So what was the purpose of the bleed down, on the lifters? Was it only to check the pushrods aren’t too tight? what is to stop them from pumping up and being too tight on startup. Or is it after the bleed down and pushrod adj. there is enough pressure on the push rod as to where the lifter can’t pump up, and put the valves out too far where they hit. I’ve always done this step but unsure why, if the pushrods just pumps back up when you fire it up. Thanks guys

 

Standard lifters have a certain amount of plunger movement from fully bled down to fully pumped up. When we adjust the pushrods we are targeting approximately the center of the range. Some people will go an extra flat or two to go a little deeper. This window on plunger range allows for the engine to shrink and grow as the engine temperature changes and the lifter always takes up the proper amount of space. When we do the bleed down, we are ensuring that the lifter plunger has bled off the oil from the valve spring pressure. The bleed down ensures that the plunger is not bottomed and also prevents any valve interference when turning the motor over due to an abnormally high plunger. When the engine is running it only takes up the clearance in the valve train, it does not overcome the valve spring pressure and fully pump the plunger all the way up to where it was pre-bleed down.

 

stock hydraulic lifters and push rods are pretty much set but it helps to have the lifter void of oil when bolting in the rockers.
on adjustable push rods, it depends upon what is the type and outcome needed. having the lifter void of oil helps to get correct setting. the best way is to remove the lifter and take them apart and reassemble dry since doing in block where there is oil still in the galley can actually enter the lifter affecting measurement if you are not careful.
with adjustable and no spacers, adjust with plunger fully up the requires number of flats to TPI to set stroke mid range.
with limiters, you adjust with plunger fully down and loose the rod from just turning free from valve spring pressure the require TPI flats to get the required setting. i set mine to allow .030 rocker to stem clearance. i run in the solid mode with just enough clearance to quite the valve train. you must factor in the rocker ratio. ex: .001 at the lifter is .017 at the valve stem.

 

Ive done this a few tomes over the years. Just wasn’t sure why. And it always seemed like when the lifters pump up it would be too tight (possably open valves) that totally makes sense, when it heats up and expands everything. More knowledge the better, thanks guys I appreciate the hel. ride safe.

 

I understand, letting the lifters bleed down prior to adjusting pushrods BUT what I don't get is the bike usually been parked since the day before and cooled off before you change out your cam and everything so why do you need to wait an extra 20 minutes before adjusting your pushrods?

 

When adjusting pushrods we set the cam at the base circle, and we extend the pushrod until it is no longer loose between the lifter and the rocker arm.

Then we adjust the pushrod the required amount of turns on the adjuster.

When we do this, sometimes the lifter piston goes down right away, but if the lifter is full of oil the piston in the lifter will not go down right away, instead; the valve gets lifted off the seat.

Eventually the oil will bleed out of the lifter and the valve will return to the seat.

That is why we wait until we can spin the pushrod with light finger pressure (to ensure that the valve is back down on the seat before we rotate the engine).

 

I fixed the statement for ya, but you got to work on the "understanding"

 

Since you've compressed the lifter adjusting the pushrod you need the oil to bleed down so you can try spinning the pushrods by hand to check adjustment. Got it.

I've always reused the stock pushrods and tightened down the rockers with the lifters on base circle hours at the end of the cam swap. I was having a brain fart trying to figure out how these lifters got pumped up while out, lol

 

Hydraulic lifters are designed to bleed off a certain amount. If they were like a Hydraulic jack, they would push to the top. That would prevent the valves from shutting.

They actually bleed off slightly thru a lift. Why race cars use solid lifter.

To make a stock Harley quite, the cam shaft has about some degrees of rotation built into them that has a slight ram before lift just in case they don't pump to base circle diameter called the clearance.

Most usually pump up in the first starting crank also.

Most lifter I have worked with have about .200 piston travel. You want to get in the middle of that.


On my last rebuild on a Jeep motor, since the valve seats are hard, I got a local shop to grind them. They were supposed to be reliable. I supplied the new valves since stem height need to be correct since rockers had no adjustments.

Told them I would build head. They didn't listen and built it.

Only after installing rockers did I discover some rockers only had a half turn of rocker bolt before bottoming.

I ended up fixing it by facing off the rocker base.

 

That’s exactly what i didn’t understand. Perfectly answered man thank you I’ve been doing this years and that actually made it click in my head. And another thing. When the lifter is pumped up, After the motor runs. Why would it not be opening the valve too far when full of oil. Is the pressure from the valve springs not letting it over fill and push the valve out too far. I still dont get that