Changing out rod bearings

[White70C20]

Hello All,

I know its been a long time since I've been on here, between work and classes it's been a busy school year.
I've recently been given a '71 C10 - 350, 4spd. I'll try to post pictures when I get it home.
The main issue it has is that my friend thinks it's spun a rod bearing. He said the last time he started it, it started knocking. He immediately shut it off, and left it parked behind his house. That was two years ago.
Without having been able to start the truck yet, I haven't confirmed the knocking noise.

Anyway, I was wondering, how hard is it to remove the oil pan on a 2wd pickup? Also, is it possible to be able to remove the rod caps and replace the rod bearings while the engine's still in the truck. Has anyone tried this before?
Thanks!

[Jurassic-1]

You can remove the pan by lifting the engine up a bit. You then can pull the bearing caps as needed. Usually if it is making noise and is a rod the fix may only be temporary. I would check the engine out before you pull the pan. Possibly start it up and give it a quick once over it could be as simple as a rocker or lifter or even a fuel pump push rod.

[White70C20]

I hadn't thought of that. Thanks! Once I get it home I'll try and get it started.

[hamjet]

If it is a rod bearing chances are the crank will have to be turned. It would be ashame to go through all the work of laying on your back and money spent just to have it run for a while just to have a rough surface on the crank to eat away at the bearing and watch the oil pressure get lower and lower. Things that would have made it spin ( if thats what it is) would be too much clearence from worn bearings, or it ran dry of oil, maybe something else. As Jurassic said, rule out the other things first...

[truckster]

Originally Posted by hamjet

If it is a rod bearing chances are the crank will have to be turned. It would be ashame to go through all the work of laying on your back and money spent just to have it run for a while just to have a rough surface on the crank to eat away at the bearing and watch the oil pressure get lower and lower. Things that would have made it spin ( if thats what it is) would be too much clearence from worn bearings, or it ran dry of oil, maybe something else. As Jurassic said, rule out the other things first...

If it is a spun bearing, it's likely damaged the crankshaft and enlarged the rod end. You can check it out by removing the pan. If you decide that you can just replace the bearing (not what I would recommend) the cheapest way to check it is Plastigage. You can buy it at most any parts store. You'll need to clean any oil and dirt off the crank surface and the inside of the rod. You put your new bearings in the halves of the rod, and then put a piece of Plastigage across the face of the rod bearing and torque it to specs (50 ft-lbs if I remember correctly). The Plastigage will come with a scale that shows what kind of clearance you have.

Of course, all of this only works if there's no visible damage to the crank. If it's gouged, the bearing is going to be eaten up pretty quickly once you start the engine.

[GASoline71]

If there is no damage to the crank... you'd be pretty lucky.

If it were me personally... I'd overhaul it.

Gary

[67 chevelle]

I have had success replacing a rod bearing in the past , it was before the knock though ,, the 350 in my truck was low on the oil pressure ,, I took the engine out turned it upside down on the stand ,, removed pan ,, and found one rod that had slight play ,, replaced the bearings on that rod and its been good ever since ,, has great oil pressure now . Crank was clean and smooth ,, if your crank is rough ,, it needs turned

[White70C20]

Thanks guys! I think I'll just try to start it the way it is and see if is a knock or not. The guy who gave me the truck isn't a mechanic, so it might not be as bad as it seems.
I am planning on rebuilding the engine in class this fall.

[hugger6933]

We are talking ifs here but if it is a bearing and if it is a spun rod the cheapest thing would probably buy a crank kit and put that in the truck

[GRX]

All great advice so far. Very understandable you want to drive the truck ASAP. If you are planning to completely rebuild the engine this fall patching up the lower end would largely be a waste of money. Speaking as one who has reconditioned countless conn rods, every one I have seen with more then a few miles on them have stretched & need to be resized at the big end. Best to do things right so you can enjoy years of worry free driving.

[Aruba1]

In my case my truck was acting up and when I pulled on the side of the road the holley flooded really bad. I went ahead and changed the oil on the side of the road and fixed the carb. I drove it home and it flooded again. This time I rebuild the carburetor, added fresh oil/filter and it has not flooded since. But when I rev it up to 2000 rpm and let it the throttle go, I can hear a quick knock in the crankcase. But I still have about 45 psi idle pressure. I am removing the engine this weekend for a 5.3L swap but I also want to replace the rod/crank bearings if the crank is not gouged and store the engine. I believe it will be okay as it only knocks (for a split second) when I rev it and let the throttle go. What do you think? Should it be okay?

[GASoline71]

Rod knock leads to catastrophic failure.

So anybody just hoping to put a band aid over a knocking rod will be in for a new engine or complete rotating assembly down the road.

I agree with GRX (who is a machinist)... at the minimum have the rods reconditioned.

99% of the time we're talking 40+ year old original unmolested internals in these hunks of iron. When it starts rotating and lets go... something will have to give... usually the block.

Not saying that putting new bearing inserts in the rods won't "fix" the problem... but if ANY rod has been knocking for even a short period of time... It can be out of round and the bolts stretched.

Gary

[VWNate1]

What Gary said .

However , if you just want it to work a while longer until you can replace the engine , go for it .

As soon as you look at the crank journals , if they're matt finish , they're toast , stop .

Same goes if blue or black .

The boob who ' rebuilt ' (B.S.) the BMC 1500 engine in my '59 Nash Metropolitan , didn't bother rebuilding the connecting rods , it had low oil pressure @ idle but ran fine for 10 + years of daily driving plus Road Rallies before I recessed a valve and decided to dip into it ~ the bearing shells were loose in the rod caps and un evenly worn because of this .

However , the .030" crank journals were fine and mikes out perfectly round so I rebuilt the entire engine apart from having the crank ground again and it's been fine ever since .

Point is , no one can tell you what you're going to find inside , this is an old 1960's tech engine that's simple and durable , give it a look , the worse thing will be : it's bad .

If you're really in a $ pinch , flip the engine and replace the crank with a good used one and slip in all new bearing shells...

[White70C20]

I'll try and start it when I get it home tomorrow. If it starts, I'll try to figure out if it truly is a rod knock or something less damaging. Someone early on in this thread suggested that it might be a lifter, rocker arm, or something else.
I'm not sure it'll start with 2 year old gas in the tank.

[tcrist]

I would get a mechanics stethoscope (or something similar) and listen real close to where the "knock" is coming from.

These motors have nylon coated teeth on the cam timing gear. I have had the nylon come off of one tooth before and stick in the timing chain. It then would hit the timing cover on every rotation.

[sawman]

I agree with gasoline71,if you already hear if knocking its to late,time for a rebuild,check to see if your timing is off,drain oil in clean container look in bottom see if theres any metal/brass,is oil pressure low,old school with engine running pull 1 spark plug wire at a time off plug and see if knock stops a lot of time you can pin point it to which cyl is making noise,been here a lot,putting new bearings in a engine that knock wont last long,if you are not planning on rebuilding the engine and don't care if you end up with a connecting rod hanging out of the block have at it,lol,good luck but if its knocking time for a rebuild,if you have to drive it,drive slow,put thicker oil in it,

[White70C20]

I brought the truck home today.

I talked to my friend more about the engine. He said that the last time he started it (2 years ago), it knocked 5 times and then he shut it off. He said he wasn't sure how much oil was in it. Could low oil cause a knock/spun bearing? If I were to change the oil and put in new, thicker oil, could that help the problem?
I'm not going to drive it much, but if I can get it so it could move under it's own power when I load it back up on the trailer when I take it back to the college that would be great. Plus, it might be fun to take it for a quick spin around town.

Thanks!

[Jurassic-1]

A rod knock is never good . Even if the oil is low there should be no excess clearance to make the engine knock and yes it can spin the bearing. I would get it started for a short time and as posted use a stethoscope to help isolate the noise and check the oil in a clean pan. You can also cut the filter open and check for bearing shavings. If there is any signs you will need to remove the motor for either a rebuild or replace the engine.

[White70C20]

Yes, I am planning on rebuilding the engine in class this fall.

[sawman]

I worked as a engine rebuilder for over 20 years,rod knock is not good everything that has to do with that bearing will have to be checked and replaced,crank reground or replaced,rod and cap connecting rod piston and check cyl for wear all get affecting by losing oil pressure when a bearing wears out,

[Aruba1]

What if I still have good oil pressure and it ONLY knocks when I rev it and let the throttle go (it only knocks for a split second or so).

[GASoline71]

Then you are doing more damage every revolution of the crank shaft. You guys keep messing around with a no kidding rod knocking and you will trash your engine. Oil pressure can have nothing to do with a rod knock.

Having a knocking sound only when you let off the throttle and a slight knocking at idle is classic symptom of a rod knocking. Serious damage is occurring.

Gary

[Jurassic-1]

Is the engine running now? Are you sure it is not a lifter? It could be possible to have oil pressure if it is not too bad . I still would do a bit more research on it and check the oil and filter. You may get lucky and have a collapsed lifter or worn fuel pump and push rod.

[GRX]

Well said GASoline. At this juncture it may be prudent to point out that oil pressure is not always a good indicator of a bad rod/bearing since most pressure sensors are located either at the filter adapter, or on top by the distributor which are before the crank. See the oil flow pattern in the following image.

[sawman]

if its a automatic put it in gear with brake on give a little gas you might here it knocking,losing oil pressure happens when bearings get worn main/rod bearings,oil gos up the connecting rod oiling cyl,bearings get bad you lose oil pressure,i agree with gasoline on how you need to check oil and filter any metal just shut it down,too many things can be wrong,if it knocks after you let off throttle as motor is winding down I would say its a bearing,the more you run it the more damage you are doing,remeber small block chevys have very small rod bearings time it gets to the knocking stage its to late,