Briggs & Stratton Crank

[RoyM]

The L-head engines are no longer available from Briggs, adapting an ohv is probably not worthwhile unless you have a donor mower. If you really want the project replace the crank if garbaged.

Then that strange as my Briggs distributor is still selling the 650, 675 and 725 series L-heads. Matter of fact the 126M02-1025-F1 which is the direct replacement for OPs motor is listed at 336.30 but you can find one on a new mower for less, buy it and part out the mower. And I know for sure that Husqvarna was still selling them on the HU675HWT trimmers as of last Fall.

When I worked for a dealer we at times buy new equipment and use it top service warranty repairs and sell new parts at a discount as take-offs.

Those engines are old stock, when they are gone that's it. Crazy isn't it? Cheaper to buy a new mower and part it out than simply replace an engine.

[Arkie]

I think maybe my crocus cloth is around 250-300 grit or if you have a belt sander belt (fine of 150 or less) you can tear off a piece of the belt about 8 inches long and not any wider than the crank throw and very, very carefully see-saw the strip polishing the crank. You do not want to remove any metal on the sides of the crank throw.
Be very careful because you will be surprised how fast the see sawing will cut a metal crank. You can finish with or start with 400 grit if desired. You do not want very much pull pressure force on the polishing cloth.
If not familiar do a practice polish run on a large bolt or metal rod in a vice and you will see the results.

Again be very careful and do not see-saw in one place all time keep circling with the crank in a padded vice and a good light.

You can even use wet/dry type 400 grit and use little oil instead of water.

Completely clean all real good when through.

[lefty]

Thanks Arkie. I saw an interesting video on youtube where a guy used a hockey skate lace. He wrapped 400 grit sand paper around the journal with some lubricant and then wrapped a skate lace around several times, which is wider and flatter than a normal lace, then by working it back and forth was able to apply constant contact around the journal at all times. Or so he claims. Thus avoiding working one side too long and throwing things out of round.

[Fulltilt]

Look, Lefty, discounting all this gibberish about outboard motors, plastigage, and crank turning with new custom made bearing inserts, just do what BG said. It's unfortunate that you can't get just a rod. But hey, right? Have you tried fleabay?
I would have no problem using W/D paper, only use at least 1200 grit. Try finer, but absolutely don't go any coarser unless to try and remove only the alum. Remember wet/dry paper is MUCH sharper than dry paper. For that reason, I usually will "sand " it on itself for a bit.
Another hint I usually do when using a new rod assy ( which isn't very often $$$$ ) is clean the rod bearing surface with carb spray or such, and then, finger rub in some moly assy lube/paste. Let the rod warm up a bit first.

As BG alluded to, it's pretty much a crapshoot....but it's also just a freakin' lawnmower motor , right?

[Arkie]

I checked my coarse roll of closed cell crocus cloth as 60 grit by 1 inch wide.

Really have to be careful with the 60 grit because it will cut steel, even hardened steel fast especially if very much see saw pull pressure is applied. You can make the 60 finer by sawing it across a round file or even a piece of steel dowel rod.

I sometimes also use the 60 use to polish a shaft that has a tight arbor pulley or it a heated bearing is still too tight on a shaft just a licks will get er dun.

With care you can keep the journal round if you anchor the crank and go for 270 degrees of wrap and don't saw in same place, constantly move the cloth.

Make a practice run on a bolt or something about size of your crank first if necessary.
If you see steel on one side and aluminum transfer in another place take a marks a lot permanent pen and color the clean steel and watch and not polish this area when going after the aluminum.
The Permanent marks a lot on bare clean steel will tell you when you are polishing the hard steel too much instead of the aluminum part.
You can also use this coloring method when polishing or turning something so as you know all is going as desired visually.
I also use the marks a lot coloring when re-grinding broken or severely dull drill bits as a indicator to confirm that both sides are even and at proper angle. (when color just goes away on one side of the bit, switch to the other side and right when it all is bare steel both sides of the bit are evenly ground and at the same angle. This method of marks a lot permanent coloring works great when using a DRILL Doctor to sharpen bits and if you change the grinding angle or settings on the sharpener you can confirm that both sides are same angle by the amount of color removed instead of just looking and listening to the sound of the grind.

[lefty]

Awesome advice. Thanks to all for the detailed posts. I'll keep everyone posted.

[Arkie]

Lefty:

I did not see your pictures you posted on page 2 of your crank just before I posted little later. I just now seen them.

Do the coloring of the crank with the wide tip permanent mark a lot pen on the cleaned journal before you start polishing and use a fine grade of 300 or more. It appears maybe the most transfer is in the center of the journal and if so instead of first polishing the whole width I would try to polish that one down first with a narrow strip of crocus using the mark a lot pen method as a reference. Assuming The journal is still round you can live with very light marks circling that journal
I've seen lots worse than that would clean up and be ok.

That one you can check for out of round before you even start. Most likely it's still ok because the scratch transfer marks are consistent around the crank.
You can check the final fitting of a used or new rod as mentioned using plastigauge.
Look for at least .0005 and max or not more than .003.
When you find a rod new or removing a used one immediately mark the rod cap so as it goes back onto the rod same and when first testing without plasstigauge lightly snug the rod cap bolts while wiggling the rod to make sure you have some clearance, just in case you have wrong rod size and it going to be too tight. Don't start torqueing rod caps down on a journal that is not going to have any clearance is my point.

[lefty]

So I went with the acid and it seems to have worked wonders. I can't see any aluminum left on the shaft. But I do have some discoloration. Kind of like a light brownish, which polishes up somewhat with a rag. I'm sure I could get it nice and shiny if needed. Do I care about the discoloration? Is that something that should be polished off?

[KE4AVB]

Oppps pushed the wrong button..

Did you neutralize the acid afterwards? If not if it will flash rust over quickly and even if you did it still needs a good coat of oil. For future rust removal projects I am ordering stuff that leaves behind an anti-rust coating. Kinda expensive but I need it for several crankshaft PTO ends on Cub ZTRs that like to rust the pulleys on especially when someone don't put the anti-seize on the shafts.

[lefty]

Oppps pushed the wrong button..

Did you neutralize the acid afterwards? If not if it will flash rust over quickly and even if you did it still needs a good coat of oil. For future rust removal projects I am ordering stuff that leaves behind an anti-rust coating. Kinda expensive but I need it for several crankshaft PTO ends on Cub ZTRs that like to rust the pulleys on especially when someone don't put the anti-seize on the shafts.

I guess I did not neutralize the acid. So do I just polish the rust off? I did the procedure yesterday.