BCM Community
Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: thejumpsuitman on October 21, 2009, 10:40:26 AM
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Is it really normal for the DD 6-71 to idle up and down? Does it have something to do with keeping oil pressure up? Every bus I have looked at with the 6-71 idles that way started up... One mechanic I talked with said it is how they are supposed to idle, but wanted to hear what you guys had to say about it.
Thanks
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Do you mean the Detroit Diesel "loping idle"?
happy coaching!
buswarrior
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Do you mean the Detroit Diesel "loping idle"?
YES! Well put... Loping idle. What is that?
happy coaching!
buswarrior
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Removed
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I would guess that is normal, simply because mine does it when first started but smooths out once it is warmed up.
Most non-electronic engines don't idle as well cold as when warm.
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I dunno why they do that but they don't have to. Mine idles dead smooth hot or cold.
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I was told by an old mechanic that it was normal and right, and he told me "Don't let anyone touch that engine. If they don't lope when they are cold, they are set too rich." Besides, it just sounds right to me, and i would hate to lose that sound! BTW, it idles perfectly smooth once warmed up.
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First off-there is no such thing as a Diesel engine running "rich"-unless it has a plugged air cleaner and belching out black smoke-then that's running rich.
I have a turbocharged, intercooled 8V-71 with 9G75 injectors, that when it starts, no matter how cold it is, it NEVER lopes, nor should it ever. If it does, you just have a mechanic that doesn't know what he is doing. My bus is the third Detroit 2 stroke vehicle I've owned, and none of them ever loped on start up. All were mechanically operated, and tuned every year. The first two were tuned at Delaney and Ahlf in Bakersfield, and my bus with Don Fairchild, also in Bakersfield (Don also worked with D and A).
Do yourself a favor and find a competent mechanic that will properly tune your engine to run smoothly all the time. Good Luck, TomC
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so what exactly causes the lope? I understand it's a tuning issue but what aspect of the tuning? BTW mine lopes for a few minutes as well and then settles done, runs purty and doesn't burn oil or run hot, so other than checking the injector clearances I am hard pressed to go messing with the governor.
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I have three 4104,s They all Lope until they warm up.
John
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8V-71, lopes for 15 seconds when i start it under 50 degrees, other than that it's smooth. I wonder if the idle is set too high, but I don't have a tach. How do you adjust idle speed anyway? I had a thought that it would be easier to engage first gear if the idle where set lower (actually the other way round, I thought that it would be harder to engage first gear if the idle were set too high...)
I think the loping has to be down to inconsistent combustion, which would point to over-fueling for the condition at hand, I would think. When the combustion chambers are dead cold, they would tend to incompletely combust, would they not?
Brian
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I guess I'll have to pay attention to my engine at idle to see if it lopes...
I do know that the idle of the engine will decrease and increase when the compressor cuts in and out. just a different load on the engine.
Correct me if I'm wrong but lope is just the engine coasting/slowing down between power strokes. You hear it in Harley motorcycles because the two cylinders fire very close to each other and then there is a long time before they fire again.
Most multiple cylinder engines are balanced in there firing order. For every power stroke of a cylinder there is a cylinder that will have a power stroke just opposite. A two cylinder engine with opposite power strokes will still lope at a slow idle because there is more time between power strokes, but the lope will seem balanced. The more cylinders you have the more overlap of power strokes and the smoother the engine will run.
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The loping is in the governor, as Dallas said, the buffer adjustment. I don't think it's a big deal to leave it that way unless you are doing a tune up anyway.
If everything is adjusted correctly, there should be no change when the air compressor kicks in. It may sound different but the RPM's should remain the same.
Incorrect buffer and low idle speed will also affect the ability to do a dead throttle start.
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Probably needs new plug wires lol.
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Maybe it's good to define a term or two... :o
what I mean by a loping idle in a Detoit is the idle speed surges up and down maybe 50 - 100 rpm on a semi-regular basis, maybe every 5 seconds or so. A pulsing change in idle speed, that's pretty regular.
Brian
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Probably needs new plug wires lol.
Uhmmm more likely moisture in the distributor cap, or bad plugs! But plug wires could be the culprit too!
;D BK ;D
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Some of you guys need to refer to the service manual, the tune up chapter, before you start talking about things you don't know anything about. Loping is caused by the buffer screw not being far enough in. You need to turn it in a little to eliminate loping but not too much that it would increase idle speed. Idle speed is a different adjustment.
3, 4 years ago, I didn't know anything about Detroits, but I wouldn't have gone on a thread like this one and start writing things that maybe I guessed or had heard from the neighbour's uncle who knew a back yard mechanic...
I have gotten a lot of good info from this board over the years, but you have to sift through so much BS and opinions and useless posts like above from guys who have apparently all day to blabber about things they don't know about.
So stay away unless you know for sure, and waist other members time and confuse them.
This is why I don't post very often.
Sorry about the rant, but I had to get it off my chest.
JC
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Now quit beating around the bush and say what you mean ;D
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I am not referring to Cody or BK.
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So... for those that know.
1.What is the down side of having the buffer idle switch off a tad?
2.Is the buffer really that far off if once warm everything is hunky dory?
3. when I look into the manual the tuning is done on a warm engine so a little lope seems possible without being a problem, hence my queries.
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Jeez Lostagain, i think you mite be talking about my post being a waist of time. I want too apologize for righting that post and waisting all the time you took two reed it. I guess if i had studied my owners manual i could have found out about the buffer screw. Of course if we all would do a hole lot more research on our questions, then their wood bee no kneed for this bored at all. ;D
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From my limited experience and knowledge:
Back in the Seventies, most 2 stroke DDs that we drove loped at idle just after starting. This is why that "lope" still puts a smile on my face when I hear it. (I'd love to have it on my cell phone as a ring tone). I don't think it hurts anything. I find with the Jakes switch that replaces the buffer screw, it has to be adjusted a little farther in so the Jakes come on. If the switch (buffer screw) is backed out so it lopes, it is too far out for the Jakes to come on. That is my experience with my 4-71. YMMV.
JC
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Great, thanks for making it evident that the loping is not uncommon. Interesting that a particular maladjustment can be so common that it can make some think it is normal.
So at what point would the loping become problematic? Or could this potentially cause any problems? Obviously it only lopes at idle, so any related problems would only occur at that time.
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I'm sure TomC and JC know what they are talking about but, as my ole grandpappy always said, if it ain't broke don't fix it.
This has to rate way down there with the very minor problems.
So, mine will stay as is until it develops something more serious than this before a mechanic puts a wrench to it.
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A loping engine will NOT hurt anything. Only if you have an automatic and it lopes all the time causing lurching in the vehicle. Good Luck, TomC
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Mine does the same thing for couple of minutes then it quits.
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Like others have said set your buffer,idle speed and starting aid with a rack adjustment and the problem will go away
good luck
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Thanks everyone for the responses. I am learning something every day.
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Lostagain.
had heard from the neighbour's uncle who knew a back yard mechanic...
The thee 671 engines I have one was rebuilt and set up by a DD in Lufkin Texas, the second had the head replaced and the rack run by one of the top DD mechanics in the Costa Mesa are ( I blew a head gasket and a great busnut who happend to have an Eagle ) he lined the guy up for me. The third was set up by Huggy Bear.
All three lop when fist start up, but idle right on the money when warm.
I do not profess to know much about engines but the above guys can clean any mechanic out there.s clock.(with the exception of Huggy as he is no longer with us).
John
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;D
WOW Now I know why my old 671 lopes after start up for a few minutes and then idles smooth. Thanks all
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johns4104s,
You mention a top DD mechanic being in the Costa Mesa area. Is this DD guru still there? I am looking for a good DD mechanic to look over my engine and sort out some minor issues, and I am in Costa Mesa. Any chance you can give me his name and number please? You can PM me, or call me at seven one four nine five seven five two eight five.
Many thanks, John
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Let me see if I can find the # and PM you.
John