Damaged Crank Gear

P

pawillie

Member
Replaced worn fiber timing gear with an aluminum one, timed and ran great before hearing a knocking sound, then a crunching noise. Dropped pan and took this pic. Some of the crank gear teeth were broke off but the timing gear still in great shape. Anyone ever had this problem?
 

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some gears were made of cast iron.
Original gears were steel.
Most likely the mesh was too tight and that cast iron crank gear didn’t like that.
the backlash has to be checked in several places ,sometimes the crankshaft wasn’t centered very well in the grinder and the gear would have tight and loose spots and sometimes the centerline for the mains is off.
Most align boring systems designed in the A era had fixtures to ensure the proper crankshaft position.
 
How much backlash is/was there between the two gears?
Edited: Damn! Kurt typed faster. I think we are both on the same track.
 
I don't want to rub it in, but this is why Ford used a fiber cam timing gear rather than metal. If something had to give because of binding or whatever, better it be the fiber timing gear than the crank gear.
 
Kurt has it right and will n has a very valid point. The fiber gear is more forgiving. As Kurt said originals are steel but all the replacements I have ever seen are cast iron. I have used at least a couple hundred without a failure. I can just about guarantee there was no clearance between the aluminum and iron gear in at least two places. That is why the iron gear failed. Kurt mentioned the crank being ground not on the true center. That is most likely from a crank grinder setting up on the front and rear main. The correct and better way is to set up on the O.D. of the crank flange and where the front gear mounts. These are non wearing surfaces, takes longer to use but will put the mains when ground back on the true centerline.
 
That's why I bought a matched set when I replaced my timing gear with a Bronze unit from Mr Dan Mc. (cheap insurance!)
 
CarlG said:
That's why I bought a matched set when I replaced my timing gear with a Bronze unit from Mr Dan Mc. (cheap insurance!)
Click to expand...
I also bought a matched set from Dan McE for my Burtz, but I was cheap and opted for the aluminum cam gear. Those are truly works of art, I almost hate to install them where they’ll be hidden.
 
The Burtz block is machined with the correct distance between the cam and crank so that there should be no problem with the aluminum cam gears. Still, I would recommend a steel crank gear and not the cast iron one. The cam gears can be bought for worn crank gears. They are a little larger. If that gear was bought then that could be the source of failure.
 
Sounds like I need to go back to the fiber gear or find a steel crank gear. The crank gear damage came about shortly after I changed over to the aluminum timing gear. Where can I find a matched set?
 
Going to a matched set of gears won't help you if the clearance between the two shafts is incorrect. You'll just wind up breaking a gear for the third time.
 
Thanks much, think I'll go with .003 fiber and steel crank gear for a better mesh and pray not much trouble getting old gear off crank. Would hurt to double check crank main clearance, as well. Keeps ya busy for sure.
 
The only easy practical way willie can go forward is to buy a cast iron gear and a new laminated fiber gear. Install and check the fit. We don't know yet any prior history which might help to decide witch way to go. With micrometers and math the center to center distance could be determined. Iron crank gear have been the industry standard on many engines. The issue is the fit.
 
My plan has always been two NEW standard sized gears. The center-to-center distance SHOULD be correct, even with an engine with some wear on it. After a re-babbit there is no excuse for it not being correct. (Although technically, the action of the gears forcing each other "apart" should technically wear the cam journal "up and to the right.") But it would take a lot of bearing wear to add up to an oversize gear.


(Bearing - stationary part. Journal - moving part)

If you mix a new oversize with a "worn" other gear, you run the risk of moving the "contact line" where the gear teeth meet. IIRC, the gears are 14-1/2 pressure angle when new. As gears wear apart this can change. New and old can change it A LOT.

And maybe cause the issue seen.

Joe K
 
If you use the aluminum gear and a new crankshaft gear and the set is tight with no working clearance, you can use yellow Timesaver to work in the gears. It will remove material from the aluminum but not the crankshaft gear. Follow the instructions and be sure to remove all traces of the Timesaver before re assembly. You can turn the engine over with the hand crank (with the plugs removed) or rig a motor to turn the engine over. I have rigged a right angle heavy duty drill motor to turn an engine over. Turn it in the normal direction, clockwise from the front, so that the oil pump works as it should.
 
Thanks so much with the info. Would like a bit more advice on Iron vs Steel crank gear. Some mention was made about the proper fit.
 
Cast iron is brittle, like glass. It will break instead of bending. Steel will bend. Mild steels will bend more than harder steels, but neither is brittle. All steels will break if enough stress is applied. The harder steels will take a lot more stress. Cast iron forms a smooth surface when repeatedly rubbed. That is why it is used for engine blocks. Cast iron will wear better because of this as long as the stress is low. Hard steels are better for high stress areas such as exhaust valve seats instead of the cast iron of the block.
 
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