440 RV engine making noise...CAm ?? Lifters ?

I have a very slight noise coming form the motor that sounds like a diesel idling but it is quieter than that. I poked around the engine with my stethoscope and I can hear it loudest on the valley pan towards the front of the engine and also on the drivers side valve cover towards the front of the engine. I just had the intake off and everything looked ok but could it be a bad cam ?
It runs pretty good overall. Has plenty of power. Motor is a 1975 440 in and RV and has 99k miles on it.
Does not burn any noticeable oil and really no oil smoke at all. No blow by.
It's not a ticking sound, is not a knocking sound. It's more like a very slight marbley sound. Oil pressure is good.
I was told by someone on my RV forum that these engines need zinc additive to the engine oil ?? But he also mentioned something a bout flat tappet and this motor has hydraulic lifters. I will see if I can record the noise with my phone but it won't be easy. As soon as I put the hood back on you can't even hear it. I do not hear it when off idle.

Flat tappet is a lifter type , they come in both solid and hydraulic. You need a good zinc oil , the current oils on the market are made for new cars with roller cams and they do not need nearly the zinc the old engines do.

I have put about 7-800 miles on it so far do you think I damaged anything ? I am working on the video as I type.

I put Valvoline 20/50 racing in it last oil change.

Here is the vid..
http://www.youtube.com/watch?v=zQLP6wxVtHE&feature=youtu.be

What Oil should I use ?
Lucas makes a classic car and hot rod oil that boasts high ZDDP. Also Valvoline makes a not for street oil.

Welcome to Moparts. Another Travco nut could make it over! I'm over on Travcoforum as well.

Ryan

For the oil, to get adequate zinc I run diesel engine oil in my flat tappet. Shell Rotella T. Another option is dedicated classic car oil with higher zinc like Joe Gibbs. Yet another is standard car oil with a zinc supplement like Comp Cams break in supplement.

If you are worried about the cam, probably best to pull the intake, roll the engine over and have a close look at the lobes. Only because cam failure can create debris and collateral damage. I would add that an engine with moderate cam already broken in may not be as sensitive to lube oil. New cam/new lifters can be quite sensitive.

Are you sure its not an exhaust leak at the manifold? RV s ate notorious for warping exhaust manifolds and it sounds similar to a lifters tick.
Keith

Quaker State 10W-30 Defy, API SL synthetic blend is said to have 1200 ppm zinc. You can get it at Walmart in 5 qt jugs. I used it the other day.

Before that I used regular SN 10w-30 for 7 months with no harm done. This is in 383 RR with factory-type valvetrain and vintage original springs.

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Are you sure its not an exhaust leak at the manifold? RV s ate notorious for warping exhaust manifolds and it sounds similar to a lifters tick.
Keith

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Yeah the passenger side ones always crack due to the heat riser.
Mine has already been replaced. I saw some very slight greyish sludge deposits in the bumps between the lifters butthe motor has 99k . Nothing I would call unusual.
It sounds like my vw tdi but not as loud. Im worried that it's a cam bearing.
What would that sound like ?
Also to check the cam could pull the valve covers and use a dial indicator ?