1978 Crown Bus Conversion

[Iceni John]

A MUI Detroit won't shut off until sufficient air has built to actuate the Skinner shutdown valve. What they did was to actuate the emergency stop that closes a flapper over the air intake in case of a runaway. You REALLY don't want to use it unless absolutely necessary because it can cause the blower to suck oil past its seals and destroy them, and that's not a cheap repair.

How well do tires that wide fit on the rims? I'm guessing you have 8.25"-wide wheels, what Crown used for 12R22.5" tires. Any clearance issues with the tie rod or brake cans? At some point I need all new tires for my bus, and 12Rs are getting pricy these days and hard to find - if 315s fit and work OK then I may consider going that route. I'm glad you didn't put lower-capacity 11Rs on instead; if nothing else, they have more revs per mile because of their smaller diameter, which messes up the drivetrain's power and torque and the bus's top speed. Besides, Crowns look weird sitting on smaller tires!

John

[o1marc]

Originally Posted by Iceni John

A MUI Detroit won't shut off until sufficient air has built to actuate the Skinner shutdown valve. What they did was to actuate the emergency stop that closes a flapper over the air intake in case of a runaway. You REALLY don't want to use it unless absolutely necessary because it can cause the blower to suck oil past its seals and destroy them, and that's not a cheap repair.

How well do tires that wide fit on the rims? I'm guessing you have 8.25"-wide wheels, what Crown used for 12R22.5" tires. Any clearance issues with the tie rod or brake cans? At some point I need all new tires for my bus, and 12Rs are getting pricy these days and hard to find - if 315s fit and work OK then I may consider going that route. I'm glad you didn't put lower-capacity 11Rs on instead; if nothing else, they have more revs per mile because of their smaller diameter, which messes up the drivetrain's power and torque and the bus's top speed. Besides, Crowns look weird sitting on smaller tires!

John

Changing tires in no way effects torque or horsepower of the motor.

[Rawlings]

Originally Posted by Iceni John

A MUI Detroit won't shut off until sufficient air has built to actuate the Skinner shutdown valve. What they did was to actuate the emergency stop that closes a flapper over the air intake in case of a runaway. You REALLY don't want to use it unless absolutely necessary because it can cause the blower to suck oil past its seals and destroy them, and that's not a cheap repair.

How well do tires that wide fit on the rims? I'm guessing you have 8.25"-wide wheels, what Crown used for 12R22.5" tires. Any clearance issues with the tie rod or brake cans? At some point I need all new tires for my bus, and 12Rs are getting pricy these days and hard to find - if 315s fit and work OK then I may consider going that route. I'm glad you didn't put lower-capacity 11Rs on instead; if nothing else, they have more revs per mile because of their smaller diameter, which messes up the drivetrain's power and torque and the bus's top speed. Besides, Crowns look weird sitting on smaller tires!

John

Yeah, I was a little bothered the guy didn't just park the bus and call me, but oh well. I am hoping it didn't cause any damage, since I didn't know that button had been pushed I tried restarting the engine like 10 times thinking it was other things, I kept the key held a few times as it would sort of keep the engine trying to turn on but it would shut off as soon as I would release the key, do you think I may have damaged anything attempting to restart the engine prior to knowing that button was used? I was able to drive it back to the parking lot 30 miles away and nothing sounded out of the ordinary and she shut off just fine. I knew I was right that the bus wouldn't shut off right away if they just moved it to park it, you would think a company that changes truck tires daily would know its not good to just turn on and engine, move the truck and shut off right away, its just not safe since engine would be cold, I never drive this bus off until its been on for at least 10-15 minutes.


As far as the tie rods, what are those, I can look into this and give you any input since you may want to change from 12 Rs just let me know what I should look for so I can give you valuable information, I don't know a whole lot they just said the 315s fit on the wheels and there was no rubbing issues :S

[Rawlings]

Is there a way for me to check if any damage was done due to the guy activating the engine emergency shut off? I was able to reset and drove bus for 40 minutes back to where I store it, I didn't notice any bad oil pressure, the temperature was fine on both transmission and water, no issues. But how would I make sure nothing is wrong in case of what you mentioned with oil being sucked and seals broken? Would this be evident when I drove it? Is it safe to assume it's fine since it drove normally back?

[o1marc]

Originally Posted by Rawlings

Is there a way for me to check if any damage was done due to the guy activating the engine emergency shut off? I was able to reset and drove bus for 40 minutes back to where I store it, I didn't notice any bad oil pressure, the temperature was fine on both transmission and water, no issues. But how would I make sure nothing is wrong in case of what you mentioned with oil being sucked and seals broken? Would this be evident when I drove it? Is it safe to assume it's fine since it drove normally back?

Stop worrying. If it blew the seals you would lose oil pressure. If there are no ill symptoms, don't worry, drive it.

[Rawlings]

Originally Posted by o1marc

Stop worrying. If it blew the seals you would lose oil pressure. If there are no ill symptoms, don't worry, drive it.

Lol I guess I'm being paranoid, never spent a large amount of hard earned money on a big rig like this before, sort of scary thought to have to think crap this may now cost me a large some to fix cause some shop guy decided to press that button without thinking wow, maybe I should let the engine warm up before trying to shut it off...or better yet..maybe I should call the owner haha

Mark thanks a lot anyways for your input , same for John thank you guys so much.

[cowlitzcoach]

Your bus with new shoes looks GREAT!

Too bad the wheels are black. Crowns just don't look right with black wheels. Yellow wheels with silver lug nuts and center hubs look really sharp when the bus is yellow. Silver wheels with chrome lug nut covers and chrome center caps look really sharp. Alcoas look even better!

If the blower seals were ruined the bus would have no power, it would be blowing smoke, and it wouldn't be running well at all.

The tie rod ends are the knuckle at the end of the tie rod that ties the left and right steer tires together and make both wheels turn back and forth together. If you don't have enough clearance when you turn the wheels 100% to the left or right the tie rod end can come into contact with your tire. The same interference can happen with the drag link, the rod between the steering box and the tie rod. You can also have interference with the springs. Just make sure that when the steering is turned 100% left or right that the tire doesn't touch anything. In the rear make sure you have enough clearance in the wheel well between the outside edge of the outside tire and the inside of the fender. Also check to make sure you have enough clearance between the inside edge of the inside dual and the springs.

When I updated the tires on my Crown I went from tube type tires to tubeless. Since I had to purchase new wheels anyway I put 24.5" wheels on and I ran 11x24.5 tires. They are basically the same size as 12x22.5 but the total cost of new wheels and 11x24.5 tires cost me less than what 12x22.5 tires by themselves would have cost me.

[Rawlings]

Originally Posted by cowlitzcoach

Your bus with new shoes looks GREAT!

Too bad the wheels are black. Crowns just don't look right with black wheels. Yellow wheels with silver lug nuts and center hubs look really sharp when the bus is yellow. Silver wheels with chrome lug nut covers and chrome center caps look really sharp. Alcoas look even better!

If the blower seals were ruined the bus would have no power, it would be blowing smoke, and it wouldn't be running well at all.

The tie rod ends are the knuckle at the end of the tie rod that ties the left and right steer tires together and make both wheels turn back and forth together. If you don't have enough clearance when you turn the wheels 100% to the left or right the tie rod end can come into contact with your tire. The same interference can happen with the drag link, the rod between the steering box and the tie rod. You can also have interference with the springs. Just make sure that when the steering is turned 100% left or right that the tire doesn't touch anything. In the rear make sure you have enough clearance in the wheel well between the outside edge of the outside tire and the inside of the fender. Also check to make sure you have enough clearance between the inside edge of the inside dual and the springs.

When I updated the tires on my Crown I went from tube type tires to tubeless. Since I had to purchase new wheels anyway I put 24.5" wheels on and I ran 11x24.5 tires. They are basically the same size as 12x22.5 but the total cost of new wheels and 11x24.5 tires cost me less than what 12x22.5 tires by themselves would have cost me.

I will have to verify this when I go to the bus tomorrow, I know I made some sharp turns today when taking it back and I turned the wheel all the way to the left and right and didn't seem any different, however I would have to check underneath when parked. I will also check the rear drive tires for what you mentioned. They did tell me the driver side steer wheel had a wheel stud that was very worn out and could possibly not hold the lug nut tight enough which can eventually force the nut to fall off. They recommended I change that wheel stud, does anyone have an idea of how difficult this is and or what a reasonable cost to fix would be like? Theres 10 of them so idk how immediate this needs to be fixed considering its only 1 of them and I drove the thing from California and nut still was in place haha.

As far as the 11x24.5 tires, did that drop your weight max? any drawbacks?

[Iceni John]

Originally Posted by o1marc

Changing tires in no way effects torque or horsepower of the motor.

Agreed, but the power and torque are then not fully developed at the road speed the manufacturer originally intended, and that will (slightly) affect driveability. You may gain one thing, but probably at the expense of something else. That's what I meant!

John

[BlackJohn]

As to the original shut down issue, I wonder what is up there. I would have a look at the ignition switch first as it is likely original. They do wear out, burn out, loosing continuity. Get it checked if you can't do it and replace if necessary. Disconnect battery before taking it out for inspection.
Something caused that so that's where I'd start.


John

[cowlitzcoach]

Originally Posted by Iceni John

A MUI Detroit won't shut off until sufficient air has built to actuate the Skinner shutdown valve. What they did was to actuate the emergency stop that closes a flapper over the air intake in case of a runaway. You REALLY don't want to use it unless absolutely necessary because it can cause the blower to suck oil past its seals and destroy them, and that's not a cheap repair.

How well do tires that wide fit on the rims? I'm guessing you have 8.25"-wide wheels, what Crown used for 12R22.5" tires. Any clearance issues with the tie rod or brake cans? At some point I need all new tires for my bus, and 12Rs are getting pricy these days and hard to find - if 315s fit and work OK then I may consider going that route. I'm glad you didn't put lower-capacity 11Rs on instead; if nothing else, they have more revs per mile because of their smaller diameter, which messes up the drivetrain's power and torque and the bus's top speed. Besides, Crowns look weird sitting on smaller tires!

John

I would agree that the reason why the bus didn't shut off when the key was turned off was because the air pressure hadn't risen high enough to pull the engine shut off back to the shut off position.

Many times when I have started a Crown long enough to move it a little bit the air pressure wouldn't have gotten high enough to shut the engine off. I have turned the key off, closed and locked the door, and walked away from the bus and eventually the engine shut off without any extra help.

On the stick shift Crowns you just put it in high gear and popped the clutch with the brakes applied. Problem solved.

[cowlitzcoach]

As far as the 11x24.5 tires, did that drop your weight max? any drawbacks?[/QUOTE]


It has been almost twenty years ago when I did that so my memory isn't that fresh. But, IIRC, the difference in weight capacity was negligible.

What I do remember was the tire was virtually the same size in width on the ground and were a little taller which raised my top speed about 5 MPH.

[Rawlings]

Originally Posted by cowlitzcoach

As far as the 11x24.5 tires, did that drop your weight max? any drawbacks?


It has been almost twenty years ago when I did that so my memory isn't that fresh. But, IIRC, the difference in weight capacity was negligible.

What I do remember was the tire was virtually the same size in width on the ground and were a little taller which raised my top speed about 5 MPH.

I have noticed on these new 315s that my top speed on speedometer is now 58mph vs 55mph and downhill it went as high as almost 65mph vs 60mph on the old 12rs.


I have attached an image of a spring that I believe is attached to the gas pedal, it seems its a little stretched out right in the middle of the spring, should I worry about this and get it replaced and if so is this a standard piece or do I need to get the part number somehow for this little metal spring?

I am also including two youtube videos I added for everyone to see the spring I am talking about and a walk around view of the bus

https://youtu.be/eXeBhZpqjnI

https://youtu.be/TP0Nq5yKd60

Let me know what you guys think!

[PNW_Steve]

Originally Posted by cowlitzcoach

I would agree that the reason why the bus didn't shut off when the key was turned off was because the air pressure hadn't risen high enough to pull the engine shut off back to the shut off position.

Many times when I have started a Crown long enough to move it a little bit the air pressure wouldn't have gotten high enough to shut the engine off. I have turned the key off, closed and locked the door, and walked away from the bus and eventually the engine shut off without any extra help.

On the stick shift Crowns you just put it in high gear and popped the clutch with the brakes applied. Problem solved.

Cowlitz,

I have been racking my brain trying to accurately describe how to shut down Detroit 2 strokes by pushing on the governor lever.

That is how we used to do it if there was not enough air pressure to operate the Skinner valve.

Can you explain it?

Definitely a better method than the emergency stop if the engine is idling. In the case of a runaway you definitely want to use the emergency stop.

[o1marc]

Originally Posted by Rawlings

I have noticed on these new 315s that my top speed on speedometer is now 58mph vs 55mph and downhill it went as high as almost 65mph vs 60mph on the old 12rs.


I have attached an image of a spring that I believe is attached to the gas pedal, it seems its a little stretched out right in the middle of the spring, should I worry about this and get it replaced and if so is this a standard piece or do I need to get the part number somehow for this little metal spring?

I am also including two youtube videos I added for everyone to see the spring I am talking about and a walk around view of the bus

https://youtu.be/eXeBhZpqjnI

https://youtu.be/TP0Nq5yKd60

Let me know what you guys think!

Stretching the spring that amount will likely show no measurable effect, if it ain't broke, don't fix it.

[Rawlings]

Originally Posted by PNW_Steve

Cowlitz,

I have been racking my brain trying to accurately describe how to shut down Detroit 2 strokes by pushing on the governor lever.

That is how we used to do it if there was not enough air pressure to operate the Skinner valve.

Can you explain it?

Definitely a better method than the emergency stop if the engine is idling. In the case of a runaway you definitely want to use the emergency stop.

I would like to know too, that way I have another method of shutting off other than the emergency shut off button. Also is there a way to test the emergency shut off button without the engine actually running, just to make sure the piece that flips over to force the engine to shut off still is functioning after they pressed the button at the shop? I don't want to test it with the engine running for obvious reasons, will it flip with the engine off and just on battery power?

[PNW_Steve]

The process is the same for all of the Detroit 2strokes. Layout of the part is a little different between the V engines and the inline engines.

Here is a description I found for the 8v71:


If you don't know where your governor on the engine is, this is a good time to have someone show you where it is. All Detroit 8V-71's (DDEC wasn't made in the 8V-71) have mechanical governors. Open the back of your engine compartment. If you start at the lower crankshaft pulley, come up until you see the other V belt pulley on the right side of the engine. Then come up further and you'll see what looks like a metal box with two levers coming out the top. One will be the on/off lever and the other the throttle. If you have a cable throttle, then the other is obviously the on/off. If you have an air throttle, just have someone sit in the drivers seat and push the throttle up and down with some air pressure in the system-the one not moving will be the on/off. In any case, if your engine won't stop with the switch, just open the rear and lean in-making sure you don't get caught in any moving parts-push with your hand on the on/off lever (might be hot!) and the engine will turn off! When you release it (it's spring loaded) the engine will be in the run position. Good Luck, TomC

[Rawlings]

Originally Posted by PNW_Steve

The process is the same for all of the Detroit 2strokes. Layout of the part is a little different between the V engines and the inline engines.

Here is a description I found for the 8v71:


If you don't know where your governor on the engine is, this is a good time to have someone show you where it is. All Detroit 8V-71's (DDEC wasn't made in the 8V-71) have mechanical governors. Open the back of your engine compartment. If you start at the lower crankshaft pulley, come up until you see the other V belt pulley on the right side of the engine. Then come up further and you'll see what looks like a metal box with two levers coming out the top. One will be the on/off lever and the other the throttle. If you have a cable throttle, then the other is obviously the on/off. If you have an air throttle, just have someone sit in the drivers seat and push the throttle up and down with some air pressure in the system-the one not moving will be the on/off. In any case, if your engine won't stop with the switch, just open the rear and lean in-making sure you don't get caught in any moving parts-push with your hand on the on/off lever (might be hot!) and the engine will turn off! When you release it (it's spring loaded) the engine will be in the run position. Good Luck, TomC

If I take a picture of different areas of the engine would you be able to point out which one it is? I added a couple pictures a few posts back of where the gas pedal spring and cables pull when it is pressed down, would the governor switch you are mentioning be around there or would it be located by the floor board under the floor of bus. When I take the floor board out I see the other side of the engine reset lever and below that I also see the starter.

[PNW_Steve]

I have not had my fingers on a 6-71 in 25 years. Forgive my failing memory.

The throttle cable should connect to one of two levers on the top of the governor. The second one is the stop lever.

It will be adjacent the head. On a "vertical " 6-71 it would be on the right side.

I think we may need Cowlitz or one of the Crown guru's to chime in here. I don't want to confuse you......

[Crown_Guy]

I've given the info here before, so, for the umpeenth time and in miniature condensed form, here it is again.

Forget about that spring on the throttle. It's fine and until it finally breaks, just leave it alone. You can find them at any hardware store. I replaced one recently, I got an assortment package from Home Depot. It's just a simple return spring. Nothing magical or part numbered about it. You'll know when it fails because the throttle pedal won't come back up all the way, but you can push on the back of the pedal to return it to idle while driving, until you can get down there and replace the spring. I'd get a package in advance and carry it as part of your on-board replacement parts kit. Like you already do, right, with oil, water, belts, fuel filters, oil filter, water conditioner, etc. and tools.

First, to answer your question of tripping the emergency engine stop damper while engine is stopped,,,, absolutely. Go ahead and check it out for proper function and that you can reset it again. That's how it's done by a mechanic anyway. It's simply a trigger-sear type release mechanism and the stop button energizes the pull-in solenoid coil to release the latch so it allows the spring driven damper plate to close off the air intake to the blower. This should be checked occasionally anyway for proper function. As you found out, it's all right there under the floor hatch in full view.

Everyone, don't over think, or complicate the normal engine shutdown operation of the governor stop lever. It simply needs to be moved about 30 degrees and held there until the engine stops. Simple and easy to understand and visualize. The air actuated piston merely pushes it in that direction with air pressure and holds it until the air bleeds out of the bus air system.....or until the key is turned on again and the driver wants to run the engine. It's not so hard to turn by hand and hold in the off position that anyone should be able to reach in and turn it and, hold it till the engine stops. Just turn it in the same direction as the air actuator is trying to move it.

The stop lever is the short one of the two. All it does is stop the engine. Or lets it run. By the way, with no air pressure or anything affecting it, the Stop/Run lever is held in the RUN position at all times. This means that if the engine is cranked inadvertently, for any reason, it WILL start and run normally. Nice if you want to bump start it, but not so nice if you are fooling around and accidentally crank it while being entangled with stuff that goes around with the engine. Could ruin your whole day.

AGAIN, the engine STOP lever is the one that the air actuator is pushing on. All you need do is move it by hand in the direction the air actuator is pushing it. It's a mechanical lever that moves the fuel rack in the head to zero fuel, overriding the governor, thus shutting the engine down. Got It? Nothing more complicated than that. It's simple to reach, it's right in front of you as you look in from the left side, and easy to move. Nothing to worry about, no fans or belts, just reach in and turn it clockwise in the same direction the air actuator is set to move it. Hold it till the engine stops. Things might be hot, so be careful and, maybe use gloves, the exhaust manifold will be hot for sure.

This functions exactly the same way on ALL Detroit 2-stroke highway vehicles I've ever seen or driven. I've even had to physically remove the shutdown actuator from the governor top plate once, due to an electrical system fault in order to allow the engine to run so I could finish the trip. Once you understand what's going on here, and it's dead simple, you can add modifications to air lines and such in order to override the normal system operations in order to regain control and finish your journey with little fuss or muss.

I concur completely that the guy at the tire shop, with no idea of what a Crown is, or how it works, tried to shut it off with out waiting for the air pressure to build up. I would have thought the brakes wouldn't release, but the primary and secondary air systems were working against him on this. Enough to release the brakes, but not enough for all the accessory systems to be up and running yet. I STRONGLY suggest that you leave instructions with future shops to NOT try starting, or move the bus, without contacting you first. Remember they have never seen a Crown before, and the DD installation has it's own special quirks we take for granted, but not everyone is clued into the secrets.

By the way, this is how we all learn and grow in our experiences with these. I know I did, and most everyone else I know has been through similar things. Welcome to the club and I bet you won't soon forget this either. You could consider putting an easily pushed aside safety cover over the emergency shutdown button to discourage inadvertent operation of the button, even by you sometimes, by an Ooopsy. All it takes is a single push to actuate the damper. Then it's time to get out and reset it by hand. Make sure the reset handle is reachable and usable from the left side engine door so you don't have to lift the floor hatch. If it needs attention to function, or possibly requires modification to a larger handle or whatever, then the time to do it is at your leisure in your yard with tools at hand, and not on the side of a road somewhere in the snow and ice, raining cats and dogs etc. Well, you get the picture. Proper, Prior, Planning, and all that can really pay off.

Anticipate in advance the critical items that can put you down, hard, full stop, and try to install plumbing and/or electrical work arounds to get around those failures, to keep on driving. For instance, Fuel filters. A spare set, mounted in place, and plumbed, so all you need do is turn valve(s) and keep on going.

An easy to use engine priming system to re-prime the engine. It can be as simple or as elaborate as you want, but it should be all plumbed and ready to go for when you eventually find yourself running out of fuel, usually in the darkest most empty stretch of highway you can imagine. At that point you'll finally find out just how hard it is to find any mechanic who really knows how to re-prime a 2-stroke, and it ain't pretty, I know this from first hand experience. But it wasn't my screw up, so I got to stand back and watch them go through three (3) count'em 3 mechanics before they found an old gray haired guy who had the knowledge and the tools at hand to get their MCI 8-71 primed and running again. You should do whatever you can to install a proper re-priming system you can handle by yourself if needed. Soon. It will save you a whole bunch of trouble later.

Running a bus out of fuel, back in the day, was a fire-able offense and we all acted accordingly. You should always be aware of your fuel state, and where to get fuel, at all times. But be prepared to recover gracefully, just in case.

You should consider one or two easily reached air fittings, front and back, maybe one with a truck style glad-hand like what truckers use on trailers. These air taps can be used to air up the bus to release brakes etc., if it needs towing, as well as for use by tools or outside accessories in a pinch.

A high current proper battery plug, to charge, or use to jump start the engine. Installed and ready to go, eliminates all the hassles with clamping on to battery posts and jumper cables. Many ideas about how to do this with house batteries and generators etc. Think it through and plan and install it ready for the day you'll need it, and you won't regret it.

Think first about how to keep the vehicle running and usable and easily limped to a service facility. This should be paramount before worrying about what kind of wood flooring or trim to use on the interior. Without a safe and reliable vehicle under you, all you have is a fancy trailer that won't be moving anytime soon, not even Spam in a can, just carpets in a can. How much fun can that be.

Stuff like this should be thought about in advance and provisions made to work around quickly when things fail on the road. This will make life much simpler and you'll have confidence you can get yourself out of nasty situations while still retaining control of your expenses.