Any experience rebuilding L31 Vortec engines? - Chevelle Tech
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post #1 of 23 (permalink) Old Sep 29th, 14, 11:22 PM Thread Starter
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Any experience rebuilding L31 Vortec engines?

I'm considering buying one of these "last of the original SBC" engines, to rebuild for my 70 Malibu. The L31 Vortecs were built for trucks mainly, from 96-99 in the common Chevys & GMCs and later till almost 2001 I believe in Express/Savannah vans and the like. I'm sure this has been covered here, certainly not news.

I've read multiple articles of people recycling these short blocks, and finding them with literally no bore wear. These L31s come with the spiders and roller cams, and obviously the one piece crank seal system. There are lots of glowing write-ups about degunking these blocks, and with bearings and perhaps a crank turning you've got a 400 lb.ft+ SBC without the restrictive flat tappet cams and their required special ZDDP oils. The L31 will run modern synthetic oils without leaks, and many claim to be able to recycle the spiders and roller lifters.

Beginning my search here in Georgia, everything I found in the local Pullapart has 200K+ miles on it. These cores are dirt cheap, but I'm also aware that this SBC has a propensity for spinning rod/main bearings.

Curious who has gone the L31 "seasoned block" route, and what you found when you peeled the onion. Was it pristine bores you found, or did the engine require an overbore and all the usual work? Were the mains/rod bearings OK, or with spun bearings requiring crank work?

Thanks in advance.
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post #2 of 23 (permalink) Old Sep 30th, 14, 3:34 AM
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Re: Any experience rebuilding L31 Vortec engines?

>>> but I'm also aware that this SBC has a propensity for spinning rod/main bearings.

Dunno where you heard this BS but it's wrong. SBCs have the least bottom end problems of any engine ever made. Why do you think millions of race car engines have been built on the SBC short?

Back to the point, most SBC EFI engines will have very little cylinder wear, even at 200K.

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post #3 of 23 (permalink) Old Sep 30th, 14, 8:07 AM Thread Starter
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Re: Any experience rebuilding L31 Vortec engines?

Claims made by various forum folks who rebuilt the L31.....not all, but some stated their findings. So Tom, you've rebuilt one of these short blocks? Did the block require at .030 bore or was it as pristine as some have suggested (CarCraft article I believe said they just honed and fitted some standard bore pistons).

BTW, I'm aware of the SBC bottom end reliability.....will try and find and link those "claims". I'm quite aware what the lack of oil / regular changes will do, but Google is finding many of these L31s at +200K with bearing issues. Endemic of the L31 (intake gasket?), or just poor maintenance....you decide.

Edit - here is one with a rod knock...shows 189K on the clock. Perhaps another water leak kill?

https://www.youtube.com/watch?v=4YUZ9I01kxo

Last edited by DET17; Sep 30th, 14 at 2:03 PM.
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post #4 of 23 (permalink) Old Sep 30th, 14, 8:21 AM
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Re: Any experience rebuilding L31 Vortec engines?

Probably too many variables to know what you are getting. A maintained 200k+ mile engine might have good bores and no bearing wear. An abused 200+k mile engine might have spun bearings and need bored. Same with any engine, whether L31 or not.
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post #5 of 23 (permalink) Old Sep 30th, 14, 8:25 AM
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Re: Any experience rebuilding L31 Vortec engines?

I've torn down a bunch that still had hone marks in all the bores. I didn't rebuild any of them, so I don't know whether or not you can drop standard pistons back in the holes.
The reason Vortec engines are known for spinning bearings is the piss poor intake gasket they came from the factory with. They disintegrate, usually by around 150K miles, and leak antifreeze into the block. Antifreeze mixes with oil and bearings are toast.

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post #6 of 23 (permalink) Old Sep 30th, 14, 8:50 AM
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Re: Any experience rebuilding L31 Vortec engines?

The last three I built for customers took a cylinder hone, crank polish, new oil pump, new timing chain, and a valve job. One was at 445,000 miles and was smoking through the valve guides.

Couple of junkers and a few clunkers.
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post #7 of 23 (permalink) Old Sep 30th, 14, 1:29 PM Thread Starter
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Re: Any experience rebuilding L31 Vortec engines?

Quote:
Originally Posted by Busted Knuckles View Post
The reason Vortec engines are known for spinning bearings is the piss poor intake gasket they came from the factory with. They disintegrate, usually by around 150K miles, and leak antifreeze into the block. Antifreeze mixes with oil and bearings are toast.
Indeed, this matches what I read on the various forums kicking around the L31 shortblock. Sage warnings given were "look for empty antifreeze jugs in trunk, and possibly a removed T-stat".

I know the spun bearings = crank/rod journals turned .010" and possibly new rods, oil pump et al. I'll show my V8 ignorance....does a spun bearing guarantee an .030" overbore due to the oil contamination?

Many I looked at in the local PnP say "rod knock" on the back windows.....as do the cores on car-parts.com
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post #8 of 23 (permalink) Old Sep 30th, 14, 1:35 PM Thread Starter
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Re: Any experience rebuilding L31 Vortec engines?

Quote:
Originally Posted by Andy's Auto Repair View Post
The last three I built for customers took a cylinder hone, crank polish, new oil pump, new timing chain, and a valve job. One was at 445,000 miles and was smoking through the valve guides.
Did any of those three have spun bearings? Crank polish sure doesn't mean spun bearing to me, but I gotta ask.

I've got 10K mile Vortec heads and intake to suit, so I'm only worried about finding a suitable L31 shortblock. I fully expect to polish/turn 010 under the crank, new Melling (or equal) oil pump, new chain, and probably deck the block to get the quench right. My concern is if these spun bearing L31 cores will absolutely require an overbore (an expense I'd like to avoid). I don't have the experience to know, the reason I'm asking you veterans.
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post #9 of 23 (permalink) Old Sep 30th, 14, 4:58 PM
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Re: Any experience rebuilding L31 Vortec engines?

Again, it depends on air filtration, whether the engine was overheated due to famous anti-freeze gasket leaks, oil change practices, etc. No way to tell if you've got worn bores in the "mystery box" until you pull the heads.
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post #10 of 23 (permalink) Old Sep 30th, 14, 10:41 PM
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Re: Any experience rebuilding L31 Vortec engines?

Quote:
Originally Posted by DET17 View Post
I'm considering buying one of these "last of the original SBC" engines, to rebuild for my 70 Malibu. The L31 Vortecs were built for trucks mainly, from 96-99 in the common Chevys & GMCs and later till almost 2001 I believe in Express/Savannah vans and the like. I'm sure this has been covered here, certainly not news.

I've read multiple articles of people recycling these short blocks, and finding them with literally no bore wear. These L31s come with the spiders and roller cams, and obviously the one piece crank seal system. There are lots of glowing write-ups about degunking these blocks, and with bearings and perhaps a crank turning you've got a 400 lb.ft+ SBC without the restrictive flat tappet cams and their required special ZDDP oils. The L31 will run modern synthetic oils without leaks, and many claim to be able to recycle the spiders and roller lifters.

Beginning my search here in Georgia, everything I found in the local Pullapart has 200K+ miles on it. These cores are dirt cheap, but I'm also aware that this SBC has a propensity for spinning rod/main bearings.

Curious who has gone the L31 "seasoned block" route, and what you found when you peeled the onion. Was it pristine bores you found, or did the engine require an overbore and all the usual work? Were the mains/rod bearings OK, or with spun bearings requiring crank work?

Thanks in advance.
I have seen my share of the L31 engines over the years and have found cylinders with wear like any other 350 block with a lot of miles, Some have a lot of wear other have very little wear, Depends on the miles and maintenance program.

Any bearing issues I have seen have been because of low oil or one I just took apart the oil pump screen was laying in the pan other then that they look fine.

The PM rods should be checked for size and roundness.

Like any seasoned block it should be line honed back to spec, decked, bored and plate honed.

Using GM fasteners I don't see much distortion as the clamping force is limited as the bolt have no washer and that friction eats up a lot of torque values.

Here is a 604 crate which is the same basic short block and I set up and honed using ARP hardware this is what I found, After the engine was raced I leaked it down and were under 3%




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post #11 of 23 (permalink) Old Sep 30th, 14, 11:24 PM
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Re: Any experience rebuilding L31 Vortec engines?

Duane,
I am going to agree with Carl. I have at least three of them in the shop right now and they are no different than any other 350 Small Block. I have seen quite a few of the basic engines out of boats also and they usually need boring. I had one just recently that did not need boring but it was a very low mileage "take out" for some type of warranty issue and had been sitting around for 15 years.

I prefer to use a torque plate on them but a lot of people just will not spend the money. Does not seem to make much difference on a stock type engine anyway. GM didn't use them and they still run a long time.

The bottom end is no different than any other small block so I don't see why they would have any more issues with rod or main bearings. One thing I will say is that they seem to last a long time before something goes wrong with them. The one in my 99 Tahoe has 170K on it and other than the usual intake gaskets at around 100k it has been problem free and still amazes me at how much power it makes.

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post #12 of 23 (permalink) Old Oct 1st, 14, 8:50 AM
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Re: Any experience rebuilding L31 Vortec engines?

Mr. Bill, the spun bearings are being confused with washed out bearings because L31s tend to make chocolate milk out of thier own oil when the plastic intake gaskets crack and mix oil and coolant. ExLife coolant seems to be quite corrosive. Never had any of my fleets actually knock the bearings past the tabs. One of the ones did take a .40 overbore. onlt because the customer wanted the cubes.

One observation is they tend not to wear out the bores after 200k like the 70s-90s did. Only seen a big ridge on the cylinders on one that had 378k on it. I really just built that one because of massive oil leaks due to blowby.

Couple of junkers and a few clunkers.
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post #13 of 23 (permalink) Old Oct 1st, 14, 10:52 AM
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Re: Any experience rebuilding L31 Vortec engines?

Quote:
Originally Posted by BillK View Post
Duane,
I am going to agree with Carl. I have at least three of them in the shop right now and they are no different than any other 350 Small Block. I have seen quite a few of the basic engines out of boats also and they usually need boring. I had one just recently that did not need boring but it was a very low mileage "take out" for some type of warranty issue and had been sitting around for 15 years.

I prefer to use a torque plate on them but a lot of people just will not spend the money. Does not seem to make much difference on a stock type engine anyway. GM didn't use them and they still run a long time.

The bottom end is no different than any other small block so I don't see why they would have any more issues with rod or main bearings. One thing I will say is that they seem to last a long time before something goes wrong with them. The one in my 99 Tahoe has 170K on it and other than the usual intake gaskets at around 100k it has been problem free and still amazes me at how much power it makes.
GM head bolts really don't distort the block that much plus being a std. bore its not going to flex as much either.

From what I have seen I use ARP bolts with the torque plate and if the 602 0r 604 crate stay with the GM hardware I have found I only torque the plate down 55 LBS. which seems to duplicate the GM head bolts.

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post #14 of 23 (permalink) Old Oct 1st, 14, 11:22 AM
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Re: Any experience rebuilding L31 Vortec engines?

Quote:
Originally Posted by Andy's Auto Repair View Post
Mr. Bill, the spun bearings are being confused with washed out bearings because L31s tend to make chocolate milk out of thier own oil when the plastic intake gaskets crack and mix oil and coolant.
Very good possibility. I got lucky when mine started leaking it went to the outside so I was getting a drip on the floor. Mine has been a very good engine, I cant complain at all.
I have noticed that the oil pressure has dropped about 10 lbs over the range. Not sure when it happened but I think it was a pretty sudden thing. I am not too concerned with it but I really should at least investigate a little It might just be the sending unit. I was talking to one of the guys at Melling about another oil pump question and thought I would ask him about mine. He said that there have been a "few" broken relief valve springs which could possibly cause it. One of these days I might get energetic and take a look but it has been at least 10K miles and 2 oil changes since it dropped and it seems to be running too good to mess with it.

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post #15 of 23 (permalink) Old Oct 1st, 14, 1:54 PM Thread Starter
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Re: Any experience rebuilding L31 Vortec engines?

Well, I'll attempt to summarize what Bill, Andy, and CNC NE have stated:

The L31 Vortec shortblock does have a proven history of bearing failures, most of which can be attributed to the intake gasket failure and the resulting oil & water mix. (Google finds tales of spun bearings/rods knocking across all GM forums).

Some find these 200K blocks with little to no bore wear (just hone & refit standard pistons), but most will require the typical overbore.

At minimum a hone & decking is required on these L31 seasoned blocks, with some recommending the torque plate to simulate the heads installed. (Opinion here - I'm doubting the additional 2% lb-ft of output torque will make any difference for my street/cruising engine, nor justify the additional cost. )


In my case, I'm looking for a "nostalgia" old school SBC for my 70 Malibu. I've already invested in the Vortec heads & intake, so a L31 would be an improvement (my opinion here) with the 1 pc. sealing system and the factory roller came/spider setup, even a factory windage tray. I hope to find a 100Kish L31 that has been well maintained, but I expect this will take awhile, or a bunch of $$$ to locate.

I'll run the numbers with my local quality engine machinist, but I expect the full boogie L31 refreshening with the aforementioned work will fast approach the $2K cost of these same engines in crate version. I'd like to be able to say "I built it myself" but we shall see where the economics point me.

Thanks gentlemen for all of the input.
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