Mystery ticking sound located - what caused it?

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roadrunnerh

roadrunnerh

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Ok my Mopar brethren. So my '75 Scamp 225/904/8.75 had a ticking sound since I purchased it last Fall. It would only make the sound when the car got good and warmed up. It would only do it in gear, not in neutral or park, and once you gave it gas and started driving it would go away.
It was driving me nuts as I used a stethoscope all over the motor and exhaust.
It turned out, the noise sounded louder when I pressed on the torque converter access plate and sure enough when I listened with the stethoscope - BINGO - that's where the noise was coming from. I jacked up the car a loosened the two center bolts holding the cover in place and the noise disappeared. What was causing this ticking? The flex plate hitting the cover ever so slightly??? PLEASE offer your thoughts! Thanks guys!
 
Didja check the torque converter bolts for tightness?, and were they the right ones?,...I'm pretty sure they should have fairly short heads w/5 lines on em, meaning they're grade 8 bolts...I'd pull the cover and check the bolts just for gits and shiggles.
 
I didn't remove the cover, just lossened the center two cover bolts.
Do you think the converter is loose?
 
Might be, but I doubt It, usually that will cause ticking on accel and decelleration. Slight chance flex plate might have a hairline crack. Hopefully It's just a slightly bent cover.
 
Hitting a critter can band that tin cover enough to cause a conflict. I'd pull it and make sure you don't have a bolt backing out.
 
Check the tightness of the 4 converter bolts. They should have thin heads, either they are loose or the end play on your crank is allowing the crank to go forwards in the block and cause the noise. Other words your thrust bearing is worn out.

99.9% chance it is you have the wrong bolts or bolt. Or they are just loose. Let's go with loose!
 
Pull your inspection cover look on the inside to see if there is any marks were some thing is making contact with it. Is the cover slightly dented?
 
Well, I removed the inspection cover and all four flexplate bolts were tight.
I could see where the inner portion of the flexplate was making slight contact with the cover. The cover itself looked good but was ever so slightly bent in toward the center radius. I pushed on it a little after I cleaned it so it would bend out away from the flexplate just a little. I bolted it back on and when I started the car no noise. I really can't tell until I run it and let it get hot - that's when the tapping would start.
Hopefully problem solved!
 
There is a thrust bearing in the center of the crank. The torque converter pushes the crank forward and wears the the thrust bearing. That end play / movement is why the noise only appeared when the trans was in gear. Some amount of end play is typical. The flex plate absorbs most of the pressure.
2 options, carry on / happy moparing or measure the end play. If you find it out of tolerence and worry about it until you convince yourself to rebuild the engine...
First option sound better huh ?
At least now you know why the noise would come and go. Good luck with it
 
roadrunnerh said:
Could the thrust bearing wear that much on a slant 6 with 48k miles?
Click to expand...

Anyones guess as to how much end play in the crank. Like I said before the flex plate absorbs most of the push ( as it should ). It may be the only thing moving.
 
A thrust bearing on an auto; rubbing head hard on that. Pilot bushing for a manual. Thrust bearing for an auto? The convertor snout won't fit in the crank.
 
green1 said:
A thrust bearing on an auto; rubbing head hard on that. Pilot bushing for a manual. Thrust bearing for an auto? The convertor snout won't fit in the crank.
Click to expand...

Sorry, I didn't mean its in the center of the diameter. It's in the center of the span. lengthwise.
 
It's just a bolt head touching the cover as it goes by.
Take it off and slightly bow it towards the front of the car and put it back on.
It's actually really common and sometimes takes more than one try to get it clear.

That's all it is, no more no less.
 
green1 said:
A thrust bearing on an auto; rubbing head hard on that. Pilot bushing for a manual. Thrust bearing for an auto? The convertor snout won't fit in the crank.
Click to expand...

Just to clear things up, the thrust surface referred to is on the side of the main bearing between the crank shaft and the bearing shell inside the engine itself. If the clearance is too much, the crank in effect rocks back and forth moving everything attached to it (internally and externally), that's why it's possible that that ''slop'' from a worn out thrust bearing surface could be dragging the converter, flexplate, and bolts into contact with the tin cover. It doesn't take much, say for example .040'' is way too much and could cause the problem. It is more common on high mileage engines especially if they have a standard transmission behind them, and wears over time.
I hope this helps.
Tom.
 
Sounds like you located the source when you played with the inspection cover. This prompts a story.

I was driving on a dirt road near Wrightwood, CA in 1986 in my 69 Dart slant when I came upon a Scout Troop in a ~66 Dart slant blocking the road and working underneath. The leader had hit a rock and bent the cover, making a terrible sound. I said good luck and drove on. A few miles later, I hit a rock with the same result. Once home, I removed the cover and bent it back. No sound in N, but when I drove the next morning, it made a racket in D and woke up the neighbors. Rebent again and fixed it. So the sound can change depending on engine speed and load and it can make a racket.
 
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