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L18 8.1L swap resource thread

ZooMad75 said:
Do what you can. Just don’t be surprised if you snap a couple. Like I said I was able to break one that had backed off a little by going a little past snug with a 3/8” ratchet handle. No power tools, just my big bear paw on it.

If I ever ran into the GM powetrain engineer that thought the stupid little studs were a good idea, I’d probably beat him senseless and shove the broken studs up under his fingernails.
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Not just gm that down sized .
 
Oxy acetylene torch for lots of heat . Washers to plug weld to first . Then 7/16 nuts for good size plug weld . Let heat soak in . You will pop a few but they come out .
 
ZooMad75 said:
Do what you can. Just don’t be surprised if you snap a couple. Like I said I was able to break one that had backed off a little by going a little past snug with a 3/8” ratchet handle. No power tools, just my big bear paw on it.

If I ever ran into the GM powetrain engineer that thought the stupid little studs were a good idea, I’d probably beat him senseless and shove the broken studs up under his fingernails.
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It was probably an engineer that was hired on after he was at Ford and part of the 4.6/5.4 development team, lol.
 
Blue85 said:
It was a weight reduction feature on an iron head, iron block big block.
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“weight reduction” quotes used ironically.

So besides being puny there some other forces at play here that the small hardware have to deal with. Expanding and contracting of stock cast iron manifolds is an issue. I don’t think Larry has had much a problem with his sanderson shorty headers on his burb, but I think my problems on mine are rooted in this.

Keep this in mind as original equipment on the 8.1’s in the workhorse lineup the exhaust manifolds were actually cast stainless steel which didn’t have the problem that cast iron does. They were more stable dimensionally through heat/cool cycles. And trust me a class a rv going up a pass will get them hot. In testing on a problem child I personally pegged out my infrared temp gun at 1200 degrees and watched the color change from dull red, to cherry red, then orange and eventually white hot. At least under warranty we were not fixing a lot of broken studs.

Problem is the workhorse rv manifolds won’t fit in a square and neither will the 800 truck manifolds (which I’m not sure if they were cast stainless or not, they are different than rv as far as the shape) so the best fitting manifolds for a 8.1 in a square are factory big block manifolds from a square. 400 truck manifolds are close, but don’t fit as well. So using a manifold designed for use with larger hardware which I think was 3/8” or 7/16” with smaller diameter studs gives a bit of wiggle room. Talking to other rv shops about the older units it was pretty common to warp the old cast iron units due to extreme heat. But those manifolds were at least “seasoned” and less likely to warp again if the face was machined flat again. If the ports were connected by extra cast material they would cut them with a band saw to allow each port to move a little on its own and seal better too. All of which has been done to mine when we originally put an 8.1 in.

I’m putting this out there just to say even when you’ve done everything perfect when it comes to these stuff still happens. I’ll probably tackle my exhaust leak this weekend and see if I have a snapped stud or not. I’m hoping I don’t but it’s not the end of the world.
 
another 8.1L vortec has awaken from its long over due slumber ............

tonight i fired up the mystery motor to me from a good almost 10 years ago i got from a solid source . it was a basket case short block / heads off / just a long block only . guy didn't know 8.1 is NOT like a bbc and stopped halfway apart and gave up on it . i got it for $300.00 bucks and now have more than that in it with all the stuff to put it back together and swap over the old motor parts i didn't have .

she popped off almost instant after a few key cycles to prime the fuel system up . few hickups and stumbles but she was purring and 70psi oil pressure on new 10-40 oil and no cooler with correct bypass done in block .

cant wait to finish it off this weekend and maybe do a spin around the block or 2 with it . . . :saweet: :burnout:
 
Experts need help . Low miles 8.1 sat on stand for years . I put the heads back on and did everything to spec . Long story why it was apart . Not that it went bad tho .

Fires up sounds good 70psi cold / 30-40psi warm 10-40 new oil . All stock no upgrades . Motor was clean . Used a old distributor to prime the motor and roll crank over also many times .

After 5 or so min running it started with a squeak like a rusty alternator chirp . Pulled belt refired still there with just motor and auto trans . Have yet to pull converter bolts and try . Stays steady up/down with rpm no better or worse .

Any idea what it might be . . . Sure hope not a bad cam roller lifter from sitting as i just put it together and not easy to pull apart at this point in the game .

Thanks and let me know what you think @ZooMad75 @Larry others .

View attachment 20250503_194518.mp4
 
Wes Harden said:
I just removed the crank pulley/dampener, and don’t see any indexing device. Does it not matter how it is installed?
Google fu has failed to answer my question.
View attachment 501730
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no index . and best money i did was the kent moore 8.1 motor tool kit . every tool was in it to make work slick as glass on these .
 
thinking it could be this possible for the noise . its not as much a tick but more a squeak and not there cold but there warm for sure .

1746397872541.jpeg
 
Do any you fellows have a link to the aftermarket accessory brackets someone was making for the 8.1?
I went looking on the google. Got nothing but LS stuff
 
so my 2002 c3500hd 8.1L/4L80-e has the random shut off problem .

i had a friend show up with a snap-on scanner tonight and we fired it up . here is the gist of it .

#3 cyl shows miss fire = zero motor skip
tps fine slow rpm increase = stalls if blip throttle
engine stall bank #2 o2 shows full info as if running . bank #1 drops off as if not running .
cranking volts shows 9.xx or less . yet new batt full charge and running 13.4-13.6 volts .

and most bizarre thing . sudden loss of communication to scanner and data stream back but lost every thing we had just seen . even the stalls before all data was still there .

we are both thinking possible computer ?

but i have no spare to test with . my 01 is stick and the 05 is to new . so i am now at the next level knowing what we saw tonight .
 
Do any of you have a picture of a notched frame for the AC compressor sitting down low in its original location on an 8.1L on a square body?
I’m just wondering how much of the frame has to be notched out, and how I can overcome that with some bracing/boxing
I’m really not happy with set up I built.
 
I don’t have a picture but I can say it’s a significant chunk to carve out and it makes getting to the pass side engine mount a nightmare.
 
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