The Stovebolt Site Forums The Shop Area Engine Shop Sticking valves

I have a 51, 235 with hyd lifters. I have broken 3 seperate intake rocker arms # 2,5,6. Each after between 25-40 miles of driving. The engine runs great and I'm real happy with it. Except for the rocker arms of coarse. The push rods are not bent. Do you suppose the intake valves are sticking? I put Marvel in the oil and gas but in 25 miles another one broke. Any ideas? Thx.

Glenn,

Are you sure you have hydraulic lifters? I thought that the only hydraulic lifters in 1951 were on powerglide equipt cars.

If the intake rockers break it is usually due to old gas gumming the guides.
How old is the gas?

A pushrod will usually bend before breaking a rocker arm. My 38 bent two because of stuck valves. I had to drive the valves out with a hammer after pulling the head.

How are you adjusting the valve lash?

1. Yes hyd lifters. 51 car eng. w/pw
2. Gas is about 3 weeks old. New tank
3. I heat the eng up, adjust out all lash and then tighten 3/4 turn more.
Some guys say adj. 1/2 turn and some say 1 full turn. Tech Article says 1/8-1/2 or your going to have http://centuryperformance.com/valveadjustment.asptrouble.
So far I'm having trouble. The valve seems to be free. When I put in a new arm the valve moves freely.It is not stuck. Any ideas?

http://centuryperformance.com/valveadjustment.asp
Sorry guys I got the incorrect address on the previous post.

i don't think your suppose to tighten valves like that on these engines like you do on a 350 or the newer chevys...someone else will be along soon to confirm this..but i think you use a feeler gauge, warm up engine then re-set them again with feeler gauge...sounds like you have them to tight...

GEC52,

I tend to agree with Tiny...it seems the push rod would always bend before a rocker would break. If a valve seized in a guide tight enough to break a rocker arm, it doesn't seem like it would "unseize" by itself.

I would focus on the rocker arms themselves. Is the assembly getting the proper amount of oil? Could the engine have overheated at some point in its life and damaged the integrity of the rocker arms?

It sure seems like you are doing everything right in the adjustment department. When you replace the rocker arms that have broken, do they break again! Short of bottoming out a spring or having the valve kiss a piston, It would appear that the cause of the failure would be the rocker itself.

Stuart

This is just a thought but could it be the hydraulic lifters themselves causing this problem?

You said:

"I heat the eng up, adjust out all lash and then tighten 3/4 turn more."

Are you setting the engine to #1 TDC (Top Dead Center)and then to #6 TDC before you do any adjustment?

Also when adjusting to zero lash, loosen the adjuster and turn the adjuster to zero lash with your fingers, not a screwdriver. Then, using a screwdriver another 1/4 turn.

Sometimes weak lifters or lifters that have been "pumped out" will give a false reading of zero. When you turn the engine over without oil pressure the lifters loose oil.

Then, when you start the engine, after the adjustment, the valves are probably going to clatter because the lifters are not completely pumped up.

If you are sure that you have ADJUSTED THE VALVES CORRECTLY,

Run the engine, faster than idle, to build up the oil pressure and the lifters. The valves are going to be loud and noisey until the lifters are again fully "pumped up". You will find that after a few minutes or so, the valves will then start to quiet down.

My 235 has hydraulic lifters and if I turn my engine over by hand 2 or 3 times when I restart it the valves are noisey but then quiet down after the lifters are pumped up.

Let's look at other areas - where are rockers breaking: towards one of the ends, or in the middle?

Are you seeing any unusual wear on the rocker arms where they connect to the head? Check the unbroken rockers for signs of wear.

Are you running a stock camshaft, springs and valves?

Have you confirmed you're getting oil to the rockers?


I can't imagine a rocker breaking unless it's sticking, holding the valve open, and having the piston smash back up and close it.

-Boyo

I think any GROSS error in adjusting the valves will make itself apparent in seconds, especially with hydraulics. Too tight and that cylinder goes on vacation. I don't think this is a adjustment issue...can't wait to see the outcome!


Stuart

I hear everything you all are saying. I think my adjustment may be alittle tight so I'll loosen to 1/4 turn. The broken arms 2,5,and 6 are all intakes. They all broke at different times and different places ie. the valve side the middle and the push rod side. The push rods are not bent. I replaced the push rods when I did the frame off. I didn't need to touch the short block. I did have the head gone thru. Could the push rods be too long? They are 11 1/4". Does anyone know the length of their hydralic push rods? They are the length of the old ones. The engine sat for 20 years. Could the metal crystalize? When its running it runs real good. More to follow.

Glenn,

Glenn,

Have you broken a new rocker arm that you replaced? This would be a big clue. As I stated earlier, I think any mechanical binding or seizing or piston contact would result in a bent push rod. If the rockers have broken, something has happened to them at some time to weaken them.

Stuart

Stuart,
No, the arms replaced have not broken. That has lead me to believe that fatigue could be a factor. I also agree with you about the valve siezing in the guide. I don't think it would loosen up right away or at all. During the adj I bring it up on #1 firing and rotate to #6 firing. As I say she runs great though I think the valve train is really noisy. She is getting oil to the rockers though as you know with these low pressure engines it is just a trickel. I'm pretty sure the lifters are pumping up because I don't get any give when pushing down on them after it has been run. I do get some give if it hasn't been run. Am I of correct thinking?

Glenn,

The only hydraulic lifters I have adjusted were on a V-8. This was always done warm, with the engine running. I am not sure I would adjust a hydraulic in any other way.

Again, my limited experience has been that once a lifter is pumped up, it will stay that way for many moons...it will not collapse or leak down. Maybe a motor will slightly worn parts will leak down.

I think this is a moot point..a distraction. If you have replaced rocker arms and they are now functioning properly, the problem is solved. If you have time to spare, you can brainstorm why it happened, but sometimes the problem gets solved without knowing what caused it.

Stuart

GEC52,

Good to hear you got it running. My valve train was still noisy after the adjustment, and I let it run for 5-10 minutes at a higher RPM and the noise disappeared a little at a time until finally it was quiet. Now when I start it, no more clatter.

Correct valve adjustment is very important.
The engine should be warmed up which takes about 1/2 hour. The difference between a cold and hot engine can be .005.

I line the ball on the flywheel up with the pointer. Remove distributor cap and rotor should be pointing to #1 plug wire location on the cap, Follow Step 1, then Step 2, then Step 3.

-- or it will be pointing to #6 plug wire-- this is OK.

If it's pointing at #6, start with Step 3, then Step 2,pointing rotor to #1, then Step 1.


Step 1. With engine set at #1, adjust - #1 exhaust & intake, #2 intake, #3 exhaust, #4 intake, #5 exhaust.

Step 2. Then, turn engine one revolution and line up ball with pointer and the rotor should point to #6 plug wire on the cap.

Step 3. With engine set at #6 adjust - #2 exhaust, #3 intake, #4 exhaust, #5 intake, #6 exhaust & intake.

When you start it up if it's noisey let it run for awhile. The noise should go away.

Keep us posted.

Could the rocker shafts be upside down ?

Tim,
That's a good question and I have thought about that. The 3 tower holes are on the top and the 6 holes are on the bottom. The shafts have larger holes on top than on the bottom due to the shoulder on the bolts. So, I can't put them on wrong. Thx Tim.

Oilrag,
Yup, thats how I do it.However, I haven't been able to quiet them down. How much do you turn them after you have taken the lash out? I have used between 1/4-1 full turn. I can hear the darn clatter over the exhaust across the street. I'm hoping my broken rocker arms have been metal fatigue because the engine hadn't been run for 20+ years. The valves arn't stuck. Plz sent any advise on adjustment. Thx.

Glenn,

Oilrag,
I just noticed the bottom of your post states 56, 235. Maybe there is a noise difference due to the fact that you have a full pressure oil system. My 235 is a 51 with low pressure. About as high as it gets is 5-10 psi. 10 when its cold and 5 after heating up. The rockers look well oiled after driving it though. It really makes you wonder how those lifters fill up.

Glenn,

I am still a little confused on this adjustment idea. If you are dealing with an engine that has been in service, and not just assembled after a rebuild, you adjust hydraulic lifters with the
engine running. These old sixes don't spray oil like the V-8s, so the mess factor isn't there.

Timing/crank position isn't a factor..start the rig, let it warm up, pull the valve cover and back each rocker off until it makes noise, then tighten it down until quiet. Then tighten it down the suggested 1/2 or 3/4 turn.

I am not familiar with the low pressure engines that have hydraulics, maybe they operate differently, but a normal engine will have NO lifter noise when adjusted properly. I think this was the point of the power glide/hydraulics combo...civilized, quite, modern!

Stuart

No one has taken my suggestion that it may be the lifters themselves. I may be wrong but I still believe the culprit may lie there. Perhaps the wrong lifters, perhaps worn out, maybe something else but it sounds suspicious to me and is certainly worth a look and not too difficult to do. The one hole I see in my logic is the fact that it has always been intakes that have broken (?) If I'm all wet it sure won't be the first time.

Dave,

I have seen your suggestion about the lifters. I haven't figured out how they could be at fault. It seems that if they are collapsed 100%, they are now solid lifters. I don't think a fully collapsed lifter can pump back up if it is adjusted "as a solid".

The minimal oil pressure only has to fill the lifter. The little disc valve holds the pressure in the lifter.

Under the worst case scenario, maybe the lifter was partially collapsed, adjusted to 1 turn after quiet, then pumped up and bottomed the valve spring, breaking the rocker arm. I don't think that could happen, mechanically speaking.


It appears the problem is solved by replacing the broken rocker arms, so one would assume that they were the problem.

I have my beach towel handy, I might be all wet too!

Stuart

I guess I really got the group goin on this one. Stuart- the eng has not been in service for the last 25 years. It sat in a barn. I did not replace anything but acouple of lifters and the carb. She started right up and does not burn or knock and runs great. I'm hoping the new arms took care of it. It drove fine yesterday. She is just noisier than hell. I do adjust it with the engine running. I think I might go for another 1/2 turn and see how that affects it. Dave- I have kept your suggestion to look at the lifters in mind. They all appear to be pumped up . There is no noticable difference in the adjustment screw heights. So, I am assuming all are pumped since not all would have collapsed. I just plugged the oiler drain side. That seemed to increase the pressure abit. I am thinking my oil pump is weak. SO, other than the noise I'm happy with the way it is running. I want to thank everyone for their advise. I'll let you if it breaks again. Thx.
Glenn,

bet those 25 yr lifters were stuck,,,were collapsed,,, and pumped up in a combination of all three... so if stuck, some were running solid... some wont pump up... so forth... in your case id think ya want noise untill they break free if they do... try runnin them a little loose and add about a quart of autotransmission fluid to the oil and run it for a while easy, (dont hotrod it) to see if it will clean up and pump up the lifters,,,then try readjusting all of them......the transmission fluid is an old trick for weak lifters....the transmission fuild wont compress as easy as oil...or sumthin like that..... anyway it worked,,,

Fatweed,
I tore down the lifters before I ran the engine. Thats why I replaced two of them. They all worked well on the bench. I might pull them again however just to check them out.
Glenn,

1950-53 Passenger W/powerglide push rod is 11 1/4" long. Part # 3835777

Also here is some good information from the 1949-53 Chevrolet shop manual about lifters and adjusting valves.

It says there is a certain amount of oil leakage between the plunger and the lifter.
It also talks about a small amount of "leakdown" is desiralbe for it eliminates the possibility of a "negative valve lash clearance condition.
Note: After the engine has been standing for a considerable length of time, a certain amount of valve lifter noise will occur when the engine is first started due to "leakdown" on those lifters which were holding valves open against spring pressure at the time the engine was stopped.
http://chevy.tocmp.com/1949_53shop/06engine/6_007.HTM

Valve lifter noise
Hard rapping - stuck lifter
Moderate rapping - leakdown or clogged air vent in pushrod seat
General noise throughout - insufficient oil supply
http://chevy.tocmp.com/1949_53shop/06engine/6_010.HTM

How to adjust valves.
Although it says 1 1/2 after zero, everyone says 1/4.
http://chevy.tocmp.com/1949_53shop/06engine/6_012.HTM

Here's a good article.
http://www.speedprint.com/Deves50/valveadjust.php

atomarc,

I agree with you about adjusting hydraulic valves on a V-8 with the engine running. That is pretty easy when the adjusting nut isn't bouncing up and down. On these 6's the rocker arm is on a shaft, and the arm is bouncing up and down. It's pretty difficult. It only took me 5 seconds to realize that I can't get a flat head screwdriver in the slot, let alone keep it there and tighten the lock nut.

Oilrag,

Great bunch of info and links you provided. I just want to note that I have adjusted many stovebolt valves, many Perkins and Caterpillar valves (solids) and who knows what else. All these had the adjuster located on the end of the rocker arm, just like the Chevy 6.

I'm not trying to be a smart arse, but it takes longer than 5 seconds to get the hang of how to do this with the engine running. The wrench gets oily and hot, and the stubby screwdriver hops around, but you get a accurate job and it doesn't take long to get the hang of it.

I worked in a auto repair shop as a kid, and this is how they did it...I didn't know any other way. The only downside to this operation is the toll it takes on the feeler gauge.

Stuart

Take this with a grain of salt because the only experience I've had with hydraulic lifters was in my old HD shovelhead. I did find out first hand there that a tiny piece of dirt or crud will keep a lifter from pumping up, resulting in constant lifter clatter. Since the truck sat for so long some crud may have come loose and contaminated your lifters. Just a thought.

Another thought (I do that once in a while ) the hydraulic lifters on my old HD were directional, meaning that the oil hole in the lifter had to be on the same side as the oil passageway in the engine. Many times I helped "fix" noisy lifters by turning them around after an unknowing person put his lifter(s) in backward.

Tiny,
You make good points. The more I read and adjust the more I'm thinking it is lifter noise and not valve clatter. Oilrag great sites. Thx a bunch.

Glenn,

bump

Chuckthetruck,
It is so cool to see these old trucks brought back to life.

Glenn,