Not Vette -- but Chevy Engine

[Steven C.]

I've been trying to track down a rattle on my '85 Trans Am, stock 4305 4-barrel.

Not very apparent at idle, becomes loud as rpms increase.

Using a long scrtewdriver as a stethoscope, I narrowed the sound down to the left bank valve cover. Upon removal, the rocker arm for #5 exhaust appeared cocked slightly to the side, and the valve spring cap showed shiny all the way around (in constrast to all others a little sludgy).

I removed the nut, ball, and rocker. The push rod is straight, and looks OK.

The valve stem tip and the rocker arm where it contacts the valve stem tip are shiny and slightly "dented".

The rocker arm stud has a groove cut in it from the rocker. It seems like the rocker is getting stuck in the groove, and actuating the valve slightly sideways.

Here's the question: Is the rocker stud pressed-in or screwed-in (I'm praying here). If screwed-in, I'll replace the stud, ball, and rocker with the head still on the engine in the car.

If pressed in, I'm thinking a can replace the entire cylinder head from the u-pull it.

Thanks in advance for reading my sad story.

Steve

[Steven C.]

Make that 305 4-barrel *NM*

[John H.]

Re: Not Vette -- but Chevy Engine

Steve -

That engine should have the factory pressed-in studs; does the valve end of the rocker arm have a "flat" contact surface, or does it have slightly raised "ribs" on both sides of the valve contact area ("rail-type" rocker arm)?

[Steven C.]

Re: Not Vette -- but Chevy Engine

John-

Appears flat, although I can see a slight valve tip impression just off center.

Steve

[Mike McKown]

It's easy to fix the stud

Just pull it, ream the hole and knock in a .003 oversize stud. If the stud isn't cut too deep, you could probably get away with leaving it alone and replacing the rocker arm with a new one. The problem is the valve stem tip. If it's rounded off from the cocked rocker, you get to pull the head and repair/replace the valve.

[Steven C.]

Thanks, Mike

I'm all set to pull it and replace with a threaded stud. I think the cut is too deep, I'm afraid it will break, and the groove is large enough to catch the new rocker. The valve stem tip appears flat. I have a new rocker/ball (from NAPA $3.64, the dealer wanted $25!).

I appreciate the advice.

Steve

[Michael H.]

Re: Thanks, Mike

Steve,

One last thing to check. A worn valve guide is often the cause of a rocker arm running off center and creating the exact problem that you have. Hopefully, all that's wrong with your car is the rocker arm and stud. You can check the guide by gently moving the valve from side to side with a small bar or screw driver. If the guide is worn badly, you will soon have a rocker arm problem again.

[Steven C.]

Thanks, Michael -- That makes a lot of sense

I'll check it, probably tomorrow. Should there be any movement? The head is still on the engine, in the car, valve is still retained by keepers/cap/spring.

I got the car cheap not long ago, because of the rattle. It burned a ton of oil when I first strated it a couple of weeks ago, but each running event since is nearly smoke-free.

I appreciate the input and advice.

Steve