Hi,

I have a new 302 in an '85 F-150 that I just got running. I am running a Holley 4160 600 CFM carb.

When the engine is idling, I get a "dud dud dud dud.." sound. It is pretty noticible from the cab and I feel a vibration in the truck. When I open the throttle, I hear the sound increase up until I hit about 1500 RPM. Then I can't hear it anymore. The engine sounds good all the way up until 4000 RPM.

I've had a motor with a bearing going out and it doesn't sound like that. The rod knock from that was very noticible at higher RPM.

I checked the plugs on the 302 and they were black and sooty... after about only 20 mins of idling. I adjusted my floats and idle needles but it ran the same. It is definately rich. The Holley carb has 59 jets in it. What size do you think should be in a Holley 600 4bbl carb on a 302?

When I let the engine back down to idle after revving it, I hear a chatter from under the valve cover (sounds like spoons clanking). So I know I need to adjust the vavles. Do you think this could account for the "dud dud dud" sound?

When I crawl under the engine, the sound is louder and has more "hammer hitting concrete" do the sound.

I checked the timing and its good. 10 degrees and it moves up when I rev it.

Any suggestions?

Thanks,
Sal

 

If you have a non- roller motor, your rockers are probably non-adjustable....they shouldn't make any noise if you're using the right parts....vaccuum advance dist? make sure you're timing it with the vaccuum to the dist disconnected and plug(so there isn't a leak) I don't think it should go up as you rev it(it will if you don't disconnect the vaccuum).....but i usually don't rev the motor when im timing it so im not 100% sure on that one. My buddy just finished installing a bowtie 350 in his demo derby car, it had a 700 edelbrock vaccuum secondaries and it was just too much carb. without rejetting he couldn't tune it down enough. he swapped it in favor of a stock ford two barrel(these carbs are 550 cfm or something and they are extremely hardy and give great throttle response because theyre only 2bbl) i would start by cutting back on the fuel to the motor, although 600 shouldnt be too much unless you have a BONE stock motor. Otherwise, I contact the people you got the "new" motor from.

 

Yeah... its not bone stock. Its got an "RV" cam that should give more power at low RPM, and an edelbrock performer intake.

 

Well, at any rate- in my experience- bottom end sounds aren't too often a good thing......

 

Did you put new pistons in? Could the noise be a wrist pin going? I had an old 240 that had a bad wrist pin on one of the pistons. Sometimes it sounded like a diesel when it idled. Sometimes it went away at higher RPMs, sometimes not. It was in a beater truck and ran it forever without any problems, but you probably would want to fix yours. You cannot adjust the rocker arms, but you can get longer push rods or use shims under the rocker arms. Check the bleedout clearance between your pushrod and rockerarm and see if its in range.

 

Its a "new" rebuilt engine... everything in it should be new.

When I was trying to get it started, I first primed the oil pump for a minute with the drill... up to 60 PSI. I had trouble getting it started at first... I had to pull it out and put it back in. When I put it back in and was turining it over before starting it, I heard a "creaking" or "squeal" sound a few times when it went around. I pulled the distributor and primed the oil pump again. The sound went away and I started the motor shortly after.

I'm really fearing that its something in the bottom end.

If anybody has any other suggestions it would be great.

 

If you are turning it over by hand you definitely should not hear a squeal. I've rebuilt a couple in my day and they don't make that noise when new. And this late model of a 302 shouldn't be that diff to turn over, either. I can't tell for sure but i'm not there, but i hate to say i have the same fear as you do. IMO- pull the motor...pop the rod caps off an make good&sure all your bearings are cherry and that the rods are in the right way- it does make a difference and they can only sit one way. There is a bevel on one side and a flat edge on the other where the bearing rides, the flat parts of the rods should but up against each other when bolted to the crank. Also, your main caps should be number 1-2-3-4(the 5th one is way different) and have arrows pointing toward the harmony balancer...1 is closest to the balancer....2 is next etc. Don't ruin that motor!!! Bearings are relatively cheap even if you have to fix em yourself or take the motor back!!!!!

 

Ok... I went out and started it up again today.

When the engine first started (it was cold) I did not hear the noise at all. Then, as the engine warmed up I started to hear it. Once it was at operating temp, I could hear it like I did yesterday.

I started pulling the spark plugs out and plugging them back in one by one.

When I got to the #3 spark plug, the sound went away. Put the plug back on and "dud dud dud dud..." take it off and it went away. Then I let the engine idle and gave it a little gas and the sound came back slightly and then went away.

So I think something is definately related to the #3 cylinder. I pulled the valve cover and everything was fine up there. I did a compression test and I got the same on all cylinders.... about 90-100 PSI on the first puff and then topping out at 150 PSI after about 5 puffs of the engine.

I drained the oil and checked it with a magnet (it was really black) and I didn't see any metal shavings. I pulled a few grit particles with the magnet, but nothing catastrophic looking.

So.... BEFORE I pull the motor back out... anybody have any suggestions?

Does what I just described here sound like a bottom end issue?

If I pull the motor and everything looks OK on the bottom end, what would you do?

Thanks,
Sal