Seized pedals

[karlt]

I've been spraying these with GT85 for a while, but they're still so welded into the cranks that I've just broken a spanner by applying extra leverage using a pole. What would you do? The pedals themselves are scrap; old strap-in things I wouldn't touch - drill out the pedal shaft from the back? Give up and replace the crankset?

[Stewart H]

If you can get the body of the pedal off then heating the pedal shaft with a blowlamp should make it consider the error of its ways, plusgas beats most other things when it comes to penetrating oil, if you squirt it onto the hot item it seems to get sucked in as the work cools. failing that drop the whole thing into a bucket of diesel and forget about it for a week or two

[mig]

both of them?

you know about the different thread orientations right?

[Mick F]

Yes, with due regard to thread direction ......... LH thread on LH pedal, RH thread on RH pedal.

Strip the pedals off the spindles and use brute force with a bench vice. Heat is good, but be careful to only heat the spindle. As it cools, stick it TIGHTLY in the vice and turn the crank. Maybe use a rubber mallet to persuade it.

[531colin]

If its steel/alloy corrosion, as seems likely, treat it like a stuck seatpost.
Try warming to dry out the oxide(?), plus-gas to replace the water as it cools.....do it a few times.
If that fails, dissolve the oxide in Ammonia solution.
violence is to be avoided, if at all possible.

[Brucey]

one thing you can cross off your list of possibilities is drilling out a pedal spindle; they are usually as hard or harder than most drill bits.

If you apply ATF and heat (use a hot air gun because it is gentler and this won't so easily soften an aluminium crank) you will see bubbles in the ATF after a while; this is steam escaping from the hydrated oxide in the joint. After a few heat-up/cool down cycles of this sort the oxide will have dried out and it will no longer grip so hard; then spindle will most likely come out OK, but you might need to strip the pedal and put the spindle into the bench vice to shift it.

cheers

[MikeF]

I've been spraying these with GT85 for a while, but they're still so welded into the cranks that I've just broken a spanner by applying extra leverage using a pole. What would you do? The pedals themselves are scrap; old strap-in things I wouldn't touch - drill out the pedal shaft from the back? Give up and replace the crankset?

GT85 and similar are absolutely useless for that application in my experience. Buy a tin of Plus Gas dismantling fluid and let it soak in that, or maybe soak in diesel oil.

[Valbrona]

At least try a proper pedal wrench and something better than GT85

[Brucey]

one of the car magazines tested all kinds of penetrants on rusted fasteners a while back and IIRC GT85 came out tops.

But penetrant is the lesser half of this battle; the real issue is the swollen (hydrated) oxide in the pedal threads, not the lack of lubricant per se.

cheers

[NATURAL ANKLING]

Hi,
Hot air gun / modern hair dryer 1200 - 1500 watts.
Dismantle pedal, grip in vise hard, warm up alluminium arm , drip water on the arm to see its above 100 C, then dont go long after that.
Or cooking oven set to 150 C. Apply oil to joint, penertrating spray will burn off and is not high pressue lube either.

USE a wooden block / hide mallet (NOT metal at all !), to thump the arm (so not to mark the arm, also works best to shock the joint), left then right, once you can move it 45 - 90 Degrees, reapply oil to the joint, reheat as neccesary.

Wind the arm back and forth, eventually you will know when to unscrew completly.

Could take you an hour, dont rush.

[PT1029]

If you are unlucky, and its all too corroded, you may loosen the pedal by turning it back and forth, then go for it. Sometime this results in the really corroded bit on the back of the crank ripping out the (I assume) alloy crank thread as it unscrews out through the crank. Then its either new cranks, or get e helicoil insert put in the crank.

I did encounter a siezed pedal recently, someone ended up dilling it out carefully with a pillar drill (think industrial workshop) and tidying it all up with a thread chaser. Interestingly, the workshop wern't too sure which 9/16" thread tap to use, as they had all sorts, but found a pair labelled "bike threads", not so technical, but sufficient!

[MikeF]

... the real issue is the swollen (hydrated) oxide in the pedal threads, ....

cheers

Surely isn't swollen oxide the problem with all corroded threads binding? Or do you mean that there is more of a problem with aluminium because the oxide is hydrated?

[MikeF]

Hi,
Hot air gun / modern hair dryer 1200 - 1500 watts.
Dismantle pedal, grip in vise hard, warm up alluminium arm , drip water on the arm to see its above 100 C, then dont go long after that.
Or cooking oven set to 150 C. Apply oil to joint, penertrating spray will burn off and is not high pressue lube either.

USE a wooden block / hide mallet (NOT metal at all !), to thump the arm (so not to mark the arm, also works best to shock the joint), left then right, once you can move it 45 - 90 Degrees, reapply oil to the joint, reheat as neccesary.

Wind the arm back and forth, eventually you will know when to unscrew completly.

Could take you an hour, dont rush.

Yes heat can help especially as aluminium expands more and more rapidly than steel, but I still think before trying anything else I would give it a really good soak in whatever fluid you choose to use, say overnight or longer if you have the patience. Not sure what you mean by high pressure lube. To me it means the lubricating film will persist even when there is high pressure between surfaces, but that doesn't really apply here.

[Brucey]

the oxide is the problem for sure, with all kinds of seized parts, but for slightly different reasons. Normally there is a spiral gap in any assembled screw thread; this is where the water gets in if there is nothing in there (like grease, copper-ease, or Loctite) that might stop it. The corrosion in an initially dry screw thread between steel and aluminium will occur where the different metals are touching one another, i.e. on the loaded flanks of the screw thread.

In some cases the fastener tension increases due to the corrosion (the corrosion 'jacks' the parts using up whatever clearance there is in the threads). Also the threads can more obviously simply bind so that the parts won't even turn easily.

in cases where the corrosion isn't too bad a penetrant can work its way into any spaces that remain, and this can help reduce the breakaway torque required. In other cases any exposed screw thread is lubricated by the penetrant and this helps the parts not seize up again or further damage themselves too badly as they are unscrewed. [The same kind of EP lubricant additives that prevent wear in highly loaded gear trains etc can help here too.]

But in the case of steel pedals in aluminium cranks, the oxide soon becomes pretty much solid in the screw thread, and penetrant cannot get in there, because there are no gaps for it to go through. In most cases the corrosion product is aluminium oxide rather than iron oxide. Because finely divided dry aluminium oxide is an effective drying agent, it soon converts to aluminium hydroxide and other forms of hydrated oxide, and it can be mostly (by weight) water. [In terms of pressure inside the assembly, several hundred psi is possible, rendering the joint as tight as it would be if it were a shrink fit.]

Which is why you need to dry it out, preferably using prolonged gentle (~150C) heat rather than brief episodes of more intense heat, which risks softening both cranks and pedal spindle.

As NA points out damaging the screw threads in the crank is a real danger; if (say) about half the part comes unseized and the other half doesn't, the remaining seized threads can just shear off and then the remaining good threads are damaged as the clogged spindle is unscrewed. Ironically the net result of all this is that the pedal spindle is likely to survive unscathed but the crank (which is usually the part that is desired) gets damaged.

BTW a standard pedal thread is 9/16" x 20 tpi, left or right threaded depending on the side.

cheers

[NATURAL ANKLING]

Hi,
Like said, aluminium will tear very easily and a impatient simply unscrew when it losens will / might well damage the thread.
If it moves (any fastener siezed) then dont go more than 45 - 90 degrees, maybe far less, add some lubricant (engine / gear oil will not be driven off so easily by additional heat) and wiggle till resistance is felt, then go back and forth.
In time repeating heat lube move it will come undone one turn but procede with care and you will have a servicable crank.

Quite often fasteners have corrosion at the back of insertion (pedal thread is reccesed so you cant get at it physically) so you can only rely on heat and lube in this case, Im no chemist but the heat will remove the water as said allowing a gap for lube.

My last siezed crank took over an hour.

Once apart wire brush the spindle threads and wipe clean, clean the crank threads of debris, then apply gear oil to a good pedal spindle and screw back and forth in to crank arm, remove and reclean parts repeat procedure, inspect pedal spindle thread for damage though unlikely as hard and tough, both sides if neccesary but be careful of crossed threads on the rear of arm

Problem with a tap it will remove metal, a pedal spindle will not as much. So be carefull retapping threads, only if all else fails.

The wood block 3 x 2 " x 18 " or hide mallet will not bounce off arm or damage it like metal hammer, apply with a dead blow not quick tap.
This is more effective than brut force, hands on arm will be too weak to move stuburn thread.
Edited for grammar