Hello Aviation Forum,
I have been attempting to research a possible Merlin Piston Ashtray that I recently acquired. I have been reading everything I can find and this forum seems to have the most knowledgeable folks so I thought I’d ask for some possible help here. What I know so far is that the bore is 137mm and the crown is concave, but it’s been cut down with the skirt removed so unfortunately there are no serial numbers. There are, however, some numbers and stamps inside the piston. Five stamps in total, one looks like a cross with RRS and then HR2, another one is RRS across with CT3???, another one says Gara1 in a circle; third ones reads “Rolls Royce ?U8”; then two numbers which are 59RT9 and BE753. Does anyone know if these stamps can be used to identify the piston any further? I tried to upload some pictures without any luck, but if anyone thinks they would be helpful I will attempt to add them again.
Many thanks for any help available.
Paul
By: Enfield1940 - 16th January 2021 at 07:56
That’s very helpful. Thank you.
By: Creaking Door - 16th January 2021 at 01:25
It is a ‘late type’; Merlin pistons fall into two basic types (early / late) that share few features with the exception of the bore, gudgeon-pin diameter and the number and position of the piston-rings.
The ‘interesting’ feature of your piston (ashtray) is the ridge along the underside of the crown; in my book that makes it a very late (possibly post-war) piston. There are Rolls-Royce Griffon pistons that have a similar ridge (and Griffon pistons that don’t).
The ‘RR’ stamp makes it a Rolls-Royce piston, as opposed to a Packard V-1650 ‘Merlin’ piston, but most Rolls-Royce pistons were made by dedicated piston manufacturers anyway (such as Wellworthy).
As for the other markings, I’m pretty sure the ‘B 4’ stamp means the piston was the number 4 piston on the B bank of the engine. Other than that the ‘serial numbers’ probably refer to material or manufacturing batches (so that pistons from faulty batches could be traced); the part-number for the piston is on the part of the piston that is missing.
Hope that helps.
By: Enfield1940 - 5th January 2021 at 21:19
Thanks. I did search the forum on this subject when I bought it and I think I’ve read most of the commentary. I was more interested in what type of Merlin it likely came from and what the markings mean. E.g. there’s a conjoined ‘RR’ logo which is presumably for Rolls-Royce.
By: avion ancien - 5th January 2021 at 17:55
If you google ‘key aero forum merlin piston ashtray’ you’ll find that this topic is something of an old chestnut that has previously has been discussed on this forum at length and that there are a number of old threads relating to it . I would provide hyperlinks but these no longer seem to work on this forum.
By: Deepthought - 29th May 2013 at 14:03
Thank you for your quick response. I had thought the same thing but it’s nice to have some additional validation.
Regards,
Paul
By: Creaking Door - 29th May 2013 at 01:24
Well, it is certainly a Merlin piston.
It is the (later) type with a shorter ‘skirt’ but other than that I cannot really tell you much more. The number / letter groups stamped into the underside of the crown are probably codes to identify material and machining batches. The other markings are probably inspection stamps.
By: Deepthought - 28th May 2013 at 23:14
Merlin Ashtray Pictures
Here are some pictures. Will appreciate any help or information anyone can offer!
Thanks very much!
Paul
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By: Creaking Door - 28th May 2013 at 07:36
A photograph would be helpful; there is a (fairly small) file size restriction for posting photographs on the forum.
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May 28, 2013 at 2:43 am