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Which GM Crate 350 4Bolt Do I Need For My 86 Truck


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I have a 1986 GMC 3/4 ton heavy duty 4WD pick up. The truck has an "M" series carbruetted 350 4 bolt engine, T-400, AC, etc. with over 200K miles. The engine has blown head gasket(s). I need to rebuild or replace the engine and am weighing my options.

 

I am told the head(s) are likely cracked also. Considering the cost of a total rebuild, replacing one or both heads, machine work, etc. it seems a new crate motor may be a better investment at very little more money than the cost of a rebuild.

 

Another option is buying a rebuilt long block out of a parts house. I have heard you only have a 50/50 chance of getting a good one so that doesn't seem like a good idea.

 

I was trying to identify the exact GM crate motor replacement and was told that GM does not offer the "M" series replacement engine any longer. My question is which crate motor would be the best replacement for my truck so as all my AC and accessories would bolt on and require no modifications?

 

Please respond to: [email protected]

 

Thanks for any help and info.

 

Dave1

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Hi- An 86' 350 is going to be hard to find a replacement for. 86 was a transition year for the small block-it had the one piece rear main but was prior to the roller cam and head bolt changes. If it was mine I would put in a 350 w/2 piece rear main seal and the four bolt main bearings. All of your stuff should bolt right up (intake, exhaust, etc) the only difference being that it has the old style rear oil seal. You can order them with the Left or Right hand dipstick so that would still be correct and all. You can order brand new long blocks from Jegs, Summit racing or your GM dealer. Cost is around $1400+ Shipping. The GM part number is 10067353 for a Goodwrench 260HP 4 bolt main w/2 piece seal. Should work like a champ in your truck. Hope this helps! Good luck and welcome to the forum! :crackup:

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  • 3 months later...

2500HD4X is on the right track with buying the gm goodwrench crate 350. Ask for the '85 model. For about $300 more you can get the HO engine with about 320 HP it has a different cam in it. You can even get votech heads on these if you wanna spend $2400 for the long block. Tthe only other thing you may need is to change the flex plate if your going from a one piece rear seal to a 2 piece. the different plate costs about $15 and it enables a 1986/87 tranny to bolt up to an 85 350. From a dealer these engines come with a 3 year 30,000 mile warranty.

As for the 50/50 chance of getting a good one. Thats a load of crap! These motors are the same off the GM line that were put in the trucks and camaros back in 85. Ive bought a bunch of them and never had a problem.

Since your truck is an '86 3/4 ton it probably has the 85 model 350 in it with the 2 piece rear seal the change for 3/4 trucks and above didnt come until 87/88 depending on your model. Hope this helps.

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As for the 50/50 chance of getting a good one.  Thats a load of crap!  These motors are the same off the GM line that were put in the trucks and camaros back in 85.  Ive bought a bunch of them and never had a problem.

 

 

 

 

 

He was refering to the "parts houses" motors... I would stick with a GM unit. I just rebuild a hotrod motor for one of my other trucks and have about $2500 into it, just cash, not my own time to assemble. The warranty I gave myself is pretty good, but if something goes wrong, it's all out of pocket to correct :jester:

 

--Mike

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