AEC V8

[cav551]

ERF:
).

The valve lift, inlet and exhaust valve head sizes and connecting rod cross section were all found to be satisfactory, as were (surprisingly) the main bearing journals of 95.184 mm diameter and 43.70 mm (front), 56.00 mm (rear), 47.65 mm (centre) and 47.72 mm (intermediate). This gives a combined projected bearing area of 235 sq.cm. Adequate.

The original big ends were inadequate by some margin because the calculated oil film pressures developed on the bearing surface were excessive. The original design used a crankpin diameter of 88.9 mm with a width of 28.5 mm. The minimum requirement for the proposed power needs an increase in area of 21%, which keeping the 88.9 diameter could be achieved with a width increase of 6.2 mm per bearing. This would take the combined projected bearing area upto 247 sq.cm, just 2 sq.cm over the absolute minimum calculated requirement. This would require a crankshaft 49.6 mm longer than the original.

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28.5 mm must be the width (or length if one identifies it that way) of the connecting rod bearing shell and not the width of the crankpin surely? We are given that the big end bolts are 14 mm diameter in the CM description of the specification. Presumably we are talking about a 3.1 mm increase in each bearing shell’s width?

[erf]

28.5 mm is the width of the original big end bearing shells.
To match (give or take) the relative loading capability of the original main bearings according to modern calculations, each big end shell needed to be 6.2 mm wider, so 34.7 mm.
This would mean increasing each crankpin’s width by 12.4 mm, hence the crankshaft needed to be 49.6 mm longer to accommodate it.

[railstaff]

I am quite sure I read an article many years ago that suggested the oil holes in the crankshaft had been drilled in the wrong place.This lead to insufficient lubrication under load to the conrod bearing.
Comparing the bearing sizes with a todays Vee eight doesn’t see that much difference.Looking at a Deutz BF8M 1015 with a rated output of 600hp sees the mains at a width of 38mm and conrod bearings at 27mm,also valve heads at 46mm and 48mm respectively.Seems AEC werent that far of the ball after all.

[erf]

I haven’t heard that about the crankpin oil hole drillings.
They were drilled on both sides of the crankpin (4 holes per crankpin), so it’s difficult to see how they were wrong, and even what difference it would have made once the oil film was established and able to withstand the pressure loading?.

[erf]

cav551:
…The fact that during experimental and production development up until withdrawal had seen four cylinder heads replaced by two which were then modified, makes clear that if new castings were required then they had been made so one can assume that the same development would continue…

There were only ever single one piece heads - the prototype engines had a single head with a split rocker shaft and two small rocker covers per head.
The production engines had the ‘A’ heads, where the casting patterns had just been modified to accomodate a single long rocker cover, but they retained the same split rocker shaft inside.

[zb_anorak]

ERF:
28.5 mm is the width of the original big end bearing shells.
To match (give or take) the relative loading capability of the original main bearings according to modern calculations, each big end shell needed to be 6.2 mm wider, so 34.7 mm.
This would mean increasing each crankpin’s width by 12.4 mm, hence the crankshaft needed to be 49.6 mm longer to accommodate it.

I guess that increasing the diameter of the big end bearings would cause clearance issues to the underside of the cylinders, given that no space was wasted according to the original design brief. However, an extra 5mm on the diameter would give about 10% more area. If all the material was added towards the crank CL, a reduction in stroke of only 2.5mm would be the only loss. The AV801/810 engine would have a capacity of 12.8 litres.

Regarding the issue of wet/dry liners, looking at the sectioned engine phots: what if the block was relieved completely in the region of the coolant passages? The liner would be made thicker, to retain stiffness. By the look of it, it’s only about 4mm thick there. By removing the joint between the two, the local bending stiffness of the section would be higher, because there would be no loss of shear connectivity between the inner and outer (If my recollections of thick cylinder theory serve me well, then some of the pressure is reacted by circumferential shear).Therefore, a reduction in total thickness could be allowed, to the benefit of coolant flow and heat capacity of the coolant adjacent to the cylinders.

Feel free to shoot these ideas down- I’m not an IC engine specialist, so it’s just the ramblings of a general head-scratcher.

[ew_car_truck_amp_bus]

Well Guys , what a pleasure reading the last posts which have not been bombarded by you know who… Newmercman has done a good job with the written warning long may the peace continue. AS well as the great posts!..

E.W.

[railstaff]

ERF:
I haven’t heard that about the crankpin oil hole drillings.
They were drilled on both sides of the crankpin (4 holes per crankpin), so it’s difficult to see how they were wrong, and even what difference it would have made once the oil film was established and able to withstand the pressure loading?.

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The problem being that on the compression stroke at 270 degrees and firing stoke at 450 degrees,roughly.It was deemed the oil drillings were not releasing the lube in the best possible position.Yes there is a film but under load its easily pushed out leaving contact.What kind of oil pressure did they operate at?

[railstaff]

One vital area we are missing is coolant temperatures were not ideal.Even with the oil cooler fitted as shown in the diagram kindly illustrated by ERF,engine lubricating oil temperatures would also have been high resulting in low viscosity of the said lube oil.This in itself would be an early demise to bottom failure.

[erf]

railstaff:
…The problem being that on the compression stroke at 270 degrees and firing stoke at 450 degrees,roughly.It was deemed the oil drillings were not releasing the lube in the best possible position.Yes there is a film but under load its easily pushed out leaving contact.What kind of oil pressure did they operate at?

The oil pump delivers 25.4 litres per minute at 1000 rpm crankshaft speed.
The relief valve is set to maintain 50 lb/sq.in. Oil pressure.

You have got me thinking about these oil holes.
I will mention it next time I see the engine design gurus, but if it were a problem, wouldn’t the bearing shell show significantly more wear in the two spots that correspond to those angles you mention? The ones I have seen (which were all ‘SA’ material) all had even wear across the entire bearing surface.

[railstaff]

ERF:

railstaff:
…The problem being that on the compression stroke at 270 degrees and firing stoke at 450 degrees,roughly.It was deemed the oil drillings were not releasing the lube in the best possible position.Yes there is a film but under load its easily pushed out leaving contact.What kind of oil pressure did they operate at?

The oil pump delivers 25.4 litres per minute at 1000 rpm crankshaft speed.
The relief valve is set to maintain 50 lb/sq.in. Oil pressure.

You have got me thinking about these oil holes.
I will mention it next time I see the engine design gurus, but if it were a problem, wouldn’t the bearing shell show significantly more wear in the two spots that correspond to those angles you mention? The ones I have seen (which were all ‘SA’ material) all had even wear across the entire bearing surface.

You by far know more than me on the AEC front,but I do remember reading about the oiling drillings being wrongly located,but that could have been on a proto type engine.I seem to remember reading the “shells” were good for 100,000 miles and required changing,but the problem was being addressed with a new crank with the drillings relocated in the journal of the crank pin.

I think we can both agree that the correct operation of the pressure relief valve is to open at 50 psi and recycle the oil back to sump.I doubt whether the pump has the capacity to maintain 50 psi hot on idle but I could be wrong.I would think more along the lines of 15psi hot idle.Maybe there lies the problem,a stinking hot 740 climbing a hill with boiling coolant,oil with the viscosity of water and very low oil pressure.

[newmercman]

Do you think the use of dry liners was an attempt to overcome the heat issues that were obvious from the start, wet liners in an engine that was obviously going to run hot would succumb to cavitation and kill the engine long before any of the other shortcomings surfaced.

Also was the cooling system pressurised to raise the boiling point? Were there less cooling system problems during winter when anti freeze was used, therefore raising the boiling point?

Purely hypothetical I know, but I’m sure that using up to date materials, oil and coolant, the V8 could be built today to the exact same design and be as reliable as anything else available.

50yrs ahead of its time perhaps…

Sent from my SM-G950W using Tapatalk

[railstaff]

I think the use of dry liners was a personal preference thing.As ERF explained the cooling issues were an inherent problem which is a shame.Of late ive sat and thought the same question as you,could it be reproduced and be reliable.In reality it should have been bomb proof back then.If we compare what was going on then to what is going on now with the average truck engine.
The weights have moved up to 44t,road speed limiters prevent runs at hills,engines have down sized,HP has increased for less capacity.
In my opinion todays engines are pushing the boundarys of engineering limits,some were operating at over 50% EGR,all are using fuel pressure around 1800 bar,most are operating with 3 bar of boost pressure.MAN being the last to adopt steel pistons to combat piston problems.Material quality and tooling I think played a major problem with this project back then.

[erf]

railstaff:
…I do remember reading about the oiling drillings being wrongly located,but that could have been on a proto type engine.I seem to remember reading the “shells” were good for 100,000 miles and required changing,but the problem was being addressed with a new crank with the drillings relocated in the journal of the crank pin.

I think we can both agree that the correct operation of the pressure relief valve is to open at 50 psi and recycle the oil back to sump.I doubt whether the pump has the capacity to maintain 50 psi hot on idle but I could be wrong.I would think more along the lines of 15psi hot idle.Maybe there lies the problem,a stinking hot 740 climbing a hill with boiling coolant,oil with the viscosity of water and very low oil pressure.

The prototype crankshafts were identical to production ones.
Interestingly AEC claimed the production engines had been fully metricated from the imperial prototypes, but this is another V8 myth.
Both prototype and production engines had crankshafts machined to imperial dimensions, although they were always specified in millimetres!. Bore size was always metric. Only the fixing threads changed from UNF on the prototypes, to Metric for production.

The AEC V8 engines, working with the oils available in the late 1960’s, could not achieve a big end bearing service life of 100’000 miles, not even close. The shells needed changing at a maximum of 50’000 miles to preserve the case hardening of the crankshaft. Running past this almost inevitably ruined the crank.

The work done by AEC in preparation for the proposed 1971 relaunch would have required a new crankshaft to run in their revised longer cylinder block, and it is entirely possible that the oil hole drillings were relocated for these.

When everything is to new tolerance, the oil pump can just about maintain 50 psi on hot idle, but I have seen worn AEC V8 engines recording a solid zero pressure on tickover when hot!.

[erf]

newmercman:
Do you think the use of dry liners was an attempt to overcome the heat issues that were obvious from the start, wet liners in an engine that was obviously going to run hot would succumb to cavitation and kill the engine long before any of the other shortcomings surfaced.

Also was the cooling system pressurised to raise the boiling point? Were there less cooling system problems during winter when anti freeze was used, therefore raising the boiling point?

Purely hypothetical I know, but I’m sure that using up to date materials, oil and coolant, the V8 could be built today to the exact same design and be as reliable as anything else available.

50yrs ahead of its time perhaps…

There is no doubt in my mind that AEC used dry liners purely for reasons of block stiffness. They had moved away from wet liner in line engine designs some years earlier due (if I recall correctly) to head gasket failure issues caused by fretting between the block and head, which was put down to the block flexing.

AEC went to great lengths to stiffen up the V8 block, including using fully fitted cross bolted main bearing caps, so they could obviously see a potential problem there. I have been trying to get a grip on ‘[zb] anorak’s proposal a couple of posts back, which could be an entirely valid point, but without knowing where the existing stress points are, it’s difficult to reach a conclusion. The AEC V8 block as it was produced was successful, in that I don’t know of any fatigue cracking at all. The head gasket issues that the AV740 suffered with were down to how the fire ring sealed around protruding liners, not block to head joint fretting.

Wet liner (or even parent bore cylinder wall) cavitation errosion can orrur whatever temperature the engine runs at. I know of some horrendous problems with old Ford Diesel engines where cavitation had erroded right through the cast iron cylinder walls. Also ■■■■■■■ of course. I have had several NT855’s over the years with failed liners, even (allegedly!) with the DCA additive at the correct strength. I remember Shotts issuing several service bulletins about it, including changing the cheminal composition of the DCA itself at one point. These days I don’t use DCA in that form at all in ■■■■■■■ engines. After listening to a lot of recent research on the subject, I now fit a plain long life coolant filter with no DCA dose, and use a well tested long life ready mixed coolant with the modern inhibitors built in, such as developed by Caterpillar, Volvo Penta, Perkins and ■■■■■■■ themselves, and then change it every five years.

There is a bit about it here from Cat…
cat.com/en_US/by-industry/m … iners.html

Getting back to the AEC V8, it runs with a very low coolant pressure of just 4 psi, which I have always felt was very low, and perhaps contributed to the localised boiling issues that the engine suffered with.
Modern coolants and oils far out perform those available 50 years ago, and there is no doubt that the AEC V8 engine will benefit immediately from them. I’m certainly hoping so anyway!.

[cav551]

There is perhaps some logic to the story about crankpin oil drillings, assuming the team were long standng employees of the company and did not incorporate new blood, then all their recent experience, and that of the company would have been with inline engines. If these drillings were incorrectly located even minimally it could perhaps be because of the geometry of a short stroke vee engine requiring a possibly slightly different position. I do not understand why, but perhaps the answer for any deviation may be found in the piston lubrication versus oil consumption problem of the vee engine, which becomes more relevant the shorter the stroke becomes. The inline AEC engines featured cross drilled main journals and crankpins. At the time cross drilling was a hot topic among engine gurus. There is a school of thought that as RPM rises beyond a certain level that this has a harmful effect upon the oil supply to the crankpins. While one would assume that the V8 did not reach sufficient RPM, does the V8 follow the inline practice?

The inline engines also incoporate a sludge trap in the bored crankpin, this is sealed by a through bolt and conical copper washers. It is very common to find upon dismantling a failed AEC engine that at least one of these bolts is not tight. So the next question is does the V 8 copy the inline engines in this respect? Also if present were any loose in the V8s disamantled? With the reported cooling problems resulting in a hot runnng engine, could the differing rate of thermal expansion of these copper washers in relation to the bolt and crankpin have been a contributory factor in bearing failure?

Staying with oil circulation, but with relevance to the piston scoring/seizure problems IIRC the inline AEC connecting rod is not drilled for small end lubrication and piston underside cooling, so again does the V8 follow with the inline engines?

All of the above may be entirely irrelevant, but has there been any mention from the Perkins engineers of any of this?

As an aside while checking workshop manuals for information I came across the following scribbled in the AEC Merlin copy, referring to the AV 691 engine liner protrusion which is printed as 0.038" above the block surface:

" Depth of flange recess in C/case changed (see DRG.A2/17121) Protrusion of liner now 0.034" "

[cav551]

ERF:
Getting back to the AEC V8, it runs with a very low coolant pressure of just 4 psi, which I have always felt was very low, and perhaps contributed to the localised boiling issues that the engine suffered with.
Modern coolants and oils far out perform those available 50 years ago, and there is no doubt that the AEC V8 engine will benefit immediately from them. I’m certainly hoping so anyway!.

While that is what one would think my oil supplier argues differently. I am aware that they wish to sell their speciality product however I go along with what they say…if only i could remember it correctly!!

According to *** oils modern oils are designed for the much closer working tolerances and greater running temperatures of modern engines. This does not necessarily suit older designed engines and particularly ones which do not have similar efficient filtration to today’s vehicles or even any filtration at all. IIRC the argument then goes that the detergent additives in modern oils carry dirt in suspension which is not removed efficiently by the filters fitted. The oil and the additives also does not work well with the greater clearance between piston and bore resulting in bore glazing and /or varnish deposits gumming up piston rings.

[railstaff]

If it had wings I think at this point this thread would take off,some well respected(by myself) views coming through now.

Taking the wet V dry liner debate.I think for the gains in cooling and with a proper counter bore and fire ring set up and I’m thinking 855 counter bore and Volvo TD122 fire ring locating in to the cylinder head,it out ways the problems of electrolysis and cavition.Which a lot of this fault was rectified with a decent earthing ■■■■■■■■ the block to eliminate static.Without doubt 855 suffered enormously with rotton liners,with an average life span of 7 years.

Getting back to the AEC I’m very surprised to see that it had the properties to be able to maintain 50 psi oil pressure on idle hot,this must only be an AEC attribute.Ive never come across another engine that does this.In theory the shorter stroke should lead to less thrust on one side of the piston and thus less scuffing of the skirt but due to the less than perfect cooling capabilitys were the liners left with excessive piston clearance to compensate for a higher degree of piston expansion which in itself will create scuffing of the skirts?Probably the real cause was as said the poor engine cooling.Would piston cooling jets have made a diiference?Basic rule of thumb,naturally aspirated engines don’t require them,my view is anything over 280hp does.These would have helped the AEC.

[gingerfold]

ERF, as Keith Roberts was also responsible for development of the TL12 engine are you aware of any of the lessons learnt from the V8 being incorporated into the TL12? Incidentally I have just discovered that 25 Marathon TL12s were exported to Bolivia and operated successfully at altitudes above 15,000 feet in the Andes.

[erf]

cav551:
…The inline AEC engines featured cross drilled main journals and crankpins. At the time cross drilling was a hot topic among engine gurus. There is a school of thought that as RPM rises beyond a certain level that this has a harmful effect upon the oil supply to the crankpins. While one would assume that the V8 did not reach sufficient RPM, does the V8 follow the inline practice?

Yes, it does.

cav551:
The inline engines also incoporate a sludge trap in the bored crankpin, this is sealed by a through bolt and conical copper washers. It is very common to find upon dismantling a failed AEC engine that at least one of these bolts is not tight. So the next question is does the V 8 copy the inline engines in this respect? Also if present were any loose in the V8s disamantled? With the reported cooling problems resulting in a hot runnng engine, could the differing rate of thermal expansion of these copper washers in relation to the bolt and crankpin have been a contributory factor in bearing failure?

The ends of the sludge traps in an AEC V8 crankshaft are sealed with core plugs. These are an interference fit, and peened in for added security, but we found two crankshafts with loose plugs.
Everyone that has seen a V8 crankshaft expresses surprise at this set up, because as you say, it was not standard AEC practice at the time, but once again was commonly practiced during engine prototyping in the 1960’s.
Having said that, some later production engines have used this set up successfully.
I won’t spoil the story, just to say the crankshaft was another thing that gave me a good kicking with my V8 engine!.

cav551:
Staying with oil circulation, but with relevance to the piston scoring/seizure problems IIRC the inline AEC connecting rod is not drilled for small end lubrication and piston underside cooling, so again does the V8 follow with the inline engines?

Yes, it does.

cav551:
As an aside while checking workshop manuals for information I came across the following scribbled in the AEC Merlin copy, referring to the AV 691 engine liner protrusion which is printed as 0.038" above the block surface:

" Depth of flange recess in C/case changed (see DRE.A2/17121) Protrusion of liner now 0.034" "

This is very interesting, because the AV740 V8 followed the AV691 specification here exactly.
I had to have a setting gauge tool made up that sat over the top of the new liners while they were being pressed in to the block to set the top protrusion at exactly 0.038”.

As far as I am aware, AEC didn’t ever issue a bulletin to change the figure for the AV740, but then the AV691’s were in production and serviced for longer. The flange recess was never changed in the AV740, and contrary to common practice from other manufacturers, the liners of both engines were not pressed fully home into the flange recess, hence the protrusion gauge.
The liners of the AV760 and AV800/801 engines were pressed (almost) fully home into the recess, which was altogether more satisfactory, and reduced the head gasket and liner cracking failures of these engines.