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Intermittent "missing" sound

Thank you for your thoughts/experience Chevypoor. I'm going out to take some pics now and I'll post them in a little bit, but I've pretty much already relegated myself to needing new heads. It didn't push air into the cooling system, but it has used some coolant since I owned it. I always attributed that to head gaskets that were on their way out, but all things put together it seems I need to throw a different pair of heads on this thing. The one head I have cleaned up good has cracks in 3 cylinders for sure, and I'm guessing the other head isn't much better, so I'm guessing I'd have a bunch of machine work costs into a pair of heads that I'd always be questioning. I guess at this point I'm on a quest for a cheap pair of heads, knowing that I'll want to upgrade again in the future. I'm glad you guys with more experience weighed in before I went much further. On any of my gas engines I've worked on in the past those cracks would have been an immediate red flag, but I thought I had read people here running heads with cracks....I guess I was mistaken. I will forever now run under the assumption that any cracks in any heads is no bueno.
 
If you have to run it, run it soft is my 2c. Save $ for new heads.
I don't see how that would cause coolant or oil loss.

Power loss and an increase in iat at the cylinder, a gauge or sensor will not pick it up. An egt gauge will. The gasses goes from the exhaust into the intake side taking up some of the space that would be oxygen for burning. It heats up the area so you have the effect of high egt preheating the air so you are more susceptible to a rise in ect.

On the 6.2/6.5 platform I have always been able to throw the $ at it, so idk how long you could run it.
Chevypoor is this the crack you experienced? Anyone else run with this crack and been good with it for a while?
 
Im with Chevypoor. If cracks are small and you did'int have issues before I'd run em. But I'd have a machine shop look at the and give there advise. My 93 had some cracks, I showed my machinist he said he could do "the dowel pin thing, but why?" "cracks are not in a coolant passage" I took that with a grain of salt but took my chances as the truck ran beautiful before and the only reason I took heads off (as some will remember) is thats when my GP's were stuck in the heads. Thats why I sell a GP removal tool now too. The 93 ran great wish I had not sold it.

fuel filter mods 003.jpg
 
Will L. said:
If you have to run it, run it soft is my 2c. Save $ for new heads.
I don't see how that would cause coolant or oil loss.

Power loss and an increase in iat at the cylinder, a gauge or sensor will not pick it up. An egt gauge will. The gasses goes from the exhaust into the intake side taking up some of the space that would be oxygen for burning. It heats up the area so you have the effect of high egt preheating the air so you are more susceptible to a rise in ect.

On the 6.2/6.5 platform I have always been able to throw the $ at it, so idk how long you could run it.
Chevypoor is this the crack you experienced? Anyone else run with this crack and been good with it for a while?
Click to expand...

The truck is still running... I have tried to buy it twice in the last three years and they will not sell it runs so well!

I will share my initiation into the 6.5 world.

I have been and always will be a Chevy guy. Did not know anything about the 6.2/ 6.5 and I find I am still learning! I worked for a company in 2010 that hired me under the premise that I would get a company truck to drive. Most of there trucks were gas Chryslers. And there was this Burgundy 95 c1500 vin F 6.5 diesel. I asked about it and was told the motor was bad. They knew I was a decent shadetree mechanic so I made the deal with them if they paid for the parts I would fix it for free. Then she would be my company truck. Did some reading here and at others forums to start the repairs. I also looked into the trucks history(they had a folder on it) and asked the employees what the knew. The truck had 305K. According to the file the IP had been replaced at 276k by known reputable shop. The trans had been replaced at 294K. The same known shop had diagnosed it as running on 5 cyliders in 2008. It had been sitting 2yrs. The guy that had been driving hated the truck because it was slow and old. He tried to kill it by running gasoline through it. I took the motor apart down to the block which I left in the truck. The bolts had backed out of the timing sprocket on the Ip and sheared one of them off. The force of the bolt head shearing off and wedging itself between the block and the timing chain sprocket broke the thrust plate on the cam. It also sheared the roll pin so the Ip was not really even turning. Everything else looked fine except for the cracked cylinder heads. I could still see hone marks on the cylinder walls. Amazingly I was told it was still was running with the IP basically dis connected! They said as soon you gave it fuel it would stall. I thought I had found the problem so I put her back together cracks and all. I re used the IP by installed a new roll pin. She ran like crap, was throwing codes, smoking, coughing. I was stumped, thinking I must have missed something I went back over my pics-I had taken pics as I had tore her down. I happened to notice that the injection lines on the back of the IP looked different in the shop manuals than what I had on my motor. So I checked the firing order of the injection lines. Sure enough they were off. The diesel shop had somehow crossed three of the lines. This explained the three dead cylinders and rough running. Put her back together again and this time I had it- she ran like a top. So this boat anchor/ worst diesel ever made had ran almost 30k on five cylinders, being fed a diet of gasoline, and being beat on by someone who hated it. It survived all of that with only a couple of minor head cracks! Last I asked about the truck (this spring) it is still running- they told me it was one of the nicest runners in the lot! And yes as far as I know it still running those same cracked heads!

I have two 6.5s that eat small amounts of coolant and I suspect the heads are cracked but like Leroy as long they are running fine I am not worried it!

BTW Chevrolet also put out a Technical Bulletin on the valve bridge cracks and the valve guide method is what is stated in the TSB as the "official" answer. They did suggest a pressure test before returning to service.

Love that motor Leroy.. that thing was sweeet looking!
 
Thank you for the replies, it has been very helpful. Unfortunately I think I've made my bed with this one financially and I have to run these heads still. I did get an opinion from the machine shop and he wasn't too concerned with the crack. Between that and how it sounds like there are enough stories of cracked heads running for a while so I don't feel too bad running them though it is certainly not my first choice. For a long term plan, I am going to save up for an engine from Ted's. In the meantime I'm excited to get this thing on the road with this bunch of improvements.
 
Hello everyone I'm new here and must say I've been chasing the same exact miss in my motor. While OBD2 data logger states there a miss it does not identify which cylinder, so after reading this I'm going for a AMG repower instead of fixing this so-called enhanced motor now, later I can pull it apart and see if it's worth a fix for another project.
 
FellowTraveler said:
Hello everyone I'm new here and must say I've been chasing the same exact miss in my motor. While OBD2 data logger states there a miss it does not identify which cylinder, so after reading this I'm going for a AMG repower instead of fixing this so-called enhanced motor now, later I can pull it apart and see if it's worth a fix for another project.
Click to expand...

Welcome.
Just to let you know I can get brand new AMG engines for the best prices. I also have a used one that has been totaly gone though that I built for my rig, but now I'd like a P400 so mine is for sale.
Email me for info if interested [email protected]
 
n8in8or said:
Thank you for the replies, it has been very helpful. Unfortunately I think I've made my bed with this one financially and I have to run these heads still. I did get an opinion from the machine shop and he wasn't too concerned with the crack. Between that and how it sounds like there are enough stories of cracked heads running for a while so I don't feel too bad running them though it is certainly not my first choice. For a long term plan, I am going to save up for an engine from Ted's. In the meantime I'm excited to get this thing on the road with this bunch of improvements.
Click to expand...
Now the financial limitations are something I understand well! I hope it runs great for you, and actually I'm running a head on mine that has a hair line crack in the same spot. One of the heads off my truck had a crack like that one that extended into the seat. I didn't use it, but thats only because I had an extra one in better shape, so it was a no brainer. I have one crack bellow one of the main bolts in my block as well. I currently have 5000 miles on the engine since its freshening up, and so far so good. The thread on my engine is here. http://www.thetruckstop.us/forum/showthread.php?42774-Poor-Boy-Special-6-5-Refresh

Matt
 
bowtiebutler956 said:
Now the financial limitations are something I understand well! I hope it runs great for you, and actually I'm running a head on mine that has a hair line crack in the same spot. One of the heads off my truck had a crack like that one that extended into the seat. I didn't use it, but thats only because I had an extra one in better shape, so it was a no brainer. I have one crack bellow one of the main bolts in my block as well. I currently have 5000 miles on the engine since its freshening up, and so far so good. The thread on my engine is here. http://www.thetruckstop.us/forum/showthread.php?42774-Poor-Boy-Special-6-5-Refresh

Matt
Click to expand...

Hi Matt, I haven't read the thread on your engine yet, but thank you for sharing your experience with your engine, that helps ease my mind a little more. That was kind of what the machinist said....he said this head is cracked like pretty much every other 6.5 on the road right now (well except for the exceptional machines you guys are building on this site!) and that I probably have more cracks in the rest of the engine....of which I have no doubt. Since it was running fine before the lifter went to crap I think I'll be ok, for a while anyway.

Nate
 
Mine is running great except for this same exhaust noise at idle however I suspect the lifter is pumping up off idle and pressure drops off at idle after a trip to town it will make more noise at idle then taper off to the same as the sound bite in this topic.

1999 GMC K2500 Burb w/post May enhanced 6.5td, timing gear set, fluid damper, CAC, hi-pops, evans waterless coolant, by-pass filtration, dual aux trans coolers, psc pump w/dual filters & coolers, amsoil, s&b, dual alts, dual fuel tanks, built 4l80, 4.10 gear sets back locker front arb, compressor, and other misc goodies.
 
That sounds like a reasonable theory. As shown in a picture above, my problem was that the retaining clip was actually broken and the cup was sitting in the lifter askew - so at the very least I had a lot of extra lash due to the pushrod sitting lower in the lifter, and possibly the lifter wasn't pumping up correctly either. Mine made a nice ticking audible in the cabin going down the road so mine got worse off of idle. Despite that, mine also ran pretty well, it didn't shake or anything really noticeable like that despite one cylinder not working as well as the others.

On a side note, I just read your signature..... that sounds like a pretty tough Sub you have there! I've always liked Subs, I probably would have bought one instead of this Tahoe, but it wouldn't have fit in our current garage so I had to get the 2 door instead.
 
n8in8or said:
That sounds like a reasonable theory. As shown in a picture above, my problem was that the retaining clip was actually broken and the cup was sitting in the lifter askew - so at the very least I had a lot of extra lash due to the pushrod sitting lower in the lifter, and possibly the lifter wasn't pumping up correctly either. Mine made a nice ticking audible in the cabin going down the road so mine got worse off of idle. Despite that, mine also ran pretty well, it didn't shake or anything really noticeable like that despite one cylinder not working as well as the others.

On a side note, I just read your signature..... that sounds like a pretty tough Sub you have there! I've always liked Subs, I probably would have bought one instead of this Tahoe, but it wouldn't have fit in our current garage so I had to get the 2 door instead.
Click to expand...

The more I think about it I'm leaning to a repower because this Burb is a keeper and I don't like being stuck in the middle of nowhere USA or anywhere else.

Thanks for the compliment, this Burb has lots of mods and hopefully I'll finally get better turbo to top it off.

I like the 2 door and you don't see too many with a 6.5 godd luck on the repair.
 
Based on what I've found inside my engine, I believe that a repower with a newer engine with the updates seems to be the better way to go. Unfortunately I don't have the budget for that right now so I am going to make my existing stuff work. I should be putting the heads back on tomorrow night and hopefully be able to wrap it up this weekend.

I do like the Tahoe because it's unique - I love the looks of confusion I get when I roll by in a Tahoe making all the diesel racquet! It's mostly when I carry extra people that I wish it was a Sub so they wouldn't have to crawl in the back to ride along, otherwise it work nicely for my needs.
 
Ok, I finally got the engine running again Monday night (10/6/14) and I've put a few hundred miles on it, so I can report back now.

First the pics:

The Harland Sharp rockers come packaged very well
rockers pack.jpg

They sure put the old rockers to shame
old v new top.jpg
old v new side.jpg
rockers bottom.jpg
rockers side.jpg

So purdy when they're installed.....Leroy, you need to come up with some clear valve covers because it's a crying shame covering up these beauties!
rockers 1 head.jpg
rockers 1 head 2.jpg
rockers both heads.jpg
valve covers on.jpg

Once the air worked out of the fuel lines and injectors I noticed that the engine did seem to run smoother, though who knows how long I've had lifter issues going on. I have not noticed a lower idle like I read others reporting, but I'm pretty sure both of those were mechanical pumps, so I'm guessing the computer would compensate and make it idle at the same rpm as normal.

The engine is running very well right now, which pleases me, but if it didn't after the work I put into it I'd be a tad disappointed! I can't say that I notice more power by the seat of my pants, but the turbo and transmission were already my limiting factors - I'm still running the GM8 so there's that obvious constriction and then my transmission has what seems to be a weak pump so it feels like it can't put all the power to the wheels. I plan on taking care of both of those problems this winter/spring but I feel good that I have a nice foundation for those upgrades.

One thing I have noticed is that it blows less black smoke when I get on it now, so that is nice, I never enjoyed just how much "coal I was rollin'" when I'd get on it before....now it's a nice haze that seems appropriate.

Something I can definitely report is a nice increase in highway fuel mileage! Before this work, the best I could get on the highway at normal highway speeds (usually ~75 mph with cruise control on) was 16mpg. Wednesday I drove to Detroit and back and checked my mileage both there and back. On the way there I drove 105 miles on the highway with the cruise set at a gps verified 76mph. Then I drove 30 miles of back roads, 50mph stop-and-go, and 30 mph in-town driving. I filled up after that just before getting on the highway again and recorded 19.97mpg!!! I was SHOCKED! On the way back however I could only run the cruise about 20% of the time due to traffic. So it was a lot of speeding up and slowing down which I'm sure affected mileage. I filled up after pulling off the highway and recorded 16.82mpg. Another factor contributing to my mileage calculations was there was a stiff west-to-east wind blowing - so that likely improved my mileage going to Detroit and hurt my mileage coming from Detroit. Despite all variables however, I feel confident that I have gained at least 2 mpg on the highway which is nothing to sneeze about. How much of that is rockers and how much of that is the switch to diamond precups from square precups there's no way to know unfortunately. Needless to say I'm very pleased and now I can't wait to do the trans and turbo upgrades.
 
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