mtskull

Several examples to be seen on this boiler:

Those brackets illustrate perfectly your incredible attention to detail: making patterns and having castings made to perfectly replicate the original, where lesser men (myself included) would have just cobbled together something that looks something like it out of some steel angle and bits from the scrap bin. Nice work.

Beyond all reasonable doubt those are the same 3 POW's; what a brilliant piece of observation!

Are you certain that somebody at some time has not attempted to turn the engine while just the one piston was corroded solid in the bore, or against a hydraulic lock? A misguided but determined effort to free the engine, using a long bar for leverage, could have had the same effect.

Yes please! Always glad to see these old vehicles being brought back to life, especially those rarer examples.

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!

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.

Puzzled and searched online for photos for ages before it hit me: I thought we were looking at the front but that's actually the rear of the bridgelayer visible in the photo. Suddenly everything is consistent with it being a Valentine. Apologies for doubting those who twigged before I did....

Having now read a bit more about the battle of Cassino, it would appear that there is little else it could be but a Valentine. I'll get my coat....

There are points of similarity with a Valentine but the two arms attached to the hull either side of the long pole don't match anything on any photo of a Valentine bridgelayer that I can find. I thought maybe Covenanter as in the photo below but the same applies. I'm sure somebody on this forum will solve the mystery, though.

Panzer bridgelayer?

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......

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

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......

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.

Spotted this in Boston, Massachusetts, last week. There is a company which uses a large fleet of DUKWs to take tourists on land & water tours of the city. I didn't fancy it myself and I definitely wouldn't fancy the idea of trying to get to Dublin on one....:shocked:

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........

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. 😀

Best of luck for today, Rick. Can't wait to see some photos!

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......

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

Not yet; where are these diaphragms to be found?

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?

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.

You are a braver man than I am, cranking the engine with a known foreign object somewhere in there, horrible noises or not. The clunk you heard when the engine stopped dead was probably a piston making contact with an inlet valve that had been jammed open by the screw, or maybe the screw becoming trapped between a piston and an open valve. If so, it was exteremely fortunate that it happened while you were turning the engine by hand and not cranking on the starter or, even worse, with the engine running. Sad to say, I fear that your options are either to do whatever is necessary to locate and remove the screw, even if it means taking the head and manifolds off, or playing Russian roulette every time you start the engine. :-(