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HB3 'searching' until warm


Ca Jon
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Just now, Ca Jon said:

Hi everyone,

Does anyone know why my hb3 searches between high and low revs until its warm?

 

I think that you mean surges. I would suggest a sticky governor/control rod/rack but it could be a fuel problem. I don't know the HB engine but older engines may have an adjustment to minimise surging.

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Something in the governor-to-fuel -pump- elements system is a bit sticky when cold, but OK when warm, or there is excessive play somewhere which takes up when warm.

 

Start at one end and work all the way to the other. Check that everything is free and there is no obvious play in pivots, spring fastenings etc.

 

N

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Thanks Tony, I dont think its fuel as it responds to throttle, just idle that it does it. 

 

2 minutes ago, BEngo said:

Something in the governor-to-fuel -pump- elements system is a bit sticky when cold, but OK when warm, or there is excessive play somewhere which takes up when warm.

 

Start at one end and work all the way to the other. Check that everything is free and there is no obvious play in pivots, spring fastenings etc.

 

N

Thanks N

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Looking at images the HA looks like a larger SL so individual injector pumps behind the side plate. On our SL4s we found that it was all too easy to allow a pump to twist slightly as it was tightened down. This can cause the control rod to stick and give those symptoms.

 

I suggest that you take the side cover off the engine when cold and move the control rod by hand and see if it jumps right back when released. If it does not then remove one linking pin at a time to isolate each pump in turn until you find one that is causing the problem. Then reconnect, loosen the pump clamp bolt and jiggle the pump while moving the control rod. When you find the control rod jumps back tighten the pump bolt and retry.  If that does nt cure the problem it is likely to be in the governor, but check the manual in case there is an idle stabilisation adjustment. The SLs had one.

 

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17 minutes ago, Tony Brooks said:

Looking at images the HA looks like a larger SL so individual injector pumps behind the side plate. On our SL4s we found that it was all too easy to allow a pump to twist slightly as it was tightened down. This can cause the control rod to stick and give those symptoms.

 

I suggest that you take the side cover off the engine when cold and move the control rod by hand and see if it jumps right back when released. If it does not then remove one linking pin at a time to isolate each pump in turn until you find one that is causing the problem. Then reconnect, loosen the pump clamp bolt and jiggle the pump while moving the control rod. When you find the control rod jumps back tighten the pump bolt and retry.  If that does nt cure the problem it is likely to be in the governor, but check the manual in case there is an idle stabilisation adjustment. The SLs had one.

 

Thanks Tony, I will try that. 

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Lots of engines do this until warmed up. As I understand it, the lubricating oil around the governor mechanism is a bit sticky when cold so the speed control of the governor becomes sluggish. Once warmed up, the mechanism works as it should. Reference videos on the net of older railway locos starting from cold, the engine speed is all over the place to start with but gradually improves as they warm up.

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3 minutes ago, billh said:

Lots of engines do this until warmed up. As I understand it, the lubricating oil around the governor mechanism is a bit sticky when cold so the speed control of the governor becomes sluggish. Once warmed up, the mechanism works as it should. Reference videos on the net of older railway locos starting from cold, the engine speed is all over the place to start with but gradually improves as they warm up.

thank you for that. Very reassuring!

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Use the decompression levers to open the exhaust valves one at a time.  When open flick the lever over and judge how snappy the valve on each cylinder is when it closes.  You're looking for a sluggish return on one or more.

Carbon build up on exhaust valves or stems will reduce compression and provide irregular running until things warm up and everybody starts chattering together.

  • Greenie 1
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