[binaiks]

Originally Posted by Ashley2

TNSTC - CBE have modified the SLF's given to them under JNnurm to ply in the Mofussil route expecially in CBE-SLM, CBE-ERD route where they are more popular. I am not sure how this was allowed under JNnurm. You have spotted those buses only

The buses are not purchased under JnNURM. TNSTC-CBE ousted all the old SLF buses from the city, while the JnNURM buses are being used in the city. The old SLF buses were suitably modified and now run on CBE-Salem and CBE-Madurai routes.

They were running JnNURM buses (especially the Marcopolos) on these routes for quite some time, but were later reverted to city service.

[Ashley2]

Originally Posted by binaiks

...
They were running JnNURM buses (especially the Marcopolos) on these routes for quite some time, but were later reverted to city service.

Not so!
Marcopolo's are still being used in Mofussil routes.
Apart from the Kovai - Erode they are also used Mettupalayam - Palani.
Kovai - Palani.

[julupani]

Originally Posted by silversteed

I'd travelled from BLR to my hometown last night (Travel review here). Observed an interesting behaviour with the bus' engine. The engine noise was at the normal levels. After travelling for close to 6 hours, the engine noise suddenly increased. It was as though some fan or something came on. After some 5 minutes, it subsided. During this brief period, I felt the engine has maxed out on the engine speed. I noticed this thing happening after some 2 hours or so. Driver didn't know much, so am asking these questions:
> What was this noise?
> Why did it come on only after 4 hours, and then after ~2 hour gaps?
> Is it something to do with the turbocharger? It was like a longish "whooooooooosh" sound.

This is definitely not a turbocharger. Simply because the turbocharger is designed to run continuously to help provide more power and torque at a particular engine speed. And a turbocharger would make more of a whining noise, like that of a pump and not a fan. Also like I said the turbo would be designed to run on a more continuous basis. It will shut off during running only if there are extended periods of low engine speeds which can cause a loss of pressure in the exhaust manifolds. A valve is closed to rebuild the pressure which takes but a few minutes. Also in large engines running not very high boost pressures you can rarely hear the turbocharger whining, simply because the engine noise just drowns it out. I have heard brand new engines running (independently before being mounted on a vehicle) at all kinds of speeds on dynos and not been able to hear the turbocharger. No way to know whether they are running except looking at the boosted pressure readings. In smaller engines, especially petrol engines, you can hear the turbocharger whining away, more so in small capacity engines with high boost turbos.

My guess is that it actually is a fan only, ie the radiator fan. In modern engines the radiator fan comes on only when required. During highway running, the amount of air moving through the radiator is already high enough, thus not requiring the radiator fan to run. If slow speed running occurs for some time then temperatures will rise causing the fan to come on, and thus the tell tale sign. This fan can still cause a high enough volume of sound to be heard over the engine.

The only other thing that can cause an audible intermittent sound is the replenishment of the air tank of the braking system. But I still doubt this as it is still not that loud.

[binaiks]

Originally Posted by silversteed

Observed an interesting behaviour with the bus' engine. The engine noise was at the normal levels. After travelling for close to 6 hours, the engine noise suddenly increased. It was as though some fan or something came on. After some 5 minutes, it subsided. During this brief period, I felt the engine has maxed out on the engine speed. I noticed this thing happening after some 2 hours or so. Driver didn't know much, so am asking these questions:
> What was this noise?
> Why did it come on only after 4 hours, and then after ~2 hour gaps?
> Is it something to do with the turbocharger? It was like a longish "whooooooooosh" sound.

I had similar experience is a KeSRTC Super Fast a few months ago. But the sound came only when the bus attained its maximum speed (The speed at which the speed governor is set to). I remember hearing somewhere that the speed governor cuts off the transmission once the speed is reached - so perhaps this is what was happening. Its certainly not of the turbo, since the turbo would be working at full swing, since the engine would be very well working at the peak band.

[silversteed]

I didn't mean it was the sound OF the turbo, but was wondering if it had something to do with the turbo's BOV or something opening up incorrectly.

It could be the speed governor, as binaiks said. When it cut off the transmission. I didn't check the speed at which this phenomenon happened.

@julupani: Are you sure it's the radiator fan? I think the fan is run by a belt and pulley mechanism, and not electrically. IIRC, the pictures of the H series engines (sorry, don't have them now) show the fan fitted of the engine block itself. From my limited knowledge of engines, I think diesels make more heat than petrols, and I guess that's the reason for having the fan running all the time. Experts, please comment

[julupani]

The diesels do make more heat than petrols, and also run at a higher temperature than a petrol engine. But cooling systems are much more efficient today than before.

Today's engines generally come with a thermo-electric switch controlling a viscous clutch attached to the fan. Only when this clutch is engaged does the fan rotate. The pulley obviously runs continuously but not the fan. When the engine is stationary obviously the fan is rotating as there is no air flow over the radiator fins. So the fan starts within minutes of the engine starting, but shuts off at speed.

Of course this is only the case with modern engines, older engines just run the fans continously like you said so.

As for a speed governor, I dont think it can cause any such sound. They work by not allowing the engine speeds to rise over a particular limit. Once the limit is reached fuel gets cut off, causing speed to fall of. You will more likely hear a short oscillation in the engine speed once the limit is hit. As fuel repeatedly gets shut off and re-opened. This is the mechanism for both electrically or mechanically governed engines.

Of course at high enough engine speeds the radiator fan would also come off to cool down the engine.

[Transsenger]

Originally Posted by silversteed

I didn't mean it was the sound OF the turbo, but was wondering if it had something to do with the turbo's BOV or something opening up incorrectly.
It could be the speed governor, as binaiks said. When it cut off the transmission. I didn't check the speed at which this phenomenon happened.
@julupani: Are you sure it's the radiator fan? I think the fan is run by a belt and pulley mechanism, and not electrically.

This sound you had noticed is caused by the radiator fan. It works on viscous clutch (fluid friction). Even though the similar type of fan is used in Tata and AL buses/trucks, the sound is more evident in AL as the Hseries engines is more refined. Now, why it happens...when the engine is started we find the fan rotating, but actually its not driven by the engine and does not take load. As the engine temperature raises above 92-95'c, the viscous clutch activates the fan. This sudden forced air circulation through radiator, caused when the fan rotates with drive from engine results in "blowing sound". After a few minutes the temperature gets lowered and fan gets disconnected. It has nothing to do with speed governor. Its only based on the engine temperature & cooling system.

[BaCkSeAtDrIVeR]

AFAIK, the speed governor does not cot off transmission. That would require modification to teh gear box / transmission system, which is not possible within the budget of a typical speed governor, which is available below 10K.

What it would cut off is fuel supply to the engine.

[silversteed]

@BSD: I didn't think on those lines.

@Transsenger & julupani: Thanks for your inputs! I had taken the same bus back to B'lore last night. The sound has nothing to do with the speed.

[binaiks]

The new design from Prakash (ZMR, something). I was excited to see this bus. The design isn't great, but is certainly different from the regular Volvo clones we see. The bus had projector headlamps, and LED Pilot lamps!

Out of excitement, I did not notice the rear profile! (I waited from 2030 to 2230 for this bus, and got carried away after taking the pic).

The bus is operated by ARC, to Chennai from Madurai.

[urzdeepu]

Originally Posted by binaiks

The new design from Prakash (ZMR, something). I was excited to see this bus. The design isn't great, but is certainly different from the regular Volvo clones we see. The bus had projector headlamps, and LED Pilot lamps!

Out of excitement, I did not notice the rear profile! (I waited from 2030 to 2230 for this bus, and got carried away after taking the pic).

The bus is operated by ARC, to Chennai from Madurai.

The design is certainly not that appealing but if they have added projectors and LED's in their headlamp sets, its a welcome move.

Also doesn't the side profile(especially to the rear end) depicts a Globus look?

[smashnerd]

Originally Posted by binaiks

The new design from Prakash (ZMR, something). I was excited to see this bus. The design isn't great, but is certainly different from the regular Volvo clones we see. The bus had projector headlamps, and LED Pilot lamps!

Out of excitement, I did not notice the rear profile! (I waited from 2030 to 2230 for this bus, and got carried away after taking the pic).

The bus is operated by ARC, to Chennai from Madurai.

The front fascia is a bit of a letdown really! Looks pretty dated, though the projector + LED combo is welcome.

[rajakumar]

Originally Posted by binaiks

The new design from Prakash (ZMR, something). I was excited to see this bus. The design isn't great, but is certainly different from the regular Volvo clones we see. The bus had projector headlamps, and LED Pilot lamps!

Wondering what purpose does the normal headlight under the hood serve? Do one need to raise the hood for the lights to be used?

[silversteed]

@binaiks, I've seen that bus many times during my Chennai days. Maybe because of the paintjob on the front, the design looks dated. But I feel without those stripes and the front grill closed down, it should look fresh.

It's called Prakash BMR-Z1, IIRC. SMK claims the luggage space is appreciably larger than their conventional bodies.

What I did not like is the wheel color. They should've painted it silver-grey, like the ABTX buses. Or added a wheel-cup like the one in Volvos.

[julupani]

The extra lights are actually used all the time. I spotted this in all Prakash built buses in my state. In fact almost all buses have these, from AZAD, Sutlej, a few local companies. I had asked a driver, they said, the headlights built in by the body company are just no good, thus extra lights are needed.

A few local companies have no started to leave out circular enclosures to add further lights.

But HNS builder from Rajasthan, have very powerful projector lamps, thus not requiring extra lights.

All info here collected from private buses in Orissa.