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'Lumpy' running Ruston Hornsby 4VSH


IanR

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Our Ruston has always had a lumpy spot on the throttle range, about 1/5 throttle or so. Fine on tickover (though I've always thought it should be able to tick over slower) and fine above the lumps too. Had a bit of time to investigate this a little but am slightly puzzled by my findings, easily done as although I'm not particularly stupid, I've never really had much to do with these oily lumps. On tickover, I cracked the injector unions one at a time, all had similar effects on the running in that the engine would not stay running at the given setting until the union was tightened again. Same amount of fuel pi55ed out from each. When wound on a bit till lumpy, each union was cracked again. This time, 1 and 4 pots slowed the revs, but 2 and 3 made no real difference. Again, equal fuel flow.

So, feeling brave, I swapped injectors 1 for 2, then 3 for 4. This time, cracking the unions when the engine was running lumpy, 1, 2 and 4 slowed the engine but the union on pot 3 mad the engine run smoother when the union was open.

The engine now has a slower smoother tickover but still has the lumpiness in the same range. Does this then suggest that the injectors are similar, ie, one or two aren't worse than the other like we first thought? Could it be pump timing on number 3? I'm going to dive in and start altering stuff just yet as I do feel the injectors could benefit a service as it must be years since they've seen any attention.

I also noticed that the exhaust valve of pot 1 is letting by as it smokes a bit from around the spring. It also smokes from around the governer lever, but that is apparently normal (ish)

Many thanks in advance to the knowledgable folks on here!!

Cheers, Ian.

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If I remember right, VSH has separate pumps for each cylinder, the pump racks from the governor have  to open each pump by exactly the same amount otherwise each cylinder gets a different amount of fuel, sometimes not enough for one  to fire. On the rack rods there will be a fine line  scribed on the left or right of each pump, adjustment of the connecting links will bring them into line so each pump works equally. On a 4 cylinder engine it's a pig of a job to get right! Imagine trying to do it on a big V16 with separate pumps- the way it's done there is by measuring the exhaust gas temperature at each cylinder and tweaking till they are all the same.

Also, the injectors on VSHs are Ruston own manufacture, not the more  common CAV, so getting new parts is tricky. Look after them!

Bill

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I don't know much about Rustons but working on the principle of starting with something that is hopefully known to be correct I would get the injectors seen to first. If that doesn't help then maybe injector pump (s) but as there is a question mark hanging over the valves perhaps that would be next on the list.

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Cheers folks, the injectors are first in line for a seeing to, any recommendations as to where to send them? Whilst they are away might be an ideal time to have the heads off and do the valves perhaps.

Ian.

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