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Why did BRM keep having so many silly failures with the P25 2 1/2 litre car?


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#1 mariner

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Posted 22 January 2022 - 16:49

Having read Doug Nye's BRM magnum Opus , Tony Rudd's book and  recently Dick Salmon's BRM mechanic book I am struck by how many little things kept going wrong on the P25. Many were put down to excessive vibration of big 4 cylinder engine but Vanwall also ran big 4 ( which also caused vibration problems but ones which were fixed) . Similarly Cooper and Lotus ran a 2 1/2 litre Climax four.

 

BRM seemed to be recognised as having very high engineering standards .They had a large drawing office, enough machine tools to build engines and at least two ex Rolls Royce aero engine men – Tony Rudd and Stuart Trevelyan 

 

Wishbones were made with tapered shapes, welded and stress relieved versus Lotus’s thick tube and brazing approach etc. I know BRM had very few serious chassis failures but brake lines kept failing which is pretty serious fault and throttle linkages often failed. “

So why so many “ niggly” failures when s few major chassis ones? Was it poor detail design, lack of reaction or did eh BRM four have some vibration modes different to the other 4 cylinder engines  I think it had  different balancing philosophy IIRC

 



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#2 Bloggsworth

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Posted 22 January 2022 - 17:36

Single rear disc brake which acted directly on the transmission possibly didn't help.


Edited by Bloggsworth, 22 January 2022 - 17:36.


#3 RobertE

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Posted 22 January 2022 - 19:41

The engine had been originally conceived as a four-valve effort, but this was switched to two - for reasons of either economy or something else - Doug would know. The valves, therefore, were huge.



#4 Doug Nye

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Posted 22 January 2022 - 21:23

Stuart Tresilian, not Trevelyan.  Strictly the car should be known as the Type 25 not P25 unless one refers solely to the engine. The various chassis iterations fell under the P27 project title.  Reliability during that period depended upon many factors including well developed and proven design - first-class manufacture - painstaking parts inspection - first-class preparation - and mechanically sympathetic driving.  Many of the brake failures involved bought-in hydraulic unions and lines - usually attributed to component supplier failure, although one would expect BRM parts inspection to have detected an incipient fault pre-assembly into one of the cars. I very much hesitate to point the figure at the team mechanics although some sloppy work in assembly caused in house fireworks from time to time.  

 

DCN



#5 Bloggsworth

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Posted 22 January 2022 - 22:05

The engine had been originally conceived as a four-valve effort, but this was switched to two - for reasons of either economy or something else - Doug would know. The valves, therefore, were huge.

And the exhaust valves were sodium filled IIRC, I seem to remember reading about valve-stem breakages.



#6 Roger Clark

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Posted 23 January 2022 - 09:12

I thought that the single real disc was satisfactory once problems caused by high rubbing speed in the original design were cured. As Doug says, frequent brake failures were caused by the hydraulics. The single disc was less successful with the rear-engined cars where their size caused the engine to be mounted higher than desirable. 



#7 Sterzo

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Posted 23 January 2022 - 11:06

If my reading of the books mentioned is correct, then Peter Berthon may have been a boss who prioritised design over development, and ideas over painstaking preparation. That's the view from my armchair anyway.



#8 mariner

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Posted 23 January 2022 - 11:17

One thing that was unusual about the first P25 engine ( thank you Doug!) was that it had only  four main bearings not five. Later on, it had an extra one added. I seem to remember some quote from Tresiilian about " putting the bearings where there were no loads" to reduce stresses?

 

The brake failures were indeed often supplier components but others used them to so it might have been BRM vibration. Even a standard "tin" master cylinder cracked at one point. Also, the throttle linkages that failed were , according to tony Rudd’s own book, Rolls Royce parts which weren't assembled properly.

 

It is a  bit of an obscure topic in many ways but I  think it did have bigger significance in the story of 1950's British F1 because the type 25 was very light ,the engine had great torque so it was a very, very fast  car until it failed. Maybe without the " niggles" it would have beaten Vanwall to the first big British F1 success, certainly Hawthorne and Collins had the speed to win GP's.



#9 Charlieman

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Posted 23 January 2022 - 11:58

It is a  bit of an obscure topic in many ways but I  think it did have bigger significance in the story of 1950's British F1 because the type 25 was very light...

A significant point, mariner. A few years later when BRM stripped down a Cooper to see how it was built, Tony Rudd reported that many BRM components and structures were lighter than Cooper -- DCN/Rudd BRM book.



#10 Doug Nye

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Posted 23 January 2022 - 12:59

Many, many Type 25 components were very well crafted and meticulously made to industrial toolroom standards.  That all took time and cost money.  In many ways BRM could have economised on both by using perfectly practical proprietary components as did the garagistes like Cooper and Lotus. But the mindset was Rolls-Royce and Mercedes-Benz Rennabteilung.  All set in a charmingly rural market town in Lincolnshire. 

 

Vanwall worked to matching, or even better standards, but were entirely free to act and react really quickly because they were ruled and directed by one man, and one dynamically-motivated, spring-steel, tough man alone.  Racing might have been just Tony Vandervell's 'hobby' - but he wasted none of his time on diversions.

 

These are several of the factors that first entranced me way back in the '50s and early '60s...

 

One other factor which played a major role in the varying racing fortunes of BRM and Vanwall was that 'the BRM' clung quite strictly to using only British-made components while in stark contrast Vanwall scoured the world's industries for the best or best-suited parts and systems available.

 

DCN


Edited by Doug Nye, 23 January 2022 - 22:35.


#11 RobertE

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Posted 24 January 2022 - 13:00

When tiny I lived for a while in Seremban in Malaya; my two most treasured toys were a BRM and a Vanwall; Dinky toys, I think. The BRM was in pale green BRP colours, so it must have been the one which featured in Hans Herrman's spectacular 'off' at the Avus. Happily, I raced them down the long dusty garden, I alone deciding on who would win! One day, I tripped and fell, sending both cars into the undergrowth. They are probably still there, as I disturbed a Cobra which suddenly popped up. It seemed huge, but I was only four - everything is huge at that age. Sensibly, I backed off,  beat a hasty retreat and avoided that end of the garden for the duration of our stay.

 

That was the closest I ever got to a BRM, until coming across Amschel Rothschild's full-sized P25 in a museum in East Sussex; I have no idea what it was doing there.



#12 rl1856

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Posted 24 January 2022 - 16:19

And the exhaust valves were sodium filled IIRC, I seem to remember reading about valve-stem breakages.

 

Were there associated issues caused by the weight of the valves ?  I recall reading that inertia of the large valves caused problems in the camshaft (hair?)springs controlling their movement.  The article I read stated that the engine had a strict rev limit as a result.   Source was an article on the P25 in Sports Cars Illustrated (precursor to Car and Driver in the US).



#13 kayemod

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Posted 24 January 2022 - 17:00

 I disturbed a Cobra which suddenly popped up. It seemed huge, but I was only four - everything is huge at that age. Sensibly, I backed off,  beat a hasty retreat and avoided that end of the garden for the duration of our stay.

 

...I have no idea what it was doing there.

 

Still too young to drive, but you should have hung on to that Cobra.

 

If it was a real one and not one of those GRP bodied replicas, it would have fetched a good few thousand today.


Edited by kayemod, 24 January 2022 - 18:17.


#14 mariner

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Posted 24 January 2022 - 22:05

The BRM P25 hwas  a very over square engine design with 102mm bore vs around 96mm for the Vanwall. That enabled the very large valves -  2.40" inlets I think.

 

The bigger pistons might have been about 10% heavier than the Vanwall ones if of similar  design. A 4 cylinder engine develops large horizontal  out of balance forces accentuated  if the con rods are short. The BRM engine had 4.8 " rods - quite short.

 

So, overall, the engine design might have generated much more vibration than the Vanwall or Climax fours of the same 2.5 litres.


Edited by mariner, 24 January 2022 - 23:22.


#15 Lee Nicolle

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Posted 25 January 2022 - 06:03

The BRM P25 hwas  a very over square engine design with 102mm bore vs around 96mm for the Vanwall. That enabled the very large valves -  2.40" inlets I think.

 

The bigger pistons might have been about 10% heavier than the Vanwall ones if of similar  design. A 4 cylinder engine develops large horizontal  out of balance forces accentuated  if the con rods are short. The BRM engine had 4.8 " rods - quite short.

 

So, overall, the engine design might have generated much more vibration than the Vanwall or Climax fours of the same 2.5 litres.

From what I have seen of those engines I was not that impressed. All online stuff however. Lets go out of our way to make somethings complex and hard to maintain. And from what I have seen Lucas electrics!

A 4" bore on modern production based engines for speedway midgets is common. And they are 2.5 litre. I doubt though any use a valve near as big. 2.08/ 1.6 is usual. With a 6" or so rod. The Sesco is based on half a 5 litre Chev. 4x3" And that form of engine has been around since the late 60s.  I believe there is also Ford based engines similar. Gaerte was using Cleveland style heads on midget engines, though I believe specially cast alloy versions like there has been for Chevs for decades.



#16 Doug Nye

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Posted 25 January 2022 - 11:34

Having had the chance to drive BRM 4-cyl, Vanwall 4-cyl, Cooper-Climax 4-cyl and Cosworth-Ford DFV V8 I believe the worst vibration of all actually came from the DFV.  Of course, it also delivered by far the most power and torque.  I recall the Vanwall engine as being marginally smoother than the BRM, but not as smooth as the still vibrant Climax - if you see what I mean.  

 

The worst 4-cyl vibes I have ever encountered, however, were from the 1908 GP Mercedes and 1908 GP Benz - both when at high speed providing one helluva bang at every second telegraph pole.   :cool:

 

DCN



#17 BRG

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Posted 25 January 2022 - 11:38

Having had the chance to drive BRM 4-cyl, Vanwall 4-cyl, Cooper-Climax 4-cyl and Cosworth-Ford DFV V8 I believe the worst vibration of all actually came from the DFV.  Of course, it also delivered by far the most power and torque.  I recall the Vanwall engine as being marginally smoother than the BRM, but not as smooth as the still vibrant Climax - if you see what I mean.  

 

The worst 4-cyl vibes I have ever encountered, however, were from the 1908 GP Mercedes and 1908 GP Benz - both when at high speed providing one helluva bang at every second telegraph pole.   :cool:

 

DCN

We all hate you, Doug.  Truly, deeply, madly...... :mad:

 

 

 ;)



#18 Roger Clark

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Posted 25 January 2022 - 12:11

Having had the chance to drive BRM 4-cyl, Vanwall 4-cyl, Cooper-Climax 4-cyl and Cosworth-Ford DFV V8 I believe the worst vibration of all actually came from the DFV.  Of course, it also delivered by far the most power and torque.  I recall the Vanwall engine as being marginally smoother than the BRM, but not as smooth as the still vibrant Climax - if you see what I mean.  

 

The worst 4-cyl vibes I have ever encountered, however, were from the 1908 GP Mercedes and 1908 GP Benz - both when at high speed providing one helluva bang at every second telegraph pole.   :cool:

 

DCN

I bet you're glad you couldn't try a Christie - 19.8 litres and front wheel drive!



#19 rl1856

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Posted 25 January 2022 - 13:59

Link to the February 1961 issue of Sports Cars Illustrated, which included in depth articles on the BRM P25, and Alfa Romeo Disco Volante.

 

The parent directory for the link contains an archive of all issues of SCI from v1-1 until it became Car and Driver, later in 1961.    

 

Jesse Alexander was their correspondent covering European racing and associated developments.  Many of his iconic photographs first appeared in the pages of SCI.

 

https://archive.org/...river_1961-02_6



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#20 mariner

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Posted 25 January 2022 - 19:16

Thank you ri1856 that article is really interesting in its explanation of the engine and its very unusual four bearing crankshaft.

 

Even more thanks for pointing to such brilliant   archive source. I am now going to read every article in that digitised  copy!!



#21 Ray Bell

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Posted 26 January 2022 - 00:35

Now that I've looked at the Sports Cars Illustrated article, and in particular the cutaway drawing, I better understand this photo I took at the Donington Museum:
 
0122-BRMcrank.jpg
 
The crankshaft from a 2.5-litre BRM, this one apparently being from a 5-main bearing model. What appears to be a built-in flywheel would seem, from the cutaway, to be mounted on a taper at the tail of the crank, while it might well be that the crank-handle fitting at the front is a screw-on addition, maybe for temporary use.



#22 raceannouncer2003

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Posted 26 January 2022 - 06:36

Thanks for the SCI link.  I just went through the first issue, July, 1955...

 

Vince H.



#23 cpbell

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Posted 27 January 2022 - 22:55

We all hate you, Doug.  Truly, deeply, madly...... :mad:

 

 

 ;)

Same here! :lol: :cool: