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mtskull

Rolls Royce B80

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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I have just re-read your post, having posted a reply, and realised my info was incorrect, so now deleted.

 

However, there are many on here who will no doubt give you all the info you want. I'm sure someone will be along soon with what you need.

 

Good luck. Steve.

Edited by Ex-boy
Incorrect information

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I have not worked on RR B80s, this range of engines was designed with parts commonality in mind. Ignition Timing is very time consuming to get right, Head gaskets are an issue on B81s, especialy with aluminium heads. Block damage between cylinders is the result if not caught in time. You will have to wait for the Martian and Saracen/Saladin boys probably at the weekend for the up to date information. Motor car people seem to be hoovering up engines and parts.

Edited by john1950

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Banisters are the usual source of parts for the B8X series engines.

 

Andy

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I tried phoning yesterday before posting their no and have had no reply yet. Have now had contact. They prefer email contact if possible, wjrbanister@btconnect.com. telephone-01797-253211 hope this helps. They have Manuals, Parts books also Engines and Spares

Edited by john1950

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Thank you; knowing where to source parts is a good start. 🙂

 

Now, has anybody experienced anything like the misfire I described? The last time I dealt with an engine running roughly like this, the problem was exhaust gases leaking into the intake side but I can't see how that would be possible with the design of the B series. Any thoughts?

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At a basic level, if you've got a good spark, compression, fuel and it's all happening at the right time then it's difficult to see what might be wrong. The logic of that is check through the various systems methodically, but I'm not quite sure I see the point in doing so when you have a known major issue with one cylinder; particularly since if your assessment of broken rings is right, the more you run it the more damage you risk doing. If your assessment is wrong, and for example it's just stuck rings where it's been sitting, by continuing you risk breaking them and again causing more damage.

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Have you cleaned and checked the carburettor as well as and especially the condition of the diaphragms?

 

Diana

 

 

 

 

Thank you; knowing where to source parts is a good start. 🙂

 

Now, has anybody experienced anything like the misfire I described? The last time I dealt with an engine running roughly like this, the problem was exhaust gases leaking into the intake side but I can't see how that would be possible with the design of the B series. Any thoughts?

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Have you cleaned and checked the carburettor as well as and especially the condition of the diaphragms?

 

Diana

Not yet; where are these diaphragms to be found?

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I believe the carburettor is somewhat similar to the Marcus Solex fitted to B60 engines and CVRT's. If you search on here you will find a diagram I placed on the forum showing the parts.

 

Alternatively look on http://www.ferret-fv701.co.uk where you will find some info.

 

Diana

 

Not yet; where are these diaphragms to be found?

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If the plugs sooty, are they fireing? It may pay you to remove plug leads on tickover one at a time and listen for any drop in revs. Rubber gloves may be needed. If the original plugs are fitted they have platinum tips and do not like to be dirty/sooty. It probably has a twin choke Solex carb, and there is not mutch to adjust. It may have dirt in the jets from stale petrol and just need a good clean.

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I believe the carburettor is somewhat similar to the Marcus Solex fitted to B60 engines and CVRT's. If you search on here you will find a diagram I placed on the forum showing the parts.

 

Alternatively look on www.ferret-fv701.co.uk where you will find some info.

 

Diana

Thank you; I have downloaded the carburettor manual, which is the correct one for the B80. 😄

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Faulty leads or a dodgy ignition coil will also cause these sorts of problems. Have you checked that the inlet manifold is bolted up to the head tightly?

 

In general they are fairly simple and reliable engines - the carbs are known to gunk up a bit and usually benefit from a clean. There should be a small mesh filter inside the fuel banjo on the carb and you can also take out the jets and let any gunk drain out.

 

Cheers,

Terry

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My Saracen also ran horribly when there was an air leak from the vacuum tank.

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Thanks very much for all the replies.

 

We have pretty much ruled out ignition issues by swapping everything from another B80 that runs sweetly.

 

I will check manifold joint and vacuum pipes etc.

 

The engine is currently sitting with a dose of Redex in No.1 cylinder in case the cause of the low compression is stuck rings.

 

Next I am going to investigate the possibility of exhaust gas induction and if that can be ruled out, now that I have the manual I'll take a look inside the carb.

 

Meanwhile, I will be very glad to hear from anyone else who has experienced a rough running B80......

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Well, we are closing in on the source of the trouble.

 

As I said before, we know there's something unhappy going on that is robbing No1 cylinder of compression, which will be investigated in due course. That said, the last thing I wanted to do was spend a load of client's money doing extensive mechanical work just to find it running as rough as before.

 

Today I eliminated vacuum leaks and exhaust induction as the cause of the rough running, so my attention turned to the carburettor. It is fortunate that this particular appliance is one of a fleet, so I was able to borrow a carb from another engine that was known to run OK. Straightaway, this engine started and ran sweetly (or as sweetly as a B80 can do on 7 cylinders).

 

Initial investigation into the carb shows some gunge and deterioration of diaphragms, so a complete strip & overhaul will follow, to run in parallel with lifting the cylinder head to see what goes on in No.1 cylinder.

 

Again, many thanks for all your kind & helpful advice. 😀

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No one has mentioned this yet, but in my long experience on B Range engines is that the Exhaust valve clearance are often not checked due to the limited access in a number of applications, especially anything armoured. The clearance can decrease over time so worth checking. I know you put oil down the bores to seal the rings, but the exhaust valve is a side valve and the oil may well have helped seal a blowing valve.

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No one has mentioned this yet, but in my long experience on B Range engines is that the Exhaust valve clearance are often not checked due to the limited access in a number of applications, especially anything armoured. The clearance can decrease over time so worth checking. I know you put oil down the bores to seal the rings, but the exhaust valve is a side valve and the oil may well have helped seal a blowing valve.

Thanks Richard; I'll check that. There has been extensive top end work done on this engine (by somebody else) in the recent past and I have to admit that I have taken it on trust that this has been done properly.

That said, on all the previous occasions that I have encountered such a profound loss of compression in any engine, it has been down to burned valves, notwithstanding that traditional wisdom would have it that the rise in compression with oil in the bore suggests a piston/ring issue. If I find that the clearances are OK when I next look at it, I'll bite the bullet and lift the head, then we shall see........

Edited by mtskull

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No one has mentioned this yet, but in my long experience on B Range engines is that the Exhaust valve clearance are often not checked due to the limited access in a number of applications, especially anything armoured. The clearance can decrease over time so worth checking.

Well, finally got to the bottom of the poor compression: EVERY valve clearance was tight but No.1 inlet valve was the main culprit, with no clearance at all. How pouring a bit of oil down the bore masked this I don't know but slackening the adjuster half a turn brought the compression right back up to match the others. This on a vehicle that has barely been run since the cylinder head was supposedly overhauled! (Note to self: remember to never take anybody else's work on trust ever again). Checking the rest of the inlet valve clearances was straightforward but I'm not surprised that exhaust valve clearances get neglected; it was bad enough adjusting them in the relatively accessible fire engine, never mind a Saracen or Stalwart.

 

The carb is apart now, revealing one very mangled main jet as well as one non-return valve that was completely blocked with powdery corrosion products. All cleaned and blown out now. There's a spare carb I can rob a jet from, so just waiting for some gaskets and diaphraghms and everything should be good to go.

 

Thanks again to Richard and everybody else who offered advice.

Edited by mtskull

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Well, finally got to the bottom of the poor compression: EVERY valve clearance was tight but No.1 inlet valve was the main culprit, with no clearance at all. How pouring a bit of oil down the bore masked this I don't know but slackening the adjuster half a turn brought the compression right back up to match the others. This on a vehicle that has barely been run since the cylinder head was supposedly overhauled! (Note to self: remember to never take anybody else's work on trust ever again). Checking the rest of the inlet valve clearances was straightforward but I'm not surprised that exhaust valve clearances get neglected; it was bad enough adjusting them in the relatively accessible fire engine, never mind a Saracen or Stalwart.

 

 

Thanks again to Richard and everybody else who offered advice.

 

Glad to here you have got to the bottom of this. It was no surprise that the oil sealed the exhaust valves for the compression test as the plugs are above the valves and oil would have gone over them before running down the bores.

 

regards, Richard

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Glad to here you have got to the bottom of this. It was no surprise that the oil sealed the exhaust valves for the compression test as the plugs are above the valves and oil would have gone over them before running down the bores.

 

regards, Richard

I am still baffled as to how the oil made a difference when it was an inlet valve that was causing the problem. Sent me barking well up the wrong tree, that did......

Edited by mtskull

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At least You have got it sorted. Tick that box. Look at the time and money asking for help saved It was worth the wait for the adjustment comment.

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At least You have got it sorted. Tick that box. Look at the time and money asking for help saved It was worth the wait for the adjustment comment.

Absolutely. A bit scary to think how close I was to taking the head off. Lesson learned: Check EVERYTHING.

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Drawing this saga to a close, today I re-fitted the original carburettor, having stripped & cleaned it and also having replaced a dodgy diaphragm with a better one robbed from a spare carb (new diaphragms on order).

 

To cut a long story short, we went for a test drive and the old Dennis ran, in the words of the owner: "Better than it has done all the time I have owned her". Much kudos coming in my direction but the credit really belongs to all of the folk on this forum who helped.

 

Thanks again, folks. Now to move on to the next fire engine in the queue. This one's a little more modern, a Dennis F45 from c. 1970.

 

Coming soon, the first instalment of the sequel: The B81 saga......

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Another B80 query: Is the "rolled blanket" type of oil filter element designed to be cleaned and re-used? I have just treated this one to an oil and filter change but at nearly £60 a go for the element and with five engines to look after, it would be good to find a way of getting a bit more life out of them.

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