I've got a question for the late Chevy gurus. I have a 250 that is making a ticking/thumping noise. It seems to be coming from the back lifter area, so I'm thinking its a bad lifter. I pulled the valve cover and checked for any loose rockers. Could there be a collapsed lifter that is still holding the rocker enough that it is firm to the touch? I rotated the engine so that I could be sure and check for slop during the compression stroke. Is there any other technique to diagnose this other than lifter replacement? I'd rather not throw the $50 at it without some assurance that I'm actually making an improvemnt.
I'm tending toward this because I've had similar experience with elderly Chevy and Pontiac v-8s where they had noisy lifters that couldn't be quietened with adjustment.
regards,
Leon
You may also want to check the push rod to make sure it is not bent. The lifter just may not be pumping up.Are all the rockers wet with oil?
A press in rocker stud could be backing out of the head. Sight down the top and make sure one is not a lot taller then the rest. Its pretty unlikely unless you have been runing the engine pretty hard, but it could happen. Joe
Dear Leon;
If (that word again) there all oiling & studs are equal. Check the rockers & see if there worn excessivly, with the pushrods involved.
Then simply adjust to specs (zero +1 turn-hot) etc.
Good luck.
i,ve had several rocker arm studs come up and thats what i,d look for first.
I had a chance to get back to this and try some more diagnosis. All the pushrods are turning, none seem to be bent. All the rocker studs are the same height. By sight anyway, I didn’t use a straightedge. With my stethoscope I was able to narrow the noise down to #6. It seemed like exhaust was louder than intake but I’m not sure. I adjusted the valves on #6 and now the tapping is almost imperceptible at idle. But at 1500 RPM or so its definitely still there. I’m thinking of getting a couple of lifters (~$8) from O’Reilly and replacing the ones at #6. What do you guys think? Is it most likely a waste? Is there any danger of making the problem worse by damaging the cam?
Thanks for any comments.
Leon
You can put new lifters on a used cam.You just NEVER put Used Lifters On a new cam. One other thing you may want to do. Is scribe a line at the base of those rocker studs. This way you can see if the studs maybe pulling out of the head. This can cause the lifters to become lose and make noise.
Usually press in studs do not pull out.
Especially if you have a stock cam & stock weak pressure valve springs.
Do you have a stock cam & stock valve springs?
If you have to continue adjusting # 6 rocker arms,maybe cam is wering out,going flat?
Go ahead & throw in some new lifters on # 6 $8.00 is not much.
MBHD
I don’t really know the history on this engine. It was the grand prize at the 2007 Rossi Goat Ranch roundup (www.inliners.org/events/Rossi07/Rossi%20picnic%2007.htm). I’m running it on a test stand right now. I want to make sure its OK before I put the effort in to install it in my 53 3100. I expect it is stock though. You’re right, $8 is not a huge investment. Its cold and rainy today, and I’ve got plenty of other chores to do, so I’ll pick up a couple of lifters this week and try it next weekend.
Thnks for the advice,
Leon
I replaced the lifters in #6.
The old ones looked fine.
Now #6 Exhaust is quiet.
#6 Intake still makes a tapping noise.
If I tighten the rocker the noise will quieten until the lifter bleeds down - then it returns.
One of the other Inliners sugggested that maybe I have a weak valve spring that can't shut the valve fast enough.
Comments?
Additonal suggestions?
Thanks in advance.
Leon
Dear Leon;
Are you going to 'zero' and then one more turn??
On all, not just the new ones and is the engine at operating temp??
Your springs are probably okay/not the problem.
Good luck.
Yep, 1 turn past 0 lash.
I only adjusted the new ones since they were the ones making noise. I use a stethoscope and listen with the probe at the middle of the rocker arm.
The engine was warm, but not to full operating temp.
If I tightened the #6 intake valve another quarter turn, the engine would run rough until the lifter bled down. The noise would go away while the valve was too tight, and then return after the lifter bled down. I didn’t try this on #6 exhaust since it wasn’t making noise.
I’ve been thinking about the valve spring idea this week and I think I agree. If the spring couldn’t close the valve quick enough, the lifter would pump up to take up the slack. That’s why they make anti-pumpup lifters for high rpm use.
I’m thinking about pulling the pushrods from #6 and making sure the noise quits to be absolutely sure its valve train noise and not piston slap or connecting rod bearing.
If I can convince myself there’s nothing wrong except valve train noise, I’ll be willing to spend $300-400 or so and replace everything from the cam up to the valve. Then I’ll have a whole new set of questions about recommendations.
What dou you think?
regards,
Leon
This may sound like a silly question, but is your oil full?
Actually, that a reasonable question. The engine is missing the disptick. I took some measurements off another 250 and I'm going to get a replacement small block stick and make new marks as necessary. But I haven't done it yet. I presume the engine has plenty of oil because the oil pressure at idle is fine(~30) when the engine is hot.
Leon
L;
What did the faces of the old ones look like??
Smooth and shiny.
I was kind of hoping to find some significant wear pattern, but there was nothing.
Leon
I had a ticking problem with #5 & #6 on my 250 several years ago. Had everyone I could get to look/listen to it. Engine builders and even the chief Chevy big block design engineer at the NSRA Nats. Tried new valve train and other stuff before having it rebuilt. Cause...#5 & #6 had scuffed/galled pistons.
Beltfed,
Did you try anything like my idea of pulling the pushrods from #6 and seeing if the noise quits?
Do you think your problem would have shown up that way?
Leon
I didn't try pulling the pushrods. As the problem was with the piston and not the valve train the problem would not have gone away with pushrod removal. In all fairness, everyone could hear the noise but couldn't decide where it was coming from. Some said valve train and others said bottom end. As the valve train, short of the cam and valves, could be replaced the easiest, that's where we started.
That's what's gnawing at me about this. I can’t be sure that its valve train and not something in the bottom end. If it is bottom end, then I’ve got a rebuild coming which will take until next year to get finished and installed. If its just valve train, then I can get it ready and install the engine this winter. To add to my frustration, I hurt my back Friday, so I couldn’t try my pushrod experiment Saturday. I essentially wasted what is probably the last good weekend this year. Oh well, got to keep it in perspective. There are a whole lot of people in this world who have *actual* problems.
Anyway, my plan is to try running it with the pushrods pulled on #6 and see if the noise is still there. Maybe next Friday. I’ll report back for everyone’s info/amusement.
I appreciate all the suggestions and commentary. It gives me the illusion of progress in between times I actually get to work on the engine.
regards,
Leon
Dear, Leon;
With the engine ideling & making the noise, 'ground out' that plug..
If it goes away, It's not a valve.
Good luck.
I got a chance yesterday to do the pushrod experiment. I pulled the pushrods from #6 and the noise continued. so I guess its probably piston slap, as beltfed experienced. I think I'm going to consider it a minor issue and proceed with installation. I've got a line on another low-mileage 250 that I can build up in parallel with debugging the install in the 53. Then I can swap in the new motor after I've gotten all the other issues solved.
Thanks for all the input, guys.
Leon
USE A BROOM HANDLE AND PUT ONE END ON SUSPECTED PLACES OF NOISE on the engine while holding other end up to you ear. it will be louder in area of noise.
Harbor freight sells a cheap stethoscope (SP)
that works OK,
Or Lisle sells them in auto parts stores(nicer unit)
Works much better than a broom handle or the old screwdriver trick
MBHD
Dear Leon;
Hank's right & It's a good thing to have around.
In this case however; just put your fingers on the rocker. If It's loose, you'll feel it.
Somehow; I still think your not adjusting them right. Are you following the instructions in the Motors Manual??
I have a stethoscope. that's what I used to isolate the problem to #6. The noise is loudest when touching the stethoscope to the rockers for #6. Not as loud for #5, almost non-existent for #4-#1.
John, I'm adjusting the valves by loosening until I can feel a perceptible click while idling, tightening till the click just goes away, then 1 more turn. But note, when I took the pushrods for #6 out of the engine, I still got the noise at ~1500-2000 rpm. The valves weren't even being used. So, it can't be related to valve adjustment for #6, right?
regards,
Leon
Dear Leon;
Adjust all the valves using the method mentioned.
If the noise is still there; "ground out" each plug one at a time & see if the noise stops.
If it does, It's in that cylinder and not a valve. If it doesn't It's not in the "top end".
Good luck.