bent push rod?
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Joined: Jul 2007
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bent push rod?
Noticed a rattle last week on my 1987 L98 at start-up. Pulled the valve cover and started checking valve adjustment using directions from the shop manual. Two push rods (#4 and #8 exhaust) rotated easily when they shouldn't have (TDC on #1). That would be the rattle.
#4 seems to bind (it will rotate about 3/4 of a turn then bind) as I rotate it while tightening the rocker arm nut to adjust it. I pulled it out and checked it (rotated it on a flat surface looking for gaps). It appears to be straight.
Is some binding normal or should push rods always spin freely then just get harder to turn when the adjustment is right?
I'm thinking that I should just replace the suspect push rod even though it looks OK. Can I just replace push rods on one side of the motor? I'd think so since the adjustment will make up for any difference between old and new. Any thoughts/experience?
#4 seems to bind (it will rotate about 3/4 of a turn then bind) as I rotate it while tightening the rocker arm nut to adjust it. I pulled it out and checked it (rotated it on a flat surface looking for gaps). It appears to be straight.
Is some binding normal or should push rods always spin freely then just get harder to turn when the adjustment is right?
I'm thinking that I should just replace the suspect push rod even though it looks OK. Can I just replace push rods on one side of the motor? I'd think so since the adjustment will make up for any difference between old and new. Any thoughts/experience?
Last edited by mbfan72; Jul 24, 2011 at 11:30 AM. Reason: typo
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
The BIG question is...
why did they bend?
poor adjustment proceedure or a mechanical issue?
The L98 roller motor really does not require much "fine-tune" adjusting of the valves. after 150,000 maybe a 1/4 turn..but unless a lifter fails or a cam lobe wears away they should stay pretty nice.
If it were me, I'd replace them all, AND replace the rockers since you;re there. Its just as easy to get a bad rocker socket as it is to have a bad rod end ball. besides, the stock steel rockers offer such an inconsistent range of ratio that you have 1.5 on one valve and 1.6 on the next. For $250 you can have some REAL rockers and even get a bump in performance.
There are a doz accepted proceedures here for adjusting, read them ALL and learn. If you;re not sure as you;re doing it, leave out that last 1/2 turn. You can come back and do that but you cannot undo a bent rod. I like to have a warm motor and get the rods to where they are easy to spin but unable to wiggle any. MAYBE a 1/4--1/2 turn more if the motor is cold.
why did they bend?
poor adjustment proceedure or a mechanical issue?
The L98 roller motor really does not require much "fine-tune" adjusting of the valves. after 150,000 maybe a 1/4 turn..but unless a lifter fails or a cam lobe wears away they should stay pretty nice.
If it were me, I'd replace them all, AND replace the rockers since you;re there. Its just as easy to get a bad rocker socket as it is to have a bad rod end ball. besides, the stock steel rockers offer such an inconsistent range of ratio that you have 1.5 on one valve and 1.6 on the next. For $250 you can have some REAL rockers and even get a bump in performance.
There are a doz accepted proceedures here for adjusting, read them ALL and learn. If you;re not sure as you;re doing it, leave out that last 1/2 turn. You can come back and do that but you cannot undo a bent rod. I like to have a warm motor and get the rods to where they are easy to spin but unable to wiggle any. MAYBE a 1/4--1/2 turn more if the motor is cold.
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
Exhaust valves on #8 and #4 will have their lifters on the base cam circle while the motor is at tdc#1. It would not be unusual to be able to rotate the pushrods at that point, especially if the lifters have bled down.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
you said that the rod was straight. why replace anything? as the man said, not unusual to have some rod rotation if lifter has bled off. if your engine valves were set at close to zero lash, rather than zero +360*, you will get rattle as you describe.
ex 4-8 are set with #1 tdcc, so if they are slightly loose, seems normal to me. adjust them at that point.
ex 4-8 are set with #1 tdcc, so if they are slightly loose, seems normal to me. adjust them at that point.
