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I'm wondering if anyone has ever truly measured the preload our motors have on the lifters?
What I mean is when the rocker assemblies are bolted down the pushrods push down so the rockers are not loose?
If you have, how did you get a true measurement? And what might it have been.
I have a reason/need to know a real measurement and a way to measure it but would like to hear if others have done it..
Do you mean the hydraulic lifters? There's too many variables to come up with a definitive answer. If the engine is not running then it depends on how much the lifters leak down and how long they've had to leak. If it is running it's going to be hard to measure...
When running it's probably going to be something like the oil pressure multiplied by the area of the piston in the lifter...
If you're assembling an engine, don't you have to check the "dry tappet clearance"? (In other words, there would be no preload as the lifters haven't been pumped up yet.)
From GM Product Service Training manual 16015.05-1D:
Long story short... a "zero lash" valve clearance (in this instance) also means zero preload... and it can compensate (within a narrow range) for variations in head gasket thickness or block deck/head deck dimensional variations.Quote:
When the lifter begins to roll up the cam lobe, the ball check is held against its seat in the plunger by the ball check spring, which traps the oil in the base of the lifter body below the plunger. The plunger and lifter body then raise as a unit, opening the valve. The force of the valve spring, which is exerted on the plunger through the rocker arm and pushrod causes a slight amount of leakage between the plunger and the lifter body.
This leak-down allows a slow escape of trapped oil in the base of the lifter body. As the lifter rolls down the other side of the cam lobe and reaches the base circle or "valve closed" position, the plunger spring quickly moves the plunger back to its original position. This movement causes the ball check to open against the ball spring, and oil from within the plunger is drawn into the base of the lifter. This restores the lifter to zero lash.
I understand these are hyd lifters and how it works..
The reason I asked is this.
I'm building a p400, big exhaust valves, PAC springs, 1.7 roller rockers, upgrading to 7/16 pushrods, etc.
When using checker springs & checker rod I can get a correct measurement and roller ride area on the valve tip, the rod maker also needs to know how many thousandths the lifter is preloaded to come up with a correct static length, we know the lifter lift will vary some during engine running so a closer than stock length will be needed as the stock length doesn't come close in this situation..
I have a way to measure this, I was just wondering if anyone else had given it any thought..
Take a new lifter and collapse it completely..
Measure the distance from the roller to the socket.... then do the same measurement with the lifter at full up position.
Calculate the 1/2 to 3/4 point of the plunger travel and use this as your datum point to calculate the length of the push rods.
As long as the plunger has a reasonable amount of travel to compensate for wear and such...good to go.
As the seats and valves wear over time the valve train will need a tad more room to allow the valve to rise a bit and also to allow the rockers and such to wear slightly.
The old BIG BLOCK hydraulics were "With lifter on base circle of the cam, adjust rocker so there is zero lash...plus 3/4 to one turn on the nut"
The fixed type were calculated to place the lifters in the sweet spot...
As long as you allow the lifter plunger to move up or down as needed you should be fine.
OMG, I didn't think I'd ever have to remember that again! (Had a friend who did it to my Ford 200-6 once (solid lifters...) ended up burning an exhaust valve. Pulled the head in the back yard, stuffed a new valve in it and drove it another 80k miles...)Quote:
Originally Posted by Robyn
On the aircraft engines we pump all the oil out of the lifters and check the clearance with a feeler gauge. As long as it falls in an acceptable range (There's an .080 - .100 variation allowed) You're good to go. Otherwise they're adjusted by substituting longer or shorter pushrods. There are a few engines that have automotive style adjustable rockers, but they're not common and don't enjoy a very good reputation, either...
Yeah...Solid lifters have to have some clearance or it does not end well..
I never liked the fixed rocker studs all that much, but it does make them easier to install for the first build (Factory)
In my younger days, I rebuilt a few gasoline GM engines, and was used to this procedure. I was surprised when I rebuilt my first 6.2L! And then I grew to appreciate the "install it and forget" nature of the fixed-type hydraulic valve-train.Quote:
Originally Posted by Robyn
Much better than the Cummins, Toyota 22RE gasser, and other similar setups that require periodic valve train adjustments, in my opinion.
Casey
Roller hydraulics are pretty nice and about as trouble free as it gets..
Just a piece of GM history
The 5.7 Olds diesel had its teething issues, most of which was bean counter failures.
The early 5.7 had regular hydraulic lifters and GM did not go to hydraulics until the very end of production and by then they could not give the 5.7 away...