| Author | Message | ||
| Johnny (63.159.129.47)
Rating: N/A |
My friend just had a truck given to him--70's GMC stake-body 10-wheeler with a 6-71 (inline), 7-speed Eaton, twin-screw, GVWR 47,250lbs. The truck isn't bad (rear air-ride is nice!), everything (including the PTO-operated winch), but the engine could stand something--it smokes like a bonfire at ANY throttle setting. At WOT, the cloud LITERALLY obscures the cab! He may keep it, may sell it--but either way, this can't be a good thing. Ideas? Also, ideas on stopping the usual Detroit valve cover hemmhorage? I realize this isn't a bus, but you guys seem to know DD's pretty well. Also, are all 6-71's such (relatively) high-revvers? This one's governor is set to 2800, & seems perfectly happy to spin 24-2500 all day. I did about 20 miles on the highway today without even realizing I hadn't put it in hi gear. | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
My best quess is that there is something not quite right with the tack drive. Maybe the tack reads 2800 but the mill is actually reving less. As far as all the smoke, it just may mean the engine is very worn. Not much can be done with that, other than major work. Same with all the oil leaks. Sounds like the valve cover gasket is gone. Cheap to replace, but may not solve the problem. Possibility the valve cover is slightly warped also, which would cause a big leak. The older Detroits did have a tendency to leak stuff. Good luck. | ||
| Johnny (63.159.129.47)
Rating: N/A |
Judging by the way this thing drove (no trouble running into its governor at 84MPH, even up hills), the engine is fine. Thru the hills, the chase car (2.5 Caravan) had trouble keeping up! It has about 620,000 miles, but the engine got an overhaul (rings, bearings, valve job & a new blower) at 480K. Oil pressure is 40-45 at a hot idle with Rotella. No turbo, BTW. Tach is cable-drive, & reads 550-600 at idle, right where a Detroit is supposed to be. If it matters, I think it's a 1970 or a 1971. | ||
| dougthebonifiedbusnut (24.218.119.24)
Rating: N/A |
Dont know a lot about dds but i did drive an 8v71 for about amonth in a big truck one of the things you notice is the engine sounds like it is turning a lot faster than it relly is | ||
| Johnny (63.159.129.47)
Rating: N/A |
OK, just got an e-mail clarifying stuff: 1) I can't read my own writing--it's 820K, not 620. 2) It's a 1971. Smoke was jet-black, BTW. | ||
| Peter Broadribb (Madbrit) (170.215.36.4)
Rating: N/A |
Johnny, I think your friend is a lucky guy. Wish I could have one given to me. Might think about turning it into a toterhome instead of doing the bus. Have you got any pics to send me? Love those old trucks. Is it a cabover or conventional style? Peter. | ||
| Johnny (63.159.129.47)
Rating: N/A |
It's a long-nose, 28' stake-body dump. If you saw the truck, you'd know why it's free--I counted 6 different-color body panels, & none straight. The grille is chicken-wire & industrial windowscreen. No pics, & I have no way to post pics, anyway. Also, the trans jumps out of 1st gear. The guy bought a new Freightliner FL70 Business Class (he wimped out & went with a slushbox), so he didn't need the Jimmy. Of course, this monster is DRASTIC overkill for picking up appliances. I KNOW he's a lucky SOB. It'd make a nice RV, but I'm scared of needing a $10K rebuild now. Also, I don't need a smokescreen.  47K GVWR would be nice, though! | ||
| Tom Caffrey (Pvcces) (64.114.233.115)
Rating: N/A |
Johnny, believe it or not, the black smoke may be much better than the usual white and blue smoke. Something I ran across quite some time back was that Detroits feed fuel through their filters and pump, supply it under pressure to all the injectors and then return the unused fuel through a restriction fitting on the engine to the tank. The only way they can build up fuel pressure is by forcing fuel through the restriction. That restriction is a calibrated hole inside a fitting. What I heard was that sometimes that restriction becomes blocked or the return plumbing gets pinched off on the way to the tank. When that happens, the pressure supplied to the injectors will climb way up. I was told that this will cause the injectors to inject way more fuel than they should. In your friend's case, it could account for a lot of black smoke and a lot of power at the same time. If the cause were too little air, then power ought to be down. Black smoke comes from partially burned fuel. The causes are too much fuel charge or too little air. In that case, the hydrogen in the fuel is burned and part of the carbon leaving the rest as soot. Since a diesel normally runs very lean when lightly loaded, it should never black smoke then. If it does, there is something wrong with its fuel or air system or timing. Blue or white smoke or some combination is usually what you see with a worn Detroit. Combine that with hard starting, and you can usually figure it's time for an overhaul. For what it's worth. Tom Caffrey PD4106-2576 | ||
| Johnny (63.159.129.47)
Rating: N/A |
Easy starting, so that's good. It got 7-7.5MPG on the drive, with lots of hills & me driving it like, well, I stole it (pushing 75-80 most of the way). | ||
| Jim Wilke (205.188.199.182)
Rating: N/A |
Johnny, start with the basics first. Black smoke is too much fuel for the amount of air going through the engine. First, check for a restricted air filter. Cheapest thing to fix. If it has an airdoor emergency shutdown, make sure it is not partially tripped. (This is a housing bolted to the blower intake with a spring loaded door inside. Older Detroits had them, newer ones do not since they changed the fuel rack levers.) Second, when you take off the valve cover to replace that gasket, take a look to see what injectors are installed. Little colored tag between the fuel supply & return fitting on the injector. It should say something like: N60 or N65 and the tag could be various colors. Also be sure all are the same & appear to be the same "age". While it is common to change only one if one goes bad, sometimes a guy trying to save dollars will only replace one at a time forever or maybe mismatch them if he doesn't check or has one that's "close" on hand. Sometimes a guy will put a set of really big injectors in to try to get extra power, but if you go past 60s or 65s you will get smoke. The next stuff won't fix it but is good to know. For the heck of it see whether it is a two or four valve (per cyl) head. Look at the fuel pipes that go from the head to the injectors. There should be a nice coat of black oil all over all tubes & fittings. If you see a fitting or area that is real clean, check for a fuel leak. If these tubes leak, it dilutes the oil with diesel which would be real bad. From your oil pressure reading it does not sound like that is happening but check while you're "in there". Does it smoke black when idling too or just when rolling? How long was it sitting unused & how long was your total trip home? Any blue smoke once it got home? (Assuming it has a thermostat & could get to 175 or so.) Jim Bob | ||
| Johnny (63.159.188.135)
Rating: N/A |
It ran 170-180 on the highway, A/C on, empty, on a 90-95-degree day. Air filter is <3 months old. It had been driven 3-4 days/week. It smoked the whole time, always jet-black. Very faint at idle. No blue smoke--though if it was very light, the black cloud couldv'e overpowered any blue smoke. | ||
| Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A |
Johnny, I had a loose cover plate on the turbo air box on a 6-71 and it blew clouds of black smoke. Really had a time finding the problem too. Richard | ||
| DON5050 (207.224.147.148)
Rating: N/A |
Johnny the most likely is pinched return line or restricted fiting is pluged just like Tom was saying the restricted fiting is in the head where the return line hooks on it should have about a 1/16 hole in it. As far as 2800 this is common on 6-71's need to keep rpm down to about 2500 most of the time. Sounds like motor is good just has fuel trouble | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
Your 10-wheeler truck goes against the governor at 80 to 85 mph? Wow, maybe the mill is really turning 2800 rpm! If it was governed to something sane, the governed road speed would only be 60 to 65 mph, which sounds reasonable. 2800 rpm on a series 71 Detroit is NOT a good idea. Oh, the engine will certainly spin that fast--your truck is an excellent example. However---such high rpm is not good for the engine. Maybe, just maybe your black smoke is rpm related? Higher rpm equals more black smoke? Wonder how much it smokes at 2100 to 2200 rpm? Sounds like you have a really cool 10-wheeler. Now all you need is a Jake!!! He he he. Good luck. | ||
| Johnny (63.159.198.122)
Rating: N/A |
Even at <1500RPM, WOT obscures the cab. It seems to relate more to throttle than RPM--it smokes even while compression-braking, but it's heaviest at WOT. Jake was a bad switch. We could've fixed it easily, but it wasn't a major thing running empty. Governor kicks in at 84MPH. It's a 2-valve, & hasn't sat longer than a week in 10+ years. I think Rube Goldberg tried to fix the oil leak--the bolts were so tight he said he was afraid he'd strip the threads. Result: seriously bent cover. It's straight now, & the leak is gone. He said he saw a return line that might be pinched, but only a bit. He'll replace it tomorrow (part store had to order it), & see what happens. Is turning the governor down (24-2500 sounds good) hard? He said he's never had any reason to mess with a governor before. The injector tag is CAKED with crap, & currently sitting in a solvent bath. His best guess is "N80", or maybe "N88", but with the caveat that the tag is so filthy that he won't be sure until the solvent bath. All 6 were replaced when the engine was overhauled, & all look like they weren't touched after that. The trip "home" was ~350 miles--Maine to Connecticut, mostly Interstates. The truck is now in western Mass, I think. It hauled its first load today: about 16,000lbs of cinderblocks (40,800lbs as weighed; tare is ~24K according to the door sticker). The guy said it handled it well, & the Jake works perfectly now. Nobody tailgated him, either. | ||
| Jim Wilke (205.188.209.11) Rating: N/A |
N80 injectors would be WAY too much fuel. Especially for a 2 valve head. When it smokes black, the fuel isn't getting burned so it is wasted. With correct injectors the truck should be cheaper to run along with more pleasant to have around! Jim-Bob | ||
| Johnny (63.159.128.26)
Rating: N/A |
Well, the verdict came in: it's not an 8, they're either "N60", or "N68" injectors. With the new return line, he says the smoke has lessened, but it still smokes quite a bit. Again, how to turn down the governor? |