cav551:
Daimler Benz managed to produce successful aero engines of this pattern during WW2. One cannot blame Leyland’s design engineers for investigating the possibilities.
Good point cav551.I’d never even gave any thought to the possibility of the 600-606 etc being fixed head designs until you’d pointed it out and which certainly seems to be the case.
But then ironically the Merlin,Meteor and Griffon weren’t known for any head to block sealing problems.
IE maybe a solution to a non existent problem that created more maintenance issues than it solved in the case of needing to replace liners,pistons and service the valves and guides and seats ?.
cav551:
The Lorry engine does get a fairly easy life in comparison with the same basic engine’s alternative applications. However for continuous duty the output and speed is usually reduced. As said thermal cycling is the main enemy, it is noticeable that city bus engines do not achieve the same mileage which lorry engines manage. This being because of the constant cycling between full load acceleration and idling at stops, the latter compounded by saloon heating using engine coolant so that following a period of idling the engine receives a rush of colder water just as it comes onto full load. The severest application being high speed rail traction viz the problems encountered with the Paxman Valenta, much of which was related to auxiliaries. The fixed head 500 series engine which was also intended in its horizontal version for citybus use offered the tantalising prospect of eliminating the eliminating the primary area affected by this heat cycling. It would be wrong to dismiss the fixed head engine idea as a complete failure; Daimler Benz managed to produce successful aero engines of this pattern during WW2. One cannot blame Leyland’s design engineers for investigating the possibilities. If they had incorporated DB’s method of liner and block location then they might have overcome one of the 500 series engine’s other failings.
railstaff:
A truck engine gets quite an easy life,its main issue as such is rapid heating and rapid cooling,so fluctuating temperatures is its main enermy.Take a look at a marine application.Admittedly cooling temperature stays constant.Full load for 24hrs day in day out.The averge 855 lasts 3 years.Again take a look at G drive,constant load at one engine speed were they are designed to run.Red hot temps in the cabinet.Oil and snot spewing out of everywere in both examples.I think you live a sheltered life.
So are you saying that MTU’s are zb because if I’ve got it right they are seperate heads ?.
One reason for using single heads are ease of production.Are you telling me you cannot see the benefit of using a single piece head?
Removing your reason of maintenance issues which doesn’t carry any weight anyway due to the fact that the job takes as long as it takes to complete correctly and with correct training and toolage.What are your reasons against?
Take a look at the MAN D28 series,if it had any production life left in it,it would still be used today.Instead MAN invested millions producing the D20/D26 series.
Scania DC12 top rating was 470hp in compound form.In the last ten years its gained one litre(DSC13) and moved to 500hp.That is 30hp surely that tells you something.
As a comparison Volvos D12 top rating was 420hp,the now D13 produces 540hp.One piece head design,im not indicating this is all down to the head but it helps give scope.
One reason for using single heads are ease of production.Are you telling me you cannot see the benefit of using a single piece head?
Removing your reason of maintenance issues which doesn’t carry any weight anyway due to the fact that the job takes as long as it takes to complete correctly and with correct training and toolage.What are your reasons against?
Take a look at the MAN D28 series,if it had any production life left in it,it would still be used today.Instead MAN invested millions producing the D20/D26 series.
Scania DC12 top rating was 470hp in compound form.In the last ten years its gained one litre(DSC13) and moved to 500hp.That is 30hp surely that tells you something.
As a comparison Volvos D12 top rating was 420hp,the now D13 produces 540hp.One piece head design,im not indicating this is all down to the head but it helps give scope.
If the disadvantages of seperate heads are as bad as you say they are in that application then wouldn’t MTU be expected to want to use one piece heads ?.
While the advantages of seperate heads and pushrods are obvious regarding the easy removal and fine placement of the heads when refitting and/or in the case of a specific internal issue just effecting one or a few cylinders.
Just like I can imagine fixing liners,pistons or knackered valves and/or valve seats for example on a fixed head design being a bleedin nightmare.
One reason for using single heads are ease of production.Are you telling me you cannot see the benefit of using a single piece head?
Removing your reason of maintenance issues which doesn’t carry any weight anyway due to the fact that the job takes as long as it takes to complete correctly and with correct training and toolage.What are your reasons against?
Take a look at the MAN D28 series,if it had any production life left in it,it would still be used today.Instead MAN invested millions producing the D20/D26 series.
Scania DC12 top rating was 470hp in compound form.In the last ten years its gained one litre(DSC13) and moved to 500hp.That is 30hp surely that tells you something.
As a comparison Volvos D12 top rating was 420hp,the now D13 produces 540hp.One piece head design,im not indicating this is all down to the head but it helps give scope.
If the disadvantages of seperate heads are as bad as you say they are in that application then wouldn’t MTU be expected to want to use one piece heads ?.
While the advantages of seperate heads and pushrods are obvious regarding the easy removal and fine placement of the heads when refitting and/or in the case of a specific internal issue just effecting one or a few cylinders.
Just like I can imagine fixing liners,pistons or knackered valves and/or valve seats for example on a fixed head design being a bleedin nightmare.
Ok so why don’t you express your train of thought to,
Caterpillar
■■■■■■■
Detroit
Volvo
Iveco
MAN
DAF
MACK
Because they all use single piece heads and have done for years,designed by engineers who know a ■■■■ sight more than you and i.I wonder why this trend has come about over the past twenty years,maybe you can explain?
railstaff:
Ok so why don’t you express your train of thought to,
Caterpillar
■■■■■■■
Detroit
Volvo
Iveco
MAN
DAF
MACK
Because they all use single piece heads and have done for years,designed by engineers who know a ■■■■ sight more than you and i.I wonder why this trend has come about over the past twenty years,maybe you can explain?
My only ‘train of thought’ is that a Scania V8 or an N14 are a lot easier to do any major work on involving head removal and refitting than something with a one piece head and/or OHC/CIH design.Simply because of their seperate heads and pushrod design.Also not aware of any disadvantages in the case of the former which would outweigh those advantages.
While I’d guess that adding to the downsides of the one piece/OHC/CIH type by going for a fixed head design would very likely and understandably result in many places turning down the job.
So are you saying that the Scania’s and the N14’s designers didn’t/don’t know what they were/are doing.
855 don’t have single heads,how long did it take to get DS14 something like.Mack choose to use single piece heads on the E9.At this point there is no way Scania are going to redesign the Vee eight,it has a cult following.
gingerfold:
When I went to work for Spillers Milling in 1981 virtually the entire artic fleet (total about 130 tractor units) was Leyland Buffalo based with a mixture of TL11 and L12 engines. There were a handful of Guy Big J’s and elderly AEC Mandators still dotted about the country at some mills. To be fair the TL11 engines didn’t give much bother in service, but their work was mainly short haul with, of course, blowing hours daily. They weren’t a particularly high mileage engine, however. Spillers had gone through the fixed head 500 engine traumas in the early '70s.
How did the L12 compare Graham?
They were similar power ratings but the L12 was better on fuel, no reliability issues that I can recall and most of the L12s did the full life of the tractor unit, average 6 years back then, without needing any attention. The TL11s were mainly reliable in service, but started to burn oil at about 200,000 miles. There were several turbo-charger failures as well.
Leyland had produced an earlier incarnation of a turbo-charged 0.680 in the late 1960s, designated the 690 engine. It was used in some 2-Pedal Beavers, but it was discontinued. Does anyone know why, or how it differed from the later TL11?
railstaff:
855 don’t have single heads,how long did it take to get DS14 something like.Mack choose to use single piece heads on the E9.At this point there is no way Scania are going to redesign the Vee eight,it has a cult following.
Absolutely the Scania has a cult following because it’s reliable,powerful,and very simple and easy to work on because of its seperate heads and pushrod design.
John Fishwick & Sons Ltd, Leyland.
Leyland National, XCW955R, Fleet No24.
This Leyland National was delivered new to Fishwicks in 1977. It was ‘retired’ in 1997 and entered into preservation.
Fishwicks had a good working relationship with the nearby Leyland Motors. They bought mainly Leyland vehicles including several prototype and ex demonstration buses. No24 was one of several of Fishwicks Leyland Nationals loaned back to Leyland Motors when new for their use by them as a demonstrator. In its later years with Fishwicks, its 500 engine was replaced by a 511. The 511 engine had come from Leyland Motors having been used in a Leyland Buffalo. After conversion from Vertical to Horizontal format, the engine was put into No24. The bus is still about, still preserved and running, and still has the converted 511 engine.
Bill Ashcroft, to whom the bus passed for preservation, took great joy in telling people that it carried a 511 engine, not a 500. He also regularly showed 511 in the route number display. The above photograph was taken at an Open Day at the Stagecoach Bus garage at Carlisle in 2012.
IIRC our member ‘Cargo’ in NZ had some dealings with the Leyland 690. It might be worth a PM.
I can answer my own question as I’d forgotten that I’d researched it when I did my Leyland Beaver book. It is worth looking at the main features of the Leyland 690 engine as some of its features, and problems, were relevant to this thread and the TL12 of the Marathon thread.
Leyland 690. (Developed from the O.680)
240 bhp @ 2,200 rpm, (more powerful than the TL11)
650 lbs. ft. @ 1,400 rpm
Holset turbo-charger.
Re-designed cylinder heads with larger inlet and exhaust valve ports.
Re-designed inlet and exhaust manifolds.
Oil cooled pistons. (used with the TL12)
Larger capacity fuel injection pump with a device to control the rack according to pressure in the inlet manifold. This was to prevent excessive fuel (and black smoke) when the engine was accelerated quickly from slow speed.
Problems in service were frequent cylinder head gasket failures and serious overheating.
Had dealings with 690s in plant apart from the odd head gasket failure not too many problems & also aircraft start generators I recall having an injection pump overhauled the pump was set up according to the test plan but the engine would not deliver sufficient power resulting in a wet start (jet engine) the fueling had been discreetly tweaked by Leyland!
As for the 0.500 engine I was in a supervisory role with a main dealer we had Buffalos fitted with replacement engines under warranty self destruct on road test the Lynx&Bison fared somewhat better the only Lynx I can recall giving problems was a 26t tractor unit, Bisons tippers & mixers very often survived to a ripe old age with no real problems apart from oil leaks due to “O” rings becoming hard with age
IIRC our member ‘Cargo’ in NZ had some dealings with the Leyland 690. It might be worth a PM.
I can answer my own question as I’d forgotten that I’d researched it when I did my Leyland Beaver book. It is worth looking at the main features of the Leyland 690 engine as some of its features, and problems, were relevant to this thread and the TL12 of the Marathon thread.
Leyland 690. (Developed from the O.680)
240 bhp @ 2,200 rpm, (more powerful than the TL11)
650 lbs. ft. @ 1,400 rpm
Holset turbo-charger.
Re-designed cylinder heads with larger inlet and exhaust valve ports.
Re-designed inlet and exhaust manifolds.
Oil cooled pistons. (used with the TL12)
Larger capacity fuel injection pump with a device to control the rack according to pressure in the inlet manifold. This was to prevent excessive fuel (and black smoke) when the engine was accelerated quickly from slow speed.
Problems in service were frequent cylinder head gasket failures and serious overheating.
The last of the TL11,s made 260hp.It would seem the TL11 was a backward step.No piston cooling and no liner counterbore.
railstaff:
When Daf released the 530 version of the 12.6 XEC engine the block material changed to Grafite steel against the lower carbon grade for the lower hp versions.Watch a clip of an engine with single cylinder heads,clearly seen is the head lifting during the firing stroke.For an example take a look at either an MAN D28 or Scania DC12 or 13 with single heads.Basically the strength stops at the face of the block or more precisely the deck inbetween the liner counterbores which on a DC13 is about 20mm.Major flex happens in this area,thermal imaging shows it.Both of these engines share a common problem,the block face frets away over time due to the heads moving.Now bolt a piece of steel across it at 100mm deep(the head) and it stiffens the block,no more fretting of the face,it doesn’t lift on the firing stoke because its clamped either side.Really speaking the block is weak,most crankcases are only 7mm thick,a wet linered block contains nothing until half way down the block.
I can see how a stiff one-piece head can prevent lifting during the firing stroke, but what causes the lateral movement, which I would guess would cause the fretting of the deck you mention on separate-head engines?
Apart from this admittedly fascinating diversion, what was the failure mode which typically killed the poor old 500? I’m gonna guess it was differential expansion causing pistons to grab the liner, or the liner to come loose and precess towards the crank, until people who have seen the actual truth shoot me down in flames and fragments of cast iron .
The thrust side of the piston pushes on the liner,trying to move it in the block.That in itself puts wear into the counterbore.The wear ive mainly seen on single head engines is always on the edges of were the gaskets would locate,in other words between the heads.Block to head joint is moving.CF refers to the vee eight Scania engine.In reality a lump of steel shaped like a triangle is laterally more stiff.Its enemy is lack of big end and to a degree main bearing area.
Pictures of earlier Leyland group engines with the cylinder head removed.
In order:
AEC AH 470. This engine had a reputation for blowing head gaskets, as can be seen there are five studs surrounding each cylinder, but poorly spaced. In addition the studs reach a long way down into the block which created difficulties with the studs stretching.In severe cases the heads would actually be dancing on top of the block… a bit like the O 500 block did on top of the crankcase. There were numerous modifications tried by the AEC but none addressed the stud spacing until the engine was superceded by the AV505 which then used 6 studs .
Leyland O 600. O 680 similar. Seven studs per cylinder, however there is only one stud on the nearside (r/h in picture) for each cylinder. In addition the short 7/16"studs on the o/s had a tendancy to pull out of the block or for the block to crack because these located in a projection.
AEC AV 590: 8 studs per cylinder. A similar arrangement to the AV 690 and AV 760 except that the AV760 studs were 9/16" diameter instead of 1/2" IIRC some of the studs were increased to 5/8" for the TL12
Good post Roy and it makes your point very well. The AHU / AVU 470s with unified thread studs cured most of the head gasket failures of the earlier engines. Why would that be?
The AVU470 engine I had in my restored Seddon was rated at 140 bhp and in the 9 years I had it never gave any problems with its head gaskets, which I had renewed at the renovation stage. Granted it was not running at anything like the stresses imposed on an engine in revenue earning service. But I know of two preserved AEC Mercurys with the non-unified head threads having head gasket failures on road runs in which I was taking part. Both Mercurys were owned by people who are meticulous in their preparations and they are in fact engineers. Going back to the engine in my Seddon the only signs I ever saw of any water being where it shouldn’t have been was when I changed the engine oil at the end of every rally season. I always used Bluecol anti-freeze all the year round and when I removed the sump plug no more than an egg cup full of Bluecol would come out first. It never went any worse in 9 years. Being a wet liner engine there must have been an ever so slight weepage from one of the liner O rings.
gingerfold:
Good post Roy and it makes your point very well. The AHU / AVU 470s with unified thread studs cured most of the head gasket failures of the earlier engines. Why would that be?
The AVU470 engine I had in my restored Seddon was rated at 140 bhp and in the 9 years I had it never gave any problems with its head gaskets, which I had renewed at the renovation stage. Granted it was not running at anything like the stresses imposed on an engine in revenue earning service. But I know of two preserved AEC Mercurys with the non-unified head threads having head gasket failures on road runs in which I was taking part. Both Mercurys were owned by people who are meticulous in their preparations and they are in fact engineers. Going back to the engine in my Seddon the only signs I ever saw of any water being where it shouldn’t have been was when I changed the engine oil at the end of every rally season. I always used Bluecol anti-freeze all the year round and when I removed the sump plug no more than an egg cup full of Bluecol would come out first. It never went any worse in 9 years. Being a wet liner engine there must have been an ever so slight weepage from one of the liner O rings.
Less of a pitch on the thread,more thread per inch and less chance to back off underload due to less of a ramp.Superb post,goes to show that with single heads how busier the deck of the block would be.As shown in them excellent pictures the clamping devise of one cylinder is also the clamping devise of the one next to as against singles were they all require their own clamping devises.But to be fair one area were single heads excel is to compensate for a low liner if you can call that correct in the first place.
gingerfold:
Good post Roy and it makes your point ve
Superb post,goes to show that with single heads how busier the deck of the block would be.As shown in them excellent pictures the clamping devise of one cylinder is also the clamping devise of the one next to as against singles were they all require their own clamping devises.But to be fair one area were single heads excel is to compensate for a low liner if you can call that correct in the first place.
Couldn’t that also make the case that the clamping effort on a cylinder on the compression or firing stroke where it needs all the clamping force it can get is being reduced by sharing it with the cylinder next to it ?.While any premise in favour of a one piece head over seperate heads would have taken out Mercedes long ago.IE the extra bolt spacing requirement isn’t exactly a major issue.
.
