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Author Topic: 1970 gmc 4905 8v71  (Read 1602 times)
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1970 gmc 4905


« on: July 05, 2007, 08:03:59 AM »

hey anybody out there know if any heavy modification needed i am takeing out my 8v71 out of my 1970 4905 and i am puting a (1982 8v71 out of a 1967 4107) any thing to watch out for befor i do this or should it be a easy swap<ps rotation should not matter since i am doing a complete swap including tranny just taking 1 craddle out and hoping to slide new craddle in any info would be cool

Never stop thinking,it"s what keeps us going till tomorrow
Jerry Liebler
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« Reply #1 on: July 05, 2007, 01:11:45 PM »

Since the 4107 is a 12 volt bus and the 4905 is 24 volt you'll need to keep your starter and alternator.  You might want to take the alternators apart without removing them from the engines and just swap the 'field' as it is the only difference and the gear installation is tricky.
Jerry 4107 1120
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« Reply #2 on: July 05, 2007, 02:38:28 PM »

Hi John,

I got your email.  I'm just a little ahead of you in the change out.  I have taken LOTS of pictures, including the 8V71 cradle, the way things were connect in on the engine, etc........if you get in a bind and need pictures.

I used the generator off my 8V71 and put it on my 6V92 (both engines are set up as 24VDC-the generator on the 92 was bad).  Before the exchange I counted teeth on both the generator drive gear, and also the ring inside both engines.  Different ratios.

You have to be very careful, if the ratios is wrong the generator can self destruct and broken pieces are inside the engine and drop through the engine gearing.  A guarantee to do engine damage.

I talked with Nick Liberti at NIMCO (very knowledgeable and has been in the bus business for years) who told me as long as I took the ring out of both engines and kept the right drive ring matched to the right generator gear on each generator (hope that made sense) it would be OK.  I removed the engine ring (believe it was 8 allen drive bolts) and generator from the 8V71 and put both of them on the 6V92.

As far as matching both 8V71s to the engine cradle, I would think they would match.  But I have learned, even if they don't, it's nothing a welding unit can't fix.  I'm having to fabricate my 8V71 cradle to match the 6V92.  Just takes more time and material, but it's doable.

Like everyone told me, just be careful your working with weight that can do unrepairable damage, to you !!  I have been using a pallet jack to move the engines and cradles around, keeping them low to the ground.  When I pulled the engine, transmission, and cradle out of the bus, I borrowed a warehouse forklift, and I'm glad I did.  It's a whole lot of weight.  I also had my neighbor present, and standing by just in case help was needed.  As long as it doesn't bind on anything it's a very straight forward removal and easier than I anticipated.

If you have any specific questions about the exchange give me an email, I"ll answer them if I can.

Chris Christensen

Chris & Cheryl Christensen
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Eagle, Idaho
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« Reply #3 on: July 05, 2007, 02:50:23 PM »

It would be really neat if you could just change the complete cradle from each bus-about an 8 hour job for 2 mechanics.  That was the original idea behind the V drive-easier R&R of the complete radiator, engine and transmission cradle.  Good Luck, TomC

Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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