The Stovebolt Site Forums The Shop Area Engine Shop Rod Wear

I've had my C20 for a couple of months now. It has the original (checked the numbers) stock 292. As the new owner, I did all the usual good stuff like changing the oil (straight 30w) and filter twice in the first 200 mi. (it was black), complete tune-up, carb rebuild, etc.
The motor runs like a champ. But, the connecting rods rattle very slightly at idle. You have to listen closely to hear the noise which goes away above about 800 rpm or so.
The stock oil pressure guage shows about 45-50lbs cold, and a hair below 30lbs warm at idle. Is that lower than it should be?
Just wondering what the life expectancy of the big 6 is when you have a little bottom end noise like this. I drive this thing very gently. No hard use, easy-does-it city driving.
I know this is something that's hard to predict, but I guess I just wanted to find out if anybody has an opinion or an experience to tell about.
Hard to imagine, but I've been working on cars about 28 years now. Mostly old European stuff. Once you start hearing anything from the bottom end on one of those, you might as well tear 'em down.
I'm really hoping I can get a year or two of use out of this one before I have to get into a rebuild.
I've heard going to 50w might help.
Any advantage to going to a heavier weight oil?

This is just my opinion.If you have bottom end noise,tear it down and fix it.Going to a 50 wt. oil will just tend to muffle the noise a little.It will not help anything.The longer you run it the worse it will get,and the more expensive to fix.

Generally, rods do not "rattle" at idle. A loose rod will have a distinct metallic ring when you rev the engine a little, just as it transitions to no load. Wrist pins rattle at idle and that means absolutely nothing. They start doing that fairly early in life and never quit but it is not a threat to your engine at all.

Your 30 lbs oil press at an idle after engine warms up to operating temp is an indication your rod bearings donot have excessive wear. the noise your hearing in all likelyhood is just as truckernix explains. also the 292 may be a bit more prone to acquire these rackets due to the piston speeds if the engine was ever turned a little hihger than is normal. I have seen these engines run many miles with these noises....Ronnie

Thanks for the info.
The sound is almost like a deisel motor sound, only a whole lot quieter than a deisel; like rolling marbles around in a wooden box.
I've heard my share of bad connecting rods and I know what they sound like when they're getting ready to let go.
This sounds kinda more like a well-broken-in tractor motor.
Never heard of wrist pins rattling as a normal thing. But I'm in Chevy territory now and eager to learn.
I just want to treat the truck well and get the most life out of it I can without blowing it up. you're thoughts and advice are much appreciated.

Hey, you will get all the GMC types all upset talking about being in "Chevy" territory! Actually the two lines of engines had a lot in common down through the years.

oops!
Actually, I'm partial to all of the fine General Motors products!
Sorry!

Well you see up here in Canada, with the AD trucks, we didn't have this class struggles! They made GMC trucks with Chevy engines and large Chevy trucks with GMC engines. Talk about your mixed breeds!

You're not hearing connecting rod noise. It would get LOTS louder as you revved the engine up. Your oil pressure is still pretty healthy too, there's no major wear in that engine. Just another thought, but you could be hearing lifter clack or other valvetrain noise. The sound could be getting transmitted so it sounds like its coming from somewhere else. Neither of these are fatal problems.
I don't know if the 292 has hydraulic or mechanical lifters or how valve adjustment is accomplished on that engine. I'm sure someone else will chime in..

It's all in the family.
Right?

What you're describing is probably piston slap. If the engine has been overheated at some time in its life, it's not uncommon for the pistons to swell, and collapse the skirts a little. After that, especially during warmup, there will be enough piston skirt clearance for the piston to flop around and make a knocking noise. If that's what's happening, ignore the noise. It is annoying, but not dangerous.
Jerry

Thanks, Jerry. That might explain it.
Like I said, it runs great and doesn't smoke at all.
So, I guess I'm ok running 30w?

The 292,s are heavy duty truck engines. The are fitted a little loose. Piston slap is pretty normal for them when they get a little older. Jerry is right it won,t cause any problem.

The 292 that's in my 63 now, would make a F*rd diesel sound good whens it's cold, the piston slap is so bad. It runs a little below thirty pounds oil pressure at idle (warm) and little over on the highway. The Compression is between 65 and 105. I just broke even on the replacement, today. A 292 with 10k (so the story goes)on a rebuilt long block. Runs a little over thirty at a very slow idle. Has between 95-110 compression. I'm hoping that sitting four years (no oil on the cyclinders) is why the compression is low should be closer to 130. Hope fully it will be on an rngine stand next weekend. :p
Larry

I used to have a worn rod. Then I got married. Problem solved.

tlorber, hope you used "plastiguage" before the wedding

it could be loose wrist pins i had a ford 6 once and it sounded like marbles at a idel it never gave me a problem i ran that car harder then a race car for years

If you want to try a different oil to quiet things down, I've had good luck with Chevron Delo 15W-40. For some reason it makes my valvetrain in both my BMW and my 261 a lot quieter. It also has a good detergent package and is relatively inexpensive. It's rated for both diesel and gas.