304 odd vibration

W

wlcantrell

New member
1978 304, flat top heads, original IH not touched internally.
No California emissions
prestolite electronic dist
90k miles on the odometer
kids have played with it for the past five years for fun and school. Check the oil, yea sure Dad!. Last spring the kids took the Scout to play in mud puddles and the Scout got a good drink of water in the intake.

A few months ago, I noticed an odd vibration,not noisy, when accelerating (it passed emissions with this problem). Happens under load and not. So, since the engine was inches deep in grime, I decided to pull it and see what was what:

replaced gaskets and freeze plugs. Freeze plugs were weeping, so May have had a problem with cyl walls overheating. Did not see that the engine itself overheated.
120 + compression in all cyl with all plugs removed.
Replaced plugs (gapped 35), coil, cap, rotor and plug harness. Checked the harness firing order like a dozen times...
"visually" inspected the valve train using the starter to turn the motor, and each valve seemed to articulate as it should.
No valve train noise.
Oil pan was free from shavings and chunks of stuff. There were a couple of aluminum shavings, kinda looked like shim stuff, but could not identify where it would have come from.

Stuffed the engine back in, and still had the same vibration. After a couple of days, pulled the plugs and #6 looked dead, no tan color on the tip. Replaced the plug and ran for a couple hundred miles. Pulled #6 again a little bit of tan, but not as much as the others. Ensured that #6 was getting spark. Oww! Yep it is.

So today I pulled the rocker assembly on that side to see if I had a bent push rod or collapsed lifter. Lifters that I pulled are slightly concave but are not collapsed. All of the rods are straight, don't see any problems with the rockers.

Whadda think? My buddies are shouting that I probably have shot the cam or a cam bearing.
 
Do you have or can you at least temporarily connect a wet op gauge? It would be helpful to know what your hot op is both at idle and during sustained cruise. Non-ferrous metal pieces in the pan could well be kibble from a failed cam bearing. Insufficient or erratic hot op readings would be confirmation. A layer of grey sludge in the pan is also indicative of sloughed babbitt from a bearing or bearings that have de-laminated. How are your engine mounts? Does the engine rock excessively to one side when the throttle is blipped? This could account for the vibration. Of course any time water is sucked into the combustion chamber, the possibility of hydro-lock exists, which can cause internal engine damage.
 
The engine mounts were replaced with other cleaner mounts when I pulled the engine. I don't have a lot of movement in the engine bay when I punch the motor. I don't have a mechanical oil pressure gauge handy at the moment.

It makes sense that the debris in the oil pan could have been cam bearing stuff. I just hadn't thought about it that away.

If I do decide to replace the cam/bearings, it would be best to re-ring and hone as well. What is the best way to take care of the composite vs steel head gasket issue? I really don't want to pull the block and have it decked at this point unless I really need to.

What about hydro lock? What would the symptoms/damage be?

Thanks
 
If cam bearing damage is conclusive, you won't be replacing the bearings without first pulling the engine.
Damage from hydrolock can include bent or broken connecting rods, a fractured head, a fractured block, crankcase damage, damaged bearings, or any combination of these.
My only head gasket experience on these engines has been with the composite design and there wasn't any surface machining involved, so I can't really answer that question.
 
scoutboy74 said:
if cam bearing damage is conclusive, you won't be replacing the bearings without first pulling the engine.
Damage from hydrolock can include bent or broken connecting rods, a fractured head, a fractured block, crankcase damage, damaged bearings, or any combination of these.
My only head gasket experience on these engines has been with the composite design and there wasn't any surface machining involved, so I can't really answer that question.
Click to expand...

Yup, pulling the engine, is a far cry from sending it off to the machine shop to be decked! If anyone can help with the steel vs composite head gasket please chime in.

Scoutboy74, thanks for your input.
 
Is this a manual trans rig? If so was the pressure plate removed. There May be mud stuck in it causing an imbalance. Since it is present load/no load it seems like a balance issue. I had a pressure plate fail once where the mount of the plate to the housing broke. I pulled the whole engine apart and sent in for balance. The pp came back from the balance shop with a big chunk of iron welded to it. I think that was a clue, perhaps is was the burnouts I was doing before the vibration started.
 
fdchappie said:
is this a manual trans rig? If so was the pressure plate removed. There May be mud stuck in it causing an imbalance. Since it is present load/no load it seems like a balance issue. I had a pressure plate fail once where the mount of the plate to the housing broke. I pulled the whole engine apart and sent in for balance. The pp came back from the balance shop with a big chunk of iron welded to it. I think that was a clue, perhaps is was the burnouts I was doing before the vibration started.
Click to expand...

Yes. Manual trans. I did not mention in my original post, the pressure plate was ground and I had the clutch pack remand. So, that could be a variable in the equation. But, the vibration has been consistent before the engine pull and after.
 
Before doing anything more like pulling the engine. Verify lifter rise on #6 and others. Not valve lift but lifter movement. Meaning pull the rocker assembly and measure the lifter range of movement...
Verify all cylinders are generating the same exhaust temperature at a sustained rpm like 2000 with no load.. A non-contact or infrared thermometer will do or a thermocouple addition to your digital vim (harbor freight). Reading taken at gasket plane or at short manifold stub just adjacent to the gasket surface. Allow enough time for things to heat up and stabilize like 2 minutes or more at rpm.

I am recommending these options based on the information you have provided here. Anything left out that you know makes this thread a wgs (wild goose chase) sorry to say..
 
Robert kenney said:
before doing anything more like pulling the engine. Verify lifter rise on #6 and others. Not valve lift but lifter movement. Meaning pull the rocker assembly and measure the lifter range of movement...
Verify all cylinders are generating the same exhaust temperature at a sustained rpm like 2000 with no load.. A non-contact or infrared thermometer will do or a thermocouple addition to your digital vim (harbor freight). Reading taken at gasket plane or at short manifold stub just adjacent to the gasket surface. Allow enough time for things to heat up and stabilize like 2 minutes or more at rpm.

I am recommending these options based on the information you have provided here. Anything left out that you know makes this thread a wgs (wild goose chase) sorry to say..
Click to expand...

Thanks for the direction. It will be a couple of days before I get back to you. As far as wgs, I'll do my best to not. What would the difference between the cold and hot oil pressures told me?
 
Hope you did't take offence from wgs but leaving out any seemingly innocuous detail could change the whole picture in some circumstances. Not saying that you did but I've been foiled by them before... :p

oil pressure changes hot to cold..... Really to many variables to say for sure what you find means. I would say that 180f degree oil @ 2500-3000 you should have oil pump releif valve pressures built up.. 35-40 psi on a sound engine, @ idle 850-1000 8-10 psi?
 
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Robert kenney said:
hope you did't take offence from wgs but leaving out any seemingly innocuous detail could change the whole picture in some circumstances. Not saying that you did but I've been foiled by them before... :p

oil pressure changes hot to cold..... Really to many variables to say for sure what you find means. I would say that 180f degree oil @ 2500-3000 you should have oil pump releif valve pressures built up.. 35-40 psi on a sound engine, @ idle 850-1000 8-10 psi?
Click to expand...

No problem! Took the rocker arm assembly off the other head last night. Visual inspection looks good, no bent rods.

Is there a good way to measure lifter rise short of a cam checker?
 
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Easy, place a cleaned (wipe it down with carb cleaner on the outside) push rod into the lifter, Mark it right where it comes through the head at the low lift point and rotate the engine till it reaches its max lift point and Mark it again. Measure the distance between the two lines.....

It May be hard to find the max lift point if bumping it over with the starter so turning the engine slowly with a ratchet on the balancer bolt will make it easier.
 
Check and make sure the harmonic balancer is tight and does not wobble on the crank. Please don’t ask me why I suggest that. :icon_mrgreen:
 
Lifter rise measures our caliper was in 12ths, so we had to round a bit. We did our best to be precise:

left (drivers) right
I .250 e .265
e .234 I .234
I .25 e .250
e .218 I .250
I .234 e .250
e .234 I .250
I .218 e .250
e .203 I .250

interesting note, all of the plugs were fouled when I pulled them. The motor now has about 400 miles since the pull. Prior (after 100 miles) they were clean and had that nice tan color to them.

Next steps: reinstall the rocker assemblies and recheck compression and check exhaust temp as requested.
 
wlcantrell said:
1978 304, flat top heads, original IH not touched internally.
Oil pan was free from shavings and chunks of stuff. There were a couple of aluminum shavings, kinda looked like shim stuff, but could not identify where it would have come from.

So today I pulled the rocker assembly on that side to see if I had a bent push rod or collapsed lifter. Lifters that I pulled are slightly concave but are not collapsed. All of the rods are straight, don't see any problems with the rockers.

Whadda think? My buddies are shouting that I probably have shot the cam or a cam bearing.
Click to expand...

1. The metal in the pan is part of a cam bearing.
2. Lifters are not concave on the bottom, unless they are worn.
3. A worn lifter base indicates a worn cam lobe.

1+2+3=replace the cam, lifters and cam bearings.

Otherwise, you are just spinning your wheels.
Sorry for the bad news.
 
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