Name that sound!

[Tiny Trucker]

Piston slap, mains, big ends, timing chain?

Motor is cold, goes away after about 5 seconds (like in video)

I've only done approx 1000 - 1500 miles since I bought it off the previous owner (a mechanic), pretty gutted to say the least.

I swear I can hear a similar but very faint sound when driving under load. I have had an engine in another car with big end knock and that gets profound at a particular rpm, which this doesn't seem to, which makes me think it might be mains.

Its a 350 TBI with 99k

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[89RCLB]

I would like to know what that noise is too, my '89 Chevy with 176K miles does the exact same thing. Once it's running I never hear anything more from it, even when getting on it. I keep waiting for it to grenade but it keeps on tickin'. I'm inclined to believe it's a rod bearing but that's a way wild guess.

 

[C30454]

It's a big end rod bearing that is on the loose side. It shuts up when it gets oil pressure. It might run for years like that if you drive it normal.

I've serviced cars and trucks for 35 years. It is not uncommon to hear many rods , just a few, or none, rattle on initial startup after an oil change. I've heard it on perfectly good motors with 20,000 miles on them.

While no one wants to hear a rod on the loose end od clearance on startup, you can't accurately use that as confirmation of an imminent problem.


If you warm the engine up fully and quickly vary the rpm between 1000 and 2000 rpm can you hear the same noise?



Tom

 

[99jeb99]

Definitely a rod knock, but I never heard it completely go away. It could last for a bit, but I wouldn't push that motor hard at all. What's the oil pressure? I'd pull a valve cover and take a peak.

Truck engine bay looks clean, but a rod knock at 100k suggests to me that someone possibly didn't keep the oil changed properly at some point in its life.

 

[Tiny Trucker]

Oil pressure is good, about 45 on the guage.

Thanks guys. I was pretty confident
it was a mains knock, but regardless if its a main or a big end it has to be fixed, so the truck has been parked up and I will use my other car until I can spring the $$$ to get the crank out and everything measured up for a new set of bearings (gaskets, main seal, cam bearings etc)

Any and all advice is and has been appreciated, cheers.

 

[Hipster]

#1 main

 

[cookseyb]

Try some 15-50 Mobil 1, my 99 5.3 had so much piston slap when cold it scared me!! That sounds like a cold start-up lack of oil main bearing issue. The heavier oil, better coating oil might improve it until you can get time-funds to repair-replace it..