Engine Issues

[bigben5054]

Went out tonight and turned the engine over by hand several times, watching the lifters.  They all seem to come up all the way.  Cam is good.

[JohnnyPopper]

Well that's a relief!

The pic that showed the valve open didn't look bent.

Sounds more like it seized in the guide.

Look forward to more news, and THANKS for keeping us updated! Means a lot.

[bigben5054]

Maybe it was a bad picture, but it was bent for sure.
I have not heard back from shop yet, but I have a new theory.  What if the gas was really old and it gummed things up enough to cause the valve to hang open and that is how it got smacked by the piston?  Embarrassingly, I don't know what kind of gas is in the truck or how long it has been in there.  I do know its the same gas from when I bought the truck in September 2018.  I have no idea how long that gas was in there before I bought it.  I also know that when I took the intake and carb off (just recently I mean), I turned the carb upside down and drained the fuel bowls.  The gas looked darn near red.  Needless to say, I need to figure out how to empty these tanks and get some fresh gas in there, but do you suppose this could be the culprit? 

[bigben5054]

Machine shop called.  He said the guides on the exhaust side were too tight, causing the valves to seize.  In addition to the bent valve, he said he had to replace 2 other exhaust valves because the stems were galled up so bad.  He suggested I pull the other head and bring it in, so I'll be doing that when time permits.

[JohnnyPopper]

I suppose bad gas can have an effect, but will wait till others weigh in...  Caustic gas?

One would think that modern guides are designed to work with the lack of lead.

These were rebuilt, right? Have you checked with the supplier?

There may have bee a bad run of parts and they are experiencing the same thing on other heads they've sold.

[bigben5054]

Machine shop said bad gas would just make it run bad.  I bought the heads off a guy that said he bought them new from one of the online places like Summit or Jegs.  Said they were supposed to be good for .500 lift cam.  He had them on his motor only briefly, but never could get motor to run right so he bought a crate motor and was selling these (and some other parts).

Now, I don't like to buy such critical engine components used from strangers, but I thought I was pretty careful about these.  No visible damage and they looked consistent with what he was saying as far as them only being run a little bit.  On top of that, I could see for myself that the guides and spring pockets had been machined (like they have to do on Vortec heads to get them to accept bigger valve springs).  And they only reason to do that machining work is to allow a higher lift cam.  The other thing the machine shop guy said was that he had to re-grind the exhaust seats because they way they had been done, the valves weren't even sitting on the 45*.  Makes me wonder about where these big parts stores source their heads from.  I  wouldn't be surprised if they are being reconditioned and machined in Mexico or something by people that might not have any business doing that work.

I wonder if my problem was a combination too little clearance and letting it get too hot on start up.  I had posted about the motor overheating on me when I was trying to break in the cam.  First time it ran about 5 minutes before I noticed the water temp gauge had pegged.  Second time it did the same thing, but I caught it faster because I was looking for it.  But she got pretty hot before I figured it out.  When I did my third run, it kept cool - never over 200 - and ran great for the 15 minutes or so I ran it.  It was right towards the very end of that long run when I heard it drop a cylinder.  I think the timing was pretty retarded when I did that too, which I understand causes excessive exhaust heat because of the late-burning fuel.

Anyway, its nice to have an answer.  Hopefully get it back together soon!

[bd]

...My problem was a combination of too little clearance...

...and insufficient lubrication.

...I bought the heads off a guy that said he bought them new from one of the online places like Summit or Jegs.  Said they were supposed to be good for .500 lift cam.  He had them on his motor only briefly, but never could get the motor to run right...

...The other thing the machine shop guy said was that he had to re-grind the exhaust seats because the way they had been done, the valves weren't even sitting on the 45*.

It would cause me to question the real reason the seller sold the heads.  And, were valves replaced after-the-fact to hide the truth - w/o fitting or machine work.  Caveat emptor!

[JohnnyPopper]

I bought the heads slightly used and they were assembled.  Just for good measure, I took them apart to wire wheel the valves and put new valve seals on them.

Sounds like you had the valves out- did you notice unusual tightness in the exhaust valves?

What blow my mind is it ran great until the end of the break in period, like 19 minutes, then the valves seized, 6 got smacked and bent, and poop ran downhill.

bd what accounts for the lack of lube? He used break in oil. No mention of overheating at this point either...

[bd]

Dissimilar metals expand differentially as they heat.  If there is insufficient clearance between the stem and the guide, there is also insufficient lubrication because of diminished space, which increases friction and heat, which decreases lubricity, and so on, until lubrication fails and one or both of the metals begin to gall.  At that point, there is zero clearance and the stem seizes.  Essentially, machine work and setup was lacking before bigben acquired the heads.  -JMO

[bigben5054]

So far, we only know of the one exhaust valve that was bent.  He replaced two other exhaust valves because of galling on the stems.  I have to pull the other head and take it in, so we'll see what he finds there.  Compression test 1-8 was 170, 165, 170, 160, 170, 0, 155, 150.  So I am not expecting any other bent valves, but wouldnt be at all surprised to find more bad valves due to seizing/galling.

I did have them apart and I did not notice any anything tight or unusual.  But I didnt measure it and we're talking about thousandths of an inch.  So probably not something I could tell by feel or eyeball.

I'll file this away in the "lesson learned" drawer and consider myself lucky that the heads weren't cracked or otherwise complete junk.

Question:  How are the valve stems lubricated once a motor is put together and running?  The valve seal should be preventing lubrication from the top side, right?  Another question, when I pull the other head, do I need to remove the block plug on that side to drain anti-freeze, or did removing the one on the other side drain them both (worked awesome by the way - not a drop of antifreeze anywhere up top).

[bigben5054]

Quick update - yes, you have to pull the block plug on both sides (got darn near another gallon out this side).  No bent pushrods or visible damage on this side.  Will take it in to machine shop later today.

[bd]

The valve guide seals don't block oil from reaching the stems, they meter the amount of oil that draws down the guides due to negative pressures in the cylinder head ports while the engine is running.  They also limit excess oil from migrating down the guides due to the pull of gravity while the engine rests.  Generally, I recommend Viton positive-stop seals used in conjunction with the square-cut o-ring stem seals that seat into the spring retainers.  Talk with your machinist.

The coolant jackets in the left and right halves of the cylinder block are physically isolated except through the water pump, cylinder heads, and intake manifold coolant passages.  So, yes, each jacket must be drained independently.

[JohnnyPopper]

Negative pressure on the intake valves right?

Exhaust valves are pressurized. Wonder how they get any oil except for gravity...

[bd]

Read up on exhaust scavenging...

Exhaust Backpressure and Cylinder Compression

[bigben5054]

Thanks for the info guys.  Very helpful.

Machine shop had to replace 3 valves on the other head and grind the seats.  All together, $185.

Back when I was planning this engine rebuild, I briefly looked at brand new, aftermarket, name brand, made in the USA aluminum heads and decided $1000 was too much to spend on this budget build.  So instead, I did this:

Bargain find, barely used Vortec heads:  $400
Required Vortec intake and gaskets:  $205
Centerbolt valve covers (another bargain find - nice tall aluminum ones):  $75
Machine work to fix bargain find Vortec heads:  $185
New set of intake/head gaskets:  $100
TOTAL:  $965

Can I have a do-over?