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View Full Version : Does a Packard Merlin have any British threads?


rickseeman
6th Jul 2022, 05:45
I assume a P-51D would be all American threads but I wondered if a Packard Merlin would have any kinky or Whitworth threads. I figured the Merlins made in the UK might. Thank you for the help.

longer ron
6th Jul 2022, 07:33
From Enginehistory.org

https://www.enginehistory.org/Collections/british_fasteners.shtml

Packard Built Merlins

An often asked question is; "did Packard replicate the British thread system when they built Rolls-Royce Merlins under license during World War II?" The answer is yes; all threads that were used on the Merlin were accurately replicated by Packard. This would include BSW (British Standard Whitworth), BSF (British Standard Fine), BSP (British Standard Pipe) and BA (British Association). Having said that, however, Packard Merlins used U.S. built Bendix injection carburetors; PD-16 for single stage engines and PD-18 for two stage engines, both of which used U.S. Unified threads. British built Merlins employed S.U. carburetors using Whitworth threads. The job facing Packard when they undertook manufacture of the Merlin was daunting to say the least. It’s bad enough having to build a complex product like the Merlin but exacerbating the situation was the fact no tool maker in the U.S. made Whitworth taps or dies. Therefore, Packard were forced into making their own. Although this created a significant hurdle to overcome, the effort was well worth it, Packard and Rolls-Royce components were interchangeable.

rickseeman
6th Jul 2022, 13:35
WOW, what a disaster. I just assumed it would be US. My brother bought a P-51 last week and so you get to thinking about support equipment and special tools you might need and that's why I had to ask. I'm into threads/taps/dies and threading on my lathe. And I've had to tackle the metric system on a few occasions and won but at age 65 I don't know if I'm man enough to take on another threading system. I hope we never have an engine problem. The Merlin is already unbelievably complex compared to the auto engines I'm used to without having to think about threads. Thank you for the information.

treadigraph
6th Jul 2022, 14:17
WOW, what a disaster. I just assumed it would be US. My brother bought a P-51 last week...

Would that we should all have such problems! ;)

Allan Lupton
6th Jul 2022, 14:42
I hope we never have an engine problem. The Merlin is already unbelievably complex compared to the auto engines I'm used to without having to think about threads.
BSW/BSF/BSP and BA taps and dies are readily available, so the amount of actual screw-cutting you need should be small, going on for zero and it should not be much of a problem for you, as US and UK use the same inch (unlike Germany and France!).
Having written that I shall add that I hope you don't get involved with the really big special threads such as that on the front of the propellor shaft.

longer ron
6th Jul 2022, 15:32
WOW, what a disaster. I just assumed it would be US. My brother bought a P-51 last week and so you get to thinking about support equipment and special tools you might need and that's why I had to ask. I'm into threads/taps/dies and threading on my lathe. .

The info I quoted will be correct for wartime/original engines - whether it still applies 100% to every Merlin still in use today might be another matter.I am not sure if any of the states based engine specialists might have at least partly re engineered any Merlins ??

rickseeman
6th Jul 2022, 16:16
Would that we should all have such problems! ;)
Well that part of it is wonderful of course. This is obviously a very big moment in our lives after being in love with P-51's for 53 years after seeing our first ones in 1969. But me being a motorhead I want to learn all about the engine and be able to diagnose/possibly fix problems.

VictorGolf
6th Jul 2022, 16:40
If it's any reassurance, I work with a company that provides flights in a two-seat Spitfire. We have used several different aircraft and the only problems, while I've been on duty have been two punctures and a small leak in the radiator. The Merlins themselves have run like clockwork in what is probably not their natural environment. A good reflection on the quality of the servicing and the reliability of the engine.

rickseeman
6th Jul 2022, 17:02
I assume you are in the UK. It would be nice if there was a 2 seat Spitfire trainer that we could fly in the US.

treadigraph
6th Jul 2022, 17:12
I assume you are in the UK. It would be nice if there was a 2 seat Spitfire trainer that we could fly in the US.
There was, Bill Greenwood flew it around the US for many years but after an accident it wound up back in the UK a couple of years ago and is now flying from Biggin Hill.

Love to see a pic of your brother's P-51D!

Commuting Pilot
6th Jul 2022, 17:28
Ditto! I love the Warbird restoration scene and would love to see a photograph of your brotherís P-51 too! 👍👍

rickseeman
6th Jul 2022, 17:28
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1134x620/mickeys_p_51_72572390b2fbc5b96d8e7aed3a7000e7f4862c03.jpg
It was restored around 2006 and converted to dual control. It's having the annual done now and he's trying to get his training completed for the insurance company.

treadigraph
6th Jul 2022, 17:58
That's a lovely piece of kit! Hope all goes really smoothly...

longer ron
6th Jul 2022, 18:05
Hi Rick
Did you see this earlier post of mine ?

The info I quoted will be correct for wartime/original engines - whether it still applies 100% to every Merlin still in use today might be another matter.I am not sure if any of the states based engine specialists might have at least partly re engineered any Merlins ??

rickseeman
6th Jul 2022, 18:22
Yes, I'm guessing the engine guys here would have to keep it original. But I will ask some of them if that's the case.

VictorGolf
6th Jul 2022, 19:48
Hi Rick
We're very lucky here in UK. There are at least 10 2-seat Spitfires flying and 3 more on the way. There's also a 2-sear Hurricane for some variety. Good looking P-51 you have.

rickseeman
6th Jul 2022, 21:00
WOW, that's wonderful. And thank you.

radeng
6th Jul 2022, 21:16
Unified threads didn't exist until about 1948. They were based on American threads, which is why so many of them are effectively identical, although some of the clearances are not identical. They have the disadvantage that unlike BA, and to some extent BSW and BSF, they are weaker, being 60 degree thread angle rather than than the 55 degrees of BSW and BSF and 47..5 degree angle of BA - which is in any case a metric thread. Plus it's the only logical thread series where each step down in is 0.8 of the pithch above e.g, 0BA is !mm pitch, 1 BA is 0.8mm, etc...It is actually the Swiss horological Thrury thread, which went down to number 27..... and was down to the tensile strength limit of high tensile steel screws available....

BA screw threads as such were adopted at Montreal conference in the late 1800s, although the first imperial standards for them appeared the early 1950.s. Prior to this , they were all speciified in metric terrms... Why change/ one can only assume because the title was 'British'......

EXDAC
6th Jul 2022, 21:23
Good to know there is still some use for my BA taps and Whitworth wrenches. They don't get used much since I left UK.

I turned down the chance to fly in a 2 place Spit is USA as I was duty tow pilot on the only available day and didn't think I would have time to swap the duty. I've kicked myself many times for that.

aroa
6th Jul 2022, 23:06
Likewise. I didn’t go for a ride in Richard Fairey’s 2 seater G-AIDN (?) many moons ago. The weather was low cloud and scattered drizzly so all that could have been done was a few low level orbits of the field. Not much chance of having a good feel.
Was to cost me 50£ …and I was on a very tight budget, about to depart the UK for Oz in an Auster.
(I lobbed into Darwin with $3 left)
I kicked myself later of course. And the butt bruise has lasted a lifetime.
Can be done these days of course, but in huge multiples of £50 !

sycamore
6th Jul 2022, 23:26
aroa..I remember that,but I heard it was £60/hr.As I was earning £3.12s6d/week,Auster flying at same,Chippy at £5,5s. an hour,it was going to take a bit of time.I can sympathise and likewise have a `bruise`....

DaveReidUK
7th Jul 2022, 06:27
Bit of thread drift ... :O

VictorGolf
7th Jul 2022, 08:35
Ballpark figure (before the latest fuel price increases) was £1 per second to operate the Spitfire. Times have changed.

GeeRam
7th Jul 2022, 18:01
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1134x620/mickeys_p_51_72572390b2fbc5b96d8e7aed3a7000e7f4862c03.jpg
It was restored around 2006 and converted to dual control. It's having the annual done now and he's trying to get his training completed for the insurance company.

It got the 'tall tail' mod when it was converted to TF spec by the looks of it.
A few TF conversions have included the 'tall tail' mod.

Has he gone to do the Stallion-51 run conversion course?

rickseeman
8th Jul 2022, 01:12
I do love the "H" tail. We have both flown at Stallion 51 (I love those guys) but he has to have the whole week long course for the insurance. Hopefully they can get him in soon.