grade of steel that is much stronger and ligher than standard steel.

Before you do anything make sure the forks aren't aluminum, simple magnet test will do.

If you are careful and take it slow I don't see an issue spreading the front forks 5mm per side. The welds should be as strong or stronger than the forks themselves. If not, the welder didn't do his job right.

Click to expand...

So you suggest that if everything goes right with the spreading there is no problem that might face after, say a crack when riding for example..

tsakis said:

So you suggest that if everything goes right with the spreading there is no problem that might face after, say a crack when riding for example..

Click to expand...

Google the bike manufacturer for weld failures. If you find any for your bike type don't do it. If the bike is properly welded the weld is not a weak point. If the welds are shoddy then it is.

I'm a half-a$$ed welder but none of my critical welds have failed. I take my time if a weld is load bearing, just as a bike builder should.

+1 to what Stanz said. My Steintrike is made from something called Stanismans St52 German steel and has a decidedly springy feel when I had to widen it for the 9C I put on. I think that this is like the cr-moly stuff the better bikes are made out of. It takes some effort to get it to the right width as it springs back a lot. The cheep Wal-mart type used bikes I have previously used on my home built trikes are cheep steel but take their set much more easily. I'm not sure that was a good thing but I never had any fail in about 12 or 13 rear test suspensions. I did learn to use torque arms though as I spun several motors in the steel dropouts, at least the cheep ones but these were on heavy trikes at 54 volts and 20" wheels.
otherDoc

imho that is a bit too far. the dropouts will have an slight angle if you do that, thus the securing bolt won't attach to the fork as well. I would swap out the fork or use another bike honestly.

Hey Nep. that's less than 1/2 inch spread or 1/4 each side. He should check with Gaerlan who builds these things. They do however make wider forks that fit the Dahon's for just such an event. It sounds ok to me in STEEL! Never alloy.
otherDoc

Well I dont mind cracking the welds while I am doing the spreading... I dont wont to risk my girlfriend from the unpleasant situation of a cracked weld while riding...

If I manage to spread it with no cracks it will be a problem afterwards?

Actually since there are forks of the correct width for the front of those folders it would be more prudent to get the right one, especially if it is for a loved one. Also my rule is to always put 2 torque arms on all front motors. I would only use STEEL front forks anyways. Nep does have a good point and I did my gonzo spreading on rear STEEL forks except for my wife's bike-e. There I got some pro help!
otherDoc

I'm going to agree with Nep, Doc, and the others who suggest that you find another fork or bike.

The problem that I see here is that you'll never know if you've damaged/cracked the fork until you:

1. Subject it to an suitable form of non-destructive testing.

2. Have it fail on you, or your significant other, while riding it.

Also keep in mind that a rear wheel failure, due to a cracked frame, seized motor, etc, can be an "exciting" event if you're lucky.

A similar front wheel failure, on the other hand, will almost assuredly result in a major crash.

If you're going to put a bunch of stress on a part that could potentially cause a metal failure, do it with a rear wheel conversion.

A broken front fork will send you flying over the handlebars. A broken rear dropout will at least allow you to skid a bit and even possibly catch yourself before your head hits the pavement by sticking a leg/arm out..

Maybe the front spreading will work, maybe it won't. I think 10mm is a lot to budge. Especially on what, a 20in. fork ?

You don't have to bend the fork in the welded part, the tubing itself is perfectly safe to bend. There are 4 bends to make, to widen the fork, and to re-align the dropouts. That means: If you need a quarter inch each side, the first bend has to give half an inch, then the second bring back the dropout a quarter inch to re-align it, do this both sides and you're OK. If you are methodic and have adequate tools, it would be done in 15 min, this would not affect strenght at all, as long as you don't bend in the weld. The rim brake mount will have a slight offset as a result, your fork will be wider but shorter, most brakes have enough adjustment to compensate.

That said, I don't like front wheel drive on a bike with any performance expectation. If you plan to go fast, power the rear wheel.

MadRhino said:

You don't have to bend the fork in the welded part, the tubing itself is perfectly safe to bend. There are 4 bends to make, to widen the fork, and to re-align the dropouts. That means: If you need a quarter inch each side, the first bend has to give half an inch, then the second bring back the dropout a quarter inch to re-align it, do this both sides and you're OK. If you are methodic and have adequate tools, it would be done in 15 min, this would not affect strenght at all, as long as you don't bend in the weld. The rim brake mount will have a slight offset as a result, your fork will be wider but shorter, most brakes have enough adjustment to compensate.

That said, I don't like front wheel drive on a bike with any performance expectation. If you plan to go fast, power the rear wheel.

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This post seems encouraging... :-O Where can I find where the welded parts are? I wont be doing it alone that is for sure, I have a friend that repair bikes I plan on using his help and tools...

I am frustrated by the answers, I really dont know what to do...
I dont have ANY preformance expectations, I just need a bike that will enable my GF to keep up with me and encourage her to use her bike for longer rides...
The motor I am reffering to is a 250w 24v motor and my GF is only 48kg! The actual difference between the motor and the forks is 9mm...
Can you give me some tips on testing the forks endurance afer the spreading to make sure it will be alright?
Any links for the special forks for electric dahons you said?

http://www.flickr.com/photos/icomunete/872320858/sizes/z/in/photostream/
http://forum.dahon.com/lofiversion/index.php?t4294.html

This guy here spredded his broadwalk fork (also 74mm, also cromoly) to 100mm(!)..
A shop named Harris Cyclery did the job... I understand that a fork made for 20in wheels is longer than a fork made for 16in but here we are talking about a whooping 26mm!!!!

Maybe I should find a proffesional here is Greece...

Harris Cyclery is a world class bike shop and generally they do it right. Still there are forks that will fit without bending on that motor and unless you have a front suspension a suitable bmx fork should be easy to find. Is your Dahon got a front suspension? I agree with Madrhino that the bending is fairly straightforward. My bike shop did it with a huge vice and a big pipe and it worked out fine with my wife's Bike-e with a 16" front wheel. Depending on the labor cost it may be cheaper to find a fork that fits. Then again, when in Greece..............
otherDoc

Well finding a fork that won't ruin the bikes identity can be a pain... It is a pink dahon d3 curve, the version that has aerographies of little flowers on it...same goes for the fork so....

I've spread chromoly forks before and it can be tough, especially if you want to keep the finish.

What I did was got a 4 pack of sponges and taped them to the forks then I slid long larger diameter pipes onto the forks and pried. Once they were spread I used a crescent wrench to pry the dropouts so they were parallel again.

If the rider was 144kg, the motor more powerful and you were trying to hop curbs it would be better to get a new fork but 48kg is nothing and it sounds like it won't be abused anyway. IMO, go for it!

tsakis said:

Well finding a fork that won't ruin the bikes identity can be a pain... It is a pink dahon d3 curve, the version that has aerographies of little flowers on it...same goes for the fork so....

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OK, you've lost me.

In this case, "ruining the identity of the bike" is the very last thing you should be worried about imo.

I'm a "function before form" type of guy and, as such, would say that you can always restore the "identity of the bike" by re-installing the original fork at a later date. You, however, might not have the option of restoring your physical well being if, and when, you suffer a serious crash due to a failure of the fork assembly.

OK, you've lost me.

In this case, "ruining the identity of the bike" is the very last thing you should be worried about imo.

I'm a "function before form" type of guy and, as such, would say that you can always restore the "identity of the bike" by re-installing the original fork at a later date. You, however, might not have the option of restoring your physical well being if, and when, you suffer a serious crash due to a failure of the fork assembly.

Click to expand...

Well you are absolutely right about this but weighting things I will go for it!

1) It is a very expensive Dahon,
2) this make has no known problems with the welds
3)I am willing to do it proffesionally.
4) we are talking for 9mm here and a lot of people attracted their Dahon fork 26mm (!) without problems..
5) the motor will be weak and the rider skinny.

So, do you have any tests you suggest me to do to ensure everything is ok after the spreading?

Unless you're gonna get it professionally inspected too, the only real test you can do is to ride it somewhat more aggressively than your girlfriend will. Maybe hop some curbs or add some weight on the front and hit some speed bumps to be sure?

Quote:
"So, do you have any tests you suggest me to do to ensure everything is ok after the spreading?"

Non-destructive testing (NDT) is the general term for what you're referring to.

Here's a few links with some very generalized information on the subject of NDT:

http://en.wikipedia.org/wiki/Nondestructive_testing

http://en.wikipedia.org/wiki/Liquid_penetrant_testing

http://en.wikipedia.org/wiki/Magnetic-particle_inspection

Note: The "liquid penetrant" and "magnetic particle" NDT are some of the least expensive NDT methods.

A local college might be able to perform one of more of these tests for you (a "welder" friend of mine completed a NDT class at our local community college back in the "80s).

I've also heard of compressed air being used as a ND means of checking for cracks in high production volume steel and aluminum tubular frames and swing arms. This was, IIRC, accomplished by pumping about 25 psi into the individual tubing sections followed by swabbing the tubing with a soapy towel or brush. This would, of course, require the existence of a hole somewhere in tubing section that was created by the component factory during the manufacturing process. These "factory" created holes are fairly common in tubular frames and the like tho (they're usually about 2-3mm in dia).

However, I'd much rather see you use a suitable replacement fork rather than spreading the existing fork out (but hey, you certainly wouldn't be the first 10,000th person or so to do so without failure).