Swapping a 1950's Simplex outer chainring
 

Looking to build some confidence after having snapped off a bolt twice in the past year, causing a major headache.

I just got a good deal on a nice shiny outer chainring for my 1950's Monark Blå Blixten, will look nice with my new pedals - the old one is still working, but the tooth are starting to look nonexistent - and the shine is long gone. The inner chainring tooth are in better condition (the outer one is all I could find anyway) so I'll be replacing just the big ring.

So what I'm worried about is snapping the 70-year-old bolts, I really don't want to end up there. Not again :foo:

It's a Simplex, this image is from VeloBase - the model is not a 100% match but the bolts are the same type: regular hexagonal up front and a strange looking round-shaped one (with a groove in the middle) in the back.


https://cimg4.ibsrv.net/gimg/bikefor...5ced8bfe3.jpeg
https://cimg5.ibsrv.net/gimg/bikefor...f3534c548.jpeg


Anyone been down this same road - any pointers?

I haven't attempted to open yet because I know my day'll be ruined if I snap something in there, so figured it's better to plan ahead/sleep on it.

I have a decent 9mm wrench close by with a shaft of about 12mm / 5 inches to give me a little torque and I'm thinking I'd get some penetrating oil from the local hardware store, let it sit a few hours and then just hope for the best. I do not know if I should apply some heat as well, never done that.

Can I just apply torque from the outward side and nevermind that strange looking nut (?) on the inside, or do I need to grab on to that groove on the inside bolt with something as well?

I’m interested in the advice you get as I have the same setup on an old Magistroni crank. If everything was like new it’s simple: you unscrew the hex head bolts like normal (the strange slotted nut is held with a big screwdriver).

However after many years they can be frozen together - the ones on my magistroni would not budge. Was thinking of trying heat next. Be aware the heads are quite shallow so easy to mar.

oh: and if you do mess up (like I did on another crank) you can use a 10mm cap screw and carefully reprofile it to have the same shape and some with a file if you are patient.

Penetrating oil is good.
Heat is good.
Use a flat screwdriver in the slot.

Not a lot of torque is needed to hold a chainring in place. No need to crank down on it. If you need to, stop, let the oil work for a couple three days, try again.

A flat screwdriver may or may not fit that bolt-slot; the bottom of the bolt might extend too far into the slot. You may need a specific chaining bolt tool - with two "prongs" to fit into that rear bolt.

Great stuff, appreciated.


So, going with the tools I got.

First cleanup all around the area, then some oil... Let it soak properly... Then, maybe if I used a soldering iron (?) to touch both sides of the bolt for a little while (say, 10 seconds) which would... Make the metal expand am I correct? And then let it cool off completely afterwards, then some more penetrating oil, let it soak again... Before actually attempting to loosen it. Or should the heat be applied while attempting to open?

Oh... Dang... You're right, I just checked and the bolt extends just a little too far, so a regular screwdriver won't do me any good here :( Another special tool to search for...

A chainring bolt tool is not really a "special tool". Those chainring nuts with the slot are standard on modern cranks as well, although slowly bring replaced by Allen (thankfully).

Give it a try before trying heat. It might come right off. If it's giving resistance then just let it soak in oil. Eventually you can try heat. Don't use a blowtorch for too long or else the chrome will flake off the bolt. You're way more likely to round out the nut slot than break the bolt here.

Soldering iron is worthless. Propane torch will not hurt a thing. Couple three minutes per bolt.

Take a sacrificial screwdriver, file away the middle bit.

And easy to grind a slot in a flat screwdriver to clear the centre.....

iab : thanks for confirming heat from a propane torch (used carefully) won’t do too much harm.

Propane doesn't get hot. Nowhere near aluminum's nor steel's melting point. Fine with bronze too. It can **** up lead though.

I have the same setup on one of the Capo Siegers (the one with almost all OEM parts). I applied penetrating oil and let it sit overnight before loosening the bolts, and it all came apart without much effort. I do have a chainring nut wrench and the proper hex socket -- good tools always help.

My penatrant of choice for steel fasteners is Kroil
"don't spoil it, Kroil it"

for the hex head, grind back a 6 point socket to provide full engagement of the bolt head.
Ans yes, thin a a wide "minus" screwdriver and notch it.

...an additional vote for both of these.

...I go on and on about this, but making your own penetrant from a 50/50 mix of acetone (from the paint store) and ATF (from the auto parts store) is a valuable addition to the world of taking old stuff apart. It's really quite superior, even to Kroil and the other stuff, Freeze Off (again from the auto parts store). You need to keep it in an acetone proof plastic container, but there are plenty of those around. I use one of those small , reusable plastic squeeze bottles that Tri Flow comes in. The little application straw makes it easier to apply precisely.

For some reason the stuff wicks into threaded interfaces better than anything else I've used. We did some comparison testing on old rusted stuff at the bike co-op here. It's magical.

+1 on grinding the socket down for flat, flush engagement, if purchase is poor, the results will also be. ;)

Success.

DIYed a rather elegant chainring bolt tool, soaked the backside of the bolts in plenty of penetrating oil overnight (I used CRC Rust Off) and the 70-year-old bolts did come off. Didn't use heat.

Couple of 'em were pretty tight, where I almost risked rounding out the nut. For anyone doing the same thing, I would recommend filing the end of the hex socket nice and flat to get a better grip - as was suggested here. I didn't do that but luckily managed anyway with a regular 6 point socket.

I couldn't resist taking off the whole assembly and cleaning all the bits and pieces and the inner chainring - as well as turning it 90 degrees to get more life out of it. Probably over-tightened everything a bit once again, but oh well.

The inner chainring tooth were surprisingly in better condition than on the (old) outer one (which is what I replaced).

Monark's ready for the summer with it's new chainring and MKS pedals.

https://cimg0.ibsrv.net/gimg/bikefor...28157b1e3e.jpg