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Rolls Royce B80


mtskull

Question

Hi

 

Not strictly an MV issue but I hope some of the wealth of experience on this forum may be able to assist me.

 

I am carrying out some work on a fleet of old Dennis fire appliances, all of which are fitted with B80 or B81 engines, some of which are military-spec replacements for the original engines. I am reasonably experienced in maintenance of older vehicles but I have never worked on a RR B series until today.

 

I would be interested to hear any general tips regarding maintenance of these engines, particularly where to obtain spares such as filters, gaskets etc. Also, some advice would be welcome regarding a specific problem:

 

One of the appliances (civvy-spec B80 Mk50a) starts and revs ok but has a persistent misfire/loss of power when under load. Compression is notably down in No.1 cylinder (all others ok) but the power loss feels worse than can be explained by one weak cylinder; it feels as though it is only running on 4 or 5 out of 8.

 

Apart from a compression test, we have swapped everything in the ignition system (Jolley engineering electronic distributor) for known good items and checked that none of the valves are sticking; the ignition timing has been statically set at 2 deg. ATDC and the firing order checked.

 

The appliance is said to have previously run well and the problems only manifested themselves after a period pf standing idle.

 

The plugs are sooty, suggesting over rich mixture; I haven't investigated the carburettor yet but I would rather know a little more about it before I do.

 

Are there any known weaknesses or issues with the B80 that might cause the problems I describe?

 

Has anybody on this forum experienced such an issue?

 

Can anybody confirm that the cylinders are numbered such that No.1 is at the the front (i.e. not the flywheel end)?

 

Compression in the poorly cylinder is restored when oil is poured in through the sparkplug hole, leading me to suspect broken piston rings. Is this a known issue?

 

Any help would be much appreciated.

Edited by mtskull
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Is it the same filter assembly as a Ferret? Can you show me a picture?

 

I know someone who has a spin on filter adapter in stock . . . .. . . .

Sorry, I have no idea what filter is fitted to a Ferret. I'll try to take a photo on thursday, when I am next on site. A spin on adapter would be a good idea if not too expensive; ideally we would need five of them!

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Another B80 query: Can anybody tell me what the differences are between the civilianand military spec. B80? 

The reason I ask is because I have been working on a military B80 (No. 1 Mk 5P) which has been installed in place of a civilian one (Mk 50M), which, I am told, ran OK but was getting tired. 

The replacement engine was bought direct from the MOD; we are using the military ignition system and the carburettor from the old engine. This carb has been stripped & cleaned, diaphragms inspected and OK; altitude control correctly set.

With this carb installed, the military engine started readily and idled OK but was clearly running weak when trying to rev; it would accelerate but hesitantly and with a lot of backfiring. When I partially closed the automatic choke by hand, it would rev up and run smoothly. I have checked for air leaks etc. and found none.

In desperation, I swapped the main jets for a pair from a B81 carb and guess what? -it now runs absolutely perfectly but I am a little concerned that I might simply have masked another problem.

Is there a reason why a military engine would be jetted differently from a civilian one?

One  possibility that occurred to me is that at some time in the past the carburettor might have been replaced with one from a B60. I'll have to go back with a magnifying glass to find out what jet sizes we are using but in the meantime can anyone tell me what the appropriate main jet sizes are for B60/80/81?

Any other suggestions  or info welcome.

Edited by mtskull
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Hi,

I see you are using a B80 which was set up to power the winch on a Centurion ARV. No problem there. Regards to the backfires, I am wondering if you warmed the engine up enough or that the automatic choke was working for the correct duration. It could be adjusted incorrectly. Depending on the variant of carbs for the B80, it could be an incorrect jet for the carb you are using. There is a RE or UE number on the side of the carb and this will denote jetting and spec. Let me know what it is and I will tell you the correct ones. You should not mix a B80 and a B81 carb as they are wide differences in jetting.

The military engine could well be set up for low grade fuel, whereas a civilian version for a fire engine would have run on a higher octane petrol.

Richard

 

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Richard,

Thank you.

 It is very interesting to know what the engine was originally intended for.

In common with the previous problem which you helped me with, I am being asked to sort issues arising from various other people's efforts, with very little record of what work has been carried out before. 

I was assuming that: a) The carburettor was the same one that was installed on the old engine and b) that it had actually run satisfactorily before. I cannot be certain that this is the case.

The auto choke is currently disconnected; I was working it manually to get it started but the engine had certainly been well warmed up; 170 Farenheit on the gauge and the choke actuating thermostat had moved to the fully hot position.

I don't propose to leave the B81 jets in that carb permanently but the improvement that they made suggests that something was very wrong with the jetting before. 

I'll have a look for the letters you mentioned and also find out the jet sizes that have been/are presently fitted.

Andy

Edited by mtskull
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28 minutes ago, mtskull said:

Richard,

Thank you.

 It is very interesting to know what the engine was originally intended for.

In common with the previous problem which you helped me with, I am being asked to sort issues arising from various other people's efforts, with very little record of what work has been carried out before. 

I was assuming that: a) The carburettor was the same one that was installed on the old engine and b) that it had actually run satisfactorily before. I cannot be certain that this is the case.

The auto choke is currently disconnected; I was working it manually to get it started but the engine had certainly been well warmed up; 170 Farenheit on the gauge and the choke actuating thermostat had moved to the fully hot position.

I don't propose to leave the B81 jets in that carb permanently but the improvement that they made suggests that something was very wrong with the jetting before. 

I'll have a look for the letters you mentioned and also find out the jet sizes that have been/are presently fitted.

Andy

OK Andy,

If you find the RE or UE number on the carb, I will send you the spec for that particular one.

regards, Richard

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On 28 December 2017 at 9:46 PM, Richard Farrant said:

OK Andy,

If you find the RE or UE number on the carb, I will send you the spec for that particular one.

regards, Richard

Hi Richard,

The carb number is UE 481.

I have checked the main jets that were originally fitted in the carb when I first worked on it; they are numbered 130, which corresponds with the ones fitted to our other B80, so maybe there's still an air leak whick I have yet to find....

Andy

 

 

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A couple more B80 questions:

Went out for a run yesterday; engine working fairly hard. Water temp steady between 160-180F, oil temp much the same. When properly hot, oil pressure at idle was only showing 5psi, increasing to 15 at fast idle and 30-40 when driving.

Is this normal, or should we be investigating the condition of the oil pump and bearings?

The other query concerns the starter motor (12 v). It works fine time after time when cold but once the engine is hot, nothing happens when pressing the starter button except that the ammeter shows a discharge of 10 Amps. I have taken the starter off, inspected it and bench tested it successfully through 100 cycles but when re-installed, the same issue arises. I initially thought that the pinion might be jamming on the ring gear but there is not even any clicking from the solenoid and turning the engine manually doesn't help (although it will start on the hand crank). I suspect that the solenoid has a fault that only manifests itself when hot but if anybody has experienced the same problem or can offer any advice,  that would be most welcome.

Andy

 

Edited by mtskull
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