roller rocker problems

[zglad]

Okay, here is the deal. Our "rebuilt" 258 seems to have a problem. One of the rocker arms is really loose. It rattles really bad and I'm not sure how to fix it. The nut on the top isn't loose, and the pushrods are all the same length, so I don't know what to do. The rocker is on the second intake valve from the firewall. When the engine turns and the pushrod raises, the rocker becomes tight kind of like it should, but when it goes back down it is really really loose. This engine has probably only been running for about 15 minutes since the rebuild, so I'm hoping that a lifter is stuck and can easily be freed. Can anyone give me some advice? The jeep actually sounds pretty smooth at idle, but the engine shakes quite a bit. Is that normal, or are these two problems related?

Thanks

Zac

[jeepin916]

well if the lifter si stuck in its bore then the pushrod wouldnt move at all but what may have happened is the lifter is defective and not building hydraulic pressure, unless you have solid lifters, and if you do then you may need to just adjust them, i would try to adjust the rocker arms first then if that doesnt work you need to pull the lifter... are they used or are they new?

[zglad]

I don't know if they are new or used. I would assume that they would put new lifters in a newly rebuilt engine, but you know what they say about assuming things. I think they are hydraulic because the rocker arms don't adjust like on a 350, or at least I don't know how to do it. Is there any way to tell?

[fourtrail]

It sounds like you have a defective lifter that is not 'pumping up'. Does the motor have good oil pressure? unless the rebuild has a radicle cam in it they are most likely hydraulic. This would cause the motor to shake bacause that cyclinder is not getting enough fuel to fire and is throwing off the balance. Find out if they replaced the cam and lifters. If they did find out if they will replace the bad lifter. Most reputable engine shops will.

[Junkpile]

Did you wipe a cam lobe out on start-up? Happens more often than you would think with generic rebuilt engines.

[zglad]

Originally Posted by Junkpile

Did you wipe a cam lobe out on start-up? Happens more often than you would think with generic rebuilt engines.

What do you mean? Would the cam literally fail on startup? Unfortunately the engine was rebuilt 18 months ago, but never started or installed until recently. It had a one year waranty, so the shop won't fix it. How much are new lifters? Can you just buy one?

[jeepin916]

lifters come in a set, and usually come with a cam i dotn know of any company that would sell u one lifter.... your better off getting a cam and lifter and installing them. it will save u the trouble in the long run..... if one failed now what will happen to the others?????

[Junkpile]

Do yourself a favor and get the guys who did the machine work to look at it and see what's going on. There's all kinds of weird stuff that they could have done. I'm running an AMC cam and lifters, springs, retainers, and roller-tipped rocker arms.....Chrysler valve locks.....Chevy hardened pushrods and adjustable guide plates, and I think the screw in studs are actually for a Ford adjustable conversion. Lots of machining. If I had a problem that I couldn't fix myself, anyone but my machinist would be somewhat lost. Small adjustments to correct valvetrain geometry often require custom parts and machining. The most likely person to quickly pinpoint the problem is the guy who setup the valvetrain.

Yes, cam lobes get wiped right off sometimes. It is usually caused by not following the cam manufacturers suggested break in procedure or not using the proper pre-lube. Another common cause is mis-adjusted valvetrain components. It's also common with reground cams and resurfaced lifters.

[jeepin916]

yea i dont get reground cams or resurfaced lifters iv heard bad things about them....

[zglad]

Thanks guys,

we took the rocker arms and pushrods back to the machine shop (Trying not to pull the engine again). If they can't find anything wrong then well have to pull the head and re-install the cam and lifters. Thanks for all of your help.

[jeepin916]

no problem let us know what was wrong good luck dude

[zglad]

Okay, since we can't take the engine back to them without pulling it, the guy asked to see the pushrods for the intake and exaust valves for the bad cylinder. To me they looked the same length, but he measured them and said that one of them was wrong. We had to get the part from the west coast so it will be a few days. I'm not trying to second guess the guy, but I don't think that the pushrod is the problem. I don't know why a difference that is so small that you can't see it would make the rocker arm that loose. I'm thinking that maybe the cam is bad, but the valve does move up and down a little bit. Are the intake and exaust pushrods a different length. I would look, but it is 20 degrees right now. I guess if that doesn't work, we will have to tow the jeep to the shop or pull the head or engine. I'll let you guys know.

[jay79cj7]

If memory is correct from when I rebuilt my head, the pushrods were the same length for all valves.

[fourtrail]

Did he say if the pushrod was too long or to short? If it was too long and the motor had been sitting that long the pre-lube on the cam may have dried out and when fired up it wore the lobe off of the cam because of the extra pressure and possible binding at full lift from the longer pushrod. At least you don't have to pull the motor to change the cam.

[Junkpile]

I'm thinking that maybe the cam is bad, but the valve does move up and down a little bit.

Take a straight edge and make sure all the rocker bosses are equally seated in the head, but you would have already noticed that. It really sounds like the cam got wiped out.