Machining a fork cap - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 36 Old 12-23-2017, 06:22 PM Thread Starter
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Machining a fork cap

This isn't specifically about a V-Strom fork cap, though I'm sure the caps on a Strom can suffer from the same issue. I know a lot of guys on here have a lot of machining experience, so I'm seeking some advice.

Like a lot of ham fisted mechanics, I bunged up one of the sides on the fork cap nut when I was removing it from my Super Tenere while changing the fork oil. It's not bad, and I'm pretty sure I'll be able to remove it again, but it got me to thinking about a better way to get the cap off than using the soft aluminum nut.

I was considering two possibilities:

1) Drill two shallow holes in the fork cap on either side of the nut, and use a pin wrench to remove the fork cap in the future.

2) Machine an aluminum donut the same diameter as the existing for cap. Drill a series of holes around the circumference of this donut (I'm thinking maybe six holes, like a #6 size). Then tap corresponding flat bottom threaded holes into the top of the fork cap, and screwing this donut to the top of the cap. Since the threaded holes would have to be pretty shallow, I figured that six of them would provide a pretty secure attachment. Then, drill holes into the donut that would correspond to the pins on a pin wrench. The donut would be 3/16" thick, which should provide plenty of depth for the pins on the wrench.

The biggest downside I can see is that I don't know how deep I could safely drill holes in the fork cap.

For those of you who have machining experience with aluminum, would this work? I've attached a photo of a Super Tenere fork cap. These things are $300-400 new, so if there was a way to salvage the old one, it would be worth a shot.

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post #2 of 36 Old 12-23-2017, 07:18 PM
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I don't know much about machining or fork caps, but I've got a sudden, inexplicable kraving for Krispy Kreme.

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post #3 of 36 Old 12-23-2017, 07:39 PM
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Take it to a machinist to get a really good answer.

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post #4 of 36 Old 12-23-2017, 07:48 PM
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Ive never had a problem or caused damage removing fork caps using a 6-point Snap-on deep well socket. These sockets are flank-drive, and apply force to the sides of a nut rather than to the corners. The key is to loosen the cap before you loosen the bike's lower triple clamp bolt. If off the bike, I I have someone hold the upper tube in their hands while I use a 3/8" impact wrench and repeatedly give the socket short bursts to loosen.

Last edited by MAZ4ME; 12-24-2017 at 10:57 AM.
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post #5 of 36 Old 12-23-2017, 08:03 PM Thread Starter
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Well, sadly, the damage is already done, so I'm looking for a solution that allows me to salvage the existing fork cap, if possible. I followed the proper sequence in loosening it but I let the socket slip off while I was loosening it.
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post #6 of 36 Old 12-23-2017, 08:47 PM
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RC, I dont know the extent of the damage from the pic, but it's possible to carefully hand-file off the damage, straighten up the sides, and as I suggested use a Snap-on 6-point socket for removal/installation. Ive had to do this when presented with damaged caps by other riders.
When servicing forks, I use a 12" 1/2"drive extension and 3/8" adapter, and position the socket dead in-line with the fork before I apply any rotational force to the cap.
That cap must be made of Unobtanium, as it was shown for $267 on MR Cycle's website.
Just asking, but what is the wrench size of that cap nut?
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post #7 of 36 Old 12-23-2017, 09:26 PM Thread Starter
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That actually isn't a photo of my particular fork cap, it's just a photo from online of a Super Tenere cap. I put it up there for reference. The damage on mine was minimal; one corner was slightly rounded off at the very top, where I allowed the socket to slip a little. I still have solid edges on the nut; however, as soft as that aluminum is, any slips in the future are just going to make it worse, so I was fishing about for a way to basically improve the way a wrench grips the fork cap.

The nut is 24mm. $267.00 is actually a good price; I've checked various websites and seen it all the way up to around $350. Dealership prices are around $425.00. Frankly, that's nuts, and this is the sort of thing that usually drives me to start thinking about another way to do it. Supposedly, a fork cap from an 05 Yamaha R6 will fit, and I did find some junked forks on eBay; only problem is that the fork caps on the R6 have two different part numbers, and only one matches the part number of the Super Ten. I'm not sure which part number goes on which fork, so I'm hesitant to buy a salvaged one from eBay.

Fortunately, this is an "I wonder if this is possible" type exercise at the moment, since I won't need to do fork maintenance for a couple years (unless I lose a seal, of course). I just think that a pin wrench that fits into holes that are near the outside edge of the fork cap would give more control and leverage that that soft aluminum nut.
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post #8 of 36 Old 12-23-2017, 09:31 PM
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You might consider welding 6 slabs onto the facets of the nut / then machine them to accept a larger size socket.

Obviously, you would identify / buy the larger socket first.

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post #9 of 36 Old 12-23-2017, 09:40 PM Thread Starter
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Quote:
Originally Posted by NVDucati View Post
You might consider welding 6 slabs onto the facets of the nut / then machine them to accept a larger size socket.

Obviously, you would identify / buy the larger socket first.
I was thinking about that too; basically, machine a much meatier hex nut out of aluminum and weld it to the fork cap, with the new nut thick enough (like 1/4") that there's plenty of edge for a socket to grip. This would be more expensive, since it involves more precise machining and welding, but at the prices they want for a new one, it still might be feasible.
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post #10 of 36 Old 12-23-2017, 10:06 PM
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Quote:
Originally Posted by RCinNC View Post
I was thinking about that too; basically, machine a much meatier hex nut out of aluminum and weld it to the fork cap, with the new nut thick enough (like 1/4") that there's plenty of edge for a socket to grip. This would be more expensive, since it involves more precise machining and welding, but at the prices they want for a new one, it still might be feasible.
Having seen some of the other things you've accomplished ... I think you could streamline the fabrication of this repair by buying two new sockets. One of them can have the top sliced off so as to be used as a jig for the welding. With hand tools you can present it to the welder ready to zap.

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