ERF:
I know it’s nearly a full year since anyone posted on this thread, but if anyone is interested there is a video (link below) of our AEC V8 engine running back in Febuary this year after a very difficult two-year restoration (yes, just the engine has taken two years!).
It has been undoubtedly the most comprehensive rebuild and re-engineering of an AEC V8 in recent years, in all probability since the AEC development days of the 1960’s!.
As I say, if it is of interest, I will write up all the faults we found - both design and failures, and what we did to improve or rectify them using modern technology and engine machining processes. It will be quite a long story, and full of technical detail that I know most people find rather boring!.
Click the ‘play’ arrow in the middle of the black page, and it will play…
Sounds & looks great, would really like to hear the information on the rebuild.
Thanks Dave.
Excellent project. Dish the dirt on every aspect of what you’ve found and changed Easy said from the comfort of our homes, bystanders, but i’m sure lot’s of us appreciate your trials and tribulations. Keep it going lads
I’m working on it guys - bear with me, spare time is very hard to find just at the minute, I might have to split it up into parts, but I’ll get it on as soon as I can.
Thank you all for your kind comments about the engine btw.
It’s now back in the restored chassis and waiting for a few more jobs to be completed before the cab goes on…it’s all a long story!.
I’m working on it guys - bear with me, spare time is very hard to find just at the minute, I might have to split it up into parts, but I’ll get it on as soon as I can.
Thank you all for your kind comments about the engine btw.
It’s now back in the restored chassis and waiting for a few more jobs to be completed before the cab goes on…it’s all a long story!.
Leyland Ash:
It sounds like a cross between a Mack V8 at idle and a ■■■■■■■ V903 when running… I was expecting to hear something more like a Perkins V8
Under load and with more exhaust muffling then it sounds more like the Perkins and maybe more like a Merc at idle ?.
Note the AEC emblem missing from the centre of the steering wheel on export models and also the Leyland emblem on the hub on the front wheels which also started to appear in the early `70s on the home market models.
It’s no wonder they got hot when you look at the chassis picture. The radiator is very small compared to the size of the engine,the header tank is tiny and the air intake will be sucking hot air in from above the engine.
Didn’t they fit a bigger header tank on the 800 series V8s?
NZ JAMIE:
It’s no wonder they got hot when you look at the chassis picture. The radiator is very small compared to the size of the engine,the header tank is tiny and the air intake will be sucking hot air in from above the engine.
To be fair the inlet manifolding and a lot of the associated intake plumbing having to be in the middle of the V is unavoidable and seems to work ok in numerous other types of V engine designs.But the radiator certainly looks like a lash up and an afterthought.With even that blocked at the front by other stuff that ideally needs to be re located. While in large part maybe a compromise that was forced on them by the limitations of the V8 type lower floored Ergo cab ?.
It would be interesting to see if using the AV 760 type cab and radiator set up would have also worked better in the case of the V8 in that case thereby providing better radiator provision and more airflow around the engine.
Although bearing in mind that Scammell also steered clear of the AEC in the Crusader obviously in that cases having nothing to do with any issues caused by air flow around the engine and radiator provision.
On the subject of the radiator set up, it’s well engineered within the constraints they had, and better than perhaps it looks. Not a ‘lash-up’ at all. Airflow is actually reasonably good, assisted by a large twelve bladed ducted fan, and not as restricted as it first appears - BUT at the penalty of it being mounted very low in the chassis, and very susceptible to damage from poor road surfaces and standing water.
Much has been said over the years about poor air flow around the V8 engine, but I don’t particularly subscribe to the opinion that it substantially added to the cooling problems. The low datum cab is not especially restrictive, and the rear of the engine is completely open, so would never create a ‘positive’ pressure of air around the engine, thus restricting air coming through in the radiator. Look at any old petroleum regs lorries, and the engines are far more enclosed and restrictive to hot air getting away than the V8 was.
The standard home market V8 radiator is actually much larger in capacity than the AV760 equivalent.
Another point worth making here is that export V8 chassis (like that one in Robert’s photo above) were much heavier built than home market chassis, the rails being two inches deeper. They were generally better equipped for rough service than home market vehicles, with a high datum cab, aluminium instrument binnacle & pedestal, AV800/801 (13.1 Litre) engine and a much thicker cored radiator to suit. It does beg the question though - with the overheating problems experienced by operators with home market AV740 (12.1 Litre) engined vehicles, why didn’t AEC fit the larger capacity export radiator to ALL of the V8 engined models? It does fit without any modification at all (even under the low datum cab), and markedly increases the coolant and cooling capacity, which can only have helped.
ERF:
On the subject of the radiator set up, it’s well engineered within the constraints they had, and better than perhaps it looks. Not a ‘lash-up’ at all. Airflow is actually reasonably good, assisted by a large twelve bladed ducted fan, and not as restricted as it first appears - BUT at the penalty of it being mounted very low in the chassis, and very susceptible to damage from poor road surfaces and standing water.
Much has been said over the years about poor air flow around the V8 engine, but I don’t particularly subscribe to the opinion that it substantially added to the cooling problems. The low datum cab is not especially restrictive, and the rear of the engine is completely open, so would never create a ‘positive’ pressure of air around the engine, thus restricting air coming through in the radiator. Look at any old petroleum regs lorries, and the engines are far more enclosed and restrictive to hot air getting away than the V8 was.
The standard home market V8 radiator is actually much larger in capacity than the AV760 equivalent.
Another point worth making here is that export V8 chassis (like that one in Robert’s photo above) were much heavier built than home market chassis, the rails being two inches deeper. They were generally better equipped for rough service than home market vehicles, with a high datum cab, aluminium instrument binnacle & pedestal, AV800/801 (13.1 Litre) engine and a much thicker cored radiator to suit. It does beg the question though - with the overheating problems experienced by operators with home market AV740 (12.1 Litre) engined vehicles, why didn’t AEC fit the larger capacity export radiator to ALL of the V8 engined models? It does fit without any modification at all (even under the low datum cab), and markedly increases the coolant and cooling capacity, which can only have helped.
That’s interesting ERF.Does that mean that the export versions reputedly didn’t suffer from cooling problems that the domestic market versions reputedly did ?.Nor were the issues isolated to just the V8 but also applied to the 760 powered versions too ?.While to my knowledge the 760 version at least seems to have worked ok even in the case of the stationary power output demands of the emergency vehicle sector.It would be interesting to know if that might have been a result of maybe a possible different export radiator spec ?.
Also bearing in mind the questions that increased radiator area,where possible,is usually accepted as trumping increased core thickness ?.While Scammell seemed to avoid the AEC V8 in favour of the Detroit 8 v 71,from an early stage,in the case of the Crusader,regardless.Which suggests that the whole question of Ergo cabbed vehicle cooling issues or otherwise was/is possibly a moot point and red herring ?.
There were never long-standing overheating problems with AV760 engine Mandators per se. The early AV691 engine Ergomatic cabbed Mandators did gain a reputation for overheating and those early models of 1966 had a small header tank on top of the radiator, and the rear cab mounted larger header tank eradicated that problem. The thinner cylinder liners of the AV760 engine also dispersed heat quicker than the thicker liners of the AV691. By mid-1966 virtually all Mandators were built with AV760 engines. AV691s were still used in Reliance coaches where radiator capacity wasn’t restricted and they were popular industrial and stationary units.
gingerfold:
…the rear cab mounted larger header tank eradicated that problem. The thinner cylinder liners of the AV760 engine also dispersed heat quicker than the thicker liners of the AV691…
This is a common held and often repeated belief, both parts of which which are in fact technically incorrect. The AV691 suffered from one of the exact same major cooling problems that the V8 did, and for exactly the same reason. A larger header tank merely gave an increase in coolant (not cooling) capacity, giving a broader margin for loss if the coolant boiled. It didn’t physically solve the engines cooling issues, which were there by design.
Believe it or not, one of the first things we found when rebuilding the AV740 V8 is that it shares an awful lot of its design (and in some cases parts) with the AV691 - the same is true of the AV800/801 with the AV760, and the latter two cool better than the first two for the same design reasons. All four of these engine designs use the same design of ‘top-hat’ or ‘flanged’ dry liner, and all four liner types are exactly the same thickness I can assure you. The difference lies in the parent bore of the cylinder block casting, which is same respectively. The straight six 691 or vee eight 740 casting is bored to 5.00mm smaller diameter than the 800/801/760, which means that the water jacket / cylinder wall is 2.50mm thinner in 800/801/760 engines, thus helping quicker heat transfer to the coolant.
The 691/740 engines use (in retrospect) quite a poor design for mounting and sealing the liners, whereby the liner is pressed into the block using a distance gauge to set the liner protrusion from the block face. As no shims are used, this has the effect of causing a small void under the flanged head of the liner as it is not pressed fully home into the counterbore in the block. The fire ring of the cylinder head gasket fitted to these engines seals onto the block deck outside of the liner circumference. Both of these engine designs suffered with circumferential cracks developing in the top of the liner when in service, especially when run hot, and with repeated head gasket failures.
The 800/801/760 engines use the same design of dry liner, but in this case the liner IS pressed fully home into the block counterbore, the liner protrusion (which is less) being set by skimming if required after fitting. The fire ring of the head gasket fitted to these engines seals onto the top of the liner, and these engines suffer much less with the cracking, and much less with head gasket failures.
Here are some photos of a sectioned AV800/801 engine that illustrate the design…
The respective thickness / thinness between the AV691 / AV760 cylinder block casting relative to the liner, and saying the liner was “thinner” for the AV760 was probably the easiest way of AEC service personnel (Harry Pick) explaining the difference to relatively non-technical users (such as myself) because it is something I can picture in my mind and understand the rationale of it. However your explanation is interesting and confirms that back in the day the AV760 never had a bad reputation for head gasket failures. But perhaps virtually any make of engine that overheats badly or boils its coolant, for whatever reason, is going to be susceptible to head gasket failure, and that holds good with modern engines doesn’t it?
gingerfold:
The respective thickness / thinness between the AV691 / AV760 cylinder block casting relative to the liner, and saying the liner was “thinner” for the AV760 was probably the easiest way of AEC service personnel (Harry Pick) explaining the difference to relatively non-technical users (such as myself) because it is something I can picture in my mind and understand the rationale of it. However your explanation is interesting and confirms that back in the day the AV760 never had a bad reputation for head gasket failures. But perhaps virtually any make of engine that overheats badly or boils its coolant, for whatever reason, is going to be susceptible to head gasket failure, and that holds good with modern engines doesn’t it?
I would say you are absolutely correct there Graham, but when the misleading (in a technical sense) liner explanation from Harry made it into print in your otherwise very accurate book about the V8, and was taken by me as gospel, it very nearly led me into an expensive mistake with my engine, which I will fully explain later!
Any engine, ancient or modern, that boils it’s coolant is in for all sorts of problems, not just failed head gaskets, that’s indisputable. Cylinder head failures are often caused by heat warpage or boiling coolant creating steam pockets in the water channels, which then allow the metal in that area to vastly increase in temperature, only to be suddenly reduced when the coolant makes contact again, resulting in a crack - a very very common AEC V8 failure, as I found.
Some good questions and answers from those above and the photo’s of the sectioned block and head certainly help. Excellent thread, looking forward to more
gingerfold:
But perhaps virtually any make of engine that overheats badly or boils its coolant, for whatever reason, is going to be susceptible to head gasket failure, and that holds good with modern engines doesn’t it?
Ironically the Jag V12 at least can be a nightmare to keep cool because of effectively being limited by the area of a 6 cylinder radiator having to cool the two 6 cylinder banks and can run up to 130 degrees C by design necessity.But in that case the wet liner design at least,with a heavy steel head gasket acting as the top deck of the block,seems to be bullet proof in terms of head gasket failure.To the point where it will usually be the block which self destructs by warping before the head gaskets let go.
On that note how did the wet liner AEC engines perform in terms of reliability and did they suffer with any of the issues being described in the case of the 691 and 740 at least ?.
Easy said from the comfort of our homes, bystanders, but i’m sure lot’s of us appreciate your trials and tribulations. Keep it going lads
