Diesel sound

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smythge

65 with a BIG BLOCK
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Last weekend I put a rebuilt 440 in my Dart. I broke in the cam @ 2000 RPM for 20 minutes, I then changed the filter and the oil. Since then I have been taking it easy, driving mostly highway speeds and alter the rpms between 1500 and 3000. Since I first started it, it has a "diesel" sound to it, not pinging but sounds a little like a diesel, it doesn't get louder or faster when I rev it up, and it doesn't sound like a knock. Runs very strong, revs up nice, I am running 93 octane gas. Timing is set at 14 intial 36 total all in at 1800 rpm. The sounds does not change if the timing is retarded, or advanced, although if it is advanced to far I can then hear it ping. It's just a constant diesel noise. I have the idle set at 800 in park and it drops to about 600 in gear. At idle the oil pressure seems low, cruising down the highway at 2000 RPMs the gauge read about 50 PSI at idle in gear it drops to around 15 PSI I am running Valvoline 10W 30

The specs are

67 block 440 bored .30 over
Steel crank, balanced
Keith Black 10:1 Pistons
Mopar performance hydraulic Cam (very mild) .434 intake .431 exhaust
906 heads with hardend seats completely redone stock rockers and shafts
Edelbrock Performer intake
Holley Street Avenger 670 Carburetor
Custom made headers

Give me your suggestions on what to look for, or if you have ever experienced anything like this

Greg
 
Do you have solid motor mounts on this car? It almost sounds like a vibration thing that rubber mounts would cure. I would invest a few bucks into a high volume oil pump though. That lil`car should be a screamer! Good luck.- Longgone
 
Yes I do have solid motor mounts, they're actually kind of a hybrid mount / plate. They bolt to the motor where normal mounts do then they come out and bolt to the frame like a motor plate would. I am going to make some new ones that mount in the same place but lay flat on polyurethane bushing to absorb some of the vibration. Right now there is so much rattling it's hard to tell where the noise is actually coming from. With 10.1 compression, what is the minimum ocatane I should be runnnig?
 
with solid mounts, tracing a noise could be a pain. But, you already know that. Are you sure it doesnt go up with rpm? There isnt much moving on it's own. Everything is in time with the engine. Some things to look for..Exh rattle, flexplate bolt(s), loose pulley or bolt(s), loud (defective) mech fuel pump, rotor/cap interference, starter drive not retracting, inspection cover bent, shifter linkage rattle, too much wall clearance with those pistons...But all these will vary with rpm to one degree or another..
 
I'll check the flex plate bolts, I did torque them and put loctite on them, but they could have come loose. I did buy a set of the chrome bouchillon performance crank and water pump pulleys, and I have had nothing but problems with them. On the old motor I had to pull them off twice they would go on fine then all of sudden the crank pulley would start to clank, they have already done that on this motor. (When I called to order the pulleys, the guy went on about they make the pulleys and they're high quality, but when I got them they had a little made in tawain sticker on them, with a little RB scratched into them) Biggest waste of $115.00. Any other ideas?
 
I am not sure on the piston clearance, I didn't build the motor, infact it was professionally built in 2002 and the guy who had it built, crashed the car it was going in. I stumbled across the motor from and a client of mine who sells mopar trim stuff, I asked if knew of a good machine shop he did some checking and found the motor. It's been sitting on an on a stand the past 4 years. I have the build sheet for it with all the specs and when I got it it was obviously rebuilt, did not have the oil pain or intake on it so I was able to inspect it. If there were clearance issues, would I there still be good compression, and have power? It idles nice, revs up good, strong power with no hesitation or stumbling or back fires. It just has a weird diesel sound to it, not a ping, not a knock more of a growling sound to it.
 
If pistons are put in on the loose side they will make noise. A forged piston needs more clearance than a cast piston because it expands when the engine gets up to operating temperature. Forged piston motors are a little rattley until they get warmed up. If the machine shop was a little overzelous with the clearances this could be the noise.

One other thing there is an old trick of putting pistons in backwards so the piston will dwell at top dead center longer because of the offset wrist pin. The motor will make more power but will also make more noise. When you had the head off you could have found out if the pistons were in backwards because the notch or arrow would have been pointing toward the rear of the motor instead of the front.

If the piston noise is light I wouldn't worry about it. But if its pretty loud it means you pistons are really rocking in the bores and you don't need that.
 
Th hypereutectics are meant to have very tight piston to wall clearance. If the block was "bored and honed .030 over" and then the pistons installed, they are in loose. It can be other stuff, I'm not meaning to panic you, but I've had wristpin noises and piston slap for years and thousands of miles on my 4 cylinders. It means lost life, and the pistons are strong, but brittle..being in "loose" means they can rock at TDC and BDC more than what would be "normal" for a hyper engine. This can lead to problems later. The only way you would know for sure is if you pulled the pistons and measured them, and the bore they are installed in. A typical good forged piston runs anywhere from .003-.005 clearance for the piston to expand when at running temp. Cast pistons dont expand as much, so they run tighter, and hypers run even tighter than that. Mopars cast pistons used expansion limiters (those heavy steel plates under the domes accross from the pin bores of the factory pistons) to run a tighter clearance with cast pistons.
 
guys thanks for the info. When I had the head off I noticed the pistons were numbered and the numbers were not upside down. The noise is not excessive, infact I can't hear it with the hood closed, but when I pop the hood I can hear it. My friend was the one who noticed it, when we were listening for exhaust leaks he had is head right down in there and of course he pointed it out to me and now that's all I can hear. I've been reading a lot about piston slap, it sounds like to little clearance is much worse than too much. I am not worried about getting 100k out of the motor, just don't want to damage something. When I get home tonight I will check if it's worse when its cold. Some suggestion were to use better oil, any suggestion on that?
 
Ok when I got home, I started it up and checked the noise cold and it is little louder, than when it is warmed up either way it is not real loud, but still annoying on a new motor.
 
If the sound seems to come from the top of the engine it`s possible that your rocker shafts are on backwards which would put the oil holes off 30 degrees. It might be something easy to check before you get in too deep.
 
I had 2 360's both with the KB pistons----I think they were kb 307????? but both engines had a diesel sound--not much, but you could hear it with the hood open. Never had any problems with them---ran in the 12s.
 
It is defenatly piston slap! I had a 440 with KBs that did the same thing, they clearanced them as loose as a forged piston, i ran & drag raced the engine for about a year, over time it got louder & louder, different weight oils didn't help much either, when i tore into the engine i found skirt damage & gouling on the cyl. walls, those KBs need a cyl. to wall clearance of .002 on a normally asperaited engine, there's still some machinest out there that don't think a piston should be that "tight", they feel it will seize up, "well" KBs won't, you may want to get it fixed if you plan on keeping it for awhile!
 
I have been driving the car all around, ran six passes at the strip this weekend, I had forgotten all about the diesel sound. I was re-reading some of my posts found this one and go curious so started it up today cold and three was no noise, let is warm up to 180 and no noise. I did change the oil to Shell Rotella 15W/40 and changed the exhaust gaskets with percy soft aluminum. My homemade headers had some exhaust leaks, maybe thats what I was hearing?
 
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