Brian Wilson
Full Access Member
- Joined
- Feb 16, 2016
- Posts
- 392
- Reaction score
- 140
Well, I may be late to the party but I'm here now! I dont belive in the gm 'piston slap' excuse. I don't believe 10 psi of oil pressure at hot idle is 'normal'. And I have personaly seen the real causes for both issues. Several times I was quoted a new engine install from the dealer if it bothers me so much.
These engines are great but have flaws. In my case I have an early 6.2 (no afm internals unlike the later 6.2 with afm components and afm turned off in tune). I had a duramax at cold idle and 10 psi oil pressure. When warm i had some ticks and 10 psi at idle. I went to the dealer many times. It was always the same BS excuses. Mind you I think they are well thought out hard to prove bogus excuses. The 6.2 does have rediculously short piston skirts which could cause slap. They are forged aluminum so have to be smaller to expand more. But 9 out of 10 times I would guess (based on actually trying to diagnose the problem) it has nothing to do with the pistons.
6.2 problems (may apply to other ls engines)
Lifters- afm lifters fail. Either yesterday or tomorrow. They are a poor design in terms of longevity and durability. And being a hydrolic lifter (afm lifter and non afm are both hydrolic) they may also not pump up or hold pressure meaning you are practically running a solid lifter that is too short for your valvetrain. In my case the rollers on my non afm lifters wore uneven. I noticed a .018 difference between the outer edges of my rollers in several of my lifters. Also i seen a .003 difference in the cup section where the pushrod rides on the lifter. The cure is to replace them all with stock ls7 lifters.
Oil pump- stock oil pump is fine in most cases. But the o-ring is a common fail point. For us with the 6.2 we have a better high volume oil pump. I went with my stock high volume pump with a shimmed spring. It is a practically free mod. Just check your clearances and install the pump properly by using a feeler gauge between the rotors and pump housing. Also make sure your relief valve isn't stuck open. That will cause bad pressure too. Also the orings on the bottom of the non afm valley cover are known to leak. Replace them or just cover them in rtv when installing. (Check YouTube for more info)
Pushrods- all my pushrods were straight. But I have seen many rods broke in half in 4.8 and 5.3 motors. And my rods showed symptoms of low oil pressure (I guess 10 psi at idle is NOT ok. Gm BS). The ends of some of my rods were worn down .011 from stock length. This may not sound like much but we will get to that later. The cure is to buy 1 piece chromoly rods in .40 wall thickness on a near stock motor. And they are comparable in price or cheaper than stock.
Rockers- when your rods wear out due to low oil, your lifters will wear out where they cup the rod and so will your rockers. Instead of a nice clean bal shape you will notice a football shape on the cup. It was very hard to measure this but using a fine dial I was able to see about a .005 difference in my badly worn rockers vs my better rockers (which were also worn. My best guess is maybe .010 from real stock rockers. I had no difference on the valve side of my rockers so could not measure any abnormal wear here (but thereally must be some wear due to the nature of the part). Also I could not find stock measurements for the valves (which also have to wear down). I went with stock replacements and new valves.
Cam bearing and cam- maybe not much of a problem in the real world. But most people think it is. If you inspect your cam bearings and see copper color you assume they are bad. This is NOT the case on a modern ls engine. The cam bearings are installed at the factory and then line honed before cam install. This is the cause of the copper color seen and is not in any way an indication of a bad bearing in this engine. The myth comes from older engines that had an older style of assembly procedure. My cam and bearings were still at stock measurements despite low oil.
And for piston slap, my pistons were perfectly round. My bores had no measurable ridge and no marks whatsoever. Real piston slap would be most evident near the bottom of the cylinder so that is where I checked first in several ls engines. And never have I seen any indication piston slap could be taking place. I have seen many ls engines (4.8 and 5.3 and 6.2) with over 250k miles and near perfect bores. A huge feat for such short piston skirts. Good job GM!
So for a summary, in my personal case, with only 145k miles, my engine had rediculous valve train wear. The tolerance of all these parts stack up.
Lifters .018 (bottom)
.003 (top)
Pushrods .011 (total)
Rockers .005
Total .037
This doesn't include the valve side of the rocker or wear to the head of the valve stem which will be multiplied by the rocker ratio (x 1.6 stock) because I had no way of measuring that.
In my case, low oil pressure played hell on every component in my valvetrain. I replace everything and I no longer have 'piston slap' or low oil pressure. And the cost was only a few hundred in bolts, gaskets, and components. I opted to do a cam and some head work and ls3 valves and a timing chain upgrade while I was at it but, my problem was stacking tolerances making my engine sound like a diesel at cold temp and tick when warm.
I hope this helps people understand the real problem with the gm ls engines. I spent days rebuilding mine and making notes every step of the way. I learned a lot and finally I have a stronger engine that has zero noise (which says a lot because of the new cam and it's .662 lift) my engine is at 5k miles after rebuild and even though I think I installed the cam 1 tooth off (fml) it has much more power at every rpm and great oils pressure at any rpm and temp. And no noise at all.
The total cost of this was around 1900$
That was for
Stainless 1 7/8 Long tube headers and ory pipe in 3.5 inch from
Geoff at EPS custom VVT cam
Ls7 lifters
.080 chromoly pushrods in stock length
All gaskets and rtv
New rocker arms
Head porting and polishing and ls3 valves
Brian tools racing valve seals and spring kit with TI retainers.
2 new engine mounts with heat shields.
Catch can
Comp VVT phaser limiter kit
Rebuilt starter with parts from a forum member.
All work done by myself with amazing tech support from Justin and Jenna at Black Bear Performance, Geoff at Engine Power Systems and the folks at Brian Tooley Racing. I can't thank you guys enough for the ongoing support and knowledge you have offered me free of charge. I will be doing a thank you post when the Denali is finished.
These engines are great but have flaws. In my case I have an early 6.2 (no afm internals unlike the later 6.2 with afm components and afm turned off in tune). I had a duramax at cold idle and 10 psi oil pressure. When warm i had some ticks and 10 psi at idle. I went to the dealer many times. It was always the same BS excuses. Mind you I think they are well thought out hard to prove bogus excuses. The 6.2 does have rediculously short piston skirts which could cause slap. They are forged aluminum so have to be smaller to expand more. But 9 out of 10 times I would guess (based on actually trying to diagnose the problem) it has nothing to do with the pistons.
6.2 problems (may apply to other ls engines)
Lifters- afm lifters fail. Either yesterday or tomorrow. They are a poor design in terms of longevity and durability. And being a hydrolic lifter (afm lifter and non afm are both hydrolic) they may also not pump up or hold pressure meaning you are practically running a solid lifter that is too short for your valvetrain. In my case the rollers on my non afm lifters wore uneven. I noticed a .018 difference between the outer edges of my rollers in several of my lifters. Also i seen a .003 difference in the cup section where the pushrod rides on the lifter. The cure is to replace them all with stock ls7 lifters.
Oil pump- stock oil pump is fine in most cases. But the o-ring is a common fail point. For us with the 6.2 we have a better high volume oil pump. I went with my stock high volume pump with a shimmed spring. It is a practically free mod. Just check your clearances and install the pump properly by using a feeler gauge between the rotors and pump housing. Also make sure your relief valve isn't stuck open. That will cause bad pressure too. Also the orings on the bottom of the non afm valley cover are known to leak. Replace them or just cover them in rtv when installing. (Check YouTube for more info)
Pushrods- all my pushrods were straight. But I have seen many rods broke in half in 4.8 and 5.3 motors. And my rods showed symptoms of low oil pressure (I guess 10 psi at idle is NOT ok. Gm BS). The ends of some of my rods were worn down .011 from stock length. This may not sound like much but we will get to that later. The cure is to buy 1 piece chromoly rods in .40 wall thickness on a near stock motor. And they are comparable in price or cheaper than stock.
Rockers- when your rods wear out due to low oil, your lifters will wear out where they cup the rod and so will your rockers. Instead of a nice clean bal shape you will notice a football shape on the cup. It was very hard to measure this but using a fine dial I was able to see about a .005 difference in my badly worn rockers vs my better rockers (which were also worn. My best guess is maybe .010 from real stock rockers. I had no difference on the valve side of my rockers so could not measure any abnormal wear here (but thereally must be some wear due to the nature of the part). Also I could not find stock measurements for the valves (which also have to wear down). I went with stock replacements and new valves.
Cam bearing and cam- maybe not much of a problem in the real world. But most people think it is. If you inspect your cam bearings and see copper color you assume they are bad. This is NOT the case on a modern ls engine. The cam bearings are installed at the factory and then line honed before cam install. This is the cause of the copper color seen and is not in any way an indication of a bad bearing in this engine. The myth comes from older engines that had an older style of assembly procedure. My cam and bearings were still at stock measurements despite low oil.
And for piston slap, my pistons were perfectly round. My bores had no measurable ridge and no marks whatsoever. Real piston slap would be most evident near the bottom of the cylinder so that is where I checked first in several ls engines. And never have I seen any indication piston slap could be taking place. I have seen many ls engines (4.8 and 5.3 and 6.2) with over 250k miles and near perfect bores. A huge feat for such short piston skirts. Good job GM!
So for a summary, in my personal case, with only 145k miles, my engine had rediculous valve train wear. The tolerance of all these parts stack up.
Lifters .018 (bottom)
.003 (top)
Pushrods .011 (total)
Rockers .005
Total .037
This doesn't include the valve side of the rocker or wear to the head of the valve stem which will be multiplied by the rocker ratio (x 1.6 stock) because I had no way of measuring that.
In my case, low oil pressure played hell on every component in my valvetrain. I replace everything and I no longer have 'piston slap' or low oil pressure. And the cost was only a few hundred in bolts, gaskets, and components. I opted to do a cam and some head work and ls3 valves and a timing chain upgrade while I was at it but, my problem was stacking tolerances making my engine sound like a diesel at cold temp and tick when warm.
I hope this helps people understand the real problem with the gm ls engines. I spent days rebuilding mine and making notes every step of the way. I learned a lot and finally I have a stronger engine that has zero noise (which says a lot because of the new cam and it's .662 lift) my engine is at 5k miles after rebuild and even though I think I installed the cam 1 tooth off (fml) it has much more power at every rpm and great oils pressure at any rpm and temp. And no noise at all.
The total cost of this was around 1900$
That was for
Stainless 1 7/8 Long tube headers and ory pipe in 3.5 inch from
Geoff at EPS custom VVT cam
Ls7 lifters
.080 chromoly pushrods in stock length
All gaskets and rtv
New rocker arms
Head porting and polishing and ls3 valves
Brian tools racing valve seals and spring kit with TI retainers.
2 new engine mounts with heat shields.
Catch can
Comp VVT phaser limiter kit
Rebuilt starter with parts from a forum member.
All work done by myself with amazing tech support from Justin and Jenna at Black Bear Performance, Geoff at Engine Power Systems and the folks at Brian Tooley Racing. I can't thank you guys enough for the ongoing support and knowledge you have offered me free of charge. I will be doing a thank you post when the Denali is finished.
