8.1L swap questions
02-06-2024, 06:46 PM
#1
Teching In
Thread Starter
8.1L swap questions
I have a 8.1L from a 2006 Topkick and a 4L80E from a 97 K30 in my garage and am going to swap them into my truck. Doing my research, I have a few easy questions for you all:
1) Do I need a spacer plate between the engine and trans or can I bolt them straight together? All my AMC/TH400's required a tin that went on before the flexplate and got sandwhiched between the engine block and transmission case. I see them available but cannot see anywhere where I do/don't need it.
2) Are my metric bellhousing bolts the same as those from a 6.0? I have no hardware to mount the trans to the engine. Can I pull any LS bolts and use those?
3) My current oil pan is the monster one (10qts in think?) from the Topkick. I plan to swap a rear sump from a 2500. Anyone know if the oil pickups are the same or do I need to grab an oil pickup when I grab the pan from the wrecking yard?
4) I read in a few different places I can use the flex plate from a 6.0/4L80E but don't need the spacer. Can anyone confirm? Also related, are the 6.0 flexplate bolts the same as the 8.1L flex plate bolts? I am assuming the bolts that held the flywheel on my 8.1L are not the same as those that hold a flexplate... right?
1) Do I need a spacer plate between the engine and trans or can I bolt them straight together? All my AMC/TH400's required a tin that went on before the flexplate and got sandwhiched between the engine block and transmission case. I see them available but cannot see anywhere where I do/don't need it.
2) Are my metric bellhousing bolts the same as those from a 6.0? I have no hardware to mount the trans to the engine. Can I pull any LS bolts and use those?
3) My current oil pan is the monster one (10qts in think?) from the Topkick. I plan to swap a rear sump from a 2500. Anyone know if the oil pickups are the same or do I need to grab an oil pickup when I grab the pan from the wrecking yard?
4) I read in a few different places I can use the flex plate from a 6.0/4L80E but don't need the spacer. Can anyone confirm? Also related, are the 6.0 flexplate bolts the same as the 8.1L flex plate bolts? I am assuming the bolts that held the flywheel on my 8.1L are not the same as those that hold a flexplate... right?
02-06-2024, 07:12 PM
#2
TECH Resident
I have a 8.1L from a 2006 Topkick and a 4L80E from a 97 K30 in my garage and am going to swap them into my truck. Doing my research, I have a few easy questions for you all:
1) Do I need a spacer plate between the engine and trans or can I bolt them straight together? All my AMC/TH400's required a tin that went on before the flexplate and got sandwhiched between the engine block and transmission case. I see them available but cannot see anywhere where I do/don't need it. The TopKick had some sort of Allison, didn't it? IDK if that will work for you. You can simply source a flex plate from a Suburban or Avalanche that had the 8.1/4L80e (technically a 4L85e, but that's really the same.) Otherwise I've never seen anything bolted other than a direct bolt on.
2) Are my metric bellhousing bolts the same as those from a 6.0? I have no hardware to mount the trans to the engine. Can I pull any LS bolts and use those? Yes
3) My current oil pan is the monster one (10qts in think?) from the Topkick. I plan to swap a rear sump from a 2500. Anyone know if the oil pickups are the same or do I need to grab an oil pickup when I grab the pan from the wrecking yard? IDK about those extra deep pans, I've never seen them. Just try the regular truck pan, if it doesn't work it would be obvious and you would know it. Going from shallow to deep is where I can see it being a problem if pick-up tube is too high in the sump
4) I read in a few different places I can use the flex plate from a 6.0/4L80E but don't need the spacer. Can anyone confirm? Also related, are the 6.0 flexplate bolts the same as the 8.1L flex plate bolts? The flex plates appear to be different. See comment about which one to get. I am assuming the bolts that held the flywheel on my 8.1L are not the same as those that hold a flexplate... right?
1) Do I need a spacer plate between the engine and trans or can I bolt them straight together? All my AMC/TH400's required a tin that went on before the flexplate and got sandwhiched between the engine block and transmission case. I see them available but cannot see anywhere where I do/don't need it. The TopKick had some sort of Allison, didn't it? IDK if that will work for you. You can simply source a flex plate from a Suburban or Avalanche that had the 8.1/4L80e (technically a 4L85e, but that's really the same.) Otherwise I've never seen anything bolted other than a direct bolt on.
2) Are my metric bellhousing bolts the same as those from a 6.0? I have no hardware to mount the trans to the engine. Can I pull any LS bolts and use those? Yes
3) My current oil pan is the monster one (10qts in think?) from the Topkick. I plan to swap a rear sump from a 2500. Anyone know if the oil pickups are the same or do I need to grab an oil pickup when I grab the pan from the wrecking yard? IDK about those extra deep pans, I've never seen them. Just try the regular truck pan, if it doesn't work it would be obvious and you would know it. Going from shallow to deep is where I can see it being a problem if pick-up tube is too high in the sump
4) I read in a few different places I can use the flex plate from a 6.0/4L80E but don't need the spacer. Can anyone confirm? Also related, are the 6.0 flexplate bolts the same as the 8.1L flex plate bolts? The flex plates appear to be different. See comment about which one to get. I am assuming the bolts that held the flywheel on my 8.1L are not the same as those that hold a flexplate... right?
02-06-2024, 07:31 PM
#3
Teching In
Thread Starter
Absolutely helps.
1) yeah, Topkicks had either the Allison auto or the Eaton Manuals. I see 6.0/4L80's are all over the yards and their flexplates seem easy to find/cheap but the 8.1's with a 4L80/85 seems to be harder to find. If I could find an 8.1 in a burb/avalanche/2500/3500 I would definitely pull it. When I was doing my reading, I saw in one or two places that the 6.0 and 8.1 flex plates are the same but it's really hard to find first-hand experience or a part number confirmation. I really dont want to spend the time/money buying a used 6.0 flexplate and then find it won't work at all. Maybe I just bight the bullet and call a full service wrecking yard/ebay to get an actual 8.1L/4L80 flex plate.
2) sweet! Thanks!
3) Yeah, my pan looks like this:
https://www.ebay.com/itm/165481124126
It fits in my chassis but the axle contacts before full bump.
4) copy. Thanks!
1) yeah, Topkicks had either the Allison auto or the Eaton Manuals. I see 6.0/4L80's are all over the yards and their flexplates seem easy to find/cheap but the 8.1's with a 4L80/85 seems to be harder to find. If I could find an 8.1 in a burb/avalanche/2500/3500 I would definitely pull it. When I was doing my reading, I saw in one or two places that the 6.0 and 8.1 flex plates are the same but it's really hard to find first-hand experience or a part number confirmation. I really dont want to spend the time/money buying a used 6.0 flexplate and then find it won't work at all. Maybe I just bight the bullet and call a full service wrecking yard/ebay to get an actual 8.1L/4L80 flex plate.
2) sweet! Thanks!
3) Yeah, my pan looks like this:
https://www.ebay.com/itm/165481124126
It fits in my chassis but the axle contacts before full bump.
4) copy. Thanks!
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strutaeng (02-06-2024)
02-06-2024, 08:25 PM
#4
TECH Resident
Absolutely helps.
1) yeah, Topkicks had either the Allison auto or the Eaton Manuals. I see 6.0/4L80's are all over the yards and their flexplates seem easy to find/cheap but the 8.1's with a 4L80/85 seems to be harder to find. If I could find an 8.1 in a burb/avalanche/2500/3500 I would definitely pull it. When I was doing my reading, I saw in one or two places that the 6.0 and 8.1 flex plates are the same but it's really hard to find first-hand experience or a part number confirmation. I really dont want to spend the time/money buying a used 6.0 flexplate and then find it won't work at all. Maybe I just bight the bullet and call a full service wrecking yard/ebay to get an actual 8.1L/4L80 flex plate.
2) sweet! Thanks!
3) Yeah, my pan looks like this:
https://www.ebay.com/itm/165481124126
It fits in my chassis but the axle contacts before full bump.
4) copy. Thanks!
1) yeah, Topkicks had either the Allison auto or the Eaton Manuals. I see 6.0/4L80's are all over the yards and their flexplates seem easy to find/cheap but the 8.1's with a 4L80/85 seems to be harder to find. If I could find an 8.1 in a burb/avalanche/2500/3500 I would definitely pull it. When I was doing my reading, I saw in one or two places that the 6.0 and 8.1 flex plates are the same but it's really hard to find first-hand experience or a part number confirmation. I really dont want to spend the time/money buying a used 6.0 flexplate and then find it won't work at all. Maybe I just bight the bullet and call a full service wrecking yard/ebay to get an actual 8.1L/4L80 flex plate.
2) sweet! Thanks!
3) Yeah, my pan looks like this:
https://www.ebay.com/itm/165481124126
It fits in my chassis but the axle contacts before full bump.
4) copy. Thanks!
Sorry, I think I got confused. I was looking at the 8.1 engine I have in my garage, but I got stuff piled and can't take a good photo. The flex plate looks different than the one from the 6.0 LS, but that's because that engine was from a 2500 HD truck, which is the Allison 1000. That's why it looks different.
Only the Avalanche, Suburbans and Express Vans with the 8.1 were mated to the 4L85E, not the HD trucks.
But on RockAuto the flex plates of the 6.0 vs 8.1 still shows a different part numbers. I'm remembering that the Allison 1000 flex plate is the same for the Duramax and the 8.1. That was my confusion.
02-11-2024, 05:26 PM
#6
Teching In
Thread Starter
Just picked up a new/open box PRW #1849600 Flexplate for $45.
I am assuming the bolts that originally held the flywheel to the crank on my 8.1L are too long for a Flexplate. True? I cannot find a part number for Flexplate bolts. Anyone know if they are too long and if they are, have a part number for Flexplate fasteners?
I am assuming the bolts that originally held the flywheel to the crank on my 8.1L are too long for a Flexplate. True? I cannot find a part number for Flexplate bolts. Anyone know if they are too long and if they are, have a part number for Flexplate fasteners?
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strutaeng (02-11-2024)
02-11-2024, 08:24 PM
#7
TECH Resident
Just picked up a new/open box PRW #1849600 Flexplate for $45.
I am assuming the bolts that originally held the flywheel to the crank on my 8.1L are too long for a Flexplate. True? I cannot find a part number for Flexplate bolts. Anyone know if they are too long and if they are, have a part number for Flexplate fasteners?
I am assuming the bolts that originally held the flywheel to the crank on my 8.1L are too long for a Flexplate. True? I cannot find a part number for Flexplate bolts. Anyone know if they are too long and if they are, have a part number for Flexplate fasteners?
I don't know the answer to your question (but would like to know the answer just for future reference.)
I can remove one of the flex plate bolts on my engine to check the length. Knowing GM, it's either one or the other, LoL.
I will post tomorrow what I find...
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rang-a-stang (02-12-2024)
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02-12-2024, 06:09 AM
#8
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Thread Starter
That would be great! I brought one of the flywheel bolts with me for reference (I am on a business trip until mid March). I am going To hit a local wrecking yard tomorrow and see what they have, too. Their website says they have 7 avalanche’s on the lot (I’m hoping at least one is a 2500).
i also ordered an oil pan and bell housing bolts. I’m trying to get as many parts as I can afford while I am away so I can hook them up and get them mounted as soon as I get home.
i also ordered an oil pan and bell housing bolts. I’m trying to get as many parts as I can afford while I am away so I can hook them up and get them mounted as soon as I get home.
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strutaeng (02-12-2024)
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strutaeng (02-12-2024)
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rang-a-stang (02-13-2024)