8v71

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8v71

Home > Discussion Forum > Mechanic's Corner - Engines

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All Messages in Thread	Author	Date
8v71	Rob Norgren	10-9-07
I'm Having Blow-By where oil comes out the pipes just after the 2 sides come together It does not happen all the time. thank you in advance
Re: 8v71	Rob Norgren	10-9-07
K the lecture is great :-) Its at idle and Idle is at 700 rpm so should I increse the idle to 1000 rpm ? And how do I take care of the Over fueling?
Re: 8v71	BUBBA THE BUS TECH	10-9-07
Your idle should be set: Curb or slow idle 550 - 650 rpm. Fast idle 1000 RPM. If you are using a dash tach take that with a grain of salt. They tend to be very in-acurate on these older units. Allowing that you have "Greyhound" ratios 2350 rpm should give you 72 to 75 miles per hour, charter, GM, or economy gears (all the same) will produce nearly 90 miles per hour @ 2350. Pretty scary as the tires on your unit are rated for 65 miles per hour max. Setting the idle speed should be done with a highly accurate meter. As the govenor controls both idle and high speed. Get both set. I recomend 2250 on the high speed, This will give good highway speed and good engine life. 2350 used to produce speeding tickets when I was a driver. Good Luck
Re: 8v71	BUBBA THE BUS TECH	10-9-07
Oil from the exsahst system is called wet stacking and is usualy caused by two things. Excessive idle time and over fueling. If you see wet stacking after a highway run you have a serious internal engine problem. The 8V71 was the choice of bus companies and fire depatments for years because they do not need long warm ups (I have started them cold reved to govenor to get air pressure and gone straight to high load high speed operation) and can be shut down any time the engine is at normall running temp without damage. If you must idle these engines make sure it runs 1000 rpm or higher and maintains 180 F at all times. These engines take damage from idling, very large damage if they are wet stacking. The oil you are seeing is actualy mostly fuel. Over fueling washes the oil off the cylinder walls and causes huge wear. I hope you don't mind the lecture. Good Luck
Re: 8v71	Rob Norgren	10-9-07
The oil is coming out of the exhaust pipes just after they come together. the 8v71 is in a 1966 MC5A and it has had a Jake Brake installed.
Re: 8v71	BUBBA THE BUS TECH	10-9-07
Out the drain tubes from the side off the block or the vent tubes from the valve covers? Both will pass a small amount of oil under load. I have plumbed the drip tubes into a 2.5 gallon jerry can with ventilation to keep the oil off the paint. The vents on the valve covers are a problem if they pass enough oil to drip on the ground or soak the back of the unit. You can pull them off and clean the wool mesh up to see if that helps, but usualy that means the engine is tired. I have seen them run an easy 100,000 miles like that though. Good luck
Re: 8v71	BUBBA THE BUS TECH	10-9-07
Part two, lecture two,;) Detroit 2 strokes over fuel when running cold at idle. To fix add load, add heat, shut off. The older style engins with an automatic can be loaded by just dropping into gear. Increase RPM to add heat and load per stroke. The problem with over fueling is that as you run the engine cold the govener adds fuel to maintain speed. This means some is not burning, thus extra fuel going into oil and out tail pipe. The curent engins from virtualy every manufacturer shut off half the engine to increase load on the rest of the cylinders. To make it worse the 8V71 will over fuel in realy cold weather imediately when falling to idle. The best thing to do is to not idle, warm up quick by not turning on interrior heat etc, When you stop, shut it off. Most transit systems that ran this engine instructed drivers to shut them off when at no more than normal operating temp and going to be idling 20 seconds or more.
Re: 8v71	Rob Norgren	10-9-07
This MCI5A Has a 4speed manual Trans. It takes time for it to air up to 90 lbs.. so whats to do for load? and to heat up faster?
Re: 8v71	Rob Norgren	10-12-07
All of the MCI5As I have seen so far have had the 8v71 in them LOL I have only seen 2 up front and personal. One was a 1974 and then mine a 1966.
Re: 8v71	BUBBA THE BUS TECH	10-12-07
Hi guys. The only 6V71/automatic I ever saw in a 5 was a glass top with 41 seats. I got passed by super Bs. Good it was slow on the hills. Just warm up on fast idle or at 1000 until the pressure is there to run it. Since we have very cold winter temps we need to do a warm up before loading the engine, If it starts without trouble (meaning it was warm enough to start with out starting fluid) it only needs 5 minutes or so. In the summer getting full air pressure on the guage and going is definatly the way to run it. Have fun, these little busses were the hot rods of the bussing industy for 3 decades that I drove. Good luck
Re: 8v71	Mark O.	10-10-07
Are you sure your -5 has an 8V-71? Most of the -5's I have seen had the 6V-71, not that the "lecture" wouldn't apply the same to any DD 2-cycle engine. 2100 for the top end is usually more than enough for a coach. Bumping the top end up to 2350 may allow you to climb a hill a little faster in a lower gear but the difference is in just a handful of minutes. I would also say amen to don't idle your engine excessively. If you have the ability to hook up to shop air before you start that would be even better. That would allow you to start the engine, put it in gear and go. Your neighbors would probably appreciate not having to hear the fast idle song of 2-cycle DD in the morning as well. I have seen coaches idle at fast idle for hours at ski areas. Most of them after idling for less than an hour had already gone way down below operating temperature. Most were kept running because of the lack of confidence the engine would restart in the cold. When those coaches left the parking lot you could see unburnt diesel fuel (yellow in color) staining the ground near to where the exhaust from those coaches hit the ground. With my buses I always started them down the road as soon as the air was up. Running downhill towards town would always warm them up faster than running them at fast idle in the driveway for any length of time. DD's were designed to be run flat out all the time. Running them easy is harder on them than running them with your foot to the floor. Just make sure that as you are running them you don't allow them to overheat (a real possibility in any MCI with twin side radiators). Mark O. Castle Rock, WA
Re: 8v71	BUBBA THE BUS TECH	10-10-07
Unless you need the extra speed the lower governed rpm will provide you with better fuel economy etc. I drove for a number of years with the 5a, 5b, 5c series and it seemed they didn't need the extra rpm as long as the freeway speed was there. To make slower more atractive the engine runs quiter and smother at 2100
Re: 8v71	Rob Norgren	10-9-07
She used to be a Greyhound she ran the Seattle to LA in the records I found on her. I'll change the slow Idle to 600 rpm and the fast Idle to 1000 rpm. and 2250 rpm on the high speed right now the high is at 2100 rpm. and stop idling her as I did not know I'm glad you where here. Bubba you are a great help. Anything else I need to know about her.
Re: 8v71	Rob orgren	10-13-07
I but the slow Idle at 475 on the gov the tag said 450-500 the fast idle at 1000 but that dropped the top to 2000 rpm and I can not seem to get it up from their LOL Got ya on the warm ups only untell the air is up. I move the Bus to warm weather and that is that if their is a hard Freeze I'm not wanting to be their LOL.