cummins 250, popping out the intake

[Pappa-G]

The truck has sat for possibly 3 years. When started it backfires through the intake. So there is either an intake valve hanging open or bad head gasket?? If it is the valve hanging open how much room is there before it starts smacking the piston? I pulled 2 of the 3 valve rocker covers and didn't feel any sloppyness in the rockers. It started snowing to hard so I didn't pull the last one. The batteries were dead so I was unable to turn the engine over. The coolant looks good (no oil funk floating around) and the dipstick wasn't dripping green and the level was good. Any ideas?
Thanks

 

[73m819]

not much room, i woulld think valve. i would even look for a bent valve or/ and pushrod

 

[Pappa-G]

Thanks Ron. This is also what I think. But how would a bent push rod keep it from closing? Wouldn't it keep it from opening completely? Also, how would I go about finding out which cylinder has the bad valve, compression check or is there a different way to tell?
Thanks

 

[CanadaDeuce]

well Ive drive semi for years, and of which many were hauling fuel, Sooooo here is a thought, may not be it but is there a chance there could be gasoline in the Diesel fuel ?, you may not have put it in but could have been dumped into tank at the station by the carrier who dumped it there, all it would take is if the driver had some gasoline in his truck tanks before he loaded and it mixed up.

A diesel engine will make alot of loud poping noices almost a backfire sound.

just a thought, If you are currious take a sample and take to a bulk agent he has a density tester and can verify if it is right for diesel.
If its out of wack you maybe not have just diesel in your tanks.

again might not be right here but thats my experience....... may not be mechanical

CanadaDeuce

 

[73m819]

the valve hiit a piston and bent, the push rod cant move the valve so it bent, this can go on till something breaks, KEEP way down the RPN

 

[WillWagner]

Re: RE: cummins 250, popping out the intake

the valve hiit a piston and bent, the push rod cant move the valve so it bent, this can go on till something breaks, KEEP way down the RPN

Could be a bent valve, but maybe not. If the cross heads are way out of adj or the intakes are real loose it will pop too. Fire it and feel the exhaust. The cold one is the problem cylinder. A bent PT will aso make it pop...changes the valve timing...same as a way loose overhead.

 

[rosco]

You can easily find which cylinder is not fireing : Start it slow and go out and hold your hand on the exhaust manifold port of each cylinder. They will begin to warm as each cylinder fires. The dead cylinder's port will be cold. With my luck, the problem is under that last valve cover. The problem can also from moisture/water, that stuck that valve open. If that is it & your lucky, with engine stopped, lube that valve stem with WD40 (or your favorite flavor), & gently bump that valve with a rubber/soft hammer. When it goes back to seat (with no cam pressure on that valve), you should be able to rotate that push rod with your fingers & see enough of it to see if its bent, when rotating.

Good Luck

Lee in Alaska

 

[73m819]

if bent, it wont come up

 

[rosco]

Naturally! But I don't recall that being an interferance engine. So maybe it just got tired of being the one left open for three years & stuck there/tappets tool loose/maybe a broken valve spring. The broken spring will let it hang down too far - then it can get bent.

Lee in Alaska

 

[rosco]

Naturally! But I don't recall that being an interferance engine. So maybe it just got tired of being the one left open for three years & stuck there/tappets tool loose/maybe a broken valve spring. The broken spring will let it hang down too far - then it can get bent.

Lee in Alaska

 

[Pappa-G]

Thanks for all the information guys! With any luck I'll have the batteries taken care of and be able to start it and trouble shoot some more on Friday. So place your bets and I'll keep you posted.

 

[Pappa-G]

And the winner is....

Ok, no more bets please.
Number one cylinder intake push rod is indeed bent. The intake valves seem to be moving nicely and the crosshead to spring minimum clearance is within specification. How the PR was bent seems to be a mystery and hopefully will forever remain that way. As it sits now the plan is to purchase another push rod and reassemble things. If the valve is also bent I am sure the noise will return. Then I will be able to check off the "has removed and reinstalled diesel head" box.
If there is any thing else that I should look at while its apart let me know.

Thanks

p.s. Where can a guy get a PR for a NHC 250?

 

[DT466Man]

RE: And the winner is....

probally napa or any diesel shop should beable to handle getting one.

go to a big truck dealer and tell them you need a pushrod for an 855 cummins. bring the bad one and one good one with you. you will ahve to explain to them that it goes in an army truck or they will ask for the serial number an all that

 

[DT466Man]

RE: And the winner is....

or a semi junkyard......and get a couple of them.....i'm more worried about what caused the pushrod to bend than the actual pushrod being bent.

they dont' bend on their own most of the time......sounds to me like the valve might of hit the piston and bent the valve....possibly overreved, or runaway.

does it shake??

 

[73m819]

RE: And the winner is....

over rev WILL get more then one pushrod, you need to check ALL the pushrods, in a over rev. the valves float and HIT the pistons, bending valve stems and pushrods, i have seen cracked heads and pistons from over rev, check the valve seat real good

 

[WillWagner]

RE: And the winner is....

Give me a p/n off the PT and i'll see if I have a"bonus" one hangin' around.

 

[gbooth]

Valve was stuck from sitting in the open position, probably had rust on the bare part that slides up and down in the guide. When first turned over pushrod bent but still was able to bump the valve a little, shook the rust off and valve spring was able to pull the valve back to the closed position. But the damage to the pushrod was done.

 

[73m819]

great that was a easy fix, i would still check the rest of the pushrods, you may have had more then one valve stuck

 

[rosco]

Too much starting fluid has been known to bend them - even to tempory locking up the engine. The stuff detonates inside the cylinder.....
Lee in Alaska

 

[Pappa-G]

The pn on the push rod is 112700 which has been superseded by pn 3046418 which is used on both intake and exhaust. I found a new set of 6 on ebay from a fella in WI. The local parts guys (napa, auto zone) couldn't locate anything.
The motor seemed to run (at idle) ok other than the pop pop pop out the intake. The exhaust port on #1 cyl was the coolest. We removed the rocker cover and restarted the engine the intake PR on #1 had a slight sway while rotating. After it was removed and compared to the exhaust PR you could see that the upper tip is geeked. Both of the valves move freely when tapped with a rubber mallet and the cross head gap meets minimum spec. Before I install the new PR I will "tone check" the cam follower (thanks Will Wagner) for a loose pin. If all looks good its reinstall the rocker housing torque to spec and reset the rocker to crosshead gaps for both #1 and #2 cylinders.
If I am forgetting something don't be shy, let me know.
Thanks
~Pappa-g