gmc 6-71 diesel blower to 6-71 blower thats usable on a big block chevy - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-09-2010, 11:12 PM
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gmc 6-71 diesel blower to 6-71 blower thats usable on a big block chevy

what do i need to convert its current state to usable in my situation? im going to be running on the street not hard core drag racing.

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Old 08-10-2010, 01:00 AM
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I believe you just get a rebuild kit off ebay which allows the thing to spin faster. But I really don't know. I just bought 3 4-71's and researched it a little.
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Old 08-10-2010, 05:31 AM
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Your best bet is to use it as a core. Buy one already done. About the only thing that is re-used is the case (if its any good). The end plates are usually modified or custom. The rotors are converted to teflon insert. All the bearings and seals are re done. Flange is cut from the case and a custom drive is fabricated..
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Old 08-10-2010, 06:20 AM
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Don't want to start a pissing contest here, but the Stock rotors ($$$) are also used. You don't need Teflon strips for the street, but what you DO need to do is to send it to a Blower Shop and have it rebuilt for the street. This involves squaring the case, converting the bearings/seals to "self contained" (rather than engine oiled), double pinning the rotor shafts, etc, and most important, setting up the correct timing and clearances. A good Shop will tell you, before they do any work, whether your case/rotors are good or bad. If the case/rotors are worn, they may be able to be saved by having them hard Anodized. You will also need a drive/coupler unit ($$$) and front bearing plate...you can get away with using the rear bearing plate. This whole thing is expensive, however, not as expensive as buying a whole new Blower...and you DON'T need a fancy polish on it ($$$)...
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Old 08-10-2010, 10:32 AM
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You obviously will also need a blower manifold, a top for mounting carbs to it, drive pulleys and belt/belt tensioner set-up.

The crank snout will need to be cut for another keyway (two total). About the only place where you can get away w/o something "extra", is the damper- the bottom drive will usually be enough along w/the belt to damp the harmonics.
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Old 08-10-2010, 11:34 AM
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Boat Bob Check your Pm's
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Old 08-10-2010, 01:32 PM
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how do i tell the blowers apart, say a 6v-71 a gmc 6-71 and a normal 6-71? i think its a gmc but im not positive, it came off a catipillar bulldozer from the late 40's.

Last edited by dman16; 08-10-2010 at 01:50 PM.
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Old 08-10-2010, 02:19 PM
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here are some pics,
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Old 08-10-2010, 03:44 PM
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Looks like the "small" version 6-71, the fins across the opening look to be flattened, not rounded.

If you remove the end plate so you can see the shape of the bore, an hourglass-shaped 5.80" diameter bore is the large case. A 5.525" diameter, more "open" bore is a small bore.

Usually the small 6-71 will have small pockets at each end of the top opening, but not always- as yours appears not to have either.

It's not a 6V-71, they have different fins on the sides, etc..
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Old 08-11-2010, 08:18 AM
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From what I can see from your pictures, the rotors appear not to be scratched or gouged up...which means the inside of the case SHOULD be in the same condition. Use some paint stripper to clean up the case, and send it off to be converted...
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Old 08-11-2010, 10:46 PM
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From here it looks rebuildable. Clean it up a little and send it in and modify for street..
Don't need strips for street. doesn't matter large case or small case , just spin the small case up a little faster 5% or so if you need it. I've run a stock type 6-71 40% OD before and they last forever.
I use just a crank hub, don't need a damper except for external balance parts. I also only run the stock key and so far it is still in one piece. You simply can not drive it hard enough to hurt it....at least not in this state. A single 1/4 in key would be nice but unless the motor is all apart it is a lot of work.
No need to polish it either. It gives a 'tough' no nonsense down to business look, plus it will radiate heat much faster due to the increased surface area over polished.

My current ride has a small case 6-71 and I've run it well over 8000 miles this year already. I drive the car nearly every day rain or shine. 5% under. Also fill it up to the bottom hole of the triangular plate with 90w gear lube. It's a bit more than usually specified but the blower will run quieter and a bit cooler in the front end.

Leave the pressure relief valve that will come on the rebuild alone. It will need the pressure to help seal the bearing seals. I usually step on it hard enough to get 5 lbs boost once a day just to make sure there is pressure int he front case. haven't added lube all year.
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