| Author |
Message |
William Guire (Will) (216.82.156.131)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 08, 2003 - 4:40 pm: | |
I'm still waiting for my manuels to arrive. In the meantime, a couple more questions (while I jockey it arround the driveway).
MC9 with 8v92
1. What should the oil pressure be at idle? It's about 15-20psi now. Goes up to 50psi or so when revved.
2. The air pressure gets low (50) and I have let it idle a bit till it comes back up.
3. The generator light came on when the air pressure was low. Is it driven or controlled by air pressure.
4. When manuvering does it help to turn the air off to the tag axles? It seemed to.
5. I have an oil leak. It seems to be coming out of a cylider on the bottom rear of the engine. it is two or three inches in diameter, a foot or so long and has a threaded hole under that seems to be where the oil is coming from.
OK, I won't ask any more for the rest of the day (maybe my manuals will arrive soon).
Thanks |
ron rice (12.228.20.219)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 08, 2003 - 5:36 pm: | |
From my experience in the charter/tour business:
1.) the detroit 2 cycle engine will hold a very low oil pressure at low idle and does not seem to hurt the engine.
2.) If the air is getting low while moving around a lot in a small space at idle speed it is because the air suspension is taking a lot and the braking is taking a lot and the system is running very slow and cannot keep up.
3.) The generator is a direct drive off the engine. The earlier model coaches had belt drive with air tighteners and this was a way to keep the driver from reving the engine before the air came up and throwing the belts.
4.) I have never been convinced that shuting the air off to the tags will help. If you can lift the tag off the ground like the prevost does you will get a slightly better turning out of the coach but it does raise the front of the coach. It is also a lot of work to get the tags up in the air for the very little that it will assist.
5.) I don't know enough about this one to help.
I wish that I had the 8V92 instead of my 6V92 but the wife and I are just happy to have an MC9. |
Jayjay (198.81.26.174)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2003 - 12:37 am: | |
Everything sounds about normal to me...JJ |
modelt (208.18.102.18)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2003 - 6:49 am: | |
Welcome to Detroit, have to agree sounds about right. |
Johnny (63.29.158.88)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2003 - 8:57 am: | |
FWIW, the 6V71 at work holds ~12-15psi at a hot idle. Doesn't seem to have hurt it, since it's pushing 760,000 miles. I agree, though--that can be a bit of a shock the first time you see it. |
J.Meyers (208.169.40.98)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2003 - 9:31 am: | |
DA-Book Recomends a minimum of 2PSI of oil pressure per 100 RPM at idle with the engine at operating temperature. |
Johnny (63.29.158.88)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2003 - 9:55 am: | |
Assuming 600RPM idle (no tach), that's about right for the bus at work. |
Gary Carter (68.27.236.15)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2003 - 1:50 pm: | |
A series 92 should not leak |
jmaxwell (66.42.92.11)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 09, 2003 - 5:30 pm: | |
Gary C: Did DD ever build one that didn't. Their 4 cycles are much better about it, but even they have a couple of spots that are prone to leak. As for the 2 cycles, the only method I ever heard of to prevent leaks after the engine has seen some use is to run them without oil or paint them CAT yellow! Leaks in Ser 71 & 92's are all relative and are best categorized by how much rather than the fact that they do. |
Gary Carter (68.27.249.167)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 12, 2003 - 4:22 pm: | |
Sorry but my 8V92TA DDEC does leak. The 8V71 I had in our 4106 did not leak, but would sometimes drip from the breather tubes. |
Buswarrior (Buswarrior) (64.229.209.74)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 16, 2003 - 3:25 pm: | |
Hello Will,
Re: Question 2 about the air going way down.
When operated efficiently, the air system should maintain operating pressure in the stop and go conditions that moving around your yard would be.
The key word is efficiently.
From the sounds of it, you either have been unneccessarily heavy with your brake foot, which uses a lot of air, or your compressor needs a rebuild, or you've got air leaks.
Most folks use too much brake pedal in the beginning when first using air brakes. Work on only pushing the pedal down far enough to do the job and no further. Pushing further just wastes your air pressure, which the compressor has to rebuild.
Here's how to check for leaks:
1) build up the air pressure to maximum.
2) shut off the engine
3) release the parking brake
4) push the brake pedal all the way to the floor and hold it there
5) once the air gauge stops moving from the use of air, watch the air gauge for 1 minute and see how much air it loses.
6) It should stay rock steady and not lose anything in one minute. For a commercial coach, law allows 3 pound drop in 1 minute.
To check for air compressor recovery:
1) build air pressure to maximum
2) tranny in neutral, fast idle turned OFF, engine just idling.
3) reduce air pressure to below 85 lbs
4) using your watch, time the compressor's ability to pump the air back up from 85 to 100 lbs.
5) If it is more than 2 minutes, it's really bad, and illegal, if it was a commercial coach.
A good compressor will build on the idle in about 30 to 40 seconds.
If you had heavy leaks in the first test, the results from the second test are not reliable.
Any questions, just holler!
happy coaching!
buswarrior |
William Guire (Will) (216.82.156.169)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 16, 2003 - 5:58 pm: | |
Thanks Buswarrior
I think it was a case of my heavy foot. And I was off & on it a bunch. I'll do the tests as suggested, but it seems to hold the air air pretty well once it is built up.
Now if I could just figure out that oil leak....
Will |
Geoff (Geoff) (66.238.120.125)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 17, 2003 - 9:04 am: | |
If the oil is coming from a cannister at the bottom of the engine this sounds like the air box drain cannister-- it should have a pipe plug at the bottom that you can drain the oil out. If it fills up quickly then you have too much oil coming out the air box drains which in a 92 series usually means the oil control rings are worn out. |