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8.1L/496 Tech

My short list of freshening up my 8.1

Johnson makes both a drop in dog bone lifter 2510r and or the ISKY 3977HYRT with the tie bar.

For converting to adj rockers ARP makes a rocker stud that is 10mmx7/16. Hopefully going to a tie bar style lifter and reducing the slop in the valve train fixes the lobe wear we saw on 2.

(Went with ISKY lifters...are actually Johnson)

GST racing seals makes a superior 1 piece rear main 10288 and timing cover crankshaft seal

King offers an inexpensive coated bearing for the rods but the mains are not coated.

Cometic MLS head gaskets and silvolite 3494 std anodized pistons were under $250.

PAC valve springs, chromoly retainers and Crower 10* locks

Raylar recommends GMs updated manifold gasket 89017539

Crower Sure Lock Rocker Arm Nuts
 
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Rockwood said:
In-laws have had a terrible time with their 8.1 suburban. Used it to tow some shit early on, and once towed a max rated weight trailer, but after that experience my father-in-law bought a gen 3 CTD Dodge, so now they're just commuting in a 10mpg pig and very occasionally towing a flatbed trailer. :shaking:

To date:

Cam lobe eroded, shrapnel ruined engine. Rebuilt (100k miles)
Lifters on rebuilt engine failed at 160k miles (recent fun with most pushrod engines it seems)
Broken valve spring at 165k miles

And yes: 1qt+ every 1,000 miles.

Not sure if these motor woes are common for 8.1s, but yeesh has this thing been a lemon.
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Oil consumption similar to what I saw in my jalopy and its common to hear about. Seems related to, unfortunately for you inlaws, not getting the updated maniflod gaskets on the last rebuild. Some also attribute the problem to the rings and pistons but couldn't confirm that on mine.

Low spring tension and non adjustable valves may play a role in the lifters rotating possibly valve float as well not mention a crappy pcv system. Hearing all sorts of lifter issues from a lot of people so I opted to go with a more reputable manufacturer so we'll see.
 
49willys_mogon said:
Oil consumption similar to what I saw in my jalopy and its common to hear about. Seems related to, unfortunately for you inlaws, not getting the updated maniflod gaskets on the last rebuild. Some also attribute the problem to the rings and pistons but couldn't confirm that on mine.

Low spring tension and non adjustable valves may play a role in the lifters rotating possibly valve float as well not mention a crappy pcv system. Hearing all sorts of lifter issues from a lot of people so I opted to go with a more reputable manufacturer so we'll see.
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Yeah. They went OEM last time. This time with the megabuck lifters.

Guess we’ll see on valve springs. It’s been sitting since they just paid someone (I know) for the lifter job, then the spring failed in weeks.
 
This video sounds like dog poo, but can anyone pin point this sound? I can’t tell if it’s a bearing or piston slap. Lasts about 30 seconds and then purrs like a kitten.

 
GM had a class action lawsuit against them in the mid 2000s over piston slap in their engines.
 
Bebop said:
Gonna have to explain that one to me.
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I'll try again. I've been using Castrol Magnatac oil in the 8.1 that's in my Workhorse coach chassis. Since I've been using it, the piston slap little clackity clack noise that happened since it was new upon cold starts has disappeared. I don't know how to explain it any better than that. Your results may vary.
 
BDK said:
I'll try again. I've been using Castrol Magnatac oil in the 8.1 that's in my Workhorse coach chassis. Since I've been using it, the piston slap little clackity clack noise that happened since it was new upon cold starts has disappeared. I don't know how to explain it any better than that. Your results may vary.
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I'm gonna give it a shot but I'd be floored if oil makes any difference. IIRC it was a machining tolerance issue.
 
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There is also reports of using a thicker weight oil helping with the clatter. I never tried it, but read about it on a GM based forum.
 
BDK said:
There is also reports of using a thicker weight oil helping with the clatter. I never tried it, but read about it on a GM based forum.
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How would this work physically?
Piston slap happens because the piston to cylinder wall clearance is too big.
Oil isn't supposed to keep the pistons upright in their bore :confused:
 
Bebop said:
How would this work physically?
Piston slap happens because the piston to cylinder wall clearance is too big.
Oil isn't supposed to keep the pistons upright in their bore :confused:
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No clue, I'm not a rocket surgeon. :flipoff2:

Maybe it quiets the noise? Maybe thicker residual oil on the cylinder walls? Maybe the Castrol Magnatac stuff sticks to the walls like it claims?

Fuck if I know, I just know when I started using that fancy stuff it quieted down the slap on start up.
 
I didn't think thr 8.1 had piston slap problems.

Side note, I run Delvac or Delo 15W-40 diesel oil in mine. Let that bitch eat...
 
Bebop said:
How would this work physically?
Piston slap happens because the piston to cylinder wall clearance is too big.
Oil isn't supposed to keep the pistons upright in their bore :confused:
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Recently replaced my pistons with these silvolites (ring specs in the link) and even after doing a cleanup pass hone the clearences aren't loose and the factory piston skirts are coated for tighter clearences.

UEM Pistons

www.uempistons.com www.uempistons.com

As far as I can tell the knocking sounds my motor had seems to be related to main and rod bearing wear due to neglect and or consumption caused by poor head gasket design and or pcv system. Other sounds such as clicking is the valve train float by low 90# spring pressure and bad lifters.

The other sounds in the video seem might be the power steering pump whining.

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Next time I'm down at the shop I'll get some pics of the piston wear. Looking the new pistons the profile ie skirts and overall height is compact compared to other pistons so it seems this would reduce slap however the rod length stroke could be culprit
 
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49willys_mogon said:
Recently replaced my pistons with these silvolites (ring specs in the link) and even after doing a cleanup pass hone the clearences aren't loose and the factory piston skirts are coated for tighter clearences.

UEM Pistons

www.uempistons.com www.uempistons.com

As far as I can tell the knocking sounds my motor had seems to be related to main and rod bearing wear due to neglect and or consumption caused by poor head gasket design and or pcv system. Other sounds such as clicking is the valve train float by low 90# spring pressure and bad lifters.

The other sounds in the video seem might be the power steering pump whining.

20240612_152012.jpg


SmartSelect_20240612-151524_Samsung Internet.jpg


Next time I'm down at the shop I'll get some pics of the piston wear. Looking the new pistons the profile ie skirts and overall height is compact compared to other pistons so it seems this would reduce slap however the rod length stroke could be culprit
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So is your 8.1l super quiet now?

This sounds like a diesel upon start up, which from reading leads me to piston slap. Cold oil pressure will bury the needle on my gauge (I don’t trust any of these gauges, and need to get a digital plug in to read off the ECU), and hot oil pressure at idle is 20 psi. So I don’t think it’s from my bearings.

Spark plugs look new, but I’m going to pull those before winter. Just trying to push off a rebuild if I can.

Also, the whine in my video is the Allison transmission, not the ps pump.
 
The pistons have short skirts and GM tolerances aren’t the best so the piston wobbles and slaps it’s way up and down the cylinder until it heats up enough to fit the bore better. At the dealer we saw trucks that burned oil and had loud piston slap for 100k+. As long as you let it warm up a bit before hammering on it, it should be ok.
 
my clatters a bit also. 245k.

My oil psi is clod 40-50psi and hot idle is 20.
1500rpm is 30ish.

Ive put 10/30 and 15/40 in it and it seems happiest with the 10w.

Ive got 20k on it and nothing has changed since the first drive i put on it. I also dont race/rage the shit out of it either.
 
M92PV4U said:
Fify.:laughing:
Do you use lucas?
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I used that lucas 200w stuff in the dodge because po did and it significantly cut down the crank case smoke/gasses.

I dont think i want to in this. I said it was happiest with the 10/30 because with the 15/40 it seemed to clatter significantly more on start up.
 
total newb said:
I used that lucas 200w stuff in the dodge because po did and it significantly cut down the crank case smoke/gasses.

I dont think i want to in this. I said it was happiest with the 10/30 because with the 15/40 it seemed to clatter significantly more on start up.
Click to expand...

I noticed mine got louder with 5w-30. Might switch to 10w-30 next year.
 
FleshEater said:
So is your 8.1l super quiet now?

This sounds like a diesel upon start up, which from reading leads me to piston slap. Cold oil pressure will bury the needle on my gauge (I don’t trust any of these gauges, and need to get a digital plug in to read off the ECU), and hot oil pressure at idle is 20 psi. So I don’t think it’s from my bearings.

Spark plugs look new, but I’m going to pull those before winter. Just trying to push off a rebuild if I can.
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My 8.1 is from an '03 3500 w 165k I bought for a donor for a project '59 International Metro you can see in the scout forum. Drove it around and scanned it prior to purchasing but should have dropped the oil pan. It sounded similar to my 6.0 clickity clack lifters and slap with lots of oil leaks.

Found a lot of helpful info on the RV and workhorse forums on these motors and currently close to wrapping up a rebuild that I wasn't planning besides a cam swap and a tune. Can't say for sure the knock slap is gone yet until I get it back in the truck to tune prior to swapping into the metro. Thats why I tried to find as much info as possible to apply to my rebuild and share my findings here.

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Another very common issue with the 8.1 is the crank pulley is more pulley than harmonic balancer (another possibilty my bearings were shot) are known failures in the RV workhorse community. They are vulcanized rubber with a provision for two belts. They are starting to go if they get wobbly. Found the best rec stock replacement is the powerbond which are now out of production and only available on Amazon or ebay.

Unfortunatety the big 4 balancer companies don't make an 8.1 version however if 5 ppl wanted one they will do a group run for $550 ea.

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The '01-'03 fuel pressure regulators going out (hot start and or too low a psi for hotter cam) Hi flow unfortunatety non adjustable
 
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