A Public service announcement for 4-speed owners

[Ceedawg]

Save the Crank | Ohio Crankshaft

They repaired mine, thrust surface, it was their crank too. Very nice job but I didn’t know they went through that whole process. Feel even better now. $200 to fix $50 up and back

 

[eldubb440]

I've been doing a some P/M on my 69 Road Runner survivor over the winter & while the radiator was out, I figured that I'd pull the water pump, balancer & timing cover off to replace the factory timing gears and chain. Of concern to me was the plastic coated camshaft gear. In spite of the car's low mileage (33,000 mils), I'm sure that plastic wasn't meant to last 52 years. No teeth were broken, which was a relief, but when I pried the crank gear off, I noticed that there was a strong 1/16" - 3/32' play in the crank, front to rear which isn't good. The next step was to pull the oil pan and #3 main bearing. Once I did that, this is what I found....

Front face of the thrust of bearing...

View attachment 1084959


Rear face of the thrust bearing...

View attachment 1084960

The actual bearing journal surface of the crank & bearing are fine with no scratches or debris imbedded in the bearing. I started thinking about what could have caused this & the only thing that I can come up with is the previous owner cranking a cold engine that sits for long periods of time while pushing the clutch in. With the clutch pedal is depressed, it pushes the crankshaft forward which in turn puts pressure on the rear of the thrust bearing & if it's dry (from sitting), this could be the end result.

Seems to make sense to me, but if anyone else has another theory, please chime in.

When I bought this car, I also bought a bunch of NOS parts & included were new main & rod bearings, so I put a complete new thrust bearing in which tightened the clearances up. There was a slight amount of wear on the side journal which made the end play slightly over spec, but I'm sure that it'll be fine. I'll be buttoning things up as soon as my cam gear set comes in & will report on things once I restart the engine.

We all know that it takes some cranking to get the gas up to the carb when th car has been sitting for a while & my advice now is to always start a cold 4 speed equipped car without depressing the clutch.

hold the phone....... if pushing in the clutch moves the crank forward, then pressure would be on the front face of the bearing, not the rear face.....the pics and description show the rear face torn up

 

[Richard Cranium]

hold the phone....... if pushing in the clutch moves the crank forward, then pressure would be on the front face of the bearing, not the rear face.....the pics and description show the rear face torn up

Nope, the pressure is on the rear of the bearing. I even had submit in the car press on the clutch with me underneath the car, and the crank pushes forward into the rear face of the thrust bearing.

 

[4mulas]

hold the phone....... if pushing in the clutch moves the crank forward, then pressure would be on the front face of the bearing, not the rear face.....the pics and description show the rear face torn up

Not quite right. The bearings are stationary in the cap and the block, as the crank moves forward the crank applies pressure to the rearward facing thrust surface.

 

[4mulas]

Nope, the pressure is on the rear of the bearing. I even had submit in the car press on the clutch with me underneath the car, and the crank pushes forward into the rear face of the thrust bearing.

Do you call your wife submit? Lol lol

 

[eldubb440]

Nope, the pressure is on the rear of the bearing. I even had submit in the car press on the clutch with me underneath the car, and the crank pushes forward into the rear face of the thrust bearing.

my bad.... I was still on my first cup of jo, and I knew I was right

I deserve a red X

 

[eldubb440]

Not quite right. The bearings are stationary in the cap and the block, as the crank moves forward the crank applies pressure to the rearward facing thrust surface.

second cup of coffee creates clarity

I need to get back in my lane and stay there

 

[Fran Blacker]

You can file the oil grooves deeper to add oil to thrust surface. Just don't go to the outer edge and increase oil loss. Need a center main might have an extra but mine are RB/Hemi.

 

[mopar 3 B]

Anyway that bearing does not spin or is not supposed to. It is cradled in the block and locked in place. Rapid hard acceleration and deceleration continuously will cause the same bearing failure. I have seen the same condition also with cars with automatic transmissions.
If the clutch in 33,000 miles caused a crank thrust bearing failure, just have to wonder how many clutch release bearing the previous owner went threw. Must have all been Cali rush hour freeway miles. I would also be concerned about differential slop ring and pinion clearances.

 

[Richard Cranium]

my bad.... I was still on my first cup of jo, and I knew I was right

I deserve a red X

I can count on one hand the amount of time's I doled out a red X and this doesn't rise to the occasion. But I'll be watching you.

 

[Richard Cranium]

Anyway that bearing does not spin or is not supposed to. It is cradled in the block and locked in place. Rapid hard acceleration and deceleration continuously will cause the same bearing failure. I have seen the same condition also with cars with automatic transmissions.
If the clutch in 33,000 miles caused a crank thrust bearing failure, just have to wonder how many clutch release bearing the previous owner went threw. Must have all been Cali rush hour freeway miles. I would also be concerned about differential slop ring and pinion clearances.

As I said in my initial post, I would tend to believe that it was most likely caused by over-cranking an engine that has sat for long periods of time with the clutch depressed.

 

[Michael_]

I dunno why one would want to press the clutch on cranking? Especially if this is taking longer...

 

[zyzzyx]

I noticed that you're not using a 360 degree grooved main bearing set. The rods only get oil
when the cross-drilled holes are in the grooved area of the bearings. No oil for 180 degrees!

 

[Cranky]

Don't know if anyone mentioned this before sticking the trans in neutral while sitting at a light is a good idea too....heck, I even do that with slush boxes.

 

[Richard Cranium]

I noticed that you're not using a 360 degree grooved main bearing set. The rods only get oil
when the cross-drilled holes are in the grooved area of the bearings. No oil for 180 degrees!

That was the factory bearing.

 

[mopar 3 B]

That was the factory bearing.

Factory bearing and perfectly fine for its intended use.

 

[mopar 3 B]

I dunno why one would want to press the clutch on cranking? Especially if this is taking longer...

Things called safety switches and idiots that could not take their vehicles out of gear would be the only reason I can think of. If the government had their way it would have been mandatory that one be seated and your seat belt fastened also. Something if I remember correctly almost happened with 74 model year vehicles.

 

[Charger Dana]

Do you call your wife submit? Lol lol

Once.

 

[Cranky]

Things called safety switches and idiots that could not take their vehicles out of gear would be the only reason I can think of. If the government had their way it would have been mandatory that one be seated and your seat belt fastened also. Something if I remember correctly almost happened with 74 model year vehicles.

Haven't drove a new stick vehicle in a long time but you have to press the brake pedal before the starter will engage with an automatic. Do you have to depress the clutch and the brake on the new stick shift junk before the engine will start??

 

[Richard Cranium]

Haven't drove a new stick vehicle in a long time but you have to press the brake pedal before the starter will engage with an automatic. Do you have to depress the clutch and the brake on the new stick shift junk before the engine will start??

Yes.