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Author Topic: 671 Vibration Trouble  (Read 3020 times)
GM0406
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« on: September 22, 2006, 04:46:58 AM »

Hi All,

Here is an update of the vibration problem on my '04.  I have been trying to find out what is wrong with the engine.  Took it to the local DD shop, and some unfortunate things happened.  First, the wife of the owner suddenly and unexpectedly died!  Next the mechanic working on the coach had a heart attack!  Not a nice situation.  We never know when we are going to meet up with phyical problems!  Anyway, they replaced all the injectors to solve what we thougth was a missing problem, but it did not get rid of the vibration.  They checked things like flywheel runout etc. but we are coming up with nothing unusual.  Now one thing that I would like experts here to comment on is the exhaust system.  It seems that George Thornhill, the previous owner of this coach had a dual exhaust system installed on this engine.  There are two mufflers vertically installed at the front of the engine.  Could this be my problem?  Bill T.
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Dallas
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« Reply #1 on: September 22, 2006, 05:02:54 AM »

Bill,
Somehow I get the impression this isn't a Detroit Dealer.

Some questions:

Did they run the rack? Did they check for oil in the coolant or coolant in the oil? Did they run a compression test both cold and hot? What were those values? What kind of shape is vibration dampner on the crank shaft in? Is the fan hub in good shape? What kind of shape is the blower in? Do you use much oil, (possible failed blower seal)?

Maybe you could describe exactly what kind of vibration you are getting?

Just some questions that come immediately to mind, other than starting with the exhaust system, which, if it had been running well at one time shouldn't be causing a problem now.

Dallas
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Len Silva
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« Reply #2 on: September 22, 2006, 06:17:35 AM »

My 4104 has a vibration at about 1500-1800 rpm.  In my case, it's the flywheel.  There is visible runout at idle. Haven't fixed it yet.

Len
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« Reply #3 on: September 22, 2006, 07:55:11 AM »

Bill- the biggest culprit, like what Dallas said, is the flywheel/clutch assembly.  One easy test is to rev the engine up in neutral and notice the vibration.  Then put it into gear still sitting still and with the clutch depressed rev again-did the vibration change?  While a visible runout at idle may not be noticed, when it revs up, can start a harmonic vibration.  Did you check your engine mounts also?  If you do have a new clutch and flywheel installed, make sure to have the whole assembly dynamically balanced together, and mark the position of the spring plates mounting to the flywheel.  Can be very frustrating to find that kind of vibration.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #4 on: September 23, 2006, 09:15:49 PM »

Bill,

Dual pipes and mufflers and split exh manifolds are stock on a 4104, they came both ways. Mine is dual.

The other setup is dual stacked mufflers with one manifold outlet. I would hate to change those babies!
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PD4107-152
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Ash Flat, AR
GM0406
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« Reply #5 on: September 24, 2006, 01:00:45 AM »

Thanks for all the replies.  I went in earlier, but this site is a little different than it used to be and it will take some time to get used to it.  Ok, let's start with what I know about this so far.  This is not only a miss, but vibrates more at some rpms than others.  And it vibrates enough to shake the steering wheel while reving the engine up in neutral standing still.  My only comparison is Joe Sawyer's '04 which was absolutely smooth and didn't vibrate or miss at all.  There is basically no smoke from this engine.  Starts immediately and sounds pretty good, but there is some kind of miss and lack of power.  George Thornhill who owned this coach and had DD in San Diego build the engine, told me that he tried to get this vibration out, but couldn't resovle it.  He replaced the harmionic balancer and had the clutch balanced and still the problem presists.  A mechanic from Royal Coach here in San Jose, checked the rack adjustments and said it was ok.  Another DD mechanic at Bay Cities, the DD dealer here checked the rack and confirmed the previous.  So I had them replace all injectors with a complete set of rebuilts.  I haven't tried it as it is still at their shop.  But Martin told me we still have the problem.  It has been suggested that there might be a bent rod.  But I checked with George, and he has never used any ether and neither have I.  Now the last mechanic indicated that he did not see as much power reduction on 2 and 5 when he defeated the injectors while checking before he replaced them.  This engine has about 70K since George had it completely rebuilt.  Haime, the mechanic that changed the injectors told me the end play on the crank was a little more than specs., but that he didn't think that would be the problem.  Also the flywheel runout was within specs.  This engine does not leak any oil period.  George put a recovery system on it which is great.  I have wondered if the problem could be related to the Jake Brakes.  I occasionally hear backfiring from the Jakes.  Now, I will check with Joe to see if his 671 had dual exhaust on it.  Maybe with dual exhaust they don't sound as smooth as with single exhaust like an old straight 6 cylinder Chevy.  But to me she misses and I'm not sure if the vibration is a result of the miss or if it is a flyweel or clutch problem.  The clutch works fine.  A little chatter when cold if you slip it instead of letting it out carefully, but promptly.  It also has air assist on the cllutch that George did a great job on.  I think they decided not to do a compression test because there was basically no smoke?  You guys here are a lot smarter than I am on this DD, so just yell at me if I am not getting this right.  After what I have said, let me know what your response is and I will call them and discuss what you say.  Thanks so much for the help.  Meantime this weekend we used the '06, which doesn't miss or vibrate.  Sure would be nice to get this '04 smoothed out.  Bill T.   
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GM0406
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« Reply #6 on: September 24, 2006, 01:07:04 AM »

One more thing.  Dallas, the fan is tight and appears to run true.  This is evidently a hard one to solve as George is pretty sharp and the DD guys in San Diego are pretty good according to him.  If you think I should press them to do a compression test, I will do it.  Bill
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GM0406
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« Reply #7 on: September 24, 2006, 01:24:10 AM »

Tom, when I go back over to Bay Cities, I will do the test you mention in gear with the clutch depressed.  But, as I said, you get this vibration in netural standing still as well as running down the road.  What confuses me is the accompanying miss and power loss.  By the way, the Iotas you told me about work great.  I have never had a battery problem since I installed those converters.  I go out and work in these coaches for hours and use all 12 Volt accessories with rock solid performance!  Bill
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Dallas
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« Reply #8 on: September 24, 2006, 02:39:53 AM »

Bill,
Hmmm, without actually listening to the engine it's really hard to diagnose any thing.

If it were a split manifold you still shouldn't have a power loss/miss when at speed.

I think I would still run a hot and cold compression check just to eliminate any possibility of a bad piston/liner, a bent valve, a burnt valve, or maybe a blown fire ring.

If 2 and 5 seem to have less droop when the injectors are defeated it would indicate that it is in one of those two cylinders because they are matched. 1-6, 2-5, 3-4.

If it were an exhaust restriction it should result in high back pressure, (the blower can't fill the cylinder with enough air), which would cause incompletely burned fuel, which would cause smoke.

It could also be caused by insufficient fuel pressure, (no less than 50psi at governor limit), or an incorrect fuel return orifice which would cause low fuel delivery and would cause uneven running.

Has anyone thought to check engine timing?

Is there a screen on the bottom of the fuel pickup tube that could be causing insufficient fuel delivery?


I'd check these things out if it were me.

IHTH,
Dallas
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n4rsn
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« Reply #9 on: September 24, 2006, 05:51:52 AM »

We had a 6-71 that viberated for a long, long time, and when we disassembled it, we found the crankshaft was broken in 2 pieces.  I don't see how it ran that long, but it did.
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gus
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« Reply #10 on: September 24, 2006, 05:14:59 PM »

My 4104 has the split exhaust and is silky smooth at all speeds and it is pretty tired.
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PD4107-152
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GM0406
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« Reply #11 on: September 24, 2006, 09:44:26 PM »

WOW!  Broken crankshaft!  I'm begining to wonder if I should watch for a known good 4 valve 671 that one of you guys removes from a part out coach, and just buy that and change it out?  Bill T.
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GM0406
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« Reply #12 on: September 25, 2006, 06:26:09 AM »

This broken crank thing has me worried.  We should be able to check this pretty quick, right?  If there is any play between the harmonic balancer and crank, then this crank is history, right?  Bill T.
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GM0406
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« Reply #13 on: September 25, 2006, 06:41:45 AM »

Whoops,  the play will be between the harmonic balancer (where it mounts to the crank) and the flywheel, if this crank is broken.  This might be the problem.  This engine does have 5" blower inlet and 4 valve head, and N-65 injectors.  Maybe that was a little hard on the crank?  Will let you all know what I find today.  Bill T.
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TomC
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« Reply #14 on: September 25, 2006, 07:52:50 AM »

N65 injectors with proper timing can make for the popular 238hp version.  This is still just loafing for this engine considering that Detroit had a 465hp marine version at the end of production.  One of the ways a crank will break is as simple as either metal fatique or an initial flaw that wasn't discovered.  Probably would be the cheapest to have yours opened up and find the problem.  Maybe a counterweight on the crank has broken off?  It will be the easiest and shortest amount of time to build up a replacement engine then swap it out.  If you do this, maybe rebuilding to turbo specs to bump the power from 238hp and 600lb/ft torque to 300hp and 900lb/ft torque (the trans is rated at 1200lb/ft) with the addition of an air to air intercooler.  I saw one 04 that the owner mounted the turbo above the transmission.  Then have the intercooler where the transmission door is now.  Would make a nice setup.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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