Got to actually see an intake valve burn today.

David G

Well-known Member
We are working on putting fuel injection on a 4000 HP natural gas engine. Another company does the injection controls, and I control the engine and turbo. Temperature sensors were added on the intake right next to the valve, one of them started running hotter and hotter due to the leaking combustion gas. They did a scope on that cylinder and sure enough the valve was being cut. This might have been starting before the conversion, or caused by debris left in the cylinder due to new intake and parts, do not know.

These engines have a pre combustion chamber that replaces the old spark plug. It is interesting, because there is an injection controller for the pre chamber, and another for the main chamber. In my view you have two places that might not have the right mixture. I guess that they have an option that monitors the coils and looks at the plasma field to determine if the pre chamber is combusting correctly. The main chamber has a pressure transmitter.
 
I felt one doing it on my uncles 292cid F250 while taking it to school to do the valve job. (about 200 miles) Interesting to learn about these big engines. Jim
 
The first one I did was high pressure (500 PSI) direct injection two stroke. This one is a low pressure (85 PSI) four stroke, with the spark plug being replaced with a pre ignition chamber / spark plug combination and port fuel injection. It took them about a dozen tries, each time upping the starting fuel to get it to fire. It was galloping pretty good after starting, not enough time to get tuned before bad intake valve was detected.
 
This is for work, this is my season to work on the natural gas compression projects before winter, usually ends up being about 3 months at various sites.
 
I've only seen one intake actually "burn".

This was on a 350 Chevy in a boat. I had done a hone, ring, and bearing job, sent the heads off and had them worked.

Put it all together, took it for a test run, all seemed good, ran good. Told the customer to take it easy the first few hours.

I suspect his idea of break in though, was to run it wide open, see if he could blow it up under warranty, just struck me as that type person.

Well, the next Monday, there it was, no compression on one cylinder...

I pulled the head, the intake valve was rusty red, like it had been glowing hot. The center was pulled in to a cone shape, and about a 1/32" gap all the way around. Didn't appear to be any damage to the piston, no evidence anything had hit the piston or valve. Took the head back to the shop that did them, they replaced the valve, cleaned up the seat. Said they had never seen that happen either.

Put it back together, guess it worked, no more complaints.
 
Think it was some of the 1988 GM truck 350s that pulled the intake valves through the seat.
 
Several of us Air Force flight line mechanics back in the 1950's "did in" the valves on our cars burning 115/145 aviation gas we swiped out of ground power units.... (MD-3's and C-26's). We tried just to mix it in with regular commercial pump fuel but, well, sometimes we used a little too much av/gas in the mixture and the valves got a little too hot I guess.
 
(quoted from post at 08:05:22 09/01/17) Several of us Air Force flight line mechanics back in the 1950's "did in" the valves on our cars burning 115/145 aviation gas we swiped out of ground power units.... (MD-3's and C-26's). We tried just to mix it in with regular commercial pump fuel but, well, sometimes we used a little too much av/gas in the mixture and the valves got a little too hot I guess.

What is 115/145? octane?
 

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