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Discussion Starter · #1 ·
Has anyone ever had a roots type set-up that back fired and lift the blower? Mind you this is a Weiand 6-71 street set-up with a "POP-Plate" on the rear of it. I know it is possible on the old ones with out the "POP" plate but I though this was suppose to prevent this. The end result was three broken studs and a laundry check. Now the motor still runs but there is a scrapping sound coming from the blower housing. I am assuming the housing is bent? The engine is fine and with new studs it runs good but there is the scraping sound. With the belt off I can turn the blower by hand and about 1-2* in the 360* rotation I can feel it scrapping. :sad:
 

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i have had them really take a backfire and live, but never lift-they had the alumn. studs that were sup. to give it up if a backfire happened-the pop off valves have a spec adjustment, but take a lot to pop-look for a bent rotor, might be scrapping the end case or the side-i wouldnt run it untill you find the scrapping-real bummer for sure
 

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Discussion Starter · #4 ·
That really sucks.
Hope it is an easy fix. What causes the condition?
Fritz
Back fire. On a blown application the back fire meets the incoming charge & it has to go somewhere. Usually the "POP" plate opens and everything is OK. It did open but I guess not in time or quick enough. I will have to pull the blower off, loads of fun, & check the inside of the case. I think the case, rotors or both are damaged / bent and is now scrapping the case. In my business I have a certified 3' x 3' level granite plate. I will lay the blower case on it and see if the case is level & true. If not the 6-71 is a large paper weigh & I will see about the BDS & The Blower Shop set-ups.

Now in the case I can find the $$$ I may build the 540 w/ 10-71 & ST1200 Lenco tranny. But the wife really wants the new addition to the house so probably a nice 8-71 for the SB will most likely happen. I'll let every one know what turns up............
 

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If there's those teflon strips on the rotors,do you think one may have gotten knocked off when it popped,and that could be scraping?
 

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Robert...the pop off plate obviously did not release the excess manifold pressure.The aluminum mounting studs and nuts are next in line to allow the mating gasket to blow.Sounds like the Bang was big and flexed the rotors and contacted the case.On inspection,it should be easy to find the point of contact.I would also look for hairline cracks closest to the rotors core.The will be hairline thick and listen for a tinkling type sound while rotating the blower on the bench.When the rotors flex and crack..material rolls around inside the hollowed out space inside the rotor.I would not run this blower without an inspection.You still have time to save the engine underneath.
 

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It is possible you just bent the rotor shafts and nothing else. If you could put the rotors between lathe centers and indicate them, you may be able to find if that is the problem. If it is a shaft problem, they can probably be repaired with new shafts. I would call one of the blower builders for info, as I'm sure they have dealt with that problem before.

If the shafts are bent, it may just be the gears binding because of the bent shafts. It could happen.
 

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Discussion Starter · #9 ·
Robert...the pop off plate obviously did not release the excess manifold pressure.The aluminum mounting studs and nuts are next in line to allow the mating gasket to blow.Sounds like the Bang was big and flexed the rotors and contacted the case.On inspection,it should be easy to find the point of contact.I would also look for hairline cracks closest to the rotors core.The will be hairline thick and listen for a tinkling type sound while rotating the blower on the bench.When the rotors flex and crack..material rolls around inside the hollowed out space inside the rotor.I would not run this blower without an inspection.You still have time to save the engine underneath.
Good info. Made a nice fire ball I must admit. I will check the case with mics & a surface plate. Didn't think of the rotors being cracked but will check that also........

If the shafts are bent, it may just be the gears binding because of the bent shafts. It could happen.
I do have access to a lathe so I will check that also.......

Robert, sorry to hear about the damage. Sounds like an opportunity for an upgrade! :D
A BDS or The Blower Shop 8-71 sure looks purdy.... :D:D:D
+++ The engine would actually run cooler at boost with a 8-71.

Then there is the 540 w/ 10-71 project ---- muaghaghaghaghagh :thumbsup:
 

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Discussion Starter · #10 ·
Well here's what I found - It would appear something got into the blower towards the rear and destroyed the rotors. ( See Pics ) I have no clue as I run filters and everything from the top hat through the carbs to the top of the blower is fine. No missing hardware or anything. I have two Aeromotive filter that have no debris in them either. This ones kindof has me bewildered.:sad::sad::sad:

Anyway - The case appears to be fine with only a few scratches here & there but they are minor. The heads are fine and there was very little aluminum fillings in the intake & zero in the oil so everything else appears to be fine. I will check the case Monday to see if it's still true. So here's the question - Can I weld up the damage on the rotors and smooth everything back out and try it or should I just send it to Hampton or someone else to repair & test it? And is it really worth the money to repair a Weiand blower or just go with a better set-up like BDS or The Blower Shop? Keep in mind that if the case is bent I will have a really COOL paper weight for my office.

After running 110 leaded & dynoing the car, I drove home about 40 miles then all this happened.......
 

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this guy is really good with blowers you should drop him a line and send him the picks plus he is cheaper then the big name brand ppl.

"blower resource" <[email protected]>
 

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wow Robert.. never seen that before.

How high were the rpms when it backfired? I was wondering if you find the reason why big roots blowers and hydraulic roller cams dont mix. I have back fired through the intake several times due to valve float but I usually blow my gaskets out. Pop off valve does little it seems. Never hurt the blower

A Weiand blower is bottom of the line, and I hear that not enough care is taken when clearancing them. You dont really need an 8-71 for a low boost street 355, and a slower turning roots blower has more leakage past the rotors at low rpm so low rpm performance can suffer with a bigger blower on the street.

That can be fixed, at least with new rotors, but a TBS, Hampton or Littlefield blowers are much nicer than a Weiand. The Blower shop billet cases are a work of art and the new BDS air-loc rotors look interesting.

mike
 

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My guess is that the blower housing distorted causing the end of the rotor to contact the end plate and flake the edge of the rotor off and then the bits chewed up a bit in that spot.

The whole blower would need to be sent out to have the clearances rechecked by someone who knows what they are doing, and assuming the blower case is not distorted too much.

I really want to know what RPM Robert was at when it happened. If high rpm, I would think it was just one of those things, if low rpm, i would have doubts of the quality and strength of the blower.

I also notoiced that rotor is a 2-lobe, straight-cut rotor. Cheaper to make and they do work fine, but a 3-lobe helical rotor is better, and a screw-type rotor is even better than that.
 

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Discussion Starter · #16 ·
wow Robert.. never seen that before.

How high were the rpms when it backfired?

A Weiand blower is bottom of the line, and I hear that not enough care is taken when clearancing them.
mike
Hey Mike......
I was on the hwy at about 4500-5000rpms and stabbed the throttle. This is the first time the engine has ever backfired. I was trying 5% overdrive w/ 110 gas. We had just got done with several dyno pulls to 6000rpm. Drove 40 miles to the house and was just playin when it happened.

I will probably go with The Blower Shop guys. I have never seen such a quality piece before.

My guess is that the blower housing distorted causing the end of the rotor to contact the end plate and flake the edge of the rotor off and then the bits chewed up a bit in that spot.
That what I thing happened. I know 100% that nothing got inside the motor so it was either that or, as you said, just one of those things.

About the 8-71 - I was possibly going that way because I may in the near future take the SB out and punch it to a 406 with a lower compression set-up. The $$ is only about $ 200 difference between the 6 & the 8. I could just wait and for now just buy a new case w/ rotors from Holley.

I have pulled the heads & all is well. No valve / piston damage and the oil was clean.
 

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HI Rob!! "That what I thing happened" is this some kind of new lingo? LOL j/k Glad to know there was no other damage. Just make sure you are not throwing good money at a bad blower. If things go wrong it could cost alot more. Let me know if you need any help or just someone to hang around. Is the "game" on tonight or did the holiday move it to the next week. Cya soon...
 

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Discussion Starter · #18 ·
That must have been my Elmer Fud voice. :D:D:D I have decided to go with a new set-up on the blower. Too many so so comments on the Weiand set-ups. I am interested in Mike's comments about going to a 8-71. I will research a little more. I think whilel I am at it I am going to replace the radiator, install the line lock & go to the manual disc set-up on the brakes. See ya soon.....:thumbsup:
 

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That must have been my Elmer Fud voice. :D:D:D I have decided to go with a new set-up on the blower. Too many so so comments on the Weiand set-ups. I am interested in Mike's comments about going to a 8-71. I will research a little more. I think whilel I am at it I am going to replace the radiator, install the line lock & go to the manual disc set-up on the brakes. See ya soon.....:thumbsup:
did you ever talk to lain at the email addy I posted the guy really knows his stuff he does custom 6-71 and 8-71 as well as others you should at lest drop him a line seriouslly
 

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Robert,

The billet blower cases from TBS are even more beautiful in real life. I was looking at one being installed on a 414" SBC the other day and I was was captivated how much nicer it was in real life. I am also looking at the the efficiency of the newer roots blowers with 4 lobes and 160 degree cut rotors. They have effeciency simiular to the screw type blowers.
 
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