detroit diesel 671 idling question

Nel · October 02, 2014, 09:21:59 AM

Hey Guys, just wondering why they say it is not good to let a 671 idle for a long period of time, also whats considered a long time , sometimes my 4104 might need 15 to 20 minutes to air up . is it better to set up a fast idle (which I do not have now?)
I noticed idle speed now is about 400 rpm and oil pressure about 50 psi when cold and 20 to 30 at 180 temp
Is that healthy? Thanks , Nelson

eagle19952 · October 02, 2014, 09:59:39 AM

20 minutes to air up is a serious problem....not what you want to hear....but it is.
idling at 400 rpm....should be 5-600, maybe a tach drive problem.
idling over 10-20 minutes, i would suggest 900-1100 rpm for longer periods especially in sub freezing temps.

others will probably say different.

bevans6 · October 02, 2014, 10:39:27 AM

The reason they say to not let it idle for a long time is that the engine cannot warm up or sustain a reasonable working temperature at an idle, with the combustion chambers running cold it does not burn all the fuel so it is passing wet soot through to the exhaust and diluting the oil film on the cylinder walls, which leads to worn out and coked up piston rings and general bad voodoo.

400 rpm seems a slow idle speed but in the range of idle speeds in my Detroit Diesel manual. It is too slow to allow the air compressor to work properly, for sure. The DOT test for compressor recovery, which is how you tell if your compressor is pumping an appropriate amount of air, is to get the bus full aired up (so it's not filling the suspension, for example), fan the brakes to bring the pressure down to 80 psi, run the engine at 1,000 - 1,200 rpm (a fast idle is around there) and measure the time taken to raise the pressure from 85 psi to 100 psi. That is the compressor recovery time. My bus does it in around 18 seconds, 30 seconds is OK, I believe the DOT test fail is 2 minutes.

Brian

Nel · October 02, 2014, 12:30:33 PM

Thanks Brian, great info to know , i will try the test . Any tips on adjusting the idle on the 671 , I would like to bring it up a little. Nelson

bevans6 · October 02, 2014, 12:51:45 PM

I don't know how to adjust the idle on a 6-71. It depends also on what style of governor you have. You should look for a manual for your engine. On my engine it involves a fair bit, it's not quite just turning up a screw (although that is part of it, to be sure). You also have to adjust the buffer, and check the no-load high speed idle (maximum speed the engine will run) because it's all inter-related. There is a couple of ways to really hurt the engine if you do something wrong, so if you've never done it before you want to really kind of suss it out before you start. Mind you the first 8V-71 I ever set up was mine, and I did it on my own with just the manual, so it can be done.

Brian

pennuja · October 02, 2014, 01:46:34 PM

I have a 71 series manual I am not sure if it is the right one but you can check.

https://diversifiedsystems.box.com/s/n1vrmzs956i9keu80ge8

bevans6 · October 02, 2014, 02:16:57 PM

Nelson, please put your bus details and where you are in your signature line in your profile. That way we can be a little more detailed in our comments.

Brian

eagle19952 · October 02, 2014, 02:21:58 PM

http://theghostbus.org/wp-content/uploads/2012/05/Detroit-6-71-Valve-Injector-and-Governor-Adjustment-Procedure.pdf

gus · October 02, 2014, 06:30:20 PM

4104s originally came with a hand throttle so if it is still there it can be used to increase the idle.

I also use mine as a cruise control.

mung · October 02, 2014, 06:46:49 PM

I don't think mine still has the hand throttle.

pennuja · October 02, 2014, 07:45:26 PM

When I let mine air up I pull the hand throttle circled in yellow, it looks like it just pulls down on the accelerator pedal on mine you can pull it out and it stays at the rpm that you leave it at I am not sure if it is supposed to be that way but it works..

Nel · October 03, 2014, 05:01:57 AM

Thanks fellas for all the great info, this forum is great and it's great to see that there are all these other bus people out there, because sometimes you feel like your the only nut out there, especially out here, there is not one person I have seen even having a clue or interest in what the heck I'm doing here with this monster in my back yard but I'm addicted, so there I got that off my chest.
Brian, Gus, Jim, Mung thanks for the info, I do have that little pull handle in Mung's picture , but it is seized, I will have to work on that.
Brian I'm looking on how to put a signature in my profile but if it doesn't go in this time, My name is Nelson , I live in West Nyack NY, which is about 30 minutes north of NYC, I bought my 4104-4519 in Sept. 2013 from a guy named Dan in NJ. He kept all kinds of info about the bus , which I found out was at one time owned by Nick Badame, who's son is in this website, I have talked to Nick Senior, real nice guy about the history of the bus while he owned it and plan on sending him pictures as I go along.
So that's it so far , bus runs great , I drive it once in a while to keep thing moving but can't wait to take it on a real trip when I'm done hopefully in the spring '15.
Thanks again , Nelson

mung · October 03, 2014, 05:30:50 AM

Interesting Jim, mine doesn't have anything where your hand throttle is. Now, does your step start right by the driver's seat? It looks like it in the picture.

pennuja · October 03, 2014, 06:02:02 AM

Quote from: mung on October 03, 2014, 05:30:50 AM
Interesting Jim, mine doesn't have anything where your hand throttle is. Now, does your step start right by the driver's seat? It looks like it in the picture.

Yeah right after the handrail see here.

mung · October 03, 2014, 06:59:53 AM

Wow. A lot different than mine.