Where did this knock come from?

[Mike T.]

Hoping some engine guys can give me some ideas.
I am working on an engine that missed badly, but didn't knock.
I finally took the valve covers off and observed the #1, #7 and #4 intake rockers weren't touching the pushrods.
The pressed in studs for those 3 rockers were also about 1/2 inch longer than the studs for the rest of the rockers.
The former owner said "It had bad gas at one time, and I drained it all out."
Theory: Did the "bad gas" varnish up and cause the 3 above mentioned intake valves to seize, and when he tried to start it, the lifter/pushrod/rocker forced the rocker stud out of the head?
Here's where my real concern lies. I adjusted the rockers to take up the gap. I turned it over several times, and all the valves moved up and down perfectly. I then started it. It ran smooth, with no miss, but it was knocking. It never knocked before. I then replaced the 3 lifters, thinking they had been collapsed/broken. Started it again, and it still knocks.
Did I ruin something, or was the damage done before, and it just showed up after I allowed the valve to function which resulted in proper combustion and power stroke.
I sure hope you can show me I didn't do the damage.
Thanks!

[Terry D.]

Re: Where did this knock come from?

Mike
What kind of motor? How did you set the valves? My guess the miss was due to valves not opening. Knock could be wrist pin, or rod but with no compression, no noise, now you have compression you hear noise. Did you do a compression test? Did you adjust all the valves? Are you sure what camshaft you are dealinh with?
Terry

[Ray G.]

Re: Where did this knock come from?

Hoping some engine guys can give me some ideas.
I am working on an engine that missed badly, but didn't knock.
I finally took the valve covers off and observed the #1, #7 and #4 intake rockers weren't touching the pushrods.
The pressed in studs for those 3 rockers were also about 1/2 inch longer than the studs for the rest of the rockers.
The former owner said "It had bad gas at one time, and I drained it all out."
Theory: Did the "bad gas" varnish up and cause the 3 above mentioned intake valves to seize, and when he tried to start it, the lifter/pushrod/rocker forced the rocker stud out of the head?


Here's where my real concern lies. I adjusted the rockers to take up the gap. I turned it over several times, and all the valves moved up and down perfectly. I then started it. It ran smooth, with no miss, but it was knocking. It never knocked before. I then replaced the 3 lifters, thinking they had been collapsed/broken. Started it again, and it still knocks.
Did I ruin something, or was the damage done before, and it just showed up after I allowed the valve to function which resulted in proper combustion and power stroke.
I sure hope you can show me I didn't do the damage.
Thanks!

Hello Mike;
Small Blocks (especially early) have a tendency to have sticky or stuck lifters, from non-use. The piston in the lifter sticks in the varnish build up area of its bore.
This leads to pulled studs when the engine is revved trying to clear the miss.
Doubt that bad gas had any thing to do with your engine problem. Except if the engine was overreved trying to clear the miss.


My next step would be to either reinstall the rocker studs and pin them by drilling through the stud tower and stud and installing a self locking roll pin. Or remove the studs and install screw-in studs.

More detail is available if you like.
Ray

[Ray G.]

Re: Where did this knock come from?

Hello Terry;
We must have been posting at the same time.
Hope I didn't step on your post.
Ray

[Kenneth T.]

Re: Where did this knock come from?

Mike,

If you have good oil pressure, try to determine which cyl is making noise. If you have a stetiscope, great or even a long screw driver will do. Just move to each cyl and hold your ear against it.

If you can find the culprit, disconnect the spark plug and see if the noise abates. That will unload the piston. If it goes quiet you may have a wrist pin problem.

Also, does the engine run smooth now that the valves are all moving? Hope it helps.

Ken

[Mike T.]

Re: Where did this knock come from?

Terry: It's a 283.
I adjusted the valves by ensuring both (Intake/Exhaust) were seated (TDC), and then I spun the pushrod with my thumb and finger and tightened the rocker nut down until the pushrod wouldn't spin freely.
I haven't done a compression test yet.
After I put the 3 new lifters in, I reset the valves with it running. I backed off the rocker nut until it clattered, then I tightened it until it quieted down. I then tightened it another half turn. I adjusted all of the valves. It has the stock cam.
Ray: You suggested that I replace/rework the 3 studs that slid out. Do you think they are moving slightlly when running, and that causes the knock?
Ken: It runs smooth now. I'll try the stethescope. My son used a rubber hose and said it sounds like it's coming from one particular cylinder. I don't know if he had the hose on the head, or the block.
Thanks guys!

[Edward J.]

Re: Where did this knock come from?

Mike take a close look at the stud bosses they will sometimes crack and the studs will not stay put.You can sometimes see the crack looking at the bosses. I recently rebuilt my 327 and found one that was bad. so I just had screw in studs installed on all of the cylinders.

I think Kens post about locating the possible cylinder that making the noise is what I do at my automotive shop when trying to locate which cylinder maybe the culprit. If you have a good pair of insulated pliers and remove one plug wire at a time and note the noise , If the tone changes you have found the cylinder.

[Gene M.]

Re: Where did this knock come from?

Mike,
If you have a bad wrist pin or spun bearing, you are going to remove the engine to repair. Turn the crank, new rod/main bearings and rings are in the future. Rebalance assembly, possible resize rods hone cylinders at minimum with machine shop. Assuming bores are not worn.

The suggestion to go to screw in studs is best option. All work could get pricey if you have all the labor done. Could be cheaper if not a matching numbers block to get a crate block assembly.