I have a similar 460 knocking noise question as was below post for the experts.

I just purchased a 1993 F250 4X4 with a 460 that has about 138,000 on it. I am hearing a slight knocking noise (seems like from the bottom end of the motor) It happens when the truck is in-between shifts (auto trans) with only a light accelerator pedal applied or when I am cruising at highway speeds (60-80) and then I lift off of the accelerator pedal letting the truck push against the motor. Any ideas? My best guess at this point is possibly lower rod bearings, but this is just a guess. What is a tel-tale way to determine the cause. I do not get any knocking noise at idle, when I hammer on the throttle or even when going up slight hill (under slight load).

Any help is greatly appreciated.



1993 F250 XLT x-cab 4x4 460 (Just Purchased) Lot's of plans

1994 F150 XL x-cab 4x2 300 In-line 6 3"lift 33's K$N filter
(Recently Salvaged and rebuilt due to Altenator wiring fire) Blessing in disguise!

 

Hoo-boy...That's a classic symptom of a rod knock, it's worst when the engine is "floating" against the drivetrain when you feather the throttle, neither accelerating or decelerating but the slightest amount.

I hope I'm wrong for your benefit, and I wouldn't feel bad about it in this case, but that's what a rod knock feels and sounds like (been there, last time it was a company-owned Chevy S-10 Blazer, oil pump failed, blew bearing immediately, 4.3L Vortec V6 engine...$4 grand to replace at a dealer)


Good luck.

-Bill in Colorado

 

[updated:LAST EDITED ON 12-Jun-02 AT 04:35 AM (EST)]Have to go with Bill and the the rods knocking.

 

Aare you guys talking push rods or connecting rods? You could just drop the oil pan to change out the connecting rod, but push rods would have to come out through the top end right?

 

Guys,

Thanks for the posts. So, if it is lower connecting rod bearings how do I take care of the problem? Can this be done in the home garage and is it recomended? I am fairly mechanical but what are the big concerns when doing something like replacing lower connecting rod bearings and do you have to remove the motor to install the bearings (it is 4 wheel drive)? I have heard in the past that if you do replace the lower rod bearings then it may cause stress on other parts of the motor and then they go out soon after so it is not recommended? do you aggree?

I have also looked into just buying a longblock 460 with a 3 year, 36-100,000 mile warranty and drop it in and it seems like they go for $1700 -$2100 any good info on costs and suppliers on rebuilts available?

:-staun

 

With 138,000 miles, I don't think it's worth replacing only the rod bearings. Who knows what else is worn out in it. You won't know until you pull the caps off the rod ends whether the crank is worn out or damaged, either. Your engine is simply at the end of the line for now.

You really ought to pull it and rebuild it or get a fresh long block.
IMO, it's just not worth slapping new bearings in there, unless you just can't afford to do anything else right now and you need the truck.

Good luck,

-Bill in Colorado

 

I was working at a dealership once and a customer bought a f250 with a 460, he came back a couple of days later complaining off the same complaint as yours, anyways it was my job to fix the problem. Well our over qualified service manager said just put rod bearings in it so after fighting the oil pan off with the engine in the truck
I plastigaged the new rod bearings and gee if there was to much clearence. So from my experince pull the engine get the crank ground and replace both rod and main bearings and if the budget allows maybe rering it Eric

 

Guys,

Thanks for all the posts, I believe I will go with my first gut instict and just drop in a new LONG block when it come to that point. The guy I am buying the truck from just took a $1000 off the price of the truck today anyway (due to the knock). $4000 total for the truck to good to pass up It's clean to.



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