I swapped my factory 1.5 rockers out last weekend with a set of 1.6 roller rockers on my 305 LO3. Engine is running great, but starting at about 5000rpm Im hearing a strange "rattling" which I never heard before the rocker swap. I'm wondering if I didn't set the lash right on the rockers. During the install, I snugged the nuts up until the lash was out, then gave each nut additional 1/2 to 3/4 of a turn (maybe that wasn't enough??). I'm not sure what else the noise could be. The only other thing I did during the rocker swap was remove the AIR pump and lines. I capped off both AIR lines on the exhaust manifolds and taped up the ends of the harness connectors for the solenoids.

Any advice? Should I go back and recheck the lash on the rockers?

 

why are you spinning that motor so high? all the LO3s i've driven have pooped out at 42-4500 tops. Also, you are probably experiencing valve float if the rockers are adjusted properly due to inadequate spring pressure.

 

I don't think I'm the only guy around pushing a 305 motor over 5000 rpm at the strip. With the factory 1.5 rockers I regulary shift at about 5300-5400 without any issue or noise. It's still pulling hard up through 5000. The factory rockers were steel and the new ones are aluminum, so I they shouldn't weigh more. But maybe you're right, maybe it is valve float.

 

i've pushed a 305 to 6500 all the time with a bigger cam, that doesn't mean a chocked LO3 should be spun that high. factory stamped rockers do not weigh much at all and your aluminum ones definately have added more mass, are they hitting on the valve covers possibly? did you elongate the pushrod hole for swapping to 1.6s, there could be several scenarios. also did you recheck lash just to be sure.

 

clearance? at higher rpm, the lifters will recieve more pressure bringing them up that final bit...

 

The new rockers are for 87' up centerbolt heads and are self aligning, so they are designed to clear my valve covers. The searches I did on this swap did not sound like any elongating of the pushrod hole is required. xpndbl3 may be right about the weight. The factory stamped rockers are small and light. Even though the 1.6's are aluminum, they are pretty beefy, so I am probably moving more mass now. If that's the root of my problem, then the only solution is to get stiffer valve springs (assuming I keep the 1.6 rockers), right?

I'll go ahead an take the valve covers back off and recheck lash. I'll also look for evidence of contact with the valve covers. Can someone confirm how far to tighten the rocker nuts after the lash is out? I've been using 1/2 to 3/4 of a turn?

 

Are you adjusting the rockers with the motor running or off? If its off, are you making sure the lifter is on the base circle of the cam when you are readjusting the rockers. I usually go a 1/4 to 1/2 turn past zero lash. But mine are noisy as all hell...

 

Yes, I'm adjusting by the book, cold. With #1 at TDC adjust about half the rockers per manual, then rotate engine one turn to #6 TDC and adjust the rest. The valvetrain is perfectly quiet at low rpm.

 

Get yourself some oil clips and try to run them while its hot and at idle. You may be experiencing valve float at the higher rpms...possibly due to an over tightened rocker. Just remove one vc at a time and loosen a rocker till it makes a loud click and then slowly tighten it back till it stops...then give it a 1/2 turn and move on to the next one.

 

What are oil clips, something to keep oil from spraying all over when valve covers are off and engine is running? Where do I get some?

So are you saying vavle float can be result from overtightening the rockers?? I thought maybe I didn't tighten the nuts enough. Good info.

 

Well I took the valve covers back off today to check the lash and rocker contact. Can't find any evidence of contact with the valve covers.

What I did find (that I missed during the rocker install) is that the pushrods are no longer centered in the clearance holes in the head. The 1.6 rockers have caused the pushrods to move towards the rocker pivot and I believe some of the pushrods are now lightly contacting the head. The pushrods don't seem to be worn or damaged, but this has to be causing extra drag on the valvetrain, possibly contributing to my high rpm noise.

So unless there is a way to enlarge the pushrod holes in the head, with the heads on the car, I need to go back to 1.5 rockers. I don't know how I would open the pushrod holes up with the heads on the car without dropping chips into the engine. Anybody ever elongated pushrod holes with the heads installed (and not have the engine take a crap afterwards)?

 

yes you definately needed to elongate the holes.
you may need new pushrods now, if they're pooched. they're cheap.

you should be able to use a 5/16" rat tail file, in a drill, elongate the slot maybe .050". don't widen it. put a rag below the pushrod slot on the head, you should be able to catch all the filings. If it were me, i'd get a friend to hold a shop vac right below where i'm elongating, that's pretty fool proof. if you have a big magnet, leave it right below as a final save. (while filing).

my original thought was that your factory locking nuts were worn and backing off. something to think about in the future, if you didn't go to polylock.

 

Sonix, What you're describing (rag, shop vac, magnet) would require the intake manifold to come off to get under the pushrod holes. I only have the valve covers off. Maybe that's what I'll need to do to open the holes up.

 

pulling the intake and putting down rags or using a vacuum with a magnet on the bottom are all good suggestions. although the way gravity works all the excess fillings should just sit in the lifter valley until you vacuum them up at the end with no worries, although putting down a few shop rags and vacuuming it up at the end would be the best way to do it. unless you want to pull the heads and do it on a bench of course.