The mighty Class 74 (some questions!)

[D7666]

As I think D7666 was talking about the weight of a cl. 74, do those actually have/retain the 'flywheel' booster that was in the cl 71's ?

AIUI 74s had the booster but no flywheel ???

You don't need the flywheel in a 74 - a 71s flywheel was to maintain traction power cross gaps; a 74 used the diesel engine.

A 71 was already 19 t 5 c axle load, same all four axles, from the BR Diagram Book issued c.1970 diagram E/4/1 => 78 t loco weight

Same book has 74 as 21 t 3 c same data => 84.6 t loco.

6.6 t increase.

Adding a diesel engine + generator + fuel tanks is going to increase weight; lose the flywheel saves a bit - I can't yet find a value of the flywheel weight alone.

But there were other additions too - 71s did not have buckeye couplers and all that push pull stuff etc - 74s got them. A single buckeye weighs c.40 kg, and that is just the moveable bit that needs to be manually lifted, the thing needs a lot of fixed metal. Twice, one at each end.

Compare a 33/0 with a 33/1 - the buckeyes and push pull stuff (and not much else was done) goes from 33/0 74 t 4 c to 33/1 77 t 6 c (data from same diagram book) => increase 2 t 2 c.

So if you take your 78 t 71, say lose a 2 t flywheel (which is pretty hefty for a flywheel) then add 2 t for the push pull / buckeye stuff and you are back to 78 t.

300 gallon diesel fuel adds c. 1 ton => 79 ton.

OK so 71s lost their pantograph, but that is peanuts, and probably more weight than that was added from the fuel tanks alone.

A Paxman 6YJ alone is around 4 t alone, according to google search, => 83 ton.

I reckon 79 t to 84.6 t then for engine + generator + cooler group is pretty good going.

Would be a bit more closer to the mark sums if the 71 flywheel weight was known.

 

[ac6000cw]

AIUI 74s had the booster but no flywheel ???

I think that is the case - having now dug more into the details of how the traction control was implemented in the 71s, it looks like it was similar to the earlier CCx/BR class 70 3rd rail locos. These used a more power-efficient motor-generator 'booster' setup (with flywheel for temporary energy storage) for traction power control instead of simple direct resistance control (like EMUs of the period used). See https://en.m.wikipedia.org/wiki/Booster_(electric_power) and https://en.m.wikipedia.org/wiki/British_Rail_Class_70_(electric)#Booster_control

I assume they had to keep the 'booster' power control system on the cl. 74 conversions (but not the flywheel). I have a recollection (from something I read years ago) that the resistor control of the generator field strength on the booster set was replaced with electronics in the 74s, to save space and weight - but I could be completely wrong of course!

 

[Harlequinuk]

I would like to say `thank you` for this incredible chat!

Have ordered the book D7666 has suggested as a lazy summer evening read.

So the crux being, nothing now exists? No engines etc?

 

[Rescars]

Reflecting on thus thread, it is interesting to see how traction engineers have approached the challenge of augmenting electric power with diesel. The approach taken seems so different from car manufacturers who have created hybrids by adding battery capacity to internal combustion vehicles.

 

[Haywain]

Reflecting on thus thread, it is interesting to see how traction engineers have approached the challenge of augmenting electric power with diesel. The approach taken seems so different from car manufacturers who have created hybrids by adding battery capacity to internal combustion vehicles.

You're looking at two fifferent things 50 years apart though. Battery technology wasn't up to much in the 1960s/1970s, and the class 74 was required for a network that was, primarily, electrified. Adding a diesel engine was the obvious solution then.

 

[Taunton]

You don't need the flywheel in a 74 - a 71s flywheel was to maintain traction power cross gaps; a 74 used the diesel engine.

Did this mean the diesel ran all the time? If not would have been a right nuisance if gapped at say Victoria station throat (apparently a regular gapping point, even with emus), waiting for the diesel to fire up.

How long did the flywheel on the 71 last? Could it do some shunting of an unelectrified siding?

 

[D7666]

Did this mean the diesel ran all the time? If not would have been a right nuisance if gapped at say Victoria station throat (apparently a regular gapping point, even with emus), waiting for the diesel to fire up.

How long did the flywheel on the 71 last? Could it do some shunting of an unelectrified siding?

No.

On electric the 74 booster set is driven off the third rail traction supply the same as a 71.

The diesel generator set powers the booster when no traction supply is present.

A 74 gapping issue is no different an inconvenience to a 73 and having to start the diesel.

_

RE. upthread, I have now found the 71 flywheel weight, Lilley and Wenyon state 2000 lb (two flywheels not one) which is about 1 ton; I used 2 ton upthread.

Same source gives 4260 lb (i.e. ~2 ton) for the diesel main generator weight.

So while I used 2 t instead of 1 t for losing the flywheel, I'd omitted 2 t for the main generator ; if you run through my post now with these values you come very close to how you get from 78 t 71 to 84 t 74.

_


There is a Learned Society paper read to I.Loco.E or I.Mech.E or similar by WJA Sykes who was the SR CM&EE engineer. I do not have a copy of it but it does have a description of the 74s part electronic control system.

I think it is in this paper that Sykes said something like one of the lessons learned was "do not extensively rebuild things" or similar in the light of the 71 to 74 job.

319s to 769s are a parallel. Just as the booster set was retained in a 74 and needed a different arrangement to power that on diesel, retaining the 319 traction pack with its need for a constant DC input (900 V IIRC) hence complexications with diesel gen set control.

With hindsight - which is always 20:20 vision - neither the 71/74 or 319/769 rebuilds would have been done in the way they were.

Then again, both were aimed at being quick and dirty cheap jobs - both low budget jobs, which is probably a root issue. The parallels are fascinating.

 

[Harpo]

Then again, both were aimed at being quick and dirty cheap jobs - both low budget jobs, which is probably a root issue. The parallels are fascinating.

Loss of corporate knowledge? Many further parallels on that front throughout the industry.

 

[thesignalman]

and ofc, a request for any photos or even video of them running would be very much appreciated.

Some photos to browse here, if of interest:

Search - class 74

John

 

[ac6000cw]

There is a Learned Society paper read to I.Loco.E or I.Mech.E or similar by WJA Sykes who was the SR CM&EE engineer. I do not have a copy of it but it does have a description of the 74s part electronic control system.

I suspect it's this one (from the IET archives) - Class 74 electrodiesel locomotives of British Rail Southern Region, with particular reference to the control system

319s to 769s are a parallel. Just as the booster set was retained in a 74 and needed a different arrangement to power that on diesel, retaining the 319 traction pack with its need for a constant DC input (900 V IIRC) hence complexications with diesel gen set control.

Controlling a diesel genset to produce a constant voltage (and constant frequency, if it's AC output) under varying loads is standard stuff for people who make and sell them for e.g. for mains/standby/auxiliary power. I remember in the 1980s running a stage lighting rig from a diesel genset - it was quite fun whacking the master lighting control fader up and down and listening to the diesel engine note changing as it coped with the load variations

With hindsight - which is always 20:20 vision - neither the 71/74 or 319/769 rebuilds would have been done in the way they were.

Then again, both were aimed at being quick and dirty cheap jobs - both low budget jobs, which is probably a root issue. The parallels are fascinating.

My own experience (as an electronics design engineer) is that doing major changes/upgrades to someone else's equipment can be fraught, because there's always something that you didn't know or is different from the information you were given (or occasionally the equipment turns out to be a can-of-worms to start with...the 'wish I hadn't started this' projects...). The late nights and and grey hairs are all part of the engineer's lot sometimes - as is the quiet satisfaction when it's 'job done' .

 

[Harlequinuk]

Thank you all! Am now the proud owners of a copy of the excellent book as suggested above. A plethora of information i assure you. It does seem the diesel worked differently to the 73 in how power was delivered to the rails

 

[Taunton]

My own experience (as an electronics design engineer) is that doing major changes/upgrades to someone else's equipment can be fraught, because there's always something that you didn't know or is different from the information you were given (or occasionally the equipment turns out to be a can-of-worms to start with...the 'wish I hadn't started this' projects...)

I feel also that such updates are often seen as "cheap", and do not have the budget of a new build. Nor do they consider aspects not directly connected with the new work, such as the steel panel you screw the new component onto turning out to be corroded, or even having been removed by some undocumented previous modification.

 

[themiller]

Greetings all!

I have a soft spot for the Class 74, im sure the reaction will be one of wide eye astonishment, but i do like the `Big Ed`. But some questions if i may!

What happened to the bogies/ traction motors/ generators etc once scrapped? Also the engines? 10 Paxman Ventura , would they be cut up as well or moved on to something else?

and ofc, a request for any photos or even video of them running would be very much appreciated.

The Modern Locomotives Illustrated magazine no.215 has a section on class 71s.

 

[D7666]

Thank you all! Am now the proud owners of a copy of the excellent book as suggested above. A plethora of information i assure you.

That is why I suggested it. Good isn't it.

 

[Harlequinuk]

Been doing alot of searching - and i came across this image - on its diesel!

Class 74 No.74007 is leaving Southampton Eastern Docks (under diesel power) with an 'Ocean Liner Express' for Waterloo. Note the Liner 'Oriana' in the background. Photo via RMWeb /quote]

 

[Ashley Hill]

At least there’s one head out of the window for the thrash!

 

[D6130]

Been doing alot of searching - and i came across this image - on its diesel!
View attachment 184991

Nice photo. Looks like the S.S. "Oriana" in the background.

 

[Big Jumby 74]

Been doing alot of searching - and i came across this image - on its diesel!

The stock looks to be a bit of a bit-sa set. Possibly one of the Mk1 8 Set's (or part of) with 4 x Mk2 FK's up front. Like the Triumph Herald.

 

[Harlequinuk]

And another! Found a photo or 2 of the controls as well

Class 74 E6110 at Bournemouth running on the diesel engine on 16th August 1973. She had just been removed from Waterloo-Weymouth passenger working, on which two very happy Lincolnshire lads had just travelled back from Southampton on. Even better we had had E6105 on the same train 2 days earlier. Happy Days. Photo and Copyright: Ian Turpie

 

[ac6000cw]

Harlequinuk said:
Been doing alot of searching - and i came across this image - on its diesel!
View attachment 184991

At least there’s one head out of the window for the thrash!

If you zoom in, it looks to me like the person leaning out is talking to a person standing on the ground (between the Triumph Herald and the train) possibly carrying an orange Hi-Viz vest - so maybe guard and shunter talking? There's also a motorcycle parked alongside the van (GUV?) at the front of the train, and it looks like the loco has a TOPS number, so post-1973.

But a lovely photo with 1970s nostalgia in spades, including the array of dockside cranes!

And another! Found a photo or 2 of the controls as well
View attachment 185012

Pre-TOPS number, and there's an Austin Maxi on the right of the car park (which came out in 1969) and I think a Chrysler 180 alongside it (launched 1971) so early 1970s photo?

Nice array of paint patches on the side of the loco too!

 

[Big Jumby 74]

And another! Found a photo or 2 of the controls as well

Bournemouth Central, E6110 is on the loco siding (as was) at the West end of Platform 2. Nice pic btw. The car park is the site of Bournemouth Central MPD.

== Doublepost prevention - post automatically merged: 28 Jul 2025 ==

van (GUV?) at the front of the train, and it looks like the loco has a TOPS number, so post-1973.

But a lovely photo with 1970s nostalgia in spades, including the array of dockside cranes!

Yes, a GUV. They were the norm by the time I became involved in diagramming those services amongst others, always at the London end for ease of unloading/loading at Waterloo. The sole first class set (FK's) was the preferred set, but quite often two trains were required on a single day, as both Canberra and QE2 were in dock at the same time, and so a second set (8 Set) would be used, augmented by other traffic spare vehicles as required, depending on circumstances on the day.
I well remember the dockside cranes along Weymouth Quay (as well as S/docks). Another time and very fond memories!

 

[ac6000cw]

Yes, a GUV. They were the norm by the time I became involved in diagramming those services amongst others, always at the London end for ease of unloading/loading at Waterloo.

Ah, so the 74 is departing/ready to depart towards London (as the GUV is at the head end)?

 

[Harlequinuk]

I think, this is the drivers view of the 74 (and the second man is the second photo)

 

[Big Jumby 74]

Ah, so the 74 is departing/ready to depart towards London (as the GUV is at the head end)?

The colour photo with the Triumph Herald and m/bike alongside, yes, that is correct. As for the B/W photo of E6110, that would appear to be just a L//E (Light Engine) shunt move about to/taking place, so no idea as to any other detail!

 

[ac6000cw]

As for the B/W photo of E6110, that would appear to be just a L//E (Light Engine) shunt move about to/taking place, so no idea as to any other detail!

I agree.

Would the 74's have got to Bournemouth mostly on parcels/mail and the Weymouth boat trains (swapped with a 33 for the Weymouth leg)?

 

[Big Jumby 74]

Would the 74's have got to Bournemouth mostly on parcels/mail and the Weymouth boat trains (swapped with a 33 for the Weymouth leg)?

Regrettably I and those I worked with in my time (diagramming) never kept any of the diagrams documents from those days, being paper orientated, as soon as one was out of date, it got binned and we started working from the next (up to date plan) and so on, so even the 33/1 diagrams which were largely based around Weymouth/Bournemouth legs of 1Wxx etc, none of us (whom I still have contact with) has any copies of same. Likewise the ED's, both 73 & 74.

Purely from an educated guess p.o.v, I would imagine one core way for a 74 to reach Bournemouth will have been the 0245 ex Waterloo Mails? There was mention Up thread (matching my somewhat very poor image of '004 approaching Woking) of an UP van working back to Clapham Yard utilising said traction. Just a thought!

PS: the very second post of this thread mentions a 13.30 Poole to Clapham Yard. My image of 004' was taken (as far as I can recall/work out) probably 4 pm ish given an hour either way, so that would tally.

 

[D7666]

I am typing here from memory so allow for 50 years of grey cell decline.

Early / mid 1970s - and discounting the 2252 Down / 2238 Up Weymouth mails that were 33s west of Eastleigh - there were two Waterloo - Bournemouth etc paper/night trains that were 74s to Bournemouth - ex Waterloo 02:15 and 02:45.

Now these did different detailed things in different timetables, so I am talking here in general.

One of the two was vans only, there other vans + 3set (BSK+CK+BSK).

These provided 2 74s at Bournemouth by the morning.

One, with the 3set and with/without vans and changing origin and destination with different timetables, worked a passenger train for schools times variously as New Milton / Brokenhurst / Totton / Eastleigh, all c. 08:00-09:00. This stock then formed a ECS c.09:55 Eastleigh - Clapham.

The other was the above mentioned Poole - Clapham vans, which ISTR was also ECS although I would have said it was c.11:30 from Poole.

I have not looked up nor gone into the blow by blow, year by year, excrutiating detail - but if interested some of this you can find in the CWN notices of the period; these won't tell you the loco types, but do gives times and consists to piece things together.
_

w.r.t. Weymouth boat trains, I am aware that people keep stating 74s worked to Weymouth if/when 33s unavailable but the truth is these must have been very v-e-r-y VERY rare and there are near zero recorded (or zero recorded in authoritative sources) instances of this. It is one of these urban rumours that has been inflated over time as if it was normal. Same applies to 73s re Weymouth boat train - you need a blue moon over GB at the same time as snowballs in the Belgian Congo and a pretty big failure at Bournemouth for it to happen beyond 1 or 2 cases over decades. I am not saying it never happened, just the stories are grossly exsggerated - and I ask for authoritative proof on any allegations it did occur wth a 74 (and my mates best school mate told me about it last week down the pub does not count).

 

[GRALISTAIR]

Most of my class 74 photos were taken on depots. I have photos of them all. I will try and post in the future when back in the UK.

 

[ac6000cw]

Regrettably I and those I worked with in my time (diagramming) never kept any of the diagrams documents from those days, being paper orientated, as soon as one was out of date, it got binned and we started working from the next (up to date plan) and so on, so even the 33/1 diagrams which were largely based around Weymouth/Bournemouth legs of 1Wxx etc, none of us (whom I still have contact with) has any copies of same. Likewise the ED's, both 73 & 74.

Purely from an educated guess p.o.v, I would imagine one core way for a 74 to reach Bournemouth will have been the 0245 ex Waterloo Mails? There was mention Up thread (matching my somewhat very poor image of '004 approaching Woking) of an UP van working back to Clapham Yard utilising said traction. Just a thought!

PS: the very second post of this thread mentions a 13.30 Poole to Clapham Yard. My image of 004' was taken (as far as I can recall/work out) probably 4 pm ish given an hour either way, so that would tally.

I am typing here from memory so allow for 50 years of grey cell decline.

Early / mid 1970s - and discounting the 2252 Down / 2238 Up Weymouth mails that were 33s west of Eastleigh - there were two Waterloo - Bournemouth etc paper/night trains that were 74s to Bournemouth - ex Waterloo 02:15 and 02:45.

Now these did different detailed things in different timetables, so I am talking here in general.

One of the two was vans only, there other vans + 3set (BSK+CK+BSK).

These provided 2 74s at Bournemouth by the morning.

One, with the 3set and with/without vans and changing origin and destination with different timetables, worked a passenger train for schools times variously as New Milton / Brokenhurst / Totton / Eastleigh, all c. 08:00-09:00. This stock then formed a ECS c.09:55 Eastleigh - Clapham.

The other was the above mentioned Poole - Clapham vans, which ISTR was also ECS although I would have said it was c.11:30 from Poole.

I have not looked up nor gone into the blow by blow, year by year, excrutiating detail - but if interested some of this you can find in the CWN notices of the period; these won't tell you the loco types, but do gives times and consists to piece things together.
_

w.r.t. Weymouth boat trains, I am aware that people keep stating 74s worked to Weymouth if/when 33s unavailable but the truth is these must have been very v-e-r-y VERY rare and there are near zero recorded (or zero recorded in authoritative sources) instances of this. It is one of these urban rumours that has been inflated over time as if it was normal. Same applies to 73s re Weymouth boat train - you need a blue moon over GB at the same time as snowballs in the Belgian Congo and a pretty big failure at Bournemouth for it to happen beyond 1 or 2 cases over decades. I am not saying it never happened, just the stories are grossly exsggerated - and I ask for authoritative proof on any allegations it did occur wth a 74 (and my mates best school mate told me about it last week down the pub does not count).

Many thanks to both of you

(Living in the Birmingham/Bradford/Manchester areas in the 1970s and only a very occasional visitor to the LSWR mainline, I don't think I've ever seen a 74 hauling a train - they were in the 'exotica' category for me).

 

[Big Jumby 74]

Weymouth boat trains, I am aware that people keep stating 74s worked to Weymouth if/when 33s unavailable but the truth is these must have been very v-e-r-y VERY rare and there are near zero recorded (or zero recorded in authoritative sources) instances of this. It is one of these urban rumours that has been inflated over time as if it was normal. Same applies to 73s re Weymouth boat train - you need a blue moon over GB at the same time as snowballs in the Belgian Congo and a pretty big failure at Bournemouth for it to happen beyond 1 or 2 cases over decades. I am not saying it never happened, just the stories are grossly exsggerated - and I ask for authoritative proof on any allegations it did occur wth a 74 (and my mates best school mate told me about it last week down the pub does not count).

Concur with you completely. Highly unlikely, but will accept confirmed evidence/proof of, if ever forthcoming. Never say never etc! I will likely be sharing a beer with one or two former Controller colleagues, amongst others, in a few weeks time, from the days of 74/73 operation, so may pose the question (assuming their memories are any better than mine!), not that the memories of one or two people is conclusive in any way, I do appreciate.
Am certain that back then, a loco failure on a Weymouth Quay boat train in the Eastleigh/Bournemouth area, would have seen either Eastleigh depot or Bournemouth Depot produce a standby Crompton if/when required.