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Old 07-08-2003, 11:03 PM
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balancer for a blower

i have a question for all the big 6-71 and 8-71 blower guys out there. what kind of dampr do you run and has any one had any trouble with theres. i have the street fluidampr on my small block chevy with a 6-71 running 13 psi of boost. today the balancer came off the front of the crank? snapped the ARP bolt and cracked the balancer right were the 2nd 1/4 " key was cut. Why I don't under stand.??? Is fluidampr a load of crap. or did i get a bad one out of the bunch. thanks 6-71 sbc

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Old 07-09-2003, 01:07 AM
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hi, I run a blown bbc 8-1 with a 871, 20% under drive for street only, and have run blown small blocks over here in the UK in the past at 400-500 hores at 7-1 comp (plenty of boost from little units). On small blocks with serpentine belts I have run standard cast dampers with no problems (would not recomend this on any other application other than the old BM 144 blower type kits). On any drive with a toothed belt I have run SFI ProRace dampers (this is the name bought in uk under and can be found on net- they are american), I have never had an issue with any damper and know the fluid dampers are rated as one of if not the best but never tried one.
I suspect the damper was flawed in manufacture as the case is supposed to be billet or forged then machined, this should not be able to crack or shatter in this manor. I have seen dampers explode when our so called drag race boys have bolted on 10 and 1471 blowers to stock bottom ends and gone racing - not.
I have also looked at the old unit I have from a previous blown motor as I generally buy a new unit for every application and can find no stress cracks or damage to the old blower damper I still have. I know this is not a lot of help but suggest taking the damper to a machine shop and seing if they can establish where the failure has started through crack detection / magnafux etc, diagnosing the failure will be the best route to preventing another and beware that all dampers can fail if the harmonics of the drive are so far away from where they like to be they can not damp out the vidration thus load up internally. there are always limits and it may be a good idea to check the bottom crank pulleys and registers (if used ) for alignment and balance etc. Not forgetting the crank balence etc, has the crank had any heavy metal added for balance that now may be in the sump etc, this does happen at extremes.
Dampers have limits, be supprised if you could surpass them but how many posts read of unbreakable parts and bomb proof race proven techniques that the home builder or novice has managed to rewrite the rules a little on.
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Old 08-27-2003, 09:49 PM
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i am rebuilding my motor right now from the same cause except mine trashed the crankshaft snout as well as the balancer, the key became like a cutting tool cut a key sized grove completly around the crank. after this happened i starting asking questions and this is what i was told; 1. check the crank bolt very often apparently the strain put on by the blower belt stresses these parts more than normal. also mine likes to backfire in the shutdown if i let off to quickly and some folks say that at that time the blower trys to run backwards. 2. the tension on that blower belt is is critical, too loose and it bunchs up and kinda trys to pass itself at mid revs you can hear as well as see it when this happens. too tight and you start to pull on the crank snout. most folks i have talked to say 1 inch play on the long side is about right. 3. if your balancer and crank have two keyways it was reccomended to me to put a key in both. 4. i was told about a strut stabalizer that i have yet to try and locate that bolts to the motor in 2 places and has like a bearing that rides on the balancer that keeps it straight under the stresses of supercharging. i have yet to buy a new balancer but this i will get a racing rated for a certain rpm type instead of the streetdamper that failed.
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Old 08-27-2003, 10:10 PM
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Sounds like the bolt backed out and the balancer failed from lack of retention, I wouldn't blame the balancer. Sounds to me like it was loose and the stress popped the head off the ARP bolt, did you locktite this critical fastener?

On rotary Mazdas there is a nut on the crank that attaches the flywheel, it is at least 2" in diameter and is called the Jesus bolt because if it comes off you'll be seeing Jesus. Because of the unique vibration of the Rotary engine this flywheel is keyed, on a milling machine taper with lock tabbed washers retaining the nut and torqued to 500 ft/lbs for racing versions. They still come loose and I red loctite them!

Your installation needs some fine tuning on this assembly, get the bolt to stay tight and the key not to walk and it will hold. Achieving this is the hard part.

I would start with permanent red loctite on the fastener and the snout/key. Cheap to do and definitely likely to solve the problem, but good luck with disassembly next time...get a torch. You could put the balancer on with a light press fit by ordering your balancer to size but again hard to remove later. Even seen some guys epoxy the whole mess together to try and make it last...it works but very messy and hard to remove also.

The red loctite is as good a method as any...and it works. Make sure you use the primer T or N, it makes for good bonding.
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Old 08-28-2003, 03:52 AM
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howziit guys,

cutting the second crank keyway and drilling for 6 blower bolts would've voided the FLUIDAMPER'S warranty, so i bought the ROMAC race balancer from BDS instead.

thanks for the heads-up on the loose ARP bolt. i'll either check it often, or use loctite.

as a sidenote, i would advise all WEIAND 6-71/8-71 supercharger owners to consider modifying their balancer-accessory pulley-blower pulley connection. WEIAND provides a 3-bolt connection from balancer to accessory pulley, then 6 separate bolts connect the blower pulley to the accessory pulley...no thru-bolts from blower pulley to balancer. this can be simply rectified by drilling the accessory pulley's 6 bolt holes completely thru, so the blower pulley can bolt directly to the balancer. then an adaptor can be machined to mate the non-standard WEIAND 2.25" pilot register on the accessory pulley, to the 2" pilot register on the ROMAC balancer. either that, or buy a new accessory pulley and blower pulley with the industry-standard 2" register.
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Old 08-28-2003, 04:30 AM
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Look at all that weight thats hanging on the end of our Crank! Not good for the very small snouts like the SBC s have. You need to run a crank hub only no balancer! the blower drive will damper the crank as good or better as a damper, and if you want to run the the boost up the 1/2 pitch belt will not get it for high RPMs. And you may want to check out some of the crank support kits , They never tell anybody about this till after you buy the blower kit and you tear the hell out your crank Etc!! A crank hub and a 8mm belt will let you run the boost and RPMS up when you want to.
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Old 08-28-2003, 07:48 PM
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that crank hub option appeals to me. qustions are where do i get one and is the thickness pretty close to that of a balancer?
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Old 08-28-2003, 08:19 PM
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You can find a hub at BDS for about $100 or less and V pulleys and spacers to line it all up, But there is a lot of other people selling this stuff.

Last edited by roys63; 08-29-2003 at 04:29 AM.
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Old 08-28-2003, 08:34 PM
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Question

every so often, you'll find yourself having to run your blower motor WITHOUT the blower belt installed.(broken belt while driving, ORRR leaving yer car at the repair shop, or anyplace you don't want the "mechanics" to enjoy a SUPERCHARGED EXPERIENCE.

FWIW, i'd ask the blower experts, if it would be ok to do so, with a crank hub.
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Old 08-29-2003, 04:16 AM
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I have spare belt, i have never broken a belt on the street , but i have tore up and wore out other stuff! SO What Are you Getting AT? 5-7 Heaven !

Last edited by roys63; 08-29-2003 at 04:28 AM.
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Old 08-29-2003, 01:37 PM
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Cool

it hasn't happened to you, but other rodders have lost their blower belts on the road. instead of calling a tow wagon, they simply drive their vehicle home.

much less HP, that's for sure, but driveable.

my blown motor's not quite done yet, but if i have to leave my truck at a repair shop(for anything other than engine repairs), i'm yanking the belt off.

it's not gonna hurt the engine...is it?
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Old 08-29-2003, 01:45 PM
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I'm building my first blower motor as well, but I've been around a few, just all marine apps. I was on the lake in a blown injected alky flat bottom, and when we took off, the top pully shot off and we couldn't get it back up and running. It made for a long paddle back to shore.
You say that you don't need the blower to function in order to run the motor, but that wasn't the case with this one. Was that just because it was injected/alky? I would think that with out the blower being hooked up, it would at least run fat as he//, if at all...
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Old 08-29-2003, 02:11 PM
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Cool

as to why your alcohol-injected blown motor wouldn't run, your guess would be A LOT better than mine.maybe the mechanical injection was providing way more fuel that the engine could accomodate WITHOUT the blower.

tell you what, when i get my blower installed soon, the first thing i'll do is a 2-mile test run...without the belt. JMO, it shouldn't hurt. in fact, i think it'll give the supercharger a chance to "break in", by spinning the rotors without the engine load. ANNND, i'll get a chance to listen for strange, grinding, unusual noises, stuff that you might not hear with the blower belt on.

of course it'll run fat with 2-750 cfm carbs and a HUGE plenum. cr should be 8.5cr with my edelbrock heads. i predict the engine will run stronger that it did previously(same cam, peanut-port heads, 8:1cr, 750 carb/rpm intake), even without the blower belt.

Last edited by 5-7heaven; 08-29-2003 at 02:22 PM.
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Old 08-29-2003, 04:35 PM
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well i know they will run ok without the belt i found out the hard way. problem is once that balancer goes there goes the water pump and alternator. as for taking the think off on purpose i have to take the radiator out to do this so i dont take it to places that have valet parking, heck i don't even go to places like that anyway. i turn my own wrenchs so i do have to worry about service techs joy riding. and if i have to take it to a shop i usually just hang with it as i like to see what is done to it while it is done. plus there just arnt too many cars where i live with a big polished blower sticking up out the hood. when i go to the track people often say i saw you on this street or that street so if somehow someone gets my keys they are prolly busted before they get to second gear if they got the guts to stand on it all the way through first.
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Old 08-29-2003, 05:33 PM
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I have tried a few high dollar dampers with the same results, wasted cranks , dampers and more, even tried a Fisher made for blower set ups. This is with the 1/4 " key added. I have run the hub with out the second key with no problems overdriven. This is with the SBC you can get a sbc crank with the BBC snout but that big bucks to set up. Now some folks are running the hub with a 1/4 " key in place of the the stock 3/16s, the crank has a better press fit to the hub and the hub and crank is stronger with out the other cut. I have done a lot of home work on this in the last 5 years and the blower motor i have now is my forth in 30 years. Much work and money went in to this one all roller , We had a lot fun with the roots blowers in the late 60s and 70s, I had 2 of the old Delta Drive set ups, what a pain to change the blower pulleys. Then we had kids and stopped messing with the hot rods till they MOVED OUT!20-25 years later! Now i fell like a kid when i hang my big foot in my 4000lb Impala , hard to keep it under 7 grand it just keeps pulling. This is under driven on pump gas about 5-6 lbs boost. Over driven on cam 2 fuel the thing in out of control opens your eyes wide open!! To each his own i guess! Have fun with the HP and be on your toes! Scott

Last edited by roys63; 08-30-2003 at 05:52 PM.
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