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WW1 Thornycroft restoration

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That is one beautiful car, Ed.  'Shiny' and 'refined' are not what we usually see on this forum as 'functional' and 'matt olive drab' are more the norm! However did you find us?

Many thanks for your thoughts. From my measurement of the original piston I think that Thornycrofts probably went for a clearance above the top ring of 0.017", between the rings, 0.012" and for the remainder of the piston, 0.005". If I hone the bores another 2 -3 thou then that would give me a general clearance of 0.008". If I take another 9 thou from the top land and 4 thou between the rings then that would give me something comparable with 'new'. I will take a good look at the rings and replace any that are obviously damaged. I am curious as to why they should have stuck in the bottom of their grooves on 2 and 3 pistons as all were quite free when I put them in. I will have to ease the grooves as well.

In the mean time, I have been pushing on with the wing brackets. They are a horrible job and no fun at all. This is not helped by my welding incompetence so there has been no satisfaction in them being nice. Oh well. They are tacked up now and ready for a proper welder to put them together for me. He is probably reading this and going 'Oh no, not again'!

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Steve   :)

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8 minutes ago, Old Bill said:

 

Many thanks for your thoughts. From my measurement of the original piston I think that Thornycrofts probably went for a clearance above the top ring of 0.017", between the rings, 0.012" and for the remainder of the piston, 0.005". If I hone the bores another 2 -3 thou then that would give me a general clearance of 0.008". If I take another 9 thou from the top land and 4 thou between the rings then that would give me something comparable with 'new'. I will take a good look at the rings and replace any that are obviously damaged. I am curious as to why they should have stuck in the bottom of their grooves on 2 and 3 pistons as all were quite free when I put them in. I will have to ease the grooves as well.

 

 

 

 

 

 

Hi Steve,

A thought has just come to me regarding your pistons. I am not sure how long it was between them being cast and when you machined them, but it was well known years ago that iron castings had to lay for a period before machining. I recollect this with motorcycle cylinder barrels. Also cylinder blocks for engines, I have had experience of several types where they were machined pretty soon after casting and then the blocks became out of line when the casting 'relaxed' (probably a technical term for this which I cannot remember).

regards, Richard

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39 minutes ago, Old Bill said:

That is one beautiful car, Ed.  'Shiny' and 'refined' are not what we usually see on this forum as 'functional' and 'matt olive drab' are more the norm! However did you find us?

Many thanks for your thoughts. From my measurement of the original piston I think that Thornycrofts probably went for a clearance above the top ring of 0.017", between the rings, 0.012" and for the remainder of the piston, 0.005". If I hone the bores another 2 -3 thou then that would give me a general clearance of 0.008". If I take another 9 thou from the top land and 4 thou between the rings then that would give me something comparable with 'new'. I will take a good look at the rings and replace any that are obviously damaged. I am curious as to why they should have stuck in the bottom of their grooves on 2 and 3 pistons as all were quite free when I put them in. I will have to ease the grooves as well.

In the mean time, I have been pushing on with the wing brackets. They are a horrible job and no fun at all. This is not helped by my welding incompetence so there has been no satisfaction in them being nice. Oh well. They are tacked up now and ready for a proper welder to put them together for me. He is probably reading this and going 'Oh no, not again'!

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Steve   :)

2 & 3 pots being amidships on the engine so maybe run slightly hotter...?

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25 minutes ago, Richard Farrant said:

and then the blocks became out of line when the casting 'relaxed' (probably a technical term for this which I cannot remember).

I think they called it "seasoning".

Googling for "seasoned castings" found this: https://www.jalopyjournal.com/forum/threads/factory-storing-castings-outside-to-age.1015700/

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Just now, andypugh said:

I think they called it "seasoning".

Googling for "seasoned castings" found this: https://www.jalopyjournal.com/forum/threads/factory-storing-castings-outside-to-age.1015700/

Weathering Mr Pugh... ☺️

Left outside to "weather"...

Basically to settle down and normalize over a period of time...before jigging up on a lathe/miller/borer for 1st & 2nd op machining process.... 

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3 minutes ago, flandersflyer said:

Weathering Mr Pugh... ☺️

Left outside to "weather"...

Basically to settle down and normalize over a period of time...before jigging up on a lathe/miller/borer for 1st & 2nd op machining process.... 

Weathering, that was it. I recall that Norton Motorcycles left the cylinder barrel castings outside to 'weather' for several months before machining.

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Posted (edited)

Steve - I like your welding jig, simple, practical and logical.

Richard, Flanders and Andy - were you talking timber I would have expected such replies. But cast iron??? No wonder it has taken the Goslings unaware being that they are metal workers. As it would have 99.5% of the rest of those who read this adventure.

However, it does suggest that as the pistons have not been "left outside" and that being closed up in the engine, then the scenario may exist that they have yet to warp to their final dimensions? (Which could also account for the ring seizures?)

If they had not finished their aging process, then the Goslings may very well find that they are now distorted and will complicate any corrective machining? Does this mean that the pistons need to be left to their own devices for a few months before any attempt to correct them is made?

Regards

Doug

(Aussie one)

Edited by dgrev
Additional questions.

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7 minutes ago, dgrev said:

Steve - I like your welding jig, simple, practical and logical.

Richard, Flanders and Andy - were you talking timber I would have expected such replies. But cast iron??? No wonder it has taken the Goslings unaware being that they are metal workers. As it would have 99.5% of the rest of those who read this adventure.

However, it does suggest that as the pistons have not been "left outside" and that being closed up in the engine, then the scenario may exist that they have yet to warp to their final dimensions? (Which could also account for the ring seizures?)

If they had not finished their aging process, then the Goslings may very well find that they are now distorted and will complicate any corrective machining? Does this mean that the pistons need to be left to their own devices for a few months before any attempt to correct them is made?

Regards

Doug

(Aussie one)

Doug,

I am aware of iron castings having to be weathered and it was a common practise with a lot of manufacturers. I recollect in my younger days having new diesel engines that were burning oil. On removing the pistons the bores were seen to show high spots. We re-linered the engines and bored them with problem solved. It was only when I noticed the casting dates on the block being close to build dates of the machine that it figured they had not been weathered. This may have happened due to strikes, shortages of casting or whatever.

I know of another engine type that had misalignment of main bearings and the only way to get over it was to use the last oversize of shells and line bore the block. All due to not leaving the castings long enough.

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11 hours ago, Old Bill said:

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Steve   :)

Hi Steve,

Looking at your pics above, your front mudguards appear to follow the radius of the wheels. From the original pictures this was not the case and there should be a straighter section at the rear. This only applies to the fronts, and the rears are as shown. I am unable to illustrate this atm. but you might want to have another look before finishing the brackets ?

Tomo

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Posted (edited)

The cast iron needs seasoning indeed. After casting, there are remaining tensions in the cast material. That is why it must be left for seasoning, sometimes for an year or more. Another way is heating - several hours at 550 degree C /if remember right/ and then slow cooling. The heating method extinguishes the internal tensions as well. IF the problem in the pistons has been caused by the cast iron remaining tensions, then the heat of the engine work has solved the problem. The engine heat has released the tensions, causing the pistons to deform, but also that has solved the problem and after straightening the pistons, there must be no further deformation. Same happens to the cheaper brake disks - they are perfect out of the box, then after some work, taking heat from the breaking process, these deform. After putting the disks on a lathe and cutting the deformations, these work again, heat again, but no deformations appear.

 

P.S. If just two of the pistons show problems, I would speculate, that these two got more heat. And not impossible, that in the future, after some harder work of the engine, the other two would heat and deform as well. Maybe it's a good idea to find instructions for the cast iron heating procedure and heat all the 4 pistons, just in case.

Edited by Ted170
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I used to deliver machined aluminium pieces some as long as 80 feet to B.A. in North Wales. I was told by an engineer there that the pieces were not required for some time, but they wanted them as soon as possible so they could start testing them, but also the material needed time for the molecular structure to adopt its natural state.

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58 minutes ago, john1950 said:

I used to deliver machined aluminium pieces some as long as 80 feet to B.A. in North Wales. I was told by an engineer there that the pieces were not required for some time, but they wanted them as soon as possible so they could start testing them, but also the material needed time for the molecular structure to adopt its natural state.

Age-hardening is a deliberate feature of many Aluminium alloys. 

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The BMW turbo F1 1500cc in-line 4cyl engines of the early 1980's used the standard cast iron blocks of the road car engines, eventually producing 850hp in qualifying trim. Apparently they did select the best quality castings from the production line, but then left them outside in the open weather for 6-12 months to settle and achieve full strength.... the newly cast pistons in the Thorny I'd suspect are a little too fresh, and could well have moved around a bit, such that it would be best to strip and measure before trying loading the engine any more. I would imagine wide tolerances might be best for an engine of this era and materials, rather than the extreme materials, lubricants and tolerances used in the miracle that is current F1 engine technology...

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Leaving castings to age was (and, to an extent still is) normal in the machine tool industry. 

A Google search "seasoned site:www.lathes.co.uk" finds a few lathe manufacturers using the phrase (none seem to use "weathered" on the same site) 

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Posted (edited)

Its a bit like seasoned timber. I think the guys doing the work will have the best idea as to what has gone wrong.

Edited by john1950
addition

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As for the BMW, I have heard, that they did not choose new blocks, instead they were collecting high milleage blocks, making sure that after years of work, heating, overheating, cooling, any possible stress in the casting has gone.

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Posted (edited)

 

We used to get gearbox castings and rough them out before they went in the bike shed for a few months, I wonder if the thought was to take tension out by removing the skin from the iron?

Edited by rog8811

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Steve just telephoned me to say that his Computer  "died" today - he has just been out to buy a new one but he will not be operational with it for a couple of days. He very much wants to reply to the comments made today and yesterday and will do so as soon as he can!

 

Tony

 

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I suspect he is in the workshop constructing the patterns to cast a new computer. 

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For sure the new PC has remaining internal tensions, so please tell him to heat it to 550 degree C, keep it at that temperature for 2 hours and then leave it to cool down. After that the PC will work for years flawless!

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I would be re-machining the pistons and leave the bores alone, other than a light hone if they need it.

This would bring then now seasoned pistons back into shape and also allow them to be machined to the running fit.  You can't recreate the block but new pistons are easier as has been demonstrated.

The BMW Formula 1 engine blocks were apparently peed on by the Engineers as the urine has a nitriding effect on the cast iron.

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Posted (edited)
19 hours ago, Ted170 said:

As for the BMW, I have heard, that they did not choose new blocks, instead they were collecting high milleage blocks, making sure that after years of work, heating, overheating, cooling, any possible stress in the casting has gone.

I read that the BMW blocks used in Formula 1 (?) in the 1970's were used 2002i blocks from standard road going cars, which seasoned the blocks. Plus the engineers would, er, micturate on them whilst in storage, the ammonia helping with the metal treatment....

Edited by Le Prof

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10 minutes ago, Le Prof said:

I read that the BMW blocks used in Formula 1 (?) in the 1970's were used 2002i blocks from standard road going cars, which seasoned the blocks. Plus the engineers would, er, micturate on them whilst in storage, the ammonia helping with the metal treatment.... 

This was in the era when the F1 rules permitted either 3 litre normally aspirated engines or 1.5 litre turbo engines. The turbo engines ran with tremendous boost so although they started off with only 500 BHP by the end of the development they were producing close to 900BHP. The BMW engine programme was run on a shoestring with them making do with whatever they had available. Stress relieved old blocks were therefore essential to the campaign.

However, we are talking about a Thornycroft here, so hone out the bores, skim the pistons, perhaps increase the ring gaps too and enjoy happy motoring with 50 trouble free horses.

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1 hour ago, Asciidv said:

This was in the era when the F1 rules permitted either 3 litre normally aspirated engines or 1.5 litre turbo engines. The turbo engines ran with tremendous boost so although they started off with only 500 BHP by the end of the development they were producing close to 900BHP. The BMW engine programme was run on a shoestring with them making do with whatever they had available. Stress relieved old blocks were therefore essential to the campaign.

However, we are talking about a Thornycroft here, so hone out the bores, skim the pistons, perhaps increase the ring gaps too and enjoy happy motoring with 50 trouble free horses.

I think that the final paragraph in your last posting is exactly right, Barry, but Steve will have the final say when he comes back on line! When he left Devon yesterday, we agreed that the Pistons had been machined parallel initially with a 0.005 clearance. We shall have the bores honed out by a further 0.003.

 The pistons will be stepped to a clearance of 0.017 above the top ring and 0.012 between the rings.

At least, that is what we talked about yesterday - but that may change!

Tony

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Don’t forget to open up the ring gap. .008 will probably be ok, but rather than take a chance to do it twice I would go just a bit bigger. Did you ever take a compression test before disassembly? 

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