L86 to L8T in '19 Yukon XL Denali

[chevman88]

After reading through @L8T BURB thread, I decided to swap out the broken L86 (Thank you GM DoD) out for the L8T. So far smooth sailing, separating the l86 from the 10l80 required a wood chisel to wedge in and work around the block until they separated. Now that the new L8T is set in place there is about 1/4" gap between it and the trans and I'm wondering if I'm going to have to use bolts to pull them together. The torque converter spins freely and I don't see anything that may have been caught between the two. If I use a pry bar to rock the motor up and down, they pivot on the dowels but won't seat all the way. Thought?

Pics for reference

 

[Bigburb3500]

No thoughts… but subscribed to follow progress. Sorry I’m no help.

 

[chevman88]

Consensus reached after talking to some of my fellow gearheads was to pull the motor just enough to wrap some emery cloth on the dowels (If I can reasonably remove them, do that) and sand them down just a touch and verify they are indeed what's hanging it up (and give her some lube). Gonna have to wait until tomorrow due to working out of a shorter garage and the weather turning to nasty sleety BS.

 

[Fless]

Good plan. I was going to suggest NOT using bolts to get a full mate.

 

[RoadTrip]

After reading through @L8T BURB thread, I decided to swap out the broken L86 (Thank you GM DoD) out for the L8T. So far smooth sailing, separating the l86 from the 10l80 required a wood chisel to wedge in and work around the block until they separated. Now that the new L8T is set in place there is about 1/4" gap between it and the trans and I'm wondering if I'm going to have to use bolts to pull them together. The torque converter spins freely and I don't see anything that may have been caught between the two. If I use a pry bar to rock the motor up and down, they pivot on the dowels but won't seat all the way. Thought?

Whoa up! I broke a transmission pump on my Chevy forcing the engine and trans back together.

There are 3 spline sets that have to line up with the deepest being the trans fluid pump. If you are successful pulling the two halves back together without breaking the mounting flanges on the transmission, the loud pop you hear will be your transmission pump breaking.

On the SECOND installation, I had a friend rotate the engine slowly with a breaker bar as the transmission was close, like yours, until the crank splines lined up and then it seated easily.

It's been some years since this project and maybe others here have more recent experience. There may even be some YTvids to show the best process.

You don't want to have to do this again.

 

[chevman88]

Whoa up! I broke a transmission pump on my Chevy forcing the engine and trans back together.

There are 3 spline sets that have to line up with the deepest being the trans fluid pump. If you are successful pulling the two halves back together without breaking the mounting flanges on the transmission, the loud pop you hear will be your transmission pump breaking.

On the SECOND installation, I had a friend rotate the engine slowly with a breaker bar as the transmission was close, like yours, until the crank splines lined up and then it seated easily.

It's been some years since this project and maybe others here have more recent experience. There may even be some YTvids to show the best process.

You don't want to have to do this again.

Agreed, I don't think I'm in this same boat as my torque converter still freely spins, however, better safe than sorry. I've broken a trans pump myself on a 4l80e and it's no fun to have to pull it all back apart to fix that.

 

[chevman88]

Pulled the motor out a tad, saw that the dowels were being self clearanced by the block and proceeded to sand them down and put some axle grease on them. Set the block back in place and the gap was smaller, but still there. Based on the dowel condition, the fact that the converter still freely spun, and how much of a pain it was to separate them to begin with I decided to use the four bolts surrounding the dowels and tighten them a bit at a time while checking the converter and only going 1-2 turns at a time before moving on to the next bolt. She's now seated all the way, so it's time to start buttoning everything else up hoping to get a first fire by tomorrow afternoon/evening.

 

[chevman88]

Note to self, just stick with OEM parts. Motor mounts were bad and I didn't pre-order them so I picked up a set from the local parts store. I ended up fighting them all day trying to get all of the holes to align as well as the little tube on the bottom to slot into the frame...no dice. Put the factory one back on and it slotted right in place like it should have. Got a new set of AC Delcos from the stealership as I REALLY don't want to have to do this again once everything is back together, so I lost a day on that. Live and ya learn.

 

[CMoore711]

Definitely interested in hearing your driving impressions of the L8T compared to the L86 once you get her all back together.

 

[B-train]

I love this post so far. I'm a curious follower as well. If my 2017 chits the bed, this will be an option for sure.

 

[Marky Dissod]

Y'all might wanna read about the experiences of @L8T BURB.
I 'technically' get why GM won't make the L8T available in Suburbans / Y XLs / ESVs,
but maybe the L8T is too reliable compared to the L86/L87?

 

[Bigburb3500]

Y'all might wanna read about the experiences of @L8T BURB.
I 'technically' get why GM won't make the L8T available in Suburbans / Y XLs / ESVs,
but maybe the L8T is too reliable compared to the L86/L87?

I THINK, key word here is THINK, it has to do more with emissions and the intended target market for the engine. The L8T is only available in HD vehicles which has a substantially different emission regulation and is “better” because of the lesser restrictions (no AFM/Cylinder deactivation). The 5.3 and 6.2 might be more “similar” from an engineering perspective which is why they appear in the regular consumer-grade vehicles and the L8T is for HD use only.
**this is a working theory**

 

[Marky Dissod]

I THINK, key word here is THINK, it has to do more with emissions and the intended target market for the engine.
The L8T is only available in HD vehicles which has a substantially different emission regulation and is “better” because of the lesser restrictions
(no Cylinder deactivation/start-stop).
The 5.3L & 6.2L might be more “similar” from an engineering perspective which is why they appear in the regular consumer-grade vehicles,
and the L8T is for HD use only.
**this is a working theory**

Substitute 'fuel consumption' for 'emissions'; the emissions profile for the L8T is substantially similar to the 5.3L & 6.2L,
with a longer stroke and an even longer rod-ratio, for better BSFC than its smaller brethren.
However, due to CAFE testing peculiarities, a 6.6L V8 will never score better MpG vs a 6.2L or a 5.3L.

As for the 'intended' market, there are a substantial number of drivers who would drive even more conservatively with a larger engine MOST of the time,
while appreciating an engine that would last far longer, yet still be ready to work (or play) harder when asked,
than an engine busy pretending to be smaller than it is by using less than 8 cylinders.

Cylinder valve deactivation is not for us - it's for CAFE. By the same token, the L8T is kept from most of the civilian population.
(Separate question: why can't civilians have rubber floors that take 5min to clean with running water, as an OPTION?)

 

[L8T BURB]

@chevman88 This is awesome! The L8T mated to the 10 speed will be amazing. I can't wait to hear about the driving impressions once the tune is honed in.

If you want insight from someone who has done numerous L8T swaps and can tune them with ease, reach out to Kevin at Big Dog Tuning. 662-213-6424. He had my tune dialed in and is very reasonably priced.

 

[Bigburb3500]

Substitute 'fuel consumption' for 'emissions'; the emissions profile for the L8T is substantially similar to the 5.3L & 6.2L,
with a longer stroke and an even longer rod-ratio, for better BSFC than its smaller brethren.
However, due to CAFE testing peculiarities, a 6.6L V8 will never score better MpG vs a 6.2L or a 5.3L.

As for the 'intended' market, there are a substantial number of drivers who would drive even more conservatively with a larger engine MOST of the time,
while appreciating an engine that would last far longer, yet still be ready to work (or play) harder when asked,
than an engine busy pretending to be smaller than it is by using less than 8 cylinders.

Cylinder valve deactivation is not for us - it's for CAFE. By the same token, the L8T is kept from most of the civilian population.
(Separate question: why can't civilians have rubber floors that take 5min to clean with running water, as an OPTION?)

You would love my current Suburban. 6.0 Vortec, LT trim with all the goodies… except cooled seats which sucks, but it has rubber floors. Freaking love it! You just completed my rant I have on a regular

 

[2015TahoePPV]

make sure you don't have an injector harness stuck between the block and the trans, that could cause your issue and you definitely don't want to tighten down on that. If its all clear, lift the trans a little with a floor jack with the engine on the mounts hovering just over the frame and use a couple of bolts to finish mating it up. You shouldn't need to really apply much torque to bring it home. If your mounts are already on the frame, then the angle between the engine/ trans might be causing a little pinch.

 

[chevman88]

Mounts are in and trans is mated. Just replaced the passenger motor mount so I still have the one parts store special on the driver side, but I didn't feel like swapping it out since it is fully installed. Didn't realize the harmonic balancer was a one time use TTY bolt, so have another one on the way that should be here tomorrow. Should be able to wrap this up after work by the end of the week and have it on the road. I've gotta work around the weather as I'm working out of a smaller 2 car garage that requires the door to be open when working on it.

My thoughts behind this swap is a more reliable family daily that can tow. MPG will be what it is, be it better or worse.

@L8T BURB - I reached out a bit when I first started and got notta for response, but I'll try again. Push come to shove I've got a basic L8T file to get me started.

 

[Bigburb3500]

Are you mating the L8T to the stock/original 10L80? Did anything need to be changed or is it a direct connect?

 

[chevman88]

Are you mating the L8T to the stock/original 10L80? Did anything need to be changed or is it a direct connect?

Bolted right up, need to keep the original flexplate due to ring gear tooth count difference though.

 

[Bigburb3500]

Bolted right up, need to keep the original flexplate due to ring gear tooth count difference though.

This is just too good to be true… can make any old GM a “new” vehicle with just bolting in new items… can’t wait to hear how the truck runs!