Anyone want to comment on the last of the AEC engines ■■?
Well sadly as we know some of the old bus fraternity have far more money than sense, which looks like being not a good thing for the remaining AV760s lurking in the hands of the scrapmen and ex military dealers. There seems to be an increasing trend that their precious Routemaster, of which there are still hundreds around, just doesn’t quite come up to scratch unless it is AEC powered. The proportion of non AEC powered buses which are no left is probably some 70%.
25 years ago what was then London Transport realised that the AV590 engines in their buses, which had overwhelmingly been the original fitment, were time and fatigue expired, with the result that overhauls were not extending reliable operational life to the extent required. A programme of repowering was commenced using in the main ■■■■■■■ and Iveco engines with a further later addition of Scania engines. To a greater or lesser extent this required surgery to the structure and newly fabricated components with the attendant discarding of the original items.
Coming up to date many of the remaining AEC Routemasters are either asthmatic, exhibiting signs of impending doom, or have already failed. The supply of AV760s, many ex military generators, is being eyed up. At first glance nothing to be over concerned about. However it seems that the non AEC owners are now looking at retro engineering their buses. This not only poses a threat to those owners of buses and lorries which actually require an AV760 engine, it is also a threat to the engines themselves. Worse is the fact that spares for the ■■■■■■■ and Iveco engines are available while AEC items are to be found in the mouths of hens.
There have been many requests from RM owners for higher ratio final drive gears because they just can’t bear plodding along at 1950’s vehicle speeds.The AV760 has been and can be, shoehorned into the engine bay, but apart from it developing too much torque for the aged gearboxes and diffs to handle at full rating, there are difficulties with missing threaded locations for auxiliaries as well as an incompatible number of flywheel mounting studs. Worse some of the generator engines lack balanced crankshafts and/or vibration dampers. The engine will not fit into the chassis without moving the radiator forward, however having done this it has been found by those who have done the conversion that the existing radiator is of insufficient capacity to meet the needs of an AV760 so the engine runs hot if held at sustained speeds. Perhaps more worrying is that the exhaust system is of inadequate bore to cope with the flow of gas from the engine resulting in excessive back pressure at high revs. Ally these last two problems to the extreme difficulty of accommodating air filtration in the space available and the perceived impossibility of routeing a larger exhaust downpipe out of the engine compartment and you have a potentially short lived AV760.
So those who may possibly be thinking of acquiring an AV760 for their lorry should be considering getting a move on before there aren’t any good engines left.
Apologies Ramone if this was not exactly the sort of answer you might have been expecting.
My own feeling is that the AV760 was an excellent engine particularly if it could be kept cool and the revs moderated. It was a noisy and thirsty beast though.
cav551:
Well sadly as we know some of the old bus fraternity have far more money than sense, which looks like being not a good thing for the remaining AV760s lurking in the hands of the scrapmen and ex military dealers. There seems to be an increasing trend that their precious Routemaster, of which there are still hundreds around, just doesn’t quite come up to scratch unless it is AEC powered. The proportion of non AEC powered buses which are no left is probably some 70%.25 years ago what was then London Transport realised that the AV590 engines in their buses, which had overwhelmingly been the original fitment, were time and fatigue expired, with the result that overhauls were not extending reliable operational life to the extent required. A programme of repowering was commenced using in the main ■■■■■■■ and Iveco engines with a further later addition of Scania engines. To a greater or lesser extent this required surgery to the structure and newly fabricated components with the attendant discarding of the original items.
Coming up to date many of the remaining AEC Routemasters are either asthmatic, exhibiting signs of impending doom, or have already failed. The supply of AV760s, many ex military generators, is being eyed up. At first glance nothing to be over concerned about. However it seems that the non AEC owners are now looking at retro engineering their buses. This not only poses a threat to those owners of buses and lorries which actually require an AV760 engine, it is also a threat to the engines themselves. Worse is the fact that spares for the ■■■■■■■ and Iveco engines are available while AEC items are to be found in the mouths of hens.
There have been many requests from RM owners for higher ratio final drive gears because they just can’t bear plodding along at 1950’s vehicle speeds.The AV760 has been and can be, shoehorned into the engine bay, but apart from it developing too much torque for the aged gearboxes and diffs to handle at full rating, there are difficulties with missing threaded locations for auxiliaries as well as an incompatible number of flywheel mounting studs. Worse some of the generator engines lack balanced crankshafts and/or vibration dampers. The engine will not fit into the chassis without moving the radiator forward, however having done this it has been found by those who have done the conversion that the existing radiator is of insufficient capacity to meet the needs of an AV760 so the engine runs hot if held at sustained speeds. Perhaps more worrying is that the exhaust system is of inadequate bore to cope with the flow of gas from the engine resulting in excessive back pressure at high revs. Ally these last two problems to the extreme difficulty of accommodating air filtration in the space available and the perceived impossibility of routeing a larger exhaust downpipe out of the engine compartment and you have a potentially short lived AV760.
So those who may possibly be thinking of acquiring an AV760 for their lorry should be considering getting a move on before there aren’t any good engines left.
Apologies Ramone if this was not exactly the sort of answer you might have been expecting.
My own feeling is that the AV760 was an excellent engine particularly if it could be kept cool and the revs moderated. It was a noisy and thirsty beast though.
That sounds like a sad but predictable situation which seems to have resulted firstly from London Transport and all the relevant preservation groups not getting together at the time of the re engine programme.By saving and storing all the removed engines and original fit components in order to take account of the understandable wishes of owners in returning the vehicles to the correct engine spec when they eventually entered the preservation scene at end of service life. 
While some of the reasoning for the programme at the time seemed to have had as much,if not more,to do with LT being instructed to meet unrealistic emissions requirements. 
As remaining serviceability and durability of the original spec bearing in mind that the vehicles were close to their retirement date anyway.On that note it is fair and understandable that bus preservation enthusiasts would be just as keen on getting their vehicles back with the correct sounding AEC power in the interests of realistic nostalgia as their commercial vehicle counterparts.Which obviously creates the dilemma that trying to do that with the 760 not only won’t work but also creates the type of knock on counterproductive problems that you’ve described.Although the Routemaster seems to have been successfully upgraded to 690 spec in the form of the RMC version in the day so maybe at least that is a better option.
Most/all of which seeming to have been caused by an act of historic vandalism which seems to have caused the problem and then LT trying to divert the blame which should rightly be sent their way for it.
As for the 760 if only AEC had saved and diverted the resources put into the V8 on a longer stroke larger capacity development of the 760 instead. 
cav551:
Well sadly as we know some of the old bus fraternity have far more money than sense, which looks like being not a good thing for the remaining AV760s lurking in the hands of the scrapmen and ex military dealers. There seems to be an increasing trend that their precious Routemaster, of which there are still hundreds around, just doesn’t quite come up to scratch unless it is AEC powered. The proportion of non AEC powered buses which are no left is probably some 70%.25 years ago what was then London Transport realised that the AV590 engines in their buses, which had overwhelmingly been the original fitment, were time and fatigue expired, with the result that overhauls were not extending reliable operational life to the extent required. A programme of repowering was commenced using in the main ■■■■■■■ and Iveco engines with a further later addition of Scania engines. To a greater or lesser extent this required surgery to the structure and newly fabricated components with the attendant discarding of the original items.
Coming up to date many of the remaining AEC Routemasters are either asthmatic, exhibiting signs of impending doom, or have already failed. The supply of AV760s, many ex military generators, is being eyed up. At first glance nothing to be over concerned about. However it seems that the non AEC owners are now looking at retro engineering their buses. This not only poses a threat to those owners of buses and lorries which actually require an AV760 engine, it is also a threat to the engines themselves. Worse is the fact that spares for the ■■■■■■■ and Iveco engines are available while AEC items are to be found in the mouths of hens.
There have been many requests from RM owners for higher ratio final drive gears because they just can’t bear plodding along at 1950’s vehicle speeds.The AV760 has been and can be, shoehorned into the engine bay, but apart from it developing too much torque for the aged gearboxes and diffs to handle at full rating, there are difficulties with missing threaded locations for auxiliaries as well as an incompatible number of flywheel mounting studs. Worse some of the generator engines lack balanced crankshafts and/or vibration dampers. The engine will not fit into the chassis without moving the radiator forward, however having done this it has been found by those who have done the conversion that the existing radiator is of insufficient capacity to meet the needs of an AV760 so the engine runs hot if held at sustained speeds. Perhaps more worrying is that the exhaust system is of inadequate bore to cope with the flow of gas from the engine resulting in excessive back pressure at high revs. Ally these last two problems to the extreme difficulty of accommodating air filtration in the space available and the perceived impossibility of routeing a larger exhaust downpipe out of the engine compartment and you have a potentially short lived AV760.
So those who may possibly be thinking of acquiring an AV760 for their lorry should be considering getting a move on before there aren’t any good engines left.
Apologies Ramone if this was not exactly the sort of answer you might have been expecting.
My own feeling is that the AV760 was an excellent engine particularly if it could be kept cool and the revs moderated. It was a noisy and thirsty beast though.
If available wouldn`t the AV505 be a better option or am i missing an alarmingly obvious reason why ?
Precisely my thinking but for the same reasons of depriving more worthy causes, on balance I come out against it.
Unfortunately the London bus enthusiast is poisoned against the AV505 due to LT’s experience of the rear mounted AH505 in the AEC Swift. In initial London use in the Swift the 505 had an average in service major failure life of about 6 months. This was mainly due to the usual AEC shortcoming of a poor cooling system design; in particular the fan drive. In spite of being only single deck the bus was also heavier than the RM both unladen and in some configurations laden as well, this resulted in an overworked and in practice underpowered vehicle; proving the point that there is no substitute for cubic capacity.
While we may like to think that the lorry engine has a harder life due to the weight it has to lug around, in practice the inner city bus engine has a much harder life, with consequent higher failure rates and a shorter overhaul life. Maximum acceleration for a few hundred yards followed by long periods of idling either at bus stops or in traffic, with cold coolant suddenly circulated around a hot engine, immediately succeeded by a very hot engine being starved of adequate coolant flow, results in severe thermal stress leading to eventual gasket failure or worse. This is what happened to the AH505 in London inner city service.
Today the engine would fit the space easily - in fact one of the prototype RMs had originally had an AV470 installed initially, but this was found to be underpowered in practice. Moreover it would satisfy the demand for greater road speed due to its considerably higher governed rpm. The enthusiast wouldn’t approve because the engine note is different to an AV590; but then so is the 760 and even the 690.
It is a little unfair to criticize London Transport for the repowering of these vehicles in the early 1990s. A great deal of effort was put into trialing several different engines. The two most suited to the bus were the Iveco - of which the company had good experience in another chassis and the DAF. The DAF was deemed too expensive and the Iveco used in reasonably large numbers , however its injection pump was on the driver’s side of the block which was a disadvantage. The larger number of engines supplied were ■■■■■■■ C series, however in the first years of their use considerable difficulties wee found not just in the surgery required to make it fit the space, but in incompatibility with the transmission. This got so bad that the vehicles were blacked by the union at one point until problems were (in fact only partially) sorted.
By 1990 the AEC AV590 had been in constant inner city use for some 30+ years. The buses themselves had been designed for a 17 year total lifespan. The design itself had originated had around 1953/4. Time had caught up with it, not only had thet engines been overhauled on numerous occasions, but certain design features were causing problems. viz the AEC rear main oil seal is a scroll which is part of the crankshaft, this inevitably became less efficient with little possibility of rectification as the engine accumulated more hours. By 1990 engine oil leaks were attracting problems at MOT. AEC had gone out of business in 1978 so the supply of blocks, heads and crankshafts available to replace scrap units had virtually dried up. There simply was no alternative other than find an alternative engine if the vehicle, which was still proving to be the most efficient mass people-mover to date, was to continue in service.
This was not the first time the company had been forced to confront obsolescence with this vehicle. If I am right with the date, the last RM to be constructed had not even rolled out of Southall before Simms ceased production of electrical and fuel injection equipment. The company engineering ethos was standardisation it was not that long before vehicles with these components were withdrawn firstly to keep others going and later for scrap.
cav551:
It is a little unfair to criticize London Transport for the repowering of these vehicles in the early 1990s.
The criticism wasn’t the obvious necessity of modifying the vehicles to extend their service life.It was the inconsiderate thoughtless approach of not doing it in a sympathetic way.Which would have allowed the preservation scene to return the vehicles to their original spec,when they were foreseeably finally retired from service.Which obviously would have meant saving as much of the removed componentry as possible either for specialist repair and re use or patterns for remanufacture in preservation.Bearing in mind that the requirements and stress on the components in question would be a lot less in preservation than in service.
As for the 690 I’d say that it sounds even more in keeping with the old Routemaster character. 
The AV 760 was with the possible exception of the 9.6 the best engine AEC ever produced. Providing it could be geared right and kept cool it gave very good service particularly in consideration of the price the customer paid for the new vehicle. It preferred the revs to be kept at a reasonable level if it was to remain trouble free. A problem was that it could be wound up to sustained higher speeds and kept there, being free revving it was also easy to over rev it particularly downhill on the motorways, leading to its probably most frequent failure - a dropped valve. It of course also suffered from cooling derived issues evidenced by the rear cab mounted header tanks on later tilt cabs. These however required the small bore ‘steam pipes’ to be kept clear if problems were not to return. The extra meat bored out of the block to accommodate the larger bore sometimes lead to more serious overheating issues. I certainly recall stripping a 760 which had dragged a liner into the sump and cracked the block in the process. This might not possibly have arisen if the block walls had been thicker. Again often due to high revs it had a habit of shedding fan blades (in fact a not uncommon AEC fault). IIRC it could be delivered with CAV or Simms inline pumps, a CAV DPA pump, or best of the lot for get up and go the Bosch in line.
As for working on the engine, It had bigger valves than its AV691 predecessor, which needed careful note in a mixed fleet of 691 and 760 powered vehicles if spare built up heads were kept in stock. It was a very tight fit indeed in the chassis and not at all easy to remove and replace. Make this a Mammoth Major 8 with front mounted tipping oil tank and I think a few choice words were in order. 
ISTRC that there was quite a lot of awkward fiddling about underneath the driver’s cab floor removing bolts which could only just be reached let alone seen before one could get the engine out. Unless supported on chassis stands at an uncomfortable working height, thus allowing the axle to drop down it was actually easier to remove the front axle in order to gain enough room for sump removal. Being larger than the 505 it was also just that bit more awkward to change the oil filter without it running up your arm. The cylinder heads were not really any heavier than the AV590, but again IIRC the head studs were 9/16" rather than 1/2" so they were more likely to stick on the carbon and with the lump being tilted over to one side slightly just a bit more difficult to lift off. With such a deep sump well it was a long old stretch from the floor reach the big end bearings with no 1 being the worst with the oil pump in the way. When it came to liner changes these were really in there tightly requiring much more pressure to pull out than the 505, but retaining the necessity to finish hone accurately to size if the aforementioned cracked block and shattered liner was not to be repeated.
Carryfast:
cav551:
It is a little unfair to criticize London Transport for the repowering of these vehicles in the early 1990s.The criticism wasn’t the obvious necessity of modifying the vehicles to extend their service life.It was the inconsiderate thoughtless approach of not doing it in a sympathetic way.Which would have allowed the preservation scene to return the vehicles to their original spec,when they were foreseeably finally retired from service.Which obviously would have meant saving as much of the removed componentry as possible either for specialist repair and re use or patterns for remanufacture in preservation.Bearing in mind that the requirements and stress on the components in question would be a lot less in preservation than in service.
As for the 690 I’d say that it sounds even more in keeping with the old Routemaster character.
A valid point, but London Buses LT or whatever their name was at the time were after all the owners of a vehicle intended for revenue earning service and publicly owned at the time. There would likely have been a few questions asked about the expenditure of taxpayers money for the later advantage of private individuals.
There were a reasonably large number of AV 690 powered buses, intended originally experimentally for the RM and taken as an optional fitment along with the Leyland 600. The 690 proved too thirsty in city use and the Leyland just a little bit more time consuming in workshop attention. The extra power available from the 690 proved necessary for the Country area Green Line versions and with full power and revs available for the high speed BEA dedicated London Airport service. These latter vehicles however requiring fully balanced engines to withstand the high revs and a small modification to the front xmember to clear the crankshaft damper.
The ■■■■■■■ C engine required considerable alterations to the cab firewall in order to clear the exhaust manifold. Due to the requirement for interior lighting bus alternator replacement is a more regular issue than it is with HGV. The ■■■■■■■ C alternator is particularly awkward to renew. The entire front and rear engine mounting arrangements had to be redesigned, unfortunately causing a problem which has never been resolved. Since the steering box has always been mounted at the same point outboard of the chassis rails as the cross member is inside them, with a far less substantial inter-rail fabrication there is now a noticeable lack of rigidity in the front chassis cross member which gives arise to a severe steering column shake encountered on rough roads.
I wonder why they never produced a horizontal TL12 for the Reliance to compete with the foreigners ■■?
Anyone got any experience with the last version of the TL12 , the Flexitorque it was fitted to the Roadtrain?
DEANB:
An article from 1980.Click on pages to read as makes it clearer.5
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Thanks for that Dean , my dad got a brand new E290 day cab Marathon and it always ran at top weight over the M62 between yorkshire and lancashire and there was quite a difference after his F86 and Mandator. I vaguely remember reading that test ,was there one for the Roadtrain with the Flexitorque TL12?.. Thanks for posting it
Further to my previous comments about the bus enthusiast fraternity buying up AV 760 engines to put in their buses and some even going so far as wanting to reverse engineer vehicles which had been repowered with alternative non AEC engines.
It appears that this has not been an overwhelming success, in fact exactly the opposite. A batch of ex MOD overhauled and then mothballed and inhibited engines were fitted to buses, only for several to suffer catastrophic failures owing to blocked oilways subsequent to the inhibiting process.
Firm i worked for as a mechanic had two AEC Mammoth Major 8x4 with the AV760 engine in. They worked 2x10 hour shifts per day and were worked hard. The engines gave very little problems in the 6 years they ran them. Can only recall one having head gaskets done twice and a set of injectors and fuel pump but this was down to contaminated diesel. They also ran 6 Leyland Octopuses with the L12 engine and 2 Leyland Buffalo tractor units one with the L12 and one with the fixed head wonder engine which was a total disaster. The L12 was a reliable engine never had any problems with liners etc/ did change a few head gaskets again these were worked 20 hours per day.
regards
Mick
Theres an article in this weeks Commercial Motor about the Leyland Marathon , the MK1 wasnt a great successs but was a flying machine , MK2 sold in much bigger numbers was basically what was written and also what a good vehicle it was considering what it cost to develop
cav551:
A valid point, but London Buses LT or whatever their name was at the time were after all the owners of a vehicle intended for revenue earning service and publicly owned at the time. There would likely have been a few questions asked about the expenditure of taxpayers money for the later advantage of private individuals.There were a reasonably large number of AV 690 powered buses, intended originally experimentally for the RM and taken as an optional fitment along with the Leyland 600. The 690 proved too thirsty in city use and the Leyland just a little bit more time consuming in workshop attention. The extra power available from the 690 proved necessary for the Country area Green Line versions and with full power and revs available for the high speed BEA dedicated London Airport service. These latter vehicles however requiring fully balanced engines to withstand the high revs and a small modification to the front xmember to clear the crankshaft damper.
.
Bumping an old thread (tut tut ) but I’m curious why the RM preservation mob aren’t as avid about refurbing 0.600s as they are AV690s. Or is it the case that 0.600s are even harder to find?