A surging Perkins...

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nicclark

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Hi,

We've got a Broom Ocean 37 with 2 Perkins HT6354's in, looked after over their 50 years and low hours overall (3000). Last year I had the injection pumps reconditioned and also all the injectors as they were all different and the pumps were leaking fuel everywhere not to mention the extra smoke over and above what's normal for this engine!

One engine went back together perfectly and runs well. The other not so. It starts on the button, idles at 600 but after about 700-800rpm, it starts to surge. I have tried everything I can think of and still have the issue which is becoming really annoying. I've taken the whole fuel system to bits, blown into the tank, checked the lift pump diaphragm, checked all connections, bled everything, changed the filter. I have also replaced the spill rail - there was a stripped thread that had bubbles in on the way back to the tank and I thought this may have been the issue, but alas not.

I don't think there is anything terrible wrong, but I'd really like to get to the bottom of it. My feeling is that it is air related, not pump related, but I am stumped.

Anyone had anything similar before?

Thanks.
 
BruceK said:
I had similar when I was sucking air through a fuel shut off valve
Click to expand...
Thanks - I am sure it's air! Only thing I have not done is clean the racor filters, witch I'll do tomorrow, but have new elements so doubtful they will cause issues. I get the feeling it's something on the engine that has been disturbed.
 
Air leaks are a common problem and normally this is the suspect for your fault, there are other issues and one is the valve settings as too much clearance gives similar problems.

Check your exhaust when you get fuel surge and if you get black smoke you are overfuelling and this is another indication of too much clearance in your valves.
 
Nick. Its defo air. When there is air in the top half of the CAV DPA pump the govenor messes about.

In the return line insert a short length of clear pipe you'll be able to see air bubbles. Then fit a new fuel supply line and dunk in a bucket of fuel. See what happens.

If its sucking air in the cause likely to be before the lift pump since that is vacuum (after lift pump is pressurised and would be leaking.

The first place I would look is the pick up in the tank. Just cos you can blow down it does not mean its ok to draw fuel from.
 
nicclark said:
Hi,

We've got a Broom Ocean 37 with 2 Perkins HT6354's in, looked after over their 50 years and low hours overall (3000). Last year I had the injection pumps reconditioned and also all the injectors as they were all different and the pumps were leaking fuel everywhere not to mention the extra smoke over and above what's normal for this engine!

One engine went back together perfectly and runs well. The other not so. It starts on the button, idles at 600 but after about 700-800rpm, it starts to surge. I have tried everything I can think of and still have the issue which is becoming really annoying. I've taken the whole fuel system to bits, blown into the tank, checked the lift pump diaphragm, checked all connections, bled everything, changed the filter. I have also replaced the spill rail - there was a stripped thread that had bubbles in on the way back to the tank and I thought this may have been the issue, but alas not.

I don't think there is anything terrible wrong, but I'd really like to get to the bottom of it. My feeling is that it is air related, not pump related, but I am stumped.

Anyone had anything similar before?

Thanks.
Click to expand...
Does it have the circular damper fitted ?
 
volvopaul said:
Does it have the circular damper fitted ?
Click to expand...
No, damper removed in the rebuild, they said this is not needed anymore.

I'm going to get the fuel and the tank cleaned as it is filthy and may never have been cleaned before. I can't see or find anywhere air could be getting in but ill keep going.

I'll try your suggestions Ben over the next day or so and see what happens. Clear hose will prove air or dirt one way or the other I guess.

Cheers!
 
nicclark said:
No, damper removed in the rebuild, they said this is not needed anymore.

I'm going to get the fuel and the tank cleaned as it is filthy and may never have been cleaned before. I can't see or find anywhere air could be getting in but ill keep going.

I'll try your suggestions Ben over the next day or so and see what happens. Clear hose will prove air or dirt one way or the other I guess.

Cheers!
Click to expand...
I’d say that’s why it’s surging , damper was fitted for that reason .
normally the cav pump is horizontal with fuel sitting g level throughout the pump , 6354 sits vertical , I was told years ago that why as it maintains a fuel pressure inside the pump before it bleeds back to the tank.
 
volvopaul said:
I’d say that’s why it’s surging , damper was fitted for that reason .
normally the cav pump is horizontal with fuel sitting g level throughout the pump , 6354 sits vertical , I was told years ago that why as it maintains a fuel pressure inside the pump before it bleeds back to the tank.
Click to expand...
That's really interesting, I did wonder about it, but the other one is absolutely perfect, and for some reason the stbd engine is slightly more inclined than the port and has an extra oil cooler because of this. I'm in contact with Diesel Bob who reconed them, so will see what he comes back with.

Clear pipe tonight, exciting!
 
So I have just put a clear tube on the return to the tank and there is no visible air coming through it. Back to the tank pickup I guess.
 
can you swap pipes going before or after primary filter to the two engines and see if the problem "moves" with the pipe?
I mean pickup pipe...
 
Thanks, I'll try both of those, really appreciate the suggestions. I was sure it was air. I checked the gearbox oil last year but will check tomorrow and will swap the fuel hoses over and see what happens....
 
Just another thought... Could the old hot start system cause this issue? Both have been decommissioned but all the fuel pipework is just hanging. Again it was fine last year but if it's open to air etc. Or has been disturbed could this be an issue?
 
Hi and thanks for the help so far... I've swapped the tank connections to the engines this morning so that the struggling engine uses the filter and tank pipe that the good one does, but this didn't make a difference. That means that it's unlikely that it's the pipe into the tank or the racor filter after it that is the issue. Gearbox oil is good, and doesn't need to be under load to surge anyway. No air as far as we can see and have put clear hose onto the return to tank and didn't see bubbles.

Any other ideas gratefully received! Is it worth changing the lift pump anyway? I have a new one, but it's a slightly different arrangement and would need to modify the hoses a bit. I also dismantled the current one and it seemed ok in terms of the diaphragm so can't think there's anything else wrong.

Anything over 1000rpm will surge, but rev it harder 1700+ and it will stop surging and settle down.

I think the only option is to get the pump tested really.

I asked a diesel pump specialist about the dampers and he said that on a hydraulically governed pump it would make a difference in removing them, but on mechanical pumps, it should not so unlikely to be the issue.

Not many other places to look really - it was running perfectly apart from leaking diesel last year, hence the pump rebuild.
 
If you run it with the return line submerged in a bucket, do you see air coming to the surface?

Is there any sign of wear on the arm on the lift pump, can you look at the cam that operates it?
 
Thanks for all the replies and suggestions - this evening we swapped the pumps over - not a quick job on a horizontal engine or one I really wanted to do. It seems it is the pump after all, as the same fault was there as soon as we started her up. I'll have to get it fixed by Diesel Bob - but have now racked up a reasonable engineering bill for no particular reason and spend lots of time covered in diesel!
 
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