need to know how to get your valve train right- the 1st time

[farmfuel]

Howdy,

Well, here I go again getting myself worried about something that hasn't even happened yet, but since our motors don't have a valve lash adjustment, Ive got a couple of questions.

When you get your heads back from a questionable machine shop, don't you worry if maybe they didn't remove (if any) enough material from the tip of the valve stem? Cause when your grind the valves, and cut the seats, the valve becomes more recessed up into the head, inturn raising the overall height of the stem (where the rocker arm meets the stem)

Here a couple of years back, I had a Cherokee with a 4.0. The valve train is the same set up as FMC or IH (no lash adjustment). I bought a long block from a shop that has since gone out of business. When I put the motor in, and fired it up, I ran it at 2K to break in the cam. I noticed off the bat it didn't sound right, and shook a little. When the motor came down to idle, it was like it had a fouled plug, or almost a dead miss. I drove it to the machine shop, and he kept it for a day and told me that he did a leak down test, and discovered the #1 IN valve wasn't fully seated. I asked what the hell, and he said "Well my son rebuilt that head, and he didn't remove any material from the tip of the stem, and when the rocker tightened down, it kept the valve open enought to not seal the chamber."

So with that being said, i referred to my Copyright 91 Navistar shop manual for the 7.3. It gives no value for distance between the tip of the valve, and the head gasket surface.

My question is: How do you check to make sure the lash is correct after overhaul? I have to replace 3 rocker arms, due to unusual wear where the rocker meets the stem.

I bought a 90 model CC from my buddy with a bad motor here a while back, and his motor dropped a valve. I guess it was ran for too long at idle? One of his rockers is SERIOUSLY damaged where it comes in contact with the stem.

All 16 rockers is pretty pricy, so I'm not really sure if I should just reinstall my old ones or not. I'll be damned if I gotta pull these heads off after spending all this time/money in this thing- just cause I was ingnorant on checking something.

[chuckster57]

Hydraulic pressure in the lifters is what adjusts valve lash. If you have the heads on a bench, just check "installed height", and if its within specs, put it together.

I have been known to take the lifters out and collapse them. Put them in a vise with a little socket on the cup and press it. You may have to press it a couple of times to bleed off the oil.

[NMB2]

You still need to check lash on a hydraulic system. On this motor you want somewhere between 1/4 turn on the low side and full turn on the high side for valve lash.

[chuckster57]

So they are like the SBC, turn the nut til the pushrod doesn't spin and then 1/4-1 turn? I always use 3/4 turn.

[NMB2]

Originally Posted by chuckster57

So they are like the SBC, turn the nut til the pushrod doesn't spin and then 1/4-1 turn? I always use 3/4 turn.

You are correct.

[farmfuel]

On SBC's, I always just tighten the rocker nut until it becomes real hard to turn the pushrod. I do this after I pump up the lifter manually in a small bottle of oil. But our motors are nothing like that set up. they have pedistals. The IH manual says to turn the timing mark on the balancer to the 11 o'clock position, so that way all pistons are below TDC, and then tighten down all pedistal bolts to 20 ft/lb.

So if you tighten the bolts x amount of revoultions, you're not getting the bottom of the pedistal to seat on the head. I'm totally confused NMB2 on what you're saying.

I was planning on bleeding down the lifters, and what you were saying Chuckster about the hydraulic operation of the lifter removing any lash does make sense, and its what I thought all along was the correct operation, but the experience I had with my cherokee's 4.0 has made me think otherwise.

The manual gives no value for installed height (regarding the valve stem height), and it also doesn't make mention of the need to bleed oil out of the lifters prior to reinstalling the head. Ive checked in both the IH manual, and this little FMC 93 IDIT manual.

[NMB2]

I read his SBC as SBF.

Its the same with all hydraulic systems, you have to have a certain amount of pre-load in the lifter for the hydraulic operation to work correctly. Too much can hang the valves, too little will cause valve train rattle and excessive wear to valve tips/rockers.

with the IDI, you will turn the bolt until you take the slack up between the lifter and the rocker. You then count your turns til the bolt is fully tightened. You want at least 1/4 turn lash, between 1/2 and 1 turn is preferable.

[LMJD]

There's a number of engines where you NEVER face the tips of the valve stems because you go through the case hardening which of course cause the tips to mushroom over time.

Cause when your grind the valves, and cut the seats, the valve becomes more recessed up into the head, intern raising the overall height of the stem (where the rocker arm meets the stem)

With hardened seats it's about impossible to grind the seats anywhere near deep enough to effect stem height. In some really severe cases where the seats are part of the head and already eroded deep into the head, that's a different story. It DOES happen, but rarely.
On any engine with hydraulic lifters it is standard procedure to rotate it by hand a couple revs before starting which will force the lifters to bleed down before firing it up. Otherwise it's not unheard of to have valves contact the pistons as Chuckster implied above. But it's not due to stem height, it's due to improper lifter bleeding.

IIRC the 7.3's don't have locknuts to individually adjust each rocker so you'd want to slowly and evenly tighten the pedistals to give the lifters a chance to bleed down then double check by rotating the engine with a breaker bar on the crank pulley bolt.

[chuckster57]

Originally Posted by farmfuel

but the experience I had with my cherokee's 4.0 has made me think otherwise.

I just replaced a head on a Jeep two weeks ago with the 4.0.. the rockers on that are like the rockers on my old ford 460. You just tighten the bolt that holds the rocker to a speficic torque and it should be right. I replaced heads on a Ford 302 last month and they were the same.

When I changed out my stock rockers on my '86 and went to full roller rockers, I did have to adjust them.

On any engine with hydraulic lifters it is standard procedure to rotate it by hand a couple revs before starting which will force the lifters to bleed down before firing it up.

Did heads on a Suburban with a 350 a few months ago and after trying the "turn it over" trick and letting it sit for a day, I ended up having to take the intake back off and hand bleeding all the lifters.

[LMJD]

Yep, before there were so many small diesels available in mid sized trucks there were LOTS of heavy duty truck gas engines and I remember the GMC and Chevy lifters were really hard to bleed down.

[farmfuel]

Originally Posted by LMJD

On any engine with hydraulic lifters it is standard procedure to rotate it by hand a couple revs before starting which will force the lifters to bleed down before firing it up.
IIRC the 7.3's don't have locknuts to individually adjust each rocker so you'd want to slowly and evenly tighten the pedistals to give the lifters a chance to bleed down then double check by rotating the engine with a breaker bar on the crank pulley bolt.

Okay, so for piece of mind, instead of manually forcing oil out of the lifter to bleed it, I'm gonna tighten down all rocker pedistal bolts until resistance is felt, then go a little more, turn the motor over a couple of times, then go back and tighten them a little more, and just keep repeating the process until all pedistals seated on the head? Doese this sound right?

So the valve spring is gonna work with the cam lobe to force the lifter to bleed down? What's wrong with manually bleeding down all the lifters, tightening all rocker pedistals, then using the engine oil pressure to fill the lifter back up? On my core engine, I removed a lifter from the block, removed the clip that holds the pushrod cup in place, then used a magnet to pull it all apart (manually bled it) It's got one hell of a little spring in there that won't allow for the pushrod to come loose, regardless of how much oil is in the lifter body.

Maybe I'm over thinking this. I just don't wanna screw up, ya know? Thanks for the help,
David

[chuckster57]

Yeah, I think you may be a little..If you have good access to the lifters, I would bleed them off first. if not then just tighten them down and turn the engine over. Then check again, and repeat as many times as needed.

I prefer to only do it once. That's why I bleed off the lifters.

[LMJD]

Okay, so for piece of mind, instead of manually forcing oil out of the lifter to bleed it, I'm gonna tighten down all rocker pedistal bolts until resistance is felt, then go a little more, turn the motor over a couple of times, then go back and tighten them a little more, and just keep repeating the process until all pedistals seated on the head? Doese this sound right?

Yessir, that or Chuckster's method.

[NMB2]

Just for clarification, I was not talking about procedure for bleeding the lifters down. Both methods posted are fine for that, although I'm generally not that careful.

What I was referring to is the actual lash. Yes its a hydraulic lifter, and yes it automatically adjusts but it has a tolerance.

When doing valve jobs, decking the heads, decking the block, swapping a cam, it is important to check your valve lash. You can either end up with not enough and you will get the lifter riding at the top of its stroke all the time, which isn't good for it, or you will actually get valve train rattle. This would mean you need longer pushrods.

If too much material was taken out and you have too much lash, this means you need shorter pushrods. The side effect of this is ramming the valves into the pistons.

On these motors preferably you want 1/2-1turn lash. 1/4 turn lash will work, but nothing less.

The way to measure this is as follows:

with the cam in position to have both valves closed on the cylinder you are working on, start tightening the rocker bolt. When you get to the point where the slack between the lifter and rocker tip is taken up this is the point you begin your measurement.

From this point, you will count the revolutions it takes to fully tighten the bolt to your torque value. It should be somewhere between 1/4 and 1 turn. These are the extremes.... 1/2-3/4 turn would be perfect.