anyone know of good books that outline the tear down of a good diesel 4-71 and rebuilding it back to run gas? I know of "A Do-It-Yourself Guide to Street Supercharging" and I plan on buying it, but it seems as with most publications it has more info on the 6-71s and less on the 4-71s. I have 22 pages out of the Detroit book that deal with the blower, but I know some of the steps are different for running gas on the street. I want to be a bit more proactive in getting all the info I need before I start than frantically calling people like Rick Dean and such when I'm in a pinch. Thanks.
All that you find on how to do a 6-71 will apply to a 4-71. It's just a shorter version on the same basic blower to feed 4 cylinders instead of 6.
do a search on here about blower stuff, alot of threads that cover it. Rick Dean has a DVD that you can buy off ebay that will go into it step by step. Jmountain is right it is the same 6-71 to 4-71. Iam in the middle of doing my 6-71 right now, really not much to it. A big part of it is to make sure you keep the rotors in phase (timing with each other) cut off the old hanging bar on the side, sealed bearing in the back teflon seals on the rotors, make sure not to lose the shims that were on the rotors behind the gears, if there was some in.....etc.....
I've read the c and cc dimensions need to be different for the 4-71 as compared to the 6-71. Anyone know what they need to be for the 4?
C=.014 for the 4 C=.016 for the 6 CC are the same On the B end, the one with out the gears, the end clearance is 4=.009 and 6=.014 This is from a 1953 GM service manual.
so Im an idiot. The c and cc dimensions stay the same. The areas to clearance are the front and back and the bottom. on a 6-71 it would be front rotor to case- .007-.008" rear rotor to case- .016" bottom of rotor to case- .004" is this the same for 4-71?
also does anyone have any info on pruning the 4-71 ? I'm guessing the case much be drill and tapped and should steel bolts or aluminum be used?
You dont need a book, been building blowers for over 20 years, just ask.. The only problem is that im Swedish so you will get the clearence in mm...you can change it to inch yourself. Best regards Blower Mike
The clearence rotor to end plate in front should be 0,08-0,15mm and the rear should be 0,25-0,35mm on a 4/71 blower for gas use.. if you want more just ask man.. Best regards Blower Mike
If you use thouse clearences your blower will be at least twice as good as thouse crap Weiand they through after you everywhere you go, sometimes they even work..
Your front rotor to case dim. is what GM calls for. Rear rotor to case is .002 more than GM. Bottom is the same as GM's. spec. The rear rotor clearance is for growth of the rotors due to heat expansion. I have seen rear covers smeared with metal from the rotors dragging, or possibly trash going thru. Anyhow, if the extra .002 short was done on a 4-71, it would be good insurance. Although when the blower is wet with gas, it should be cooler than a dry blower on a Diesel. And air box pressure on the 6-71's was about 7 psi anyway at full RPM's. And the heat developed is a function of the pressure, So if you are running 7 lbs boost, you would be right there with what they were designed to handle. And a very simple task to mount the rotor in a lathe and face off .002 from the end of the rotor. But test assemble it first to see how much you really need to take off. It's possible after all these years that the rotors arent the origs anymore and rotors were selective fit to cases when new.
Piece of advice: find your manifold and drive before diving into the 4-71 blower build. For some engines, they are pretty damned hard to find.
that little 471 won't move enough air to feed a 346 flat-cad....just my opinion. You'd end up having to seriously overdrive it...not a good thing to do. A 671 would be a MUCH better match.
The front cover and drive snout and such are the same mountings, but the question is having the right lenght of stuff up there so it all comes out right for belt alignment. I think your choice of the 4-71 for that Cad engine is good for a street motor. 5 lbs sounds nice.
the plan was to find one "close" to working and shimming the lower pulley to work and/or cutting the drive down on my lathe. I don't have enough blower experience to just make my own front drive, but I'm sure I could cut one down if need be. Seems simple enough. I'm way more worried about screwing up the blower rebuild than getting the drives to work.
The blower rebuild is really simple. The GM manual tells you about all the special tools you need. But you really don't have to have all that stuff. If you get an assembled blower, check the timing and clearances before you take it apart. If it's close enough, and most are, you just need to clean, change the bearings and seals and reassemble. We are talking street use here, 5 psi, not 52 lbs boost top fuel. The shims under the gears are what times the rotors, If the timing is good, you just put the same shims back where they were. Important that when you pull the gears, you pull them both at the same time. work them off a little at a time so that the rotors don't bind. Same thing going together. Once the gears are seated, stuff a shop towel in the gears to bind it up while you torque the bolts that hold the gears on. no gaskets between the end plates and the case. Make sure there are no burrs or dings on the surfaces there. File them off.
I think my blower is one of the ones that needs to have the rotors flipped? I was going to remove the shims and machine the opposite pulley the shimmed amount if the clearances are right. pics of my blower...
Richard Hansen (Hansen's Supercharger Service, Long Beach, CA) used to do a 'standard' prep on 6-71s: the first thing he did was reverse the rotors, end for end (as a pair, both got removed one end, and turned around) He then went about phasing and setting end play. Neoprene seals, steel gears (some stock GMC blowers had cast gears, Rich replaced with steel) and new bearings. Oil was provided from an overhead vial. This was 1962. (Joe Reath and a host of others used his blowers) Do they still reverse them? (I was led to believe it was due to the blower going from 'scavenging hot exhaust' to pressurizing intake...and a method of securing the drive) Please expand on this?
I thought some blowers sat on one side of the engine and some sat on the other so some spun from the "back" and some spun from the front" so that they could use the same internals. which means if you have a blower that was spun from the back(which I think mine is) then you have to flip everything so the drive gears are at the front. But this is stuff I've read and I have no hands on experience. So someone can come along and confirm this or straighten me out.
Correct for a race build, but not for a mild street motor. And I'd suspect he wouldn't be using a Cad 348 flathead for much race usage in first place. But, to pump it up just a little for the street sounds like a good combination and likely more period looking than a oversized 6-71, especially with some V belts.
I'm prob going to roll with a 2" cog belt. I dont really have the room for multiple v. But from what I gather 2" cog is just as correct. I will be pruning it as well. But the EFI on top the blower will be far from "correct". everything I build is a mixture of everything and anything I think is cool. So being period correct is the direction Im going with small deviations every now and then.
This picture shows the drive end. the gears should be under that cover. Would not this be the end you would attach the drive snout to? The drive gears are in the right place and the drive coupler is on the driver's side. And the rotation direction is right, clockwise on the driver's side rotor. The ball bearings are on this end. The end plate gets used over, the green cover had a hose to cover the blower drive shaft, the fuel pump mounted to the 3 bolt flange. The green cover gets replaced by the new drive snout. GM calls this the rear of the blower cause it drove from this end from a coupling and shaft that came off the timing gear-train and the timing gears were on the flywheel end of the engine, thus the rear of the engine.
I thought the other side was the side the snout bolts to cause it has the 6 bolt flange? Im so confused. I though all the "front" components could be reused and it was the "back" cover that needs to be replaced. Which if this is right then the cover with the 6 bolt cover is the "front"....no?
Yeah, the one you got, that six bolt flange had the engine governor attached to it and the water pump on the 3 bolt. GM called it the front cause it was on the fan end. i think that a lot of the confusion comes from the application of the particular blower when it was new. Yours looks like , if you stood at the flywheel end, the blower would have been on the left side of the engine. this would have been a normal application for an transit bus. And I think the preferable core to start with. Now if the block was rotated 180 degrees, the blower would be on the right side of the engine, the timing gears still at the back, but the same blower case could hang off the flange (that's always on top) Now the drive would actually be on the other end of the case, but still on the rear of the blower. sounds screwy, but draw a little picture and see how it would work. The drive is still at the top, it's like a mirror image, front to back. and the cool part is it's all done with the same pieces put together differently. there were even engines that had the camshaft on the other side and the head on backward. Again all done with the parts, just put together different. And then too, there were left and right, clockwise and counterclockwise versions of all these engines, too. the GM Diesel was a marvel of interchangeable engineering. The started making them in 1938 and I guess still make some for military and marine, but no more highway engines.
Can't see where the gears are, gears are always on the drive end. There were also ones that had the 6 bolt flange on the drive end. Late models had the hose connection like the green one.
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