350 knocking (1 Viewer)

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HawkDriver

HawkDriver

Joined
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Hey folks,

Well in the past week I've pushed the 40 farther and faster than I ever had before, totaling about 8 hours of running at about 2700-3000 RPM. Well just as I pull in on my street she starts making a "rod knocking" sound. I'm pretty familiar with the sound, in fact my car is in the shop getting this same problem fixed under warranty right now. I just had the oil changed the day before this last trip.

The thing is that it goes away and comes in and out on it's own at and just above idle RPMs. I've ran it a total of about 1 minute since it started. I am almost positive that it's not in the flywheel clutch area nor in the trans. I was pretty sure that when I pulled the pan I'd find a loose rod cap/bearing but they all seem tight and there are no chunks in the pan, just the normal fine filings. I even had the wife start it up with the pan off for about 5 seconds to try to locate the noise, couldn't but I'm fairly certain it's in one of the aft 4 rod/main areas.

The only other thing I could think would be the pump shaft or possibly a lifter. I'm pretty sure it's not a lifter though, and when it's there it's constant and rapid just like a rod knock.

So, I'm trying to plan my actions. Right now I have the pan off, I'm thinking of putting it back on and filling it up again then trying to locate it once more. Then pull the trans and clutch to completely isolate the engine.

If it continues should I pull the rod caps and then main caps and check the bearings? I would normally hesitate to pull those once they're broken in but I'm pretty sure one's bad.

Or should I just pull them now before all that work to see?


Any suggestions or thoughts? Thanks.
 
Drop the rod caps, one at a time after marking them with a dot (using a punch) on the cap and the rod to mark how they came apart, and see what kind of mess you have. If the crank is not tore up and the rod is not hot or hammerd, clean up the crank, install new rod bearings and run it.


Good luck!


-Steve
 
Sho Nuff...

Thanks for the encouragement, it probably saved me many hours. :beer:

Well here's what I found. The journal in the pic is #7-8 and at first it looked good on the one side but this was on the other. :frown:

Then the bearings are #8-1 Left to Right. #8 is bad, 7 is fine, then 5 is really bad and the rest are pretty $hitty.

I'm gonna play it safe and just pull the crank and pistons/rods and get em machined. The cylinder walls all looked nice so far. But then I'm just worried, do I stop there and assume that the top end will hold together fine for a while, or do I pull the whole damn thing and rebuild it? Whaddya think?

It's been a while (about 8 years) how much is fair for a crank turn and rod machine?

How fawkin ironic: My wife's car is in the shop for the same thing which is the reason I had to drive the 40 on the trips, only to come back and have em both be fawked with the same problem :rolleyes: . Now I'm without trans. Car better be done by tomorrow, it's been a freakin week. :mad:

It's about time I had to get dirty workin on the beast. :D It'll be fun.
Rods 008 (Medium).jpg
Rods 011 (Medium).jpg
Rods 016 (Medium).jpg
 
In all honesty man, I would run some 240 or 320 1" wide emery cloth on that throw, put in new bearings, torque it up and see how it is. I have dressed far worse than that, and they are still running fine. Those bearings are washed out some, but I have seen far worse.


But, if you have nothing but money and time, pull the engine, and install a new crate engine! :beer:



Good luck!


-Steve
 
A few things make me wonder though.

Looking at the backs of the bearings and the rod surfaces themselves, it seems like the "majority" of the contact was only on the top and bottom as if they were out of round instead of perfectly round which might have contributed to the failure. Possible bad rebuild previously?

And/or were they just fine before the trip and I rode it too hard, or were they on their way out and the trip just pushed em over? Hmmmmm.

And what the heck is normal RPMs for a 350, what is the redline. Prolly depends on the block and components... Mine's got 2 bolt mains.

Thanks. :beer:
Rods 006 (Medium).jpg
 
I'm with Poser, clean'em up and run it.

Otherwise check out the prices of new cranks at Summit or Jegs before you head to the machine shop. That way you don't pay more to get your old crank ground vs. buying a new crank. If the bores are round, straight and in spec you might also consider a new rotating assembly (crank, rods, pistons; all balanced) instead of messing with old stuff. Cheap part prices are one of the reasons to run a SBC in the first place! :D

Nick
 
Right!


A set of standard rod bearings at Wall Mart are what, 20.00us?
 
Redline for most "normal" (read passenger car/light truck/not high performance) SBC is 5500 rpm. 2 bolt mains are perfectly fine up to around 500 hp so I wouldn't sweat that at all. The cruise rpms you mentioned are not an issue for a 350 as long as the oil pressure stays where it needs to be.

Nick
 
HawkDriver said:
Very true! I like the idea. Um, these ones are already .040.
Click to expand...



.040...


Might have fun finding them at Wally World...



Good luck bud!


-Steve
 
Yes I know it's obvious but just to confirm, these are .040 right? And THESE seem to be the least expensive easiest to find bearings. I think I should be good to go with these. Any objections?

One other thing, should I pull the main caps and check em out too? And I havn't seen emery cloth rolls forever, where can I pick some up, TSC?

What do you think caused this to happen? Just their time to go, or is there some other problem I need to address?

Thanks fellas!
rod (Small).jpg
 
Like Steve said, those bearings don't look bad. When the engine was running did you pull the plug wires one at a time to see if you could make the knock disappear? It looks like close to normal wear for an engine with fair miles on it.

Your mention of it coming and going causes me to believe you may bolt it back together and find the knock remains. A bad enough cam lobe or collapsed lifter can make it sound like it's on the bottom end and it can even be caused by a stretched timing chain slapping the timing cover.

Since whoever built that motor was cheap enough to put in a -0.040 crank I wouldn't doubt it was built with all used parts and no concern for proper tolerance.
 
Last edited:
The wear patterns on those bearings don't look out of round to me. Those look like they wore normally.

Throw a micrometer on the jounals if you're worried about it.


If you pull the crank, I sure wouldn't mess around with a 040 crank. You can buy one already conditioned off of eBay for about what it would cost to remachine that one.
 
If the noise does remain after work on the crank, I'd suspect a lifter. My experience with 350s is that sometimes the hydraulic lifters will stick and create intermittent knocking.
 
Yeah, I was thinking it might be a lifter too.

Nope, didn't pull the plug wires, good idea. :frown:

The sound surely was coming from the back end so I don't think it was the T chain.

Yes, after looking closer, they appear to be worn normally. It was the marks on the back side of the bearings and on the rods that got me thinking they were, but like you said the wear seems to be even across most of the bearing.

I'll go with those Ebay bearings since it's cheap to try and if it's still there I'll pull the intake and check the lifters.

Thanks guys. :)
 
Since you will be waiting for the bearings....go pull the intake... ;)



:beer:
 
On the road again!

I'm happy to announce that I got the bearings installed and it fixed the knock. :D

Only ran it for a few miles but so far so good.

Thanks everyone.

:beer: :beer: :beer:





I ended up using 280 emery strip cloth and polished those grooves right out. For any future readers I'd recommend that if possible do two rods at a time so it will be easier to turn the crank in order to polish all the way around without the other rods getting in the way. :cheers:
 
I'm coming in late on this thread, but here's my .02.

The wear on the top and bottom of the bearings is normal. That is where most of the strees occurs. The piston pushes hardest and the shock load is hardest when it is at the top of it's stroke on the intake/power transition. The loading on the rod (tension, not compression) is highest when the piston reaches the top again and is yanked down by the crank on the exhaust/intake transition. It's normal to see more wear on the matching section of the bearing.

Personally I would not have reused a crank in that condition without machining. I'll be curious to see how long/well it holds up for you. I'm hoping it holds up. I'd not be disappointed to discover that I'm overly finicky about what is acceptable when it comes to bearing surfaces..

I've got a 350 I'm going to have to open up in the next month or tow to replace bering in. It was run low on oil for a very short time and has not held good pressure ever since. (Idles at about 12 and only holds 35 at 2500-3000 rpm. I'm hoping that I will find accelerated wear on the bearings but a crank that doesn't have issues. :(


Mark...
 
Thanks Mark,

What you said about wear patterns makes sense. I'm also wondering how far this fix will hold up but it was too cheap and easy to not try it. I might just have to keep another set of brngs and cloth as spares for long trips to get me home. If it fails again I'll likely go with a crate engine.

I'll surely post up again with any further developments.
 
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