MC-8 Manual Trans. Shifting

[DrivingMissLazy]

I strongly suspect that running it up to the speed limiter as you are shifting to higher gears would be the proper rpm.
Richard

[TomC]

Jeremy- I took a bus trip in Europe a few years ago and the bus was a DAF with a 12 liter engine in it (12 meter bus).  It had a 8 speed fully syncroed  trans in one gear shift.  The driver always (except on a steep hill) started in 2nd, skipped to 4th, then up the gears where at 100 km/hr he was cruising at a nice 1500 rpm.  For max fuel economy-on the flat notice where you can shift and have the engine come down to around 1200 rpm.  But for pulling a grade, just rev to the governor and shift.  Personally, I would slowly rev the engine until the governor hit, just to make sure it works.  My guess that will be around 2500 rpm.  500 cubes is not a very big engine (8.2 liters).  Is your engine a V-8 or 6 cylinder?  If it is a V-8 it might be the Detroit fuel pincher from years back since Bedford and GM are in bed together.  If it is a 6 cylinder, then it's probably a Bedford-which are good engines.  Don't be afraid to rev the engine.  You're not going to hurt it-they always set the governor way below max rpm for the engine-especially the Brits-being as conservative as they are with engines.  It can be as bad to run the engine to slow as running against the governor all the time.  Besides, you'll probably never put enough miles on the engine to get it close to being worn out. 
Like your bus size!  I have a 40ft'r, but next time I would like to use a 35ft x 102"-as long as the floor goes all the way to the rear of the bus with no engine or radiator intrusion-then I can just about use the same floor plan as I got now with my 40 footer's 3ft intrusion to the rear with the engine (transit bus).  Good Luck, TomC

[Jeremy]

Jeremy- I took a bus trip in Europe a few years ago and the bus was a DAF with a 12 liter engine in it (12 meter bus).  It had a 8 speed fully syncroed  trans in one gear shift.  The driver always (except on a steep hill) started in 2nd, skipped to 4th, then up the gears where at 100 km/hr he was cruising at a nice 1500 rpm.  For max fuel economy-on the flat notice where you can shift and have the engine come down to around 1200 rpm.  But for pulling a grade, just rev to the governor and shift.  Personally, I would slowly rev the engine until the governor hit, just to make sure it works.  My guess that will be around 2500 rpm.  500 cubes is not a very big engine (8.2 liters).  Is your engine a V-8 or 6 cylinder?  If it is a V-8 it might be the Detroit fuel pincher from years back since Bedford and GM are in bed together.  If it is a 6 cylinder, then it's probably a Bedford-which are good engines.  Don't be afraid to rev the engine.  You're not going to hurt it-they always set the governor way below max rpm for the engine-especially the Brits-being as conservative as they are with engines.  It can be as bad to run the engine to slow as running against the governor all the time.  Besides, you'll probably never put enough miles on the engine to get it close to being worn out. 
Like your bus size!  I have a 40ft'r, but next time I would like to use a 35ft x 102"-as long as the floor goes all the way to the rear of the bus with no engine or radiator intrusion-then I can just about use the same floor plan as I got now with my 40 footer's 3ft intrusion to the rear with the engine (transit bus).  Good Luck, TomC

Hi TomC

Thanks for the reply - some useful information there which sounds about right for my engine, though mine is perhaps geared a bit lower than that. As you say, my engine is on the small side, although they still used the same engine in the full size 56-seat versions of the Paramount (mine was only a 35-seater). My Bedford is the only bus I have ever driven so it's hard to make comparisions, but I would say the power of mine isn't much more than 'adequate', and the capacity is certainly smaller than other equivalent buses, though it does have the turbo.

To answer your question, it's a straight six - Bedford's own design as far as I know. Apparently there are 'low' and 'high' pressure turbo versions of it, but I've no idea which mine is - as you say, I suspect both are fairly de-tuned anyway. The military are very big users of Bedford 500s in their 4x4 trucks, so I guess it is regarded as being basic and dependable, which suits me fine.

I originally got quite close to buying a Volvo B10M coach (very common over here), which have a 12.1 litre engine, but was steered toward the Bedford by a couple of people who said that although the Volvos (and I guess their equivalents) make great long-distances coaches, the Bedford engine would be better suited to a motorhome, being simpler and cheaper to repair and maintain, and using a lot less fuel.

The engine in my bus is mid-mounted, so the floor is flat all the way to the rear as you describe. You do of course lose some bagge bay space at the front with the mid-engine, but then you get a very large boot (trunk) at the rear to replace it.

Jeremy

[Jeremy]

I strongly suspect that running it up to the speed limiter as you are shifting to higher gears would be the proper rpm.
Richard

Richard

The speed limiter I was describing is an electrical device that locks the throttle cable when a pre-set road speed is acheived - it doesn't actually control the engine RPMs in the same way that a mechanical governer does.

There is a sticker on the driver's window on my bus that records the yearly testing of the speed limiter as part of the annual safety inspection of the bus - just like the tachograph which measures drivers' hours, the speed limiter is a legal thing rather than something done by the manufacturer.

Jeremy

[Ednj]

When I drive this bus, I usually grind gears during downshifts

David

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David
When you downshift,between the first time you push down the clutch pedal and the second time.
Put your right foot right to the floor and keep it there.

[Tony LEE]

"Put your right foot right to the floor and keep it there."

only works (and does work perfectly) if you begin the downshift at a speed just a little higher than the limited speed of the lower gear.

[buswarrior]

Drat and darn....

we need some video to link to.

trying to describe downshifting in words does not work.

My coach is automatic, showing a 10 speed tractor trailer downshift doesn't help...

happy coaching!
buswarrior

[pvcces]

Jeremy, I think that your concern about revving your engine up to governed speed is misplaced. EVERY diesel has a governor; they are necessary becouse of the way that fuel injectors work.

The governed speed is not the danger mark; it is the upper end of the normal working range.

I have some of the same biases that you do; when I don't have to get the maximum power, I shift before I reach governed speed, too. My reasons may be a little different than yours.

I know that injectors increase their output as their stroke rate rises. But, looking at the torque curve, I see that torque rises with RPM and then falls off. Since I know that fuel is increasing, I reasoned that fuel economy must be a little better while torque is rising than when it levels off or falls.

When possible, I try to operate the engine at the best mix of RPM and torque that is still safe for the engine. In our standard timed two stroke, that seems to be between 1100 and 1600 for light loads and 1500 to 1950 for hard uphill pulling.

It may interest you to know that many transits are run right against the governor when they get on the freeways, because they are geared so low. With one more gear, their economy improves quite a bit.

For what it's worth.

Tom Caffrey

[DrivingMissLazy]

I suspect there is quite a difference in shifting than in normal operation, especially as regards mpg.

The relative short time that an engine would be at the governed rpm during shifting as compared to the time that the coach is driving down the road at the most economical rpm would generally be insignificant. Just run it up to governed speed, shift and quit worrying about lt. LOL
Richard