The Bridge at Dozan, Bolan Pass, near Quetta, Pakistan

The Bridge at Dozan, Bolan Pass, near Quetta, Pakistan
The bridge carried both road and rail over a creek bed. The bed had to be dug out by hand over many days, with much help freely given by locals. Click on the photo and scroll down, to bring up the story of this bridge. Go to: to find more.

Monday, October 3, 2011

The Fuel Isn't Getting to the Engine

The 40-gallon fuel tank: pretty battered from encounters with rocks, ships, humps in Pakistani roads, who knows?
(click on any photo in this blog to enlarge it)

A fairly basic necessity: the fuel from the tank must get to the diesel injector pump on the engine.
And it did, for long enough to move the bus around the yard at Craigend Farm, where restoration is proceeding. Then it didn't.
On the side of the engine, on the timing case for the mechanically-minded, is a normal-looking diaphragm lift pump to suck fuel up from below: it had been overhauled expertly and shouldn't be any problem. Nevertheless another was fitted ; still no result.
To check if there are any blockages, due to sediment or corrosion or even leaves blown into the very large filler hole, a very effective trick is to blow compressed air backwards down the pipe joining tank to lift pump. No result.
Another strong possibility is that one of the several joints in the pipe has loosened, allowing air to be sucked in, instead of fuel. Air is lighter than fuel, so the pipe fills with air and the fuel stays where it is. As well as a loose joint there is a chance that where the pipe passes beside part of the underframe, it has rubbed through due to vibration over the years. Either way it's a case of examining the pipe minutely along its entire length.

The inside of the tank may have rust particles accumulated in its base, where the pick-up pipe rests. Blowing through with compressed air won't get rid of the particles: it just dislodges them for a while.
At left is a rather remarkable shot from Andy: the inside of the fuel tank photographed through the small aperture in its side, where the fuel gauge fits.*  (not sure what the yellow bits are, ed.)   The hole at the top is the filler, about 100mm. (4 inches) in diameter, so it can be filled very quickly without slopping. The vertical tube is the pick-up pipe, sitting in a rough strainer in the base.
*Yes the fuel gauge is on the tank, not in the driver's cab. It's not something you need to look at very often. The fuel consumption rate is a pretty steady 10 miles per gallon, so if you've done 390 miles the tank  probably has only another ten miles in it.  And in service with a bus company, the tanks are refilled at the end of every day's shift, regardless, so every bus starts the new day with a full tank.
 Looking on the bright side, it's best that this problem surface now, not on a Motorway in France.

An aside: The reader might ask: why go to all the trouble of taking out the tank just to see if there is a blocked pipe?   A truism often spouted by the old hands in the mechanic's game is: "sometimes the longest way is the fastest way". Take the whole thing apart, inspect it, put it back together and then you know exactly what went wrong, and why, and how to prevent it happening again.

Watch this space, for the final solution to this so far baffling problem.

Update 20th October

The air in fuel line - issue is coming closer to being resolved.  When John came over 2 weeks back to relieve me from my frustration ; testing each fuel line section one by one; sucking raw diesel then spitting out; finally concluding maybe the pipe dropping into tank may be faulty . . . he then dropped the main fuel tank, lodged it in his van and disappeared destined for an old-school expert somewhere in Falkirk.

Well, that guy has long since gone out of business, as had the next one.  Now the tank has found its way to Bridgeton awaiting another caring oldie to caress and fix the 64yrs old equipment . . . and so it goes on.

Meanwhile, last Monday I determined to shift the bus to gain better access for roof work, but found that even from the bottle . . . no consistent uplift of fuel.

So, senhor dismantled the lift pump (all that was left since the lines had been tested by John and the tank was gone . . . ) and . . . shouldn't there be a small coiled spring above the fibre washer/valve?  Cliff and John mumbled yes, of course, Andy . . .  but neither could expand.

This morning, I took the complete lift pump to Pattersons, the diesel profs around here and, tomorrow morning I collect repaired unit, in full working order.  Then . . . back to the bottle (of fuel, temporarily strung up behind the engine).

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