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Thread: 366 GM truck motor

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    Senior Member amscontr's Avatar
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    366 GM truck motor

    We recently bought a GMC 7000 off of Ebay and it has a worn out 366 in and we're tossing around the idea of either rebuilding this motor or finding a rebuildable 427. I'd like to slip a small diesel in it's place but we don't want to spend 20 grand on a 2 grand truck.
    I'll post a pic of the truck it came from a junkyard in WV and we had it trucked back here maybe one of you might even recognize this truck.
    The motor in it is a 366 GM Target motor so at one time someone must have replaced it. The truck has been sitting for a couple years so we replaced the carb, plugs, wires, etc. I'm thinking possibly pulling the heads or the whole thing and tossing in a 427. I had a similar truck years ago with a 427 that ran great, but I'd like to give this motor a chance. I have spent some time doing some research via discussion forums, Hot Rodding, Truck Pulling, etc. and talked to some folks around here and some praise the 366 and others claim it to be a "boat anchor".
    I'm just kinda looking for some feedback from some real life folks who might of ran these motors in trucks and would appreciate any tips or advice.

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    Drove a new GMC 366/4bbl/dual exhaust/5-speed 26' box truck back in the late 70's.
    Was fun-would easily 'take' a few cars off a light. On e-way no problem getting up to 70 then it would back down to 65 (governor). Most of the time it was lightly loaded. Ran way stronger than similar 90's Ford 370/2bbl/5-speed.

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    i have a 366 in a '79 C65. the truck has definitly been worked throughout it's life. they're gauges that don't work among other things. as far as the engine it is very suprising to me. definitly not a powerhouse but it does deliver the goods. i have overloaded it a time or two and the truck has made it up every mountain i have asked it to. maybe not at daytona speeds but it gets there. i plan on working on updating the truck over the winter. for the money it has been worth it. i can park the truck a few weeks then start it and run when i need it. when the engine goes i wil replace it with a crate 366. just don't see how a 427 would be that much better. it would be great to be able to drop a small diesel in it but haven't heard too much good about diesels from that era that would bolt in. it would also effect the gearing. much easier to stay with the gasser.
    good luck,
    Last edited by capt_met; 11-25-2009 at 07:01 PM.
    '79 Chevy C65 dump truck,
    '94 F-350
    Bobcat B300 TLB
    Root Grapple
    Box Blade
    12" & 24" backhoe buckets
    24' equipment trailer

  4. #4
    Senior Member amscontr's Avatar
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    Here it is
    Attached Images Attached Images  

  5. #5
    Senior Member amscontr's Avatar
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    Quote Originally Posted by capt_met View Post
    i have a 366 in a '79 C65. the truck has definitly been worked throughout it's life. they're gauges that don't work among other things. as far as the engine it is very suprising to me. definitly not a powerhouse but it does deliver the goods. i have overloaded it a time or two and the truck has made it up every mountain i have asked it to. maybe not at daytona speeds but it gets there. i plan on working on updating the truck over the winter. for the money it has been worth it. i can park the truck a few weeks then start it and run when i need it. when the engine goes i wil replace it with a crate 366. just don't see how a 427 would be that much better. it would be great to be able to drop a small diesel in it but haven't heard too much good about diesels from that era that would bolt in. it would also effect the gearing. much easier to stay with the gasser.
    good luck,
    Well I had one with a 427 and the only difference I see is a little more HP and torque. I finally got this thing running right yesterday and I'm going to give it a chance. I found a decent old 427 tall deck some guy was going to build a stroker motor out of and changed his mind. I figure I'll tear it down and rebuild it and have it for a standby motor. This truck and the one I before like it have air brakes and air system which will enable me to put an air release tailgate, air operated hoist, and maybe an air PTO shifter. The body is a J&J Body out of Somerset Pa. and the hoist and PTO levers are on the outside next to the tailgate handle, it all looks factory. The only problem with the bed is the tailgate with some rot on the dirt shedders.
    As far as the diesels go I think the only diesel they put in these trucks were a Detroit 8.2, they say that there's not enough hood clearance for a 3208 unless you go with a Topkick hood. I was reading some interesting stuff on another discussion forum about a blower or even a turbo on a 366.
    Anyhow the price was right compared to the junk I seen around here and to me it was worth the time and travel putting a new life in this old truck.

  6. #6
    Junior Member Gmc7210's Avatar
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    366 Gm truck motor

    I have this motor in my dump truck, an 85 GMC 7000 5+2 hydraulic brakes 23160 GVW. With the split rear end this thing pulls pretty strong. I've heard that these engines are bulletproof and i believe it. Ive wound the snot out of mine pulling heavy loads up big hills, and although i was barely moving at the top, it just took it. Mine has low miles but it doesnt use any oil or make any lifter clatter. definetly a good engine

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    The 366 was a good motor, lots of low end torque and they are not near as bad as a 370 Ford on fuel consumption. I always found their fuel and ignition systems less tempermental than a Ford.

    Instead of an overhaul you might look into a crate engine from a Chev or GMC dealer. Prices are not too bad and you get a decent warranty.

    I'd stay a long ways away from a 8.2L diesel, one of the better boat anchors built by GM. Stay away from the 3208 Cat as well. You might look at a 3100 series Cat instead. It would take some modification, but would be a good engine for this size rig.

    Good Luck!

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    Thats a nice looking GMC amscontr.The big block chevys are good engines.I've ran them in everything from chevelles,novas,pickups, & c-70 trucks.Talking about old trucks & chevy engines,I have an old 1966 chevy c-60 that had a in line 292 engine from the factory.The truck has a low geared 2 speed axil & 4 speed tranny.We put a 350 small block in it after the 292 wore out.The truck pulls great with the small block & low gears in the back.I would dang near put it up against a big block truck.Good luck with the GMC project.
    Last edited by td25c; 11-26-2009 at 09:27 PM.

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    366 is tough little engine. BUT!! the one thing you don't want to do is rev the motor without a load on it. You can actually sit and watch the block swell and contract as you rev it. almost a twin to the 396

  10. #10
    Senior Member amscontr's Avatar
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    Quote Originally Posted by 25c View Post
    Thats a nice looking GMC amscontr.The big block chevys are good engines.I've ran them in everything from chevelles,novas,pickups, & c-70 trucks.Talking about old trucks & chevy engines,I have an old 1966 chevy c-60 that had a in line 292 engine from the factory.The truck has a low geared 2 speed axil & 4 speed tranny.We put a 350 small block in it after the 292 wore out.The truck pulls great with the small block & low gears in the back.I would dang near put it up against a big block truck.Good luck with the GMC project.
    Thanks, I was ready to give up on the motor until I got the motor running right (I hope?), the truck has been sitting for a couple years and I was told most likely it was a stuck valve. I switched carbs, tuned it up and changed fuel filter and it seems to be running and starting good now. Someone was telling me on another forum about a Detroit 4-53t that came in some of these medium duty trucks. That might make an intersting switch down the road if I decdide to get creative??
    Who knows for now the 366 will get it's chance. The engine says "Target Motor" on it I guess it's not OEM? It's defineatly going be less of a headache then the 1988 Ford F350 dump we have with a 460/7.5 electronic nightmare!
    Last edited by amscontr; 11-28-2009 at 08:08 AM. Reason: mispell

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    Senior Member amscontr's Avatar
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    Quote Originally Posted by surfer-joe View Post
    The 366 was a good motor, lots of low end torque and they are not near as bad as a 370 Ford on fuel consumption. I always found their fuel and ignition systems less tempermental than a Ford.

    Instead of an overhaul you might look into a crate engine from a Chev or GMC dealer. Prices are not too bad and you get a decent warranty.

    I'd stay a long ways away from a 8.2L diesel, one of the better boat anchors built by GM. Stay away from the 3208 Cat as well. You might look at a 3100 series Cat instead. It would take some modification, but would be a good engine for this size rig.

    Good Luck!
    that's what I hear about them 8.2's, I had a seires 50 Detroit in a '94 Freightliner FL 106 that had plenty of power it was just heavy on the front end and would do a nose drive in soft dirt.
    A smaller diesel with a jake brake and 13 spd. would be the ultimate in a medium duty dump, but I'm sure it would be a "PITA" with maint. etc.

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    366 engine

    Quote Originally Posted by amscontr View Post
    Thanks, I was ready to give up on the motor until I got the motor running right (I hope?), the truck has been sitting for a couple years and I was told most likely it was a stuck valve. I switched carbs, tuned it up and changed fuel filter and it seems to be running and starting good now. Someone was telling me on another forum about a Detroit 4-53t that came in some of these medium duty trucks. That might make an intersting switch down the road if I decdide to get creative??
    Who knows for now the 366 will get it's chance. The engine says "Target Motor" on it I guess it's not OEM? It's defineatly going be less of a headache then the 1988 Ford F350 dump we have with a 460/7.5 electronic nightmare!
    As stated, if you have to replace the engine, I would go with a crate engine. Unless you are able to do it yourself, you will save money with the crate engine and you will have a warranty.
    I have been through these engine swaps and you can get into a bunch of work and money and in the long run it isnt worth it. Most of the time, you can buy a diesel truck, for what you would have in a replacemnt engineTo change engines, you have to worry about tranny and rear end ratios, being correct. From an old GM53 series mechanic, say away from them on a swap, its possible, but its a OK engine, if its already installed, then all you have to do is maintain it
    As far as the tailgate, there are lots of good used tailgates, in the salvage yards. I have bought a new one from the factory for around $500 (for a 16ft bed and high tailgate) I have built them myself, its not that much trouble, if you know how to weld
    Cut out the rust and replace the bad metal with new.
    Good Luck, and keep us posted

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    Hi, I have a 1980 gmc 7000 with the 4-53 turbo, great truck and the little detriot really makes it. It's pretty quiet (for a detroit) because of the turbo.

    Pretty good on fuel also. The only thing I don't like is the hydraulic brakes, I just had to put a new hydrovac unit and all new brakes lines. Make sure your brake lines are in good shape because if one line lets go, you have NO brakes. Mine has the single line system, not sure what you hve.
    Good luck with the truck!
    Dave

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    Senior Member amscontr's Avatar
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    Quote Originally Posted by Woodboatdave View Post
    Hi, I have a 1980 gmc 7000 with the 4-53 turbo, great truck and the little detriot really makes it. It's pretty quiet (for a detroit) because of the turbo.

    Pretty good on fuel also. The only thing I don't like is the hydraulic brakes, I just had to put a new hydrovac unit and all new brakes lines. Make sure your brake lines are in good shape because if one line lets go, you have NO brakes. Mine has the single line system, not sure what you hve.
    Good luck with the truck!
    Dave
    Thanks,
    This truck has air brakes, one major reason for buying it. With the air system I can add an air operated tailgate, hoist controls and maybe a air shift PTO. Plus if I decide to pull a trailer I can run air to the rear for trailer brakes. Right now it's a toss up as far as switching to a diesel with fuel prices and fuel taxes.
    I found a pretty good deal on a 427 tall deck that I'm pretty sure I'll buy and go thru it and keep as a spare/backup.
    I have been doing some research on those 4-53's and most info I have seen is favorable.

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    I have a 87 GMC 7000 parts truck for sale

    I live in north AL and I am probally a long way from you but i have a 87 disc brake 366 engine parts truck that i just bought.The 366 runs and seems good i would sell the complete truck for $650 firm.

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