Avoid Doing Damage When Adjusting a Tight Fin

fin block

You can hardly wait to try the latest setup numbers for your ski. But when you loosen the fin block, and try to move the fin, it won’t budge. Not wanting to give up on this new setup, you urge the fin along with one of the adjustments set screws. But what you can’t see is that even though the fin did move, it suffered significant damage.

Adjustment Screw Damage on the Fin

Forcing a tight fin to move cuts grooves into the fin, making accurate fin adjustments impossible

There’s a good chance that whoever moved this fin before you damaged it too, even if it was at the factory. And unless you remove the fin to file out these adjustment screw grooves, you’ll never be able to adjust the fin with any accuracy.

To avoid inflicting this kind of damage on your fin, you’ll have to set the fin block up so the fin moves more easily when it is loose. Here are the main causes of fin tightness:

  • Fins that rarely get moved often get stuck to the block by corrosion, even in fresh water
  • Fin thicknesses can vary dramatically, even fins from the same manufacturer
  • The slot through the ski may be too tight
  • The slot in the fin block may be too tight, and
  • The fin block may not line up perfectly over the ski’s fin slot.

It’s easy to remove the fin to inspect it and to clean off any built-up corrosion if necessary. If the slot through the ski is tight, it can be widened with small files and/or sandpaper—if you have a lot of patience. And there’s not much you can do about variations in fin thickness, other than getting a thinner fin. This leaves fin block modifications as the most common fix.

Making the fin block wider is a good place to start. If it’s a two-piece fin block, loosen the six screws fastening the block to the ski and tighten the fin into the block just enough to barely hold it in place. Now tighten the two halves of the fin block back onto the ski. This centers the fin block over the ski’s fin slot, and it locks down the two halves of the fin block in a position that is wide enough for easy fin movement.

If it’s a one-piece block, remove it from the ski and see how easily you can move the fin around in it by hand. If the fin moves easily when the block is out of the ski but is tight when the block is mounted back onto the ski, there’s either a tight ski slot, or a misalignment issue.

If the fin is gripped too tightly by a loose fin block when it’s removed from the ski, the sides of the block will need to be spread slightly. This can be done using a large standard screwdriver as a wedge to gently spread the two sides at either end of the fin block. Make sure you don’t damage or burr the edges in a way that will impede fin movement. If you do, file it out. The goal is to spread the sides just enough that the fin is still barely held in place when the fin block is loose.

Fin Block Widening

Adjusting the Gap in a One-Piece Fin Block

Gently tap a screwdriver into the top and bottom at both ends of the fin block to stretch the fin gap slightly wider

With the block now barely holding the fin in place, screw the fin block back onto the ski. If the fin is tight again after mounting the block to the ski, regardless of how loose the fin clamping bolts are, it’s clearly a misalignment issue. If you plan on doing lots of future fin adjustments, you can either purchase an aftermarket two-piece fin block, or modify your existing one-piece block so it can be centered over the ski’s fin slot. Often, all that’s needed are screws with smaller heads, like Allen bolts. Sometimes a little Dremel work is needed.

Offset Fin Block Inserts

These pictures show an extreme example of how the fin block inserts can be offset from the slot in the ski’s tail. Fortunately, fin slots themselves are usually very accurate, so sorting out the block is all that’s necessary.

If the misalignment is really bad, the ski’s manufacturer will likely replace it under warranty. But this misalignment doesn’t affect the ski’s performance at all, it just makes adjustments more difficult. So if you just want to set your fin and forget it, the following procedure will get the job done—without damaging the fin.

For every fin move, you’ll have to loosen the fin within the fin block (three bolts) and loosen the fin block itself from the ski (six screws into the ski). Loosening the fin block so there’s about a 1/8” gap between it and the ski should be enough. Move the fin out of harm’s way by hand, turn the adjustment screws as much as you think necessary. Then by hand, move the fin snugly up against the adjustment screws in their new position. Tighten the fin into the block and the block back onto the ski before measuring to see if you have the fin where it needs to be. If not, keep repeating the above, loosening everything, moving the fin by hand, and retightening everything before remeasuring. It’s a slow process but will allow you to accurately move your fin into place with no damage.

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