Oversize Lifters

[83Blzr62]

I rebuilt my 6.2 a while ago and it seems great except for one issue. It has a lifter tick that I cannot figure out and the oil pressure is a little lower than I would like (15 psi at hot idle (700 rpm) and 45 psi at 2000 rpm while hot). What bothers me most about the oil pressure is that when I cruise at 40 mph with the TC locked I get about 30 psi with the engine at around 1100-1200 rpm.

Anyways, I tore it down and checked everything I could at the time - cam, rod, main bearing clearances and all the oil passage freeze plugs. Everything was in spec and accounted for,s o I replaced the lifters with new hoping that was the issue. Well, it still does it.

I read recently that oversize lifters may have came in these things. Well I never checked that and ditched the old ones so I will never know if mine came with some bigger lifters.

Has anyone ever seen an elusive oversize lifter? What size should std. and oversize lifter bores be? If you have an oversize lifter are you willing to sell?

Thanks,
Kyle

[DmaxMaverick]

That's a new one on me. Never heard of it for this engine, and I don't know if they would be available, off the shelf, anywhere.

I wouldn't suspect the lifters as the cause of low oil pressure. A lifter issue may be the result of low pressure, but rarely ever the cause. An inferior oil pump or cam/bearings would be much more likely. How are you measuring the pressure? The dash gage? If so, get a known, accurate test gage on a port to verify accuracy. A new/different sender and/or gage may also be used, but may be only less inaccurate (notoriously).

Did you replace the relief valve? They can get tired (or fouled) over time.

What oil are you using? (sometimes, it's only that simple)

That said, the pressure you are seeing is well within minimum spec. Oil pressure interpretation can be misleading, in that, more is not necessarily better.

[83Blzr62]

Thanks DMaxMaverick,

The reason I suspect it may be a lifter, is because if I have a std lifter in an oversize hole, there may be 0.010" extra clearance leading to low oil pressure and that lifter not getting pumped up. However, I have only seen MorePower on this forum and MaxPF on a different site mention oversized lifters as a possible so I doubt they exist also.

I have new auto meter electric gauges and even checked it with a cheap mechanical gauge from autozone.

As for the oil pump, I ordered a new one from a late 90's squirter block, so I thought I would have high oil pressure. When it is cold, I have seen up to 60 psi at idle and it peaks around 85 psi at speed, but as it warms it goes down.

As for the relief valve, which one are you referring to? I did replace the plugs and valves under the oil filter.

As of oil, I am currently using Rotella T 15W40 and I am thinking about changing to their synthetic 5W40.

[DmaxMaverick]

High volume pumps on non-squirt engines are bad. More "pressure" isn't good, and the 6.2L engine isn't designed to use that pump. It's possible the volume has overwhelmed the relief and bypass valves.

The lifter bores can be sleeved, but you'd have to go to a custom/performance shop and have oversize lifters made. Still, I don't think that's the problem. With the high-volume pump, that additional clearance shouldn't make any significant difference, and probably wouldn't with a standard pump. If you're able to get 60-85 PSI when cold, the problem isn't the lifter bore. If it were that bad, it wouldn't allow pressure, at any temp or speed.

I'm not a fan of Rotella with any GM Diesel engine, but I don't think switching to Rotella [fake] synthetic will make a difference. Perhaps another brand, such as Mobil or Delo may be a better choice.

There are too many other possibilities to attack the least likely suspect first. Cam, main, rod bearings, vacuum pump, oil pump mount, relief/bypass valves, etc. are much more common.

[john8662]

I've never seen one either.

The block will be stamped above the cylinder's lifter bore where the OS lifter goes. Look for an OS stamp just above the parting line where the cylinder head meets the block (that flat rail).

The ticking can also be related to the timing gear set. I had a 6.2 that with the gear set in it ticked no matter what. I removed it and went back to chain. I'm not sure what the issue there was.

As for these lifters. It seems that if they're not primed from new, some will fail. The lifters you get straight from current production AMG are pre-pumped up. Those I've told about this think I'm crazy.

I've had nothing but bad lifters every time I build one of these engines, until i went with the AMG ones. I think that if you start one of these engines w/o primed lifters, you damage them. Next engine build I'm working on that will get test run extensively on the stand will have the lifters primed in the engine w/o pushrods and valvetrain hardware ever torqued on them. Then torque it all down up top, and bleed it again with oil.

I'd like to make a jig on a bench with an elec or mechanical oil pump and pre-prime them all.

J

[83Blzr62]

Ok, I have already rechecked the cam, rod and crank bearings so I am certain that is not the cause.

DmaxMaverick - Your theories are too much pressure bypassing valves or the oil pump mount is not flush? What bypass valves? The oil cooler and oil filter bypass valves?

Do you think the high flow pump may have forced out a lifter galley plug to some extent?

When I do take it apart I will double check the lifter sizes vs bore just to verify, but I am fairly convinced that is not the issue.


Thanks,
Kyle

[TrenchFoot]

While dropping my lifters back in last week as part of my 3-year engine rebuild, I read the section in the GM unit service manual about the lifters. The manual stated that if oversized lifters are used, both the lifters and the block would be stamped (think it was either with an O or OS). So while this seems extremely rare, you probably can skip measuring the bores and just look for the stamping next to them.

[83Blzr62]

So they do exist then. Did the book have a picture of where the marking was on the block?

[TrenchFoot]

There was no picture. I can't remember the exact wording, but it said the stamp would be adjacent to the bore.

[TrenchFoot]

From the 1993 Light Duty Truck Unit Repair manual (ST 333-93):
"Some engines will have both standard and 0.010-inch oversize hydraulic lifters. The oversize lifter will have a "10" etched on the side. The block will be stamped "O.S." on the cast pad adjacent to the lifter bore and on the top rail of the cylinder case above the lifter bore."

No pics of either though.

[83Blzr62]

Thanks TrenchFoot. I will look for it and report back here if I actually find some. Could this be referring to gas engines and not necessarily the diesel?

[TrenchFoot]

Nope, no way it was referencing another engine. The Chevy Unit Repair manual is broken down into chapters for each engine, tranny, and xfer case. It's actually a lot more useful during a rebuild than a Chilton's/Haynes or even the factory shop manual for your truck. I'd highly recommend finding one on eBay.