knock knock now what

[asatxj]

Earlier this week many suggested that I locktite the flex plate bolts to eliminate a tap/knock I have developed. I did that and the noise remains. It doesn't sound as harsh as a bad rod bearing. starts after the engine is warmed and idles for about 1 minute. Rev it pst 1000rpm and it goes away, let off and it returns. Engine has 55k and gets an oil change next week. Oil level is full and it gets 10w30 every 3k miles. Runs well, very strong. I hate to think bearings as the engine is young and all looked good before I installed it last summer.Exhaust leak? Ideas?
TIA
asat

 

[DaveD in Canada]

Have another look at the flex plate, check carefully for a crack. I saw a post where it was suggested the noise from a cracked flex plate diminishes under load. If its not that, perhaps invest in one of those inexpensive automotive stethoscopes, its a great tool for pinpointing noises!
How is the oil pressure? I'm assuming this was a rebuilt engine that now has 55K on it, was it fitted with new undersize bearings and reground crank, or just replaced the bearings? Doubtful its rod bearings, as I would think the noise would get worse as rpm increases or under load.

 

[asatxj]

The motor is out of a 97 with original miles. I didn't see any thing out of the ordinary on the flexplate. I had a really good view of it as I was turning it. The bolt that was not as tight as the others looked as if some moisture had seeped from the hole (tiny amount of rust there) but I wiped it off and everything looked solid. Next move will be the 'scope I think. Just for grins i'll put 10w-40 in it next time. My oil sender doesn't work well but we inspected the pump and it appeared fine. I'll grab one of those shortly too. The local AZ needs to give me my own parking space.

 

[AndyS]

Could it be a lifter that isn't maintaining pressure? Warm engines make less oil pressure at idle than when cold, so it might only show up then. Revving the engine up over idle might make just enough pressure to pump it up again...

Or is the sound coming from the rear of the motor? (Sorry - didn't see your original thread for a description...)

Andy

 

[asatxj]

Rear lower Andy. I may have to invest in a flex plate. I'll have the guy that did the motor swap with me put it in since I don't have the time to do such a task and last I heard he was unemployed. I'm sure he can knock it out in a day or so. Might even have to get a new trans mount too.
Any one remember who sells them other than the stealership?

 

[Eagle]

When the flex plates crack, it isn't a radial crack. It's an annular (circular) crack that forms right around the outer perimeter of the steel reinforcing ring for the 6 bolts holding the flex plate to the crankshaft. It can be seen from beneath the vehicle with the inspection plate removed if you take a long pry bar and pry the bottom of the flex plate away from the block. You will need a strong light, however. The crack doesn't go all the way around (initially), so you should repeat the inspection several times, rotating the flex plate +/- 60 degrees each time.

Quick test: Start engine. Leave at idle. I assume yours knocks. Put in gear with foot on brake. Knock should reduce in intensity. Apply slight throttle, in gear. At around 1200 to 1500 RPM the knock should go away. If so, suspect the flex plate.

 

[asatxj]

Yup Eagle, I've done exactly what you suggest (idling put in gear etc) and it responds as you say. I guess I'll go get a new one and have my friend install it. I can't tie my dad-in-law's garage up that long since I can't take a day or two off to work on it. Since it just started I hope it will live a week or two of limited use until I can get the parts. I'm gonna get sick of driving the wife's Caravan!! anyplace other than the Stealer who sells them?

 

[Eagle]

The one I bought was a Crown, but they seem to have recently revamped their web site and I can't find flex plates.

The nice thing about Crown, though, is that they use Chrysler part numbers. Get the part number from your dealer parts deptartment, look up the nearest Crown dealer in your area, and call them.

 

[asatxj]

Sounds good. Do they carry transmission lines too? mine are leaking and we might as well to that "while we are there".

 

[RichP]

This seems to be popular set of postings lately or is it my imagination that I'm seeing alot of flex plate issues. Anybody tracking the years and such ??. What causes these flexplate problems ?? Loose bolts lead to cracking flex plates ??

 

[asatxj]

I don't know what has brought on the rash of them. When I tightened the four that bolt into the TC only one was not totally snugged down and it was only loose by a minute amount. Since the fault usually happens around the center of it the cause must be movement at the perimeter. "wobbling" so to say. Mine went 215k miles before trouble. I would be interested in the causes beyond a loose bolt. Eagle? anyone?

 

[Eagle]

I don't know what has brought on the rash of them. When I tightened the four that bolt into the TC only one was not totally snugged down and it was only loose by a minute amount. Since the fault usually happens around the center of it the cause must be movement at the perimeter. "wobbling" so to say. Mine went 215k miles before trouble. I would be interested in the causes beyond a loose bolt. Eagle? anyone?

I have no theories on cause. The one I replaced was an '88 Ledo with a65,000 miles. Although I bought it from a guy in another town, in turn he bought it from the daughter of a neighbor on my own street. I spoke with them and she sold it because of the knocking noise. The guy had dropped the oil pan assuming it was rod bearings, and when that didn't work his father decided it needed an engine and made him sell it.