Lifter preload and pushrod questions.

[glockr]

I'm having some "interesting" problems with a brand new 318. It's running a Comp Cams XE268 cam and Comp Cams adjustable s/s rocker arms. It doesn't seem like there's any slack in the pushrods, but on every cylinder where the lifter is sitting on the base part of the cam, I can hold the pushrod and very easily rotate it.

1. Is this normal?
2. If the lifters were preloaded, wouldn't it put enough force on the pushrods to make them at least a little difficult to rotate?
3. If the lifters aren't correctly preloaded, how likely is that to cause bent valves?
4. If the machine shop claims the valves are sticking because of "bad gas" what defense (if any) do I have?
5. If it is a machine shop problem, would it be reasonable to expect them to pay to have the engine R&R'd so they can fix it (I can't see any way to get the driver's side head off with the engine in the car)?

Thanks,
Ken

 

[Cudafever]

I'm having some "interesting" problems with a brand new 318. It's running a Comp Cams XE268 cam and Comp Cams adjustable s/s rocker arms. It doesn't seem like there's any slack in the pushrods, but on every cylinder where the lifter is sitting on the base part of the cam, I can hold the pushrod and very easily rotate it.

1. Is this normal? Yes
2. If the lifters were preloaded, wouldn't it put enough force on the pushrods to make them at least a little difficult to rotate? No, spring inside lifter is vary small. Hyd pressure bleed off when eng is shut off.
3. If the lifters aren't correctly preloaded, how likely is that to cause bent valves? Likely, Better chance of bending a push rod
4. If the machine shop claims the valves are sticking because of "bad gas" what defense (if any) do I have? Who build this eng/heads.......who installed the heads?
5. If it is a machine shop problem, would it be reasonable to expect them to pay to have the engine R&R'd so they can fix it Depends, need more detail of what the machine shop did for you (I can't see any way to get the driver's side head off with the engine in the car)? What car is this?


Thanks,
Ken

What is the problem? don't run, makes noise??????

 

[glockr]

After can break in and road test, #7 cylinder died (popped out pushrod on exhaust. Cam doesn't look flat but valve are sticking open briefly before closing. Engine was built with all new parts and assembled by the same shop that did the machine work. Installation was by another shop that also converted the car from an auto to a stick. It's a 66 Barracuda, the header flange on drivers side covers the outer row of head bolts. Machine shop owner says sticky valves might have been caused by bad gas. Car has sat for about 6 years, but engine was built last fall (Aug 2009).

 

[Cudafever]

Is the push rod/s bent?
Do you have compression in that cyl?(us a push rod from another cyl if need be)

How long did you let the motor set, after rebuild, before you started and broke in the cam?

You said you have adj rocker arm.....right. do you know how to set and or check "preload" of the lifters?

this is what need to be figured out before you worries much about removal of head.

 

[glockr]

Is the push rod/s bent?

Push rod is straight

Do you have compression in that cyl?(us a push rod from another cyl if need be)

I doubt it; When push rods retract as the cam rotates, the valves stick open for a little bit before closing. Engine builder checked this.

How long did you let the motor set, after rebuild, before you started and broke in the cam?

Engine sat for about 6 months. Started and broken in by shop that did the installation. They have a lot of experience with hot rods (that's all they do) and they did ask me if it had a flat or roller cam so I guess they know how to break in an engine.

You said you have adj rocker arm.....right. do you know how to set and or check "preload" of the lifters?

I'm assuming preload was set by by the engine builder.

this is what need to be figured out before you worries much about removal of head.

Engine builder said heads need to come off to see why valves are sticking. How likely is it that bad gas could cause this? Engine builder says very likely. Others have said "maybe but doubtful" to "no way." If it WAS caused by bad gas I guess I just learned an expensive lesson, I just want to make sure it really WAS caused by bad gas and the machine shop isn't just CYA'n themself.

Cheers,
Ken

 

[Brian Hafliger]

Push rod is straight


I doubt it; When push rods retract as the cam rotates, the valves stick open for a little bit before closing. Engine builder checked this.


Engine sat for about 6 months. Started and broken in by shop that did the installation. They have a lot of experience with hot rods (that's all they do) and they did ask me if it had a flat or roller cam so I guess they know how to break in an engine.


I'm assuming preload was set by by the engine builder.


Engine builder said heads need to come off to see why valves are sticking. How likely is it that bad gas could cause this? Engine builder says very likely. Others have said "maybe but doubtful" to "no way." If it WAS caused by bad gas I guess I just learned an expensive lesson, I just want to make sure it really WAS caused by bad gas and the machine shop isn't just CYA'n themself.

Cheers,
Ken

Regular pump gas after some time turns to varnish. When you smell it, it stinks unlike reg. fresh gas.
When you introduce this into the HOT engine, it burns on to the valve stems causing them to stick in the guides (usually open). I still do some old time tractor engine work for local guys who bring in their not so old heads that have sat for a year or more with pump gas in the tanks and after some short run time won't run anymore.
I have to "beat" the valves out of the guides with a long punch!

I see this alot in boat engines also, when they sit all winter with pump gas in the tanks.

 

[abdywgn]

possibly valve guide clearance issue or valve stem material "balling up". with the valve in the stuck open position, give it a tap with a non-metallic faced hammer. lightly. had a big block do this, guy did not want to put new guides in so installed new valves with oversizes stems. clearances were not correct and it would stick open.