View Full Version : all 16 pushrods bent
so i finally got around to pulling the engine out of my 01. tore it down and all 16 pushrods were bent. i can only find 1 piston that has signs of valves hitting it so i am left wondering what bent all the other pushrods. i had just put headgaskets in it about 1000 miles before and i knew i had one set of valves adjusted a little on the tight side and that was the one that hit the piston. yes i was beating on it pretty good while pulling my 7k trailer up a hill. can someone tell me what would bend all the pushrods?
So you had the heads off before. What gaskets did you use? Did you have the heads shaved any--and how much. I'm in the middle of replacing my head gaskets right now and don't want to run into any clearance problem. Sounds like maybe they took too much off the heads and the gasket was not thick enough.
Why did you adjust the valves so tight. I can't imagine that alone would cause them to hit the pistion. I would think if they were too tight, they would not have closed all the way and you would have known that cylinder was off.
So you are saying they are bent on both sides--even the side with no apparent clearance problem. What is "bent" way bent, or slightly bent? I had this problem once on a old datsun. I couldn't see where the valves hit the pistons, but the machine shop pointed it out to me. Those valves came down at an angle. The duramax valves are flat to the head and it may be very hard to tell that they hit. It would be interesting to know what the normal clearance from the valves to the piston is.
So you had the heads off before. What gaskets did you use? Did you have the heads shaved any--and how much. I'm in the middle of replacing my head gaskets right now and don't want to run into any clearance problem. Sounds like maybe they took too much off the heads and the gasket was not thick enough.
Why did you adjust the valves so tight. I can't imagine that alone would cause them to hit the pistion. I would think if they were too tight, they would not have closed all the way and you would have known that cylinder was off.
So you are saying they are bent on both sides--even the side with no apparent clearance problem. What is "bent" way bent, or slightly bent? I had this problem once on a old datsun. I couldn't see where the valves hit the pistons, but the machine shop pointed it out to me. Those valves came down at an angle. The duramax valves are flat to the head and it may be very hard to tell that they hit. It would be interesting to know what the normal clearance from the valves to the piston is.
i adjusted the valves to .10 instead of .12 because thats what i read to do on this site. i didnt mean to get one to tight but i did on 1 piston. it is not tough to tell which valves hit the piston, in fact its very obvious. all the pushrods are bent even ones that didnt hit anything. as far as gaskets i used grade c. with the machine shop they told me they only took off the very minimal amount to clean them up.
Well LB7lbz, sorry no one else has offered another thought. I think you have to accept what the evidence suggest--all the valves hit the pistons. Why do I say this?
Since you didn't say how much the pushrods were bent, I'm guessing very little--except for maybe the two that have visible evidence of hitting the piston.
The pistons and valves are flat to each other and it would only take a "kiss" to bend the rods. Something has to give. After they were bent, probably on the first revolution or when it heated up, they would just be touching with no force each time after that. Then the combustion over time obscured the evidence of the kiss between the piston and valves.
I have discovered in my own search for information that machine shops around here know very little about the duramax heads--unless they can say they have done them before. We used to have a number of good automotive machine shops around here that no longer exist. I called and went to visit with some that remain and discuss my heads. One admitted that I should take it somewhere else, another gave me all sorts of reasons that my questions weren't a concern--like valve clearance if they shaved the heads. Then they admitted they had not done any duramax heads. etc. etc. They said they couldn't even remove the injector cups--no tool. On the phone talking to some out of state that had done them and offered reman heads, they told me that you had to recut the valves into the head and grind them off to bring back to stock. This confirmed what I expected that the valve to piston clearance is very close. The auto machine shops around here kept telling me that no valves were that close to the pistons except in racing vehicles.
So, not knowing how many thousandths the shop took off, how do you know the grade c gasket was thick enough? a "minimal" amount to a machine shop could be .012. Thats what the locals guys told me they would take off--maybe .010 to clean them up good.
My truck already had the grade c on one side from the factory.--B on the other side. There is a range for each gasket. If we take the worst case, from the min on the b .0374 to the max on the c .0433 = .0059. So under best conditions, if you had grade b stock, you couldn't take off more than .0059 and have the grade c make up for it. Since you would probalby somewhere in the middle, then cut that in half to .003. If you had grade A to start you would be a little better off. I think my reasoning is sound here. if not, let me know.
So if they took off any more than .003 or .004 and you had grade b or c head gaskets as stock--indicating the amount of piston protrusion, then in my opinion, to be safe, you would have to redo all the valves to recess them back to spec in the head--and shave the length of the valves accordingly. If they didn't do this, then you tapped the pistons. You may want to check the valves to see if they bent. Less likely though since they have solid shafts and there are two for intake and exhaust, the pushrod would be the weak link.
Option--a thicker aftermarket gasket such as cometic. This seemed to be my only option since I already had grade b and c gaskets and GM didn't offer anything thicker. After looking at the cost of cometic gaskets, the cost to machine and test my heads, I just decided to spend a little more and buy new heads and not worry about any clearance problems and use OEM head gaskets.
i hear what u are saying bud but why would i be able to drive the truck 500 to 1000 miles before this happened? if the tolerences were too close then shouldnt it have happened right off? i am no engine expert and thats why i am looking for answers here. thnx for your replies
DmaxMaverick
09-09-2011, 12:30
It isn't surprising you aren't getting much response on this. I'm sure there are more than a couple folks here left scratching their heads over this, including me. Thanks Ken, for jumping in.
The Duramax is a zero-clearance engine. This means, the piston to open valve clearance at TDC will cause contact. Your tight valve adjustment on the one cylinder isn't the problem. Something else is at play here. While the tighter adjustment would certainly cause that cylinder to show more sign of contact, it would take a very specific chain of events to cause all cylinders to contact, or bend pushrods. Either something mechanical has changed the valve timing, or there was additional friction in the train (causing delayed valve return). It isn't likely that more friction caused this across all 8 cylinders, at the same time. Something common to both banks, and all valves caused this. It takes in excess of 6K RPM's to float the valves, but it would quite obvious if that happened. The first thing I would look at is the timing. The cam is gear driven, so the likelihood of it jumping time is extremely unlikely. However, the cam gear may have come loose, or a gear or cam may have broken.
I don't think the gasket thickness is a primary factor. If it were, the problem would have been immediate. The same with the tight valve adjustment.
Valves can contact and leave little to no sign of it. Even with enough contact to bend pushrods. To see the "invisible" sign of it, use a straight-edge (steel ruler, etc.) and very lightly scrape straight across the piston crown. Repeat until a pattern appears, or you reach the crown coating surface (stop). Go slow and use very little pressure. If the surface is clear of any soot/carbon, use a fresh stick of soapstone in the same manner. If there's been any contact, it will show up.
GMC Tech
09-09-2011, 13:44
Saw this once before. Pin that aligns the tcamshaft gear to the camshaft broke and it allowed the cam to jump timing. Bang all the pushrods bent. If you have the engine out, pull the front cover and check the camshaft drive.
right now i am leaning towards what gmc tech is saying. i sprayed the top of the pistons tonight with brake clean and wiped them up good. i can still only find 1 that contacted valves. to answer a question from a few posts back all the pushrods were bent alot not just a little. it should also be noted that i had to drive for aways because i wasnt in a good spot to just pull over with a 24 ft trailer. anyway tonight i got the uppper and lower oil pan off and found alot of metal in the pan. 1 piece was from the lower valve cover. there were also several pieces about 2 inches long,curved and flat. not sure where they come from, maybe pieces of a bearing. i will know more after tomorrow and will keep you guys updated. on a side note swapping in an lb7 from a c4500 requires alot of swapping stuff off my old engine. bonus is the drivers exhaust manifold dosnt have the crimp on the c4500s. thanks again guys
Sorry to hear that it sounds major. Good luck with your problem, and let us know what you find out. I was leaning towards the valves hitting the pistons, since you had recently pulled the heads. Cam was another thought, but seemed less likely- not knowing all the other information.
Metal in the pan does not sound good--a piece from the valve cover? I guess the kind of metal would give you a clue as to where it came from. The only other thought I had originally was that you lost oil lubrication and the valve stems scalded into the guides and prevented them from opening, but that seemed less likely as well. Maybe if they stuck open, when the pressure that was on the rods released from the lifter, the rod fell down and then came out of the rocker assembly. I would think the odds of that happening on both sides at the same time would be slight. Maybe happening to just one could cause a chain reaction of some sort. Were any of the pushrods out of captivity?
The cam would be common to both sides and what GMC Tech says sounds like a probable cause, but it seems the valves would still have had to hit the pistons
I guess we may never know for sure. It could have just been time for something to fail.
More Power
09-11-2011, 13:48
Saw this once before. Pin that aligns the tcamshaft gear to the camshaft broke and it allowed the cam to jump timing. Bang all the pushrods bent. If you have the engine out, pull the front cover and check the camshaft drive.
What he said....
Being 2 thou tighter than spec on one set wouldn't do it. Consider yourself lucky that it resulted in "only" bent push rods. Fairly cheap fix, just time consuming.
Let us know how this plays out.
Jim
DmaxMaverick
09-11-2011, 14:18
In regards to the metal you found in the pan:
Depending on what you meant by "curved and flat" pieces, these could be either broken pieces of the cam trust plate (washer), or pieces of front cover baffle. If the cam gear were loose, it could certainly grind away at many items close by.
Not likely any large pieces from under the valve covers or valley. The drain ports are too small. The oil drain passage of the front cover (around the crank) is large enough, however.
Drag a magnet through your drain oil and pan. This will separate the steel from aluminum pieces. All the pieces must be identified to determine the extent of damage. This could mean the difference between catastrophic and trivial.
A worst case could be a piece of a piston skirt. Maybe a picture would help identify it.
i couldnt get the timing cover off today because i dont have a 36mm 12pt socket to get the balancer off. the pieces of the lower valve cover i found had the threads from where the upper valve cover bolts go into it. broken in 2 places front and rear of lower cover. as for the curved flat pieces they are kind of shaped like a ( j ) and they are thin and flat. something deffinetley ground at them or ground them off something. anyway i will have the socket tom and know the whole story. on another note what is my motor worth as it is. it has good heads w arp studs, good cp3,turbo, manifolds,block, fuel system etc. i have an interested party but have no clue what its worth. thnx again
i took pics but everytime i try to upload them it tells me the file is too big, sorry
DmaxMaverick
09-11-2011, 18:02
i took pics but everytime i try to upload them it tells me the file is too big, sorry
Looking forward to the pics. Upload them to your account Photo Album (http://www.thedieselpageforums.com/photopost/index.php) and link them into the post. Easy and free.
With all the pushrods bent, I wouldn't trust the heads. I'm gonna go out on a limb here, but I don't think there's any way that happened that doesn't include all the valves hitting (all the) pistons.
With all the pushrods bent, I wouldn't trust the heads. I'm gonna go out on a limb here, but I don't think there's any way that happened that doesn't include all the valves hitting (all the) pistons.
thnx for the tip on the pics jon. tried it and after waiting 15 minutes decided i had enough. by not trusting the heads i am assuming you mean the valves,because i dont see how valves hitting pisons can hurt the actual head. i agree they must have hit, however there is little to no sign of it except 1 piston, which leads me to believe that the rods are very weak and will bend way before the valves will. anyone got any idea what this parts motor is worth?
so the pin in the end of the cam came out in 2 pieces. it was cocked off to the side which would explain the timing jump and the bent pushrods. still havnt figured out where the metal came from. the cam trust plate looks good as does everything behind the timing cover. i will try again later to get some pics on.
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