Compression Question

[BAMM71]

Hey all, long-time lurker here.

I recently acquired a 71 C10 with a 350/3 speed (on the floor). It was, of course, running and driving and then I ripped the exhaust loading it on the trailer...which snapped the manifold...this can go on and on.

It had what I thought was a misfire. Pulled the cap and rotor (HEI) and replaced those, plugs, and wires. The same hitch in the giddy-up was still there. I pulled the plugs and the number 3 plug looked brand new :/ I did the compression test 140-145 in every cylinder and ZERO in number 3. I pulled the valve cover and nothing seemed amiss...turned it over and one spring on intake side wasn't compressing. I hit it with some cleaner and let it soak and then everything was moving properly again. Stuck a cloth in the cylinder and bumped it and the cloth went flying. So confused. I was thinking if it were a hole in the piston I would have no pressure. This is new territory for me but I'm open to thoughts and suggestions and not scared to get dirty.

[geezer#99]

Sounds like a sticky valve on #3.

[BAMM71]

Originally Posted by geezer#99

Sounds like a sticky valve on #3.

Thoughts on unsticking said valve or posts/links that may be helpful?

[geezer#99]

You already got lucky letting it soak.
Likely best to remove that rocker, spring and retainer, hold up the valve with air or a rope and clean it some more.

[BCOWANWHEELS]

bet lobe on cam is bad

[BAMM71]

Update:

I did some digging and read a bunch on valve lashing. I hit it with the feeler gauge and it was a little on the tight side so I gave it a 1/4 turn. Not sure if it's a combination of soaking and the valve lash turn but I'm up to 80psi in that cylinder dry which is promising. So, I don't think it's the piston (good) but I'm thinking I"m going to rinse and repeat the cleaning method to try to get more carbon out. I think if I can get 120 out of it, I'll be happy. I can pull the heads this winter and play that game. I started it up and let it get warm and then checked the plug and it looks like it's finally getting some love versus looking brand new which is a good sign to me.

I'm reading that pouring Chemtool or Seafoam etc down the carb directly may have an impact on burning some of that carbon off and that may help. i'll do that tomorrow and then I'll pull all the plugs again and get a compression reading. I guess that's going to bork the plugs but buying new plugs is cheaper then a top end rebuild.

[Steeveedee]

Leaking intake valve seals can leave enough deposits on the stems that you can get little flow past them. I've seen some little-old-lady cars that I was amazed they even ran, there was so much crud deposited on the valves. Approach the loosening of those valves carefully, because it can fall off in clumps and really make a mess of things...if that is what it is.

[geezer#99]

Originally Posted by BAMM71

Update:

I did some digging and read a bunch on valve lashing. I hit it with the feeler gauge and it was a little on the tight side so I gave it a 1/4 turn

That’s interesting!
You don’t set lash on a hydraulic cam with a feeler gauge.
With a solid lifter cam, you do.
With another 1/4 turn you might have the valve slightly off it’s seat.

To clean carbon build up on pistons I use free stuff. Water right out of the tap.
Trickle a bit in the carb at a high idle. Water turns to steam. Don’t use much. Maybe a cup.

[BAMM71]

Thanks for the response, I’ve got a lot to learn. You’re referring to the loosening I did l, not the idea of burning that carbon off via chemicals, yeah?

[Steeveedee]

Originally Posted by BAMM71

Thanks for the response, I’ve got a lot to learn. You’re referring to the loosening I did l, not the idea of burning that carbon off via chemicals, yeah?

Yes. I'd be careful with that, since if there is a lot, it could make a mess, get stuck on the valve faces and seats, etc. There are products that you can use to get rid of the carbon (again, if that is what it is) when there isn't a lot of it. You probably would have to take the intake manifold off to verify that, though. Do you know how the truck was driven in the past?

[BAMM71]

@geezer

I"m not afraid to admit I'm still learning all these things. I was researching a lot and sounds like what I did was not appropriate or ideal. Here's one for you then, a couple of the rockers were jiggly. Do those need to be tightened down or do I leave them be? (ain't broke, don't fix it?) Regardless, the difference in sound and compression is factual so, I'll not mess with those anymore and focus my efforts on cleaning carbon and see if that yields the results i'm looking for.

I've never heard of pouring water down the carb but a quick google search here and on other forums seem to align with your thoughts! I appreciate the insight and I"ll give it a rip tonight and give you an update.

[geezer#99]

Lifters/rockers can be jiggly.
The water treatment comes from a time way back in the past. In the early 60’s. Dishonest mechanics used to do the ‘six ounce’ tune up. They’d use 6 ounces of tap water trickled in the carb to clean out the carbon. Zero cost to them in parts, happy customer since it ran like new. That eventually went away when customers caught on and wanted to see their old plugs.
Remember!
Don’t pour, just trickle on a warm motor.

As a side comment, I can hear keyboards being tapped saying’ don’t do that, you’ll ruin your motor’!!

[AussieinNC]

Originally Posted by geezer#99

Lifters/rockers can be jiggly.
The water treatment comes from a time way back in the past. In the early 60’s. Dishonest mechanics used to do the ‘six ounce’ tune up. They’d use 6 ounces of tap water trickled in the carb to clean out the carbon. Zero cost to them in parts, happy customer since it ran like new. That eventually went away when customers caught on and wanted to see their old plugs.
Remember!
Don’t pour, just trickle on a warm motor.

As a side comment, I can hear keyboards being tapped saying’ don’t do that, you’ll ruin your motor’!!

If you do the water clean out correctly you will not hurt any of the engine parts....I use a small spray bottle filled with tap water....get the engine warmed up then set idle around 1500....with the air filter off, just trickle small amounts of water directly into the carb intake...the engine speed will drop a little, but will recover...the water combines with the fuel and air and creates a process that burns off carbon deposits...

On the rocker clearance...
if its hydraulic cam there should be zero lash when the engine is running...with engine running, back the rocker off until it clacks, then slowly tighten down a quarter turn at a time until the clack stops,,,then one more quarter turn....

If its a mechanical cam, set rocker clearance around 12 thou with the piston at TDC on compression stroke....it might be a little noisy but at least it will have clearance.

Let us know how it goes....

[BAMM71]

thank you all

Tried some water and still received the same results after I put it back together. I think the only logical step is to pull the intake manifold and see what I can see. Hopefully, something sticks out at that point. Otherwise, it's pulling the head on that side...and if I'm pulling one, I reckon I might as well pull them both.

[AussieinNC]

Before you rip it apart try the following:

Remove the rocker cover on the offending side....grab a dial indicator and measure the amount of lift on each valve...make sure the dial indicator is in line with the valve stem.

Turn the engine by hand in normal direction of rotation.

If the lift measurements are all around the same value, the issue is more likely a burned or partially bent valve.

If the valve that was "stuck" has a lower lift value than the others, it is most likely a bad cam lobe or a collapsed lifter or both.

To me, it sounds like a partially bent valve or burned valve, or as others have indicated it may be a bad cam lobe....

If its a bad lobe, do yourself a huge favor and pull the engine and do the repairs on a stand,,,,think about it....unknown engine history, misfire due to low compression on one cylinder, if you pull the heads with the engine in and then find excess bore wear....even replacing the freeze plugs is so much easier with the engine out.

If its a bad lobe, and sticky valve /s, I can almost guarantee the piston rings are most likely stuck and valve guides worn...

Remember to have fun...

[Steeveedee]

Yup, smarter to check that before doing a valve job. I'm suspecting that when the heads come off, there's going to be enough ring ridge that a bore job would be in order. In for a penny...