Secrets of MKS Chain Tensioners Revealed

I’ve enjoyed a set of MKS chain tensioners for three years.  When I first installed the tensioners, I didn’t fret about the lack of instructions.  It didn’t seem possible that they could be installed improperly–there isn’t much to them.  I’ve since discovered there is a bit more to think about.

Yesterday I removed my rear wheel to fiddle with my tire.  The tire didn’t seem properly seated (there was a low spot that I could feel through the saddle at low speeds but the rim was true and round).  The tire was loose on the rim, but with some wiggling here and there during inflation the tire  seated properly all the way around and the low spot is gone.  Easy installation comes with a minor cost.  Back to the chain tensioners.

While returning the rear wheel to the frame, I considered again whether the chain tensioners were properly installed.  First, I originally had the washers on the outside of the dropouts (more properly called fork ends when the opening is horizontal and to the back, but I don’t want you to think I am talking  about the front of the bike so I will use the term dropout throughout).  That I haven’t changed (and more on that later).  Second, I originally had the yoke installed with the MKS logos facing out, as shown below.  That’s changed now.  Here is the yoke as I had it installed originally. 

Turns out the yokes are not symmetrical–their orientation can matter.  The tensioning screw is offset toward the non-logo side.  In the picture below, the bulgy non-logo side is on the left and the flat logo side is on the right.   

Careful inspection helped me discover I should turn the yokes around to have the non-logo side on the outside when the washers are outside the dropouts so that the tensioning screws run in a straight line to the washer.  That’s what I have done now. 

Even more careful examination suggests I can orient the yoke either way on this frame.  Again, as a general rule you should have the non-logo side of the yoke on the same side as the washer, but orienting the yoke the wrong way (washer and yoke logo on the same side) worked on my frame because the dropout isn’t as thick as the cavity on the yoke.  When I had the yoke the wrong way around, the yoke was able to scoot itself toward the outside of the dropout to allow a nearly proper line for the threaded rod.  Still, no reason to settle for nearly perfect.  Learn from my mistake and do it right!

Was that hard to follow?  If so, maybe some more pictures will clear things up.  Below is a picture of the yoke oriented the wrong way (logo side of yoke and washer on the same side of the dropout).  In both pictures the washer is facing up and is just under my finger–the top digit with no nail showing).  I’m holding a piece of metal along the inside of the washer (under the washer) to take the place of a dropout (should have used something of another color–next time).  You can see that a dropout would not sit flush with the edge of the yoke.  It would line up in the middle of the cavity and continue down from there if it was thicker than the metal I show in the example.  Close to OK if your dropout is really thin, but not OK if the dropout is as thick as the cavity in the yoke.  If your dropout is thick, the yoke would be forced down in the picture below and the threaded rod would be misaligned.  It might seem OK as you are putting it all together, but as everything is tightened up problems would arise.  Looks like my washer bent a bit from my original install, as the threaded rod seems to come out of the washer at an angle.  Nothing serious, but I would be interested in seeing a new set side by side with mine.  If the angle was even steeper, I would expect the threaded rod to bend or break.

Below is a picture of the yoke oriented properly (the non-logo side of the yoke on the same side as the washer).  Again I am holding a piece of metal to take the place of the dropout.  

Oriented properly, you can see that the yoke would not be pulled out of line even if your dropout is as thick as the cavity in the yoke.  Since I am still running my washers on the outside of the drop outs (and there is the other mystery which I will get to in a second), I should have yokes oriented so that the non-logo side is out (as shown below).

More than enough of that.  Yoke orientation is only one of two riddles.  The second is where to put the washers–inside or outside the dropouts.  Since my frame is spaced at 120mm and my hub is spaced at 120mm, I placed the washers for the chain tensioner on the outside of the dropouts (as shown above) and never thought about it again.  Seemed like there would be no other to do it, but I was wrong. Today I found a forum thread on locating the washers.  In the thread, one voice (“onetwentyeight”) stood out as informed and confident and people generally fell in line.  Onetwentyeight said keirin racers run the chain tensioners on the inside of the dropouts (and that their frames are perfectly spaced to make room for the washers).  The frame spacing information was for me pretty persuasive (only a couple of millimeters difference to accommodate the washers, but I am sure keirin racers want things just so).  It is also telling for me that, as I demonstrated above, if the washers are on the inside of the dropout, the logo side of the yoke should face out.  Seems like MKS would want their logos to be seen from the outside of the dropouts.  With that, I am considering it settled that the manufacturer meant for the washers to go inside the dropouts.  Let me know if you disagree.

Should I do what keirin racers do?  It would be easy enough to spread my frame as I installed the wheel to clear the chain tensioner washers on the inside of my dropouts.  Even so, why bother?  Seems like the washers do their work just as well on the outside of the dropouts.  Also, installing the wheel is easier with the washers on the outside (I don’t have to pull the dropouts apart as I install the wheel).  Finally, I am only a little embarrassed to admit that I like that the painted outside faces of my dropouts are protected from damage when the axle nuts are tightened.  Onetwentyeight conceded that running the washers outside the dropouts is fine but he considers it sketchy to tighten the axle nut on anything but the frame.  He lost me there.  Why I should be worried about tightening axle nuts onto the chain tensioner washers as opposed to the frame itself?

Granted, the teeth on the integrated washer on my axle nuts (shown above) will be biting into the chain tensioner washer rather than the dropout, but, as pointed out by “trevsi” in the same thread, no matter where you put the chain tensioner washers, you are going to loose the benefit of the gripping teeth on either the cone locknuts (inside the dropout) or the axle nut washer (outside the dropout).  Further, I don’t think it matters if you lose grippy teeth action on one side or even both sides of each drop out.   With the chain tensioner in place, the work of keeping the axle in place is divided between the chain tensioner and the axle nut/dropout/cone locknut pressure interface.  I am not hercules, but with these two mechanisms working together nothing budges for me (and I don’t tighten the axle nuts all that tightly).  Any of you strong folks found otherwise?

What else?  Got a great little grease gun from  Isn’t it a gem?  Made in Houston, Texas by Dualco.  I hope to find some very light grease to use in it, and then this grease gun will be my dedicated freewheel greaser.  I have been hoarding Sachs freewheels over the last couple of weeks.  Some are used and among those some are smoother than others.  I even had a couple that wouldn’t turn at all.  I held those in a freewheel vise and used a freewheel removal tool to gently torque them until the freewheel mechanism moved.  Then I dripped Phil Wood tenacious oil in the seal and in the hole on the body and they are now working really well.  I do think some of my rougher examples would benefit from being pumped full of very light grease, though.  The NOS ones will get Phil Wood tenacious oil only.  I have a pretty good supply of Sachs freewheels now, so I should step away from eBay before things get (more) out of hand.

That’s that.  Take care!


10 responses to “Secrets of MKS Chain Tensioners Revealed

  1. Hello, what did you decide to do regarding using your MKS chain tensioners? I’m currently using a Surly chain tensioner on the drive side however I’m considering switching to something that is less noticable as the Surly is quite noticable. If I’m viewing your pictures correctly, it appears that your rear hub that has spacer nuts that can be removed to allow for the tensioner to be mounted on the inside. Would that work?

    • Thanks for coming by and writing. I am sure I could remove or swap-in thinner spacers on the hub to reduce its over locknut dimension and then run the tensioners on the inside, but its easier to run the tensioners on the outside and I see no downside. A collateral benefit of my lazy approach is that the hub would still fit well if I decided to stop using the tensioners. Not likely, but I will jump on any rationalization for laziness! Hope your weather is nicer than ours. Weatherman is threatening snow! Take care.

  2. Randal would you Besos able to run some measurements for me, in milimetres?
    I would need diameter,the width of the tab that slide into the dropout and thewidth of the two notches on the stopping part,the one stamped mksthat clamp on the aft of the dropout.The ideais to know the axle sizeand if it will fit my custom dropouts.Thanks mate,great article btw.

  3. Thanks for the thorough explanation! I’ve ordered a pair of these online and will install on my SS once it comes in.

    Other side thoughts… It’s been a couple of years since you posted this, I was curious if you still use them or not. It doesn’t seem to be a very popular part on SS forums, and a lot of people think it’s not necessary and would rather just retighten the chain slack every so often. Are there any down sides? (besides becoming lazy to check things) Thanks!

    • You’re welcome! They’re still on that bike and I’d never take them off. The wheel stays put despite the massive watts put out by my older vegan pedaling sticks. No down sides. Take care!

  4. Interesting article, thanks. I just bought a pair of the MKS chain tugs, here in the UK, from SJS cycles. Mine came with quite detailed instructions from MKS which are quite intricate. My problem with the installation was that the rectangular block which slides into the dropout is a very tight fit. I think this is due to the paint on the inside of the dropout. My dilemma now is whether to file it out so I’ve got a decent fit…

  5. Mine came with instructions as well! As the years pass, it seems MKS becomes more sympathetic to the end user. According to their instructions the tensioner should be installed on the inside of the dropout, and the logo should be facing outwards!

    • Thanks for the factory update! Glad to know I guessed correctly. Since these are intended for use by track racers on frames with room for washers on the inside, it makes sense MKS would instruct users to place the washers inside and have the logos facing out, but if your frame lacks the space, I’d still suggest placing the washers on the outside with the logo facing in and then have a careful look at alignment.

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