Is this motor a goner?

[65standard]

I have been struggling trying to get the 250 engine in my junkyard rescue truck running right. Idle is the biggest issue. I replaced the plugs, intake gasket, and rebuilt the carb. It still won't low idle.

I did a vacuum test and it only has 11 inches of vacuum. Sounds like a vacuum leak, but I can't find one. Then I do a compression test.

Cylinder 1-6 are 155, 155, 0, 160, 165, and 155.

Then I pulled the valve cover and found the intake valve stuck on the #3 cylinder. This looks fatal to me.

[geezer#99]

Squirt some penetrant around the stem and wack the valve tip with a hammer. Put a block of wood on the tip.

[chip46wis]

Agreed but somewhat gently on the hammer and graduate from there.

[swamp rat]

I'd use a soft dead blow hammer on the top of the valve of you have it, definantly use a block of wood with a steel hammer, try and get the valve to move free. There is a good posibility the piston may have struck the valve and ether bent or broke it. This is when a goos micro camara can tell a lot going in thru the soark plug hole.


I'd alsoull the lifter inspection cover, pull the pushrood and see if its bent, see if the lifter is frose up on the lifter bore or if it moves, if it is you need to try and remove it, once out see if it and the bore are galled up, try and clean them up.

[65standard]

I'll try to spray it with oil and break it loose. But when I see a valve stuck open, I'm thinking it is bent because the motor ate a bolt or something down the carb.

[kwmech]

Is it stuck or is the spring broken

[hamjet]

I'd be concerned using a block of wood to hit against. if its soft wood like pine you're liable to sink the valve stem into the wood and then when the wood makes contact with the retainer you're likely to pop the keepers out and the spring will pop out. Be carful you don't hit on the retainer, thats all. Worst case is you'll have to pull the head and get it cleaned up with valve job. Unusual for the intake to get gummed up.

[hamjet]

"""I'm thinking it is bent because the motor ate a bolt or something down the carb.""" do you think thats what might have happened?

[65standard]

Well that is my first thought since I don't know the history of this truck. But it may be just stuck because it sat in the junkyard for 18 months before I rescued it.

[GRX]

Was the engine run with bad gas? Very bad gas? Smells like Turpentine. I have seen *many* intake valves stuck in the guide because of sticky varnish from bad gas. Like geezer said try spraying some solvent around the guide. Denatured alcohol works well for that. Then strike it with a plastic hammer.

[Norgermish]

Originally Posted by GRX

Was the engine run with bad gas? Very bad gas? Smells like Turpentine. I have seen *many* intake valves stuck in the guide because of sticky varnish from bad gas. Like geezer said try spraying some solvent around the guide. Denatured alcohol works well for that. Then strike it with a plastic hammer.

Excellent point about the gas. Also to allay bent valve thoughts I don't think there is ever any interference between valve heads and pistons on these engines. Pretty sure the open valve does not extend past the combustion chamber. Now when the intake was off and a not or bolt may have squirrled into the port, that could be a problem. Bad gas makes a lacquer and it creeps up the valve stem and will definitely hang a valve

[NTIMID8R]

Remove the spark plug for that cylinder and use an air blower with a rubber tip and see if it will move back up with a little air pressure. Better than prying up on it and risk bending it if it's not bent yet. Like others said, may just be gunked up. Also works if you need to change a valve spring.

[mgchevyparts]

How about rebuilding it so it's correct and will run good.

[enaberif]

Originally Posted by NTIMID8R

Remove the spark plug for that cylinder and use an air blower with a rubber tip and see if it will move back up with a little air pressure. Better than prying up on it and risk bending it if it's not bent yet. Like others said, may just be gunked up. Also works if you need to change a valve spring.

This is a good idea but a better one is to actually pressurize the cylinder then tap gently on the top of the valve stem. This will help it become unstuck and allow it work properly.

You only need a few psi for this to actually function.

[WIDESIDE72]

Originally Posted by Norgermish

Excellent point about the gas. Also to allay bent valve thoughts I don't think there is ever any interference between valve heads and pistons on these engines. Pretty sure the open valve does not extend past the combustion chamber. Now when the intake was off and a not or bolt may have squirrled into the port, that could be a problem. Bad gas makes a lacquer and it creeps up the valve stem and will definitely hang a valve

x2

[65standard]

Yes, it has about 45 minutes run time with orange rusty looking gas. I have since pulled the tank and cleaned it along with the lines and carb.

[GRX]

Cool deal. Glad you got it running. The reason behind the stuck valve was obvious. Seen it many many times. Be sure all the old fuel is flushed out and you should be good to go.

Originally Posted by 65standard

junkyard rescue truck

Originally Posted by 65standard

Yes, it has about 45 minutes run time with orange rusty looking gas. I have since pulled the tank and cleaned it along with the lines and carb.

[snipescastle2]

anytime I ever had a lifter start ticking on me, I added half a quart of atf to the oil. the detergent in the atf helps break up carbon and varnish and stopped the ticking noise, then I just did another oil/filter change. I have never used seafoam, can't vouch for it. but atf sure worked for me. I would get your fuel tank boiled out to remove any varnish/deposits that may still be in there. One note, when you see a Gasloline tanker filling up the tanks at your favorite gas station, keep driving until you get to a station where there isn't a tanker filling the tanks, reason being, once they start filling the tanks, it stirs up all the crap and debris on the bottom of their tanks, the pumps have a fuel filter on them, but I wouldn't trust that.....just my opinion.
HTH,
Ben Smith

[GRX]

Hmmm ... I'd lay money down that is what caused it. Especially since it is one of the center cylinders. Hopefully the piston did not smack the valve.

One time a guy dropped off an old Dodge 225 slant 6 engine to be rebuilt. Long story short ... after bringing the head back three times with stuck intake valves, and complaining we made the guides too tight, he finally flushed out the fuel system. Problem solved. The smell & varnish on the valve stems told me instantly what happened but he was too stubborn to listen.

[65standard]

Thanks for the tips. I will try to unstick the valve. I'm hoping to save it since I just put a new exhaust on it. And I finally got the exhaust to stop smoking so bad. The thing is the motor runs good now above 1500. Below that it sneezes through the carb.

[hugger6933]

Instead of tapping it down what about a gentle pry upward after spraying some carb cleaner on that valve to see if you can "degunk" it? That would be after the inspection cover is removed to make sure the lifter isn't stuck in the bore or you have a bent pushrod. I would spray carb cleaner on that one valve then pry up a little then push down a little about the same amount you get it to move up. If you do that a couple times it will move a little more each time you make it move. Jim

[Coley]

I also agree with the possible broken valve spring theory. I recently went through this issue on a cylinder that went to '0' psi compression.
Look very closely at the spring and run your fingers around all the coils to either identify that possibility....or eliminate it.
Coley

[65standard]

I'll mess with it tonight. Yesterday's fun factor was at zero too. I feel better today with new hope to save it. I just want to thank everyone with all of their advise.

[SCHRUMGMC]

Yikes !!!

That doesn't look good

[65standard]

Okay, good news. I got the valve to pop up after 15 minutes by using compressed in the cylinder, carb cleaner, and gentle taps. Then I sprayed some WD40 around the stem and put the pushrod ans rocker back on. Did another compression test on that cylinder and it is 150psi.

This tells me the valve and piston are not damaged. Now, what is the correct procedure to do to prevent the others from sticking. I'm also worried that I might have flushed out the rings on that cylinder from the carb cleaner.

Thanks again for all of the great advise everyone, much appreciated.