413 cold rattle/knock

[rattlenbang]

Hi all, I just picked up a 24' 1972/73 Empress Class A with a 413. It was a where-is, as-is purchase, and had been sitting for 4 years. The previous owner said that the old carb started leaking fuel and he freaked out and parked it (an anxious sort, he told me he felt lucky his head didn't get blown off). I put a new holly 600 on it and did a complete tune, but what concerns me is the rattle that it makes when cold. It's fairly loud at first, but greatly decreases as the engine warms up, and returns when it's under load and pulling.

I wish I could say if it was simply valve noise or con rod knock, but I'm just not familiar with these old big V8s and it's really hard to tell exactly where the sound is coming from. It's not really a fast light tick tick like you might expect from valve lash, but it's also not the loud metallic clack you get from a bearing. The engine only has 51,000 miles so I would be surprised if there was something major wrong with it. Any hints or suggestions?

[Stripe]

I know what you said about the valves and such, but have you given any thought to the oil and if it may have gone "south" for the winter?
Could have lost some viscosity?  maybe even oil pump pickup?

Also, are you 100% sure it's the engine (I have to ask) and not the transmission?

Oh, and I know it's a '70's rv, but does it have a clutch fan or did the PO install an aftermarket electric thermo controlled fan?

Oh, and Pics too..   Wanna see what your new toy looks like!

Fredric

[maxximuss]

I'm not 100% sure but it may be a piston Knock/skirt issue from what you mentioned about sound at cold and then under load warmed. Does it seem more like a loud rattle than a connecting rod knock? It all so could be if the carb had been leaking for a long time before he realized it the cylinders could have been washed down with too much fuel causing cylinder wall wear. I would change the oil if you haven't all ready and check it for any contaminates or a fuel smell before doing anything else.

Another thing that may have happened one of the cylinders may have been flooded of fuel with the bad leak and may have damaged a piston. Known as hydraulicing the engine.

Sorry I don't mean to scare you on this, I hope that it is just something minor. I'm basing my ussumptions on what you said about the bad carb leak. Like coach said you may want to check to see if it is something else actually making the noise. 

I forgot to mention could just be that the timming is out as well. Too much advance will cause this noise as well.

All so the carb you put on may be running to lean, yet another reason for the rattle.

[rattlenbang]

This thing is going to give me (more) grey hairs. The p.o. had made a helluva mess of the rear light wiring - like a giant spider had projectile diarrhea all over the rear section. 8 hours to get it wired right. noticed tonight the throttle cable must not be set right; no kickdown and no secondaries opening, the new Holly carb floats are sticking, and flooding, & occasionally the accelerator pump doesn't squirt. I took it for a drive and once the truck fully warmed up, oil pressure gauge said zero, one water temp gauge said 210, another one said 190 (yes it has 3 temp gauges, the stock one not working), the extra fuel gauge said empty and yet the engine sounded perfect. I added a can of seafoam and it might have helped with the engine noise. None of the stock gauges work, and I don't think much of the aftermarket ones either. I have no idea what's going on.

What have I done?

Someone asked for pics, but after pasting them in here, they didn't show up. They are in the odd ball and rare RV photo gallery. You can recognize it by the orange shag rug and upholstery!

[rattlenbang]

The carb was leaking externally not internally, before I replaced it. I'm starting to think the noise might be valve lash - a sticking lifter. Timing has been set, and everything tuned up. I hope that noise goes away and stays away after my seafoam wash. It has a functioning clutch fan and the noise is definately coming from the left bank of cylinders, about midships. I want to replace the old oil as soon as the seafoam has had a chance to run through and wash out the old crud.

[M & J]

Marvel Mystery Oil works too.

[LJ-TJ]

   
• i?? Marvel Mystery Oil worked on my sticking valves.

[Froggy1936]

Hi I have seen and heard bent connecting rods hitting the bottom edge of the clyinder wall (bent from hydraulic lock up from fuel flooding or flood water entering air intake) Amazingly the shortened stroke hardly effects idle The easiest way to check is pull the pan ! Rod bearings can be inspected at the same time . Diagnoising wich cly it could be by shorting out plug wire to 1 cly at a time wile at 2000 RPM the noise should change on effected cly  Good hunting  Frank

[rattlenbang]

It really seems to vary from day to day; yesterday it was quite noticeable, the day before I thought the seafoam cleared it. Aside from that the engine runs so smoothly. Wondering if I really need to worry considering how well it runs.

[M & J]

I can assure you Marvel Mystery Oil will do no harm. My father used it for years and years and I have used it in older engines that have sat for a while.. In the gas and/or in the oil. I always keep some in my garage.

[LJ-TJ]

I use it in my airplane. Works great.

[Mytdawg]

Once you get it all cleaned out and get some fresh oil in it I would also recommend some Lucas oil treatment.  It's made a hell of a difference in my older engines.  I'm still rocking a 1985 S-10 Blazer with a crappy 2.8 as a field truck up north.  It makes all kinds of noise when the oil is first changed, couple squirts of that stuff quiets it right down and smooths out the idle.  Been running like crap for 28 years...   :)rotflmao

I've heard some harmonic balancers make a knocking noise before but can't say if the Dodges are susceptible to that.

[ClydesdaleKevin]

Our first RV, The Ark, had a 413 and the same loud rattle/knock coming from the driver's side, especially when it was cold.  Had about 40K miles on it.  Turns out it was the exhaust manifold, either a crack or a gasket, not sure which since we ran it that way for a couple of years (fulltimers here, and lots of miles!) and it never got worse, but never got better...then we upgraded to a larger rig with a Chevy 454.  That said, it was really loud when it was first started, and got a lot quieter once the metal heated up and swelled, causing the leak to be less noticeable.  Ran fine though, nice and smooth...just not quiet at all.



Kev

[rattlenbang]

Honestly, that is kinda what it sounds like. It's weird how exhaust leaks can sound mechanical, but I"ve run into that before with other vehicles. It's like a metallic knock, but just a little "softer", not so hard and crisp. I did wonder about leaking exhaust and tried to put my hand down there to feel for it, but with the airflow from the fan and the great heat the manifolds give off, plus very limited room, I really couldn't tell. I've heard that manifold cracks are fairly common with BB Dodges.

[DaveVA78Chieftain]

Take a 1 1/2 to 2 ft section of garden hose to act as a stethoscope to isolate where the exhaust leak is.  End of hose might might get burnt a little but no big deal.  Better than burning your hand.

Dave