Engine Rattle Under Load

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86f250straight6
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Engine Rattle Under Load

Post #1 by 86f250straight6 » Mon Jan 08, 2018 8:20 pm

Ok I'll try to keep this long story as simple as possible lol. My truck the 86 with a 91? 190k miles 4.9 motor has a pretty loud rattle under load. It has done this ever since I swapped the motor, but the exhaust was louder and the truck had other issues so I could never really isolate the noise until now. What I do know-
It is most definitely an engine noise. Transmission is fresh, flexplate is new with arp fasteners for crank to flexplate and arp locking nuts for the converter with loctite as well. The dust shield is off at the moment to eliminate it as a problem however i shimmed the starter to compensate for the missing dust shield so it won't hit the flexplate. I had the oil pan off last month to replace the gasket, while doing that I replaced the rod bearings which showed some normal to moderate wear on the upper bearings but not enough to cause a knock (I've seen much worse that never knocked). I did not measure anything that I took apart, just did an eyeball job. The rod journals were immaculate so I went back together with .001 bearings to compensate for wear and put it all back together. The main bearings all looked great, all the cylinder bores still have cross hatching, the cam looked good from underneath, compression is good on all 6, I have zero blowby, my oil pressure is always above 40 before and after the work and reaches the top end (I can pull the oil cap and see good flow across the #1 rocker arms)

What I have not done yet, is pull the timing cover and inspect the gear, I know I should have just torn down the whole motor but when I had the oil pan off there were no pieces of anything in the pan just the typical goop you would expect for 200k miles so I assumed the cam gear must be ok. Also the head has never been removed so I have never inspected the piston tops only from the bottom side.

Could this be lifters? The dreaded piston skirt problems I've heard of? The motor is so smooth at idle, the noise only happens under load when accelerating, I can only get the noise in park when I blip the throttle just a quick rattle as the rpms go up and its gone and again when I let off. To add to this I'm running 5w40 synthetic, used to run 15w40 but the 5w really quieted things down in cold weather. Timing is set at 8* and I have driven with the spout unplugged and nothing changed so I don't think this is a detonation issue.
What am I missing here? This noise is driving me crazy it's so loud, but runs great. Im trying to avoid yanking the engine as I still put the truck to work 2 or 3 days a week so I can't have a lot of downtime for the forseaable future. I know that I have really gone about working on this truck the wrong way and should have yanked the motor instead of replacing one part at a time while keeping it on the road, but as they say hindsight is 20/20 lol. Any suggestions?
I'm trying to build a truck that I can't break :bang:

blmhawkeye
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Re: Engine Rattle Under Load

Post #2 by blmhawkeye » Mon Jan 08, 2018 8:51 pm

Do you have any way of taking a video while driving it under load to give more information?

First thought is engine knock from having distributor to far advanced, check of your base timing may be helpful.

86f250straight6
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Re: Engine Rattle Under Load

Post #3 by 86f250straight6 » Mon Jan 08, 2018 9:14 pm

its definitely a mechanical engine noise. Like i said in my first post, timing is currently at 8* and when i run it with the spout unplugged (no advance) i have the same noise. I have advanced the timing and tested it from 14* to 0* and it doesnt ping until i get over 12*. I know my timing is accurate as i matched the tdc notch on the balancer with 0* on the sawtooth scale using a piston stop. I willtry to get a video tomorrow and upload so you can hear what im hearing. It sounds like a marbles are bouncing on top of the pistons
I'm trying to build a truck that I can't break :bang:

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THE FRENCHTOWN FLYER
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Re: Engine Rattle Under Load

Post #4 by THE FRENCHTOWN FLYER » Wed Jan 10, 2018 3:12 pm

Assuming the rod bearings are correctly clearanced, I am going to guess cracked piston skirts. 200K on the original stock pistons is asking a lot.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

wallen7
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Re: Engine Rattle Under Load

Post #5 by wallen7 » Wed Jan 10, 2018 5:24 pm

My question is if the crank was in good shape why the .001 bearings, did you check the clearance? Was the noise the reason why you changed the bearings? I am with the FTF it is probably a cracked shirt on a piston. You can pull plug wires 1 at time and listen for difference in sound when you accel and let off. That might clue you as to which cylinder to look for. I don't think it would be timing gear for that kind of noise.

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bubba22349
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Re: Engine Rattle Under Load

Post #6 by bubba22349 » Wed Jan 10, 2018 5:27 pm

X3 on the pistons, also if your using a mechanical fuel pump somtimes they can be worn so badly on the pump arm pivot that it causes quite a loud knock. Good luck :thumbup: :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

86f250straight6
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Re: Engine Rattle Under Load

Post #7 by 86f250straight6 » Wed Jan 10, 2018 9:09 pm

I did the rod bearings as cheap insurance while I had the oil pan off to replace the gasket. They were showing wear but never knocked before, and i already had the rod bearings from a previous project so i threw them in figuring.001 would compensate for 200k miles of smooh wear. I didnt bother to measure anything since the old bearings looked good enough to just slap the pan back on and let it ride. Im surprised that if I have a cracked piston where i couldnt see it that i still had cross hatching in all the bores. I would figure they would come apart pretty quickly upon cracking.

I guess at this point im gonna have to yank the motor and replace the pistons and cam gear, and all the other stuff I didnt do the first time. I was hoping for someone to tell me what I wanted to hear lol but Ive convinced myself that the noise is too loud to be lifters or anything easy and that I might as well go over everything and do it right.
I'm trying to build a truck that I can't break :bang:

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THE FRENCHTOWN FLYER
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Re: Engine Rattle Under Load

Post #8 by THE FRENCHTOWN FLYER » Thu Jan 11, 2018 8:51 am

Well my attitude would be that engine gave me 200K - it doesn't owe me anything.
Yank it.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

wallen7
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Re: Engine Rattle Under Load

Post #9 by wallen7 » Thu Jan 11, 2018 9:54 am

Amen!

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