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Old 05-23-2004, 04:08 PM
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74norton 74norton is offline
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Question Supercharger noise?

Hello

I just purchased a dodge truck with a 69 440 and a B and M Streetcharger supercharger. I know how superchargers work but I have never owned one. I think something may be wrong with mine and I am looking for some help troubleshooting.

Here is some background. The motor in the truck was recently rebuilt using forged 8:1 pistons. The supercharger was also rebuilt. The motor has a relatively new Holley 750 double pumper on it and a mild hydraulic cam. The motor runs nice and cool and sounds just like all my other big blocks. I picked up the truck this weekend and drove it about 150 miles home. It ran fine and seems to make great power and sound good too.

Here is the problem:

After my trip yesterday I started to hear kind of like a grinding noise coming from the charger. It sounds kind of like some marbles are rolling around in there. I used a stethoscope to listen around to the engine and it seems like the noise is coming from the shaft/neck area of the charger near the pully that drives the shaft. The drive belt appears pretty tight with about ¼ inch deflection in it. The truck seems to run fine but the noise seems to be getting louder.

My questions are:

Is this noise normal with a supercharger? (I am assuming it is not)
Is it possible that the front pully bearing on the shaft is going?
If this bearing seizes is it something that will stop the crank or will it shred the belt first?
Where can I find a schematic of the charger and can I just get a new bearing at the local auto parts store?

I really appreciate any assistance in this matter.

Thanks

Charles

81 dodge truck- blown 440
67 Sattelite – 4spd 440
76 volare – super six
48 stude pickup with 392 h
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Old 05-23-2004, 05:35 PM
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i would suspect the bearings in the supercharger. you never said if it is a rootes type blower or not, but i will assume it is, since those are the most common superchargers. and no, it wont stop the crank. it may or may not shred the belt, either. it COULD destroy itself, though and send chunks of aluminum into the engine. even if the belt dies, there will probably be significant damage to the blower even if not to the engine.

if it IS a rootes type blower, you should get it fixed NOW, if it hasnt already destroyed itself... the vanes on the rotors only operate with .002-.0025" of clearance, and any scratches or dings on the aluminum rotors will reduce its usefulness. cracks in the rotors mean it is junk!

as for damaging the engine, as long as the rotors dont break up, the engine will die (stop running, not expire) long before it suffers any real damage, but it will likely suck a lot of oil past rings and valves, and maybe turn the seals in the blower inside out. you have to picture what would happen if you could pull a 20" or so vacuum on an intake manifold that had the carb mounting completely blocked. the engine wont run because it wont be getting any air.

what damage will result from one of the other aftermarket systrms, i dont know. it depends on the system design and component location. anything on top of the engine with a pretty much unrestricted access to the intake manifold will put the engine at risk in the event of a catastrophic failure. also, anything belt-driven (not turbocharged) will contribute to engine damage, since when bearings fail, since things dont just "freeze up", but are driven to the point of destruction by the belt and engine.

in case you dont know what a rootes type blower is, it is the supercharger like you will see on the top of the engine on almost every supercharged competition engine, regardless of make. they are commonly sized like "4-71", "6-71", "8-71, "12-71"or "14-71" depending on the size of engine they are intended to go on. this designation comes from the size of engine that detroit diesel intended for it to go on, where the first number is the number of cylinders and the 2nd number is the displacement (in cubic inches) of each cylinder. thus a 6-71 blower is for a 6 cylinder engine with a displacement of 71 cubic inches per cylinder... or 426 total cubic inches. these numbers are most applicable to physical size, though, since these blowers can be under-driven, 1:1 (direct), or over-driven, depending on the amount of boost desired. i have a friend (of sorts) that runs a 14-71 on top of a keith black hemi using alcohol... laid out a 0.990 60 foot time on his first ever pass with that car!!! talk about LETHAL... but that is another story
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Old 05-23-2004, 06:41 PM
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Thanks for the note and the info.
I know that the guy who I got the truck from said the charger was recently rebuilt and he is an honest guy. I know that I have no way to tell how well it was rebuilt but I want to try and think of other things besides the bearings. I did some research and I am wondering what you think about this info I read on kenny bell's site:

"The clicking or rattling noise is caused by an
uneven engine idle or surge which creates torsional vibrations that are transmitted to the crankshaft pulley.
Some engines use a rubber or viscous dampener in the crank pulley to help absorb these pulse vibrations. Many
of the new engine designs eliminate these dampeners and are therefore more sensitive. In any event, a slight
lope, whether it be audible as with a cam or an inaudible tune up problem, will result in the crankshaft pulley
"jerking" the serpentine belt back and forth. This uneven undampened belt oscillation jerks on the supercharger
pulley and shaft which is connected to the supercharger gears with a coupler. The lash/clearance in the coupler
is responsible for any noise - not the gears. There is no lash in the supercharger gears. However, there is some
normal wear or lash (clearance) in the coupler. This can be felt by turning the supercharger pulley fore and aft.
Again, "lash" does not mean there should be any noise.
: This lash is very slight 0-.060".A½" lash indicates"

Does this sound like it could be my problem? I know that when using the stethescope, the noise seemed to be coming from the front pully not the actual internal rotors.

I think it might be possible that I have a vaccum leak or the engine just needs some timing to smooth it out. I have been reading that charged motors like advanced timing.

Also, Holly bought B and M and they have a supercharger tech line:
270-781-9741
I am going to call it tomorrow to see what they have to say.

Thanks

Charle
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Old 05-23-2004, 06:54 PM
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i suppose there may be something to that post. clearances are pretty tight in those things, and there is enough rotating mass to make things want to run a constant speed. any fluctuation in idle speed might cause things to "bump" together. and no, there should be no clearance in the gear drive... the gears are helical cut, similar to but different than the dist drive/cam gear. different than because they run parellel to each other rather than at right angles. i do need to say that the last time i saw the inside of a rootes blower was over 30 years ago, and i am sure there have been changes.

bottom line is that if the thing was rebuilt by someone who knew what he was doing, and you cn trust the person you got it from, it probably isnt in failure... BUT... new things (bearings, seals, etc.) HAVE been known to fail.

so... i would figure that thing out ASAP... wouldnt want to see a golf-ball sized chunk of aluminum headed for a combustion chamber...
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Old 05-23-2004, 07:03 PM
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74norton 74norton is offline
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Duly noted

Of course we all know that murphys law was created for us car nuts.

I dont know the person who did the work too well but I know that they are honest and died in the wool mopar drag racers. The more I research about blowers on the web, the more I find about chatter being a relatively normal part of the deal.

I think my call to holley's charger tech line will help provide some good answers as will hooking a timing light and vaccum gauge up the truck to make sure it is dialed in right. Since I got it yesterday I am still having too much fun hammering the throttle and hauling butt. The thing reall does move. A blown 440 is pretty cool!

Thanks

Charles
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Old 05-23-2004, 10:30 PM
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lol... i bet! i put a naturally aspirated 440 in my pickup... the gas milage sux... but i get a lot of attention at the strip. truck looks like crap, but runs good. the 1/2 ton trucks that show up there are all slower if they are daily drivers, and they have about a 1000 pound weight advantage. 15.1127sec @ 91.78 mph isnt too shabby for a 5000 pound truck. it also sets off a LOT of car alarms... lol.
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