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Author Topic: Fast idle question  (Read 1511 times)
lostagain
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« on: January 31, 2013, 12:05:56 PM »

6V92TA.

As I am completing the tune up after installing new injectors, I notice two devices for fast idle.

Air line comes from a Skinner valve (operated by the switch on the dash) to feed air to a cylinder that pushes the speed lever on the governor to give me about 1200 rpm.

Just upstream from that air cylinder is a T in the air line. That line feeds, through a pressure regulator, into the idle adjustment screw housing at the back of the governor. That, as I understand it, activates a little piston that pulls on the idle screw to increase the rpm.

They both come on at the same time, being fed off the same air line from the Skinner valve.

When the bus is running, I will play with the regulator to see if it varies the fast idle rpm.

So why is there two ways to get fast idle? Or do they works in conjunction with each other? Does anyone else have the same setup?

I never looked before because the fast idle always worked fine.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
luvrbus
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« Reply #1 on: January 31, 2013, 12:17:32 PM »

The one you are speaking of JC is a holding cylinder that holds the governor at a certain speed when the fast idle is engaged all manual DD 2 strokes with a fast idle have that setup if not it would be off to races 

I have repaired a few 2 strokes people have plugged the line because the cylinder was leaking then flipped on the fast idle not a pretty sight
« Last Edit: January 31, 2013, 12:35:11 PM by luvrbus » Logged

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bevans6
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« Reply #2 on: January 31, 2013, 12:36:45 PM »

My fast idle is an air cylinder that is connected to the buffer screw.  It adds spring pressure via the buffer screw to raise the idle speed.  There is a tee to another cylinder with a push rod that locks the speed control lever 100% closed so the main throttle control is locked out.  there is nothing at all connected to the idle speed control, which is under a cover at the back of the governor, under a plate that has all the throttle cable mounts and such on it. 

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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« Reply #3 on: January 31, 2013, 12:44:56 PM »

Brian, what JC is telling is true that is the way the 92 series are hooked up when they had a throttle delay that is a air cylinder the old governor socket does no good working on his lol all 3 need to work in conjunction don't play around in that area to long JC fwiw
« Last Edit: January 31, 2013, 01:13:21 PM by luvrbus » Logged

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lostagain
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« Reply #4 on: January 31, 2013, 02:21:33 PM »

Thanks guys, I get it. I will look some more later. My engine does not have a throttle delay. It has a starting aid screw, and a Jake switch/buffer screw.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
luvrbus
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« Reply #5 on: January 31, 2013, 03:24:10 PM »

You will run across other configurations also I have one here a limiting speed governor high speed variable unit from a cement truck that will go from idle to full speed with regulated air from that housing not the throttle that maybe what you have
The only thing with the above setup you don't need a fast idle cylinder it's all done at the speed adjustment cover pretty neat setup I can sell all I find because of the price of the combo Jake/Buffer switch
« Last Edit: January 31, 2013, 04:05:18 PM by luvrbus » Logged

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lostagain
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« Reply #6 on: January 31, 2013, 04:08:10 PM »

I'll be ready to start it tomorrow. So I will see what happens when I turn up the regulator. I was reading in the manual about the variable speed you're talking about. I think that's what the regulated air does on the idle speed adjusting screw. A concrete mixer would have the regulator in the cab.

I looked again at the cylinder on the speed control lever. It definitely looks to me like it will push on the lever to increase the rpm, rather than hold it so it doesn't go too fast. I'll have a better look to see what it does with the fast idle on and off with it running tomorrow.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
TomC
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« Reply #7 on: February 01, 2013, 08:49:19 AM »

Or you could get rid of all that and just use a King Cruise control for the fast idle. Good Luck, TomC
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« Reply #8 on: February 01, 2013, 05:07:09 PM »

OK, all back together! It takes a long time to re-install all the intake plumbing which I had off to install the new turbo. I also had to fab up a piece of steel pipe 4" at one end and 3 1/2" at the other with a 30 degree angle,  to go between the turbo and the air horn on top of the blower. Then put the exhaust pipe back on between the right manifold over to the Y pipe below the turbo on the left side. And lots of other odds and ends I won't bore you with. No wonder truck shops don't like to work on buses.

Anyway, after adjusting the idle speed and the Jake/buffer switch, I looked at the fast idle operation: the air cylinder pushes the speed control lever on top of the governor all the way to full fuel. The air line to the idle speed housing at the back of the governor pushes a piston that pulls on the idle speed adjusting screw to increase rpm. That pull is limited by a nylon lock nut which if you turn it in or out decreases or increases engine speed to what you want for fast idle. So I see what Clifford was talking about now. Turning the pressure regulator up or down doesn't have any effect on speed. It was, and I left it at 100 psi. Does anyone know what it should be set at?

Fun learning new things...

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
luvrbus
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« Reply #9 on: February 01, 2013, 05:39:38 PM »

Must be a MCI thing the regulator on yours Eagles with the same hookup are a direct line into the skinner valve

good luck
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Van
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89' Silver Eagle 15/40 6V92MUI Boulder City,NV




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« Reply #10 on: February 01, 2013, 06:25:41 PM »

Atta boy JC! Always nice when you kin git in there , hands on and get it sorted out.  Wink

 I'm,Not bored  Grin
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lostagain
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« Reply #11 on: February 01, 2013, 06:48:15 PM »

Eh Van! What kind of work do you do at B&B? Building and fixing buses I guess? Fill us in.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
luvrbus
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« Reply #12 on: February 02, 2013, 06:41:38 AM »

Van will learn a lot from Gary he is master been around a long time and does know buses of all kinds,I just hope Van does not use the same hair dresser lol
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Van
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89' Silver Eagle 15/40 6V92MUI Boulder City,NV




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« Reply #13 on: February 02, 2013, 07:29:09 AM »

Clifford I told Gary what you said verbatim, lol he almost fell outta his chair laughing, holding his hair in place of course Grin
JC, Gary asked me to come in and help out with doing services on some of the customers busses. this past week been doin some services (Brakes,bearings,lube) on an 01 Eagle so  Gary and Joe can finish up some interior upgrades. Next week, same cheese for a MCI 102, I am assuming Grin that is in shop currently. also just in the shop is Zappos late model Prevost, an XLII LeMirage  which will be getting 4 14' slide outs Shocked Clifford is right, Gary is a Master at this stuff, but when it comes to anything I am not sure about mechanically there is Da Book and my friend Clifford that I will always turn to Wink Smiley
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lostagain
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« Reply #14 on: February 02, 2013, 07:46:20 AM »

Good for you Van, sounds like a good job for a bus nut.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
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