Intermittent valve problem?

[IDIBRONCO]

I'm working on my 1985 F250. 6.9, 4 speed, n/a, headers, typ4 cam, new bb injectors from Mel installed 6 months ago, new return line kit also from Mel installed at the same time, future plans for turbo. I went out at 6:30 this morning to put on the Moose Jr. pump I got a couple of days ago. I got it put on and went for a test drive. It ran great! I went a couple of miles down the highway, turned around and headed back to town. As I was slowing down for the city limits, I heard an awful noise from the engine and it started to miss badly. I shut it off and coasted to a stop onto a side street. I opened the hood and couldn't see anything. I started the truck and still the same issue. I eased it the 3 blocks to my driveway and noticed that the problem came and went, but was always there under acceleration. I took off the air cleaner and it's blowing compression back through the intake when the problem is happening. The engine was remanufactured by the place I was working at and installed by me in 1998. I know the lifters were all new although I don't remember the brand. The pushrods and rocker arms were all new then too. Miles on engine unknown since the speedometer wasn't working when I bought the truck. It blew a head gasket last spring. I studded the engine while it was out. There was very little wear in the cylinders so I don't think it has too many miles on the engine. I know that the pump couldn't do this could it? I haven't gone any deeper on it. I'm going to do a couple of errands and then mow the lawn so it will have time to cool down. I will pull the valve covers off this afternoon to look in there. Any other advice? Suggestions?

 

[chris142]

Sticking intake valve?

 

[79jasper]

^ Or intake valve seat.

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[icanfixall]

All the above mentions could be the problem as could a bad lifter. Pulling the vavle covers is the best idea but. I would try loosening each injector line to see if you can isolate the problem cylinder. Hopefully it a cylinder on the drivers side because thats the easy side to get the cover off.

 

[IDIBRONCO]

Well I just got in from an unexpected late night (for me) with some friends. I pulled the valve covers off. The second cylinder back, on the intake valve, the rocker arm "fulcrum" is cracked. I guess that's what you'd call the part that the bolt goes through. I didn't feel like going any farther and I put everything back together. I'll pull the rocker arms off tomorrow and try to check the valve if I can. I have a feeling that I'll be pulling the engine. If I do, that would be a good time to rering it and put in all new bearings.

 

[icanfixall]

Glad you found the problem. What side and what cylinder was this. You can look between the intake bolts that fastens the intake port to the heads for the cylinder number. Its cast into the manifold. Those 6.9 rockers are not very good. We can only buy the better 7.3 rockers these days and thats a good thing too. check ebay for a set. You may find them listed for around $75.00 per complete set.

 

[IDIBRONCO]

I was tired and forgot to write that it was on the passenger's side, second cylinder back. I didn't even look at it today. I also forgot to mention that the rockers are the 7.3 style. I wondered about a lifter too, but I'm not sure how a lifter could cause the problem. If, for some reason, a lifter would stick and not compress, wouldn't a valve hit the piston? Here's another question. Since I already installed head studs, when I put the heads back on, do I just torque the nuts once, or would I still do it 5 times like the first time? I'm just assuming that I'm going to be pulling the engine and removing heads.

 

[79jasper]

I would do the normal torque sequence.
Don't just go straight to the final number.

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[icanfixall]

The idea of retorquing a stud is not a good idea. Our head gaskets are designed to be tightened down once and once only. As for your original 5 torques, Thats to break in the friction on the nut to stud threads and the nut to washer. But mostly the nut to stud threads. Once done its not needed again. The second cylinder back on the passenger side is the number 3. All the cylinders on that side are odd numbered and on the drivers side they are even numbered.

 

[smithman]

Thats to break in the friction on the nut to stud threads and the nut to washer. But mostly the nut to stud threads.

Always follow the torque pattern, exactly as written, every single time. The fasteners interact with each other as you torque the head down and the preload changes even after you torqued a bolt as the rest of the pattern progresses. The fastener that was torqued 1st in the pattern has now lost some of its preload when the fasteners nearest to it were torqued. This is another reason why the bolts are torqued in multiple times in steps.

 

[IDIBRONCO]

I'm going to check the lifters first, but I have a feeling that I'll be pulling the engine out. I just have another project I have to do first. I hope I can get that one done by the end of the weekend. As for the torque on the studs. Just one time is what I was thinking, but I just wanted to be sure. Thinking about Chris142"s first response, it seems to make the most sense to me. Assuming a sticking valve, what's the solution? New valves? New guides? Both?

 

[icanfixall]

Ok after rereading this question about torquing studs I need to add this based on whats been said here. Following the factory torque is very important. Our heads require 2 different patterns. Steps are also important. Do not try to tighten one stud to the max lbs and move to the next. You follow the steps in lbs and sequence. Now as for tightening and loosening 5 times.. Nope. Never has to be done again. Sure hope this straightens out any questions.

 

[IDIBRONCO]

Thanks for the help.