Is it necessary for the pushrods to rub on the heads were they pass trough the heads? I'm tearing mine down and they appear like they are rubbing excessivley. I thought they were guided by the rocker arms. There are no guide plates so do they just ride on the sides of the holes in the head??? Thanks!

 

Is it a narrow slot that the pushrod passes through, or a gaping hole?

 

Very narrow.

 

Any ideas?

 

That is how most Chevy pushrods are kept in line. At some point around 88 or so GM changed to different rockers that were "self aligning". Basically where the rocker rides on the valve, there are indents on either side that keep it from sliding off the valve. I heard some engines ended up with both.

Unless the pushrods are physically worn into (check by measuring diameter) then they're fine.

 

I had an engine a few years ago that had slotted push rod holes on one head, and round holes on the other head. All the casting numbers, hardware, etc matched. I have no reason to believe it didn't come that way from the factory. It ran fine.

 

I've got GM 1.6 rollers on it. They seem to be self aligning. Yes there is wear on them, you can feel it with your fingers. It just seems like more friction and metal shavings in the engine. Would it hurt if I opened the holes up so they didn't touch? Thanks!

 

As long as there is some method to keep the pushrod in line, it will be fine. Having two is kind of contradictory and could cause issues but for some reason GM didnt seem to care. It may be that your aftermarket rockers center a little differently and is causing some bind.

Drew... why am I not surprised? Sometimes I wonder if line workers did things to try and be funny.

 

The rockers have 2 "washers" that keep it on the valve. So it is safe to open the holes in the head up?

 

Replace the rockers

 

Why replace the rockers? They have less than 1k on them. They are the GM rollers, made by crane I believe.

 

They're self-aligning, so they're not compatible with your head.

 

The stock rockers were self aligning too... It shouldn't matter having the slotted heads and self aligning rockers, but if it really bugs you open up the slots. Don't swap to non-SA rockers unless you're adding guide plates.

 

Pics would be invaluable right about now to answer your question. What casting number are the heads though? They could have been changed at some point to a set thats incompatible with self-aligning rockers, if thats what you have. Self-aligning rockers have a little tab on either side of the end that pushes the valve down to keep it centered over the valve stem.

There are 3 ways GM used to align the rockers:

A) narrow slots in the heads, non-self-aligning rockers
B) self-aligning rockers, big holes in the heads
C) guide plates, big holes in the heads, non-self aligning rockers

You can only use one of those methods, when you combine them you will have issues.

 

Yes, but they were the silly stamped factory ones with the lazy little bumps on either side of the stem.

 

Exactly. The aftermarket ones probably have a lot closer tolerance and that may be a problem.

Are you having issues with just a couple pushrods, or all of them? What kind of wear do you have? Clean the pushrod if need be, and measure them.

 

Yeah, but if they originally were dependent upon the rockers for proper alignment. Swapping to non-SA rockers will leave that job up to the heads that weren't intended to do that job.

Are the pushrods wearing from contact with the heads? Or are the rockers wearing from contact with the valves? It's not really clear from the thread so far...

 

From the sounds of it he's got narrow-slotted heads, which will control alignment just fine.

 

I'd be more inclined to think the problem is the slots in the heads aren't long enough to clear the push rods with 1.6 rockers. I wouldn't trust the heads to do the job if they came with SA rockers to begin with. I'd keep the rockers, and clearance the heads. But that's just my opinion.

 

Drew, you are correct. I mocked it back up and found the slots aren't long enough for 1.6's. I need something called a Louis tool to drill the slot longer. Thanks Brother.

 

And new pushrods.

 

Similar question don't mean to thread jack but, I just picked up an 87 TPI engine and the rockers are stamped with narrow holes on one head and the others aren't quite as small, what benefits will I see switching to roller rockers? My last engine had them when I got it is it just a reliability thing or is there a performance benefit to using them?

 

Can't you just use a drill bit?

I've never even heard of a special tool for elongating the push rod slots in the head.

 

Good to hear the culprit is identified.

Here's a link to a Louis tool...



http://www.compperformancegroupstore..._Code=Pushrods

And the backyard alternative...



http://www.chevyhiperformance.com/te.../photo_08.html

I have no personal opinion of one method vs the other. Google finds all kinds of articles on modifying heads to clear 1.6 rockers.

 

The Louis tool is to elongate the slot, keeping its same width so you can still use non-SA rockers. The alternative is to hog them out like Drew's backyard alternative picture, and use SA rockers.

 

Well I used the louis tool and just finished the porting. I dropped the heads off at the machine shop. The machinist really liked my porting job! He was really surprised when I told him it was my first set! Thanks for the help Guys!