Specialoid Pistons in MkV

[NeilR]

The MkV engine I have started to rebuild had a pair of Specialoid pistons fitted. There's quite a lot of surface marking on the crowns - probably down to careles decoking, but it looks like the numbers are M-37837, and LL-1. Were these  standard fitment? The cylinder bores measure up standard (at the top), so I was wondering why they might have been fitted otherwise.
They are light at 168g. The JP+30 ones I have are 272g - seems a lot extra for 30 thou. I'm thinking they might have been fitted to wring a bit more power out?

Cheers,

Neil

[tck]

If they are really Specaliod then they are light . When fitted to Vincents, Specaloids were lots lighter than the Hepolite alternative. Alas I belive Specaloids have long ceased to be available for anything.  :cry:If they were available and still being manufactured then the Vincent owners would have tracked them down.

[eddie]

Hi Neil,
          The Specialoid pistons were specified for the 'Plus' machines. According to the provisional handbook for the 'Plus', the pistons for the '80' were 'Specialoid Lo ex', and for the '90' 'Specialoid Y Alloy'.
      I have in the past measured standard Mark type pistons and found that they are oval turned, being about 4thou smaller across the gudgeon pin than across the thrust faces, whereas the Specialoid pistons for the 'Plus' were round.
   Hope this helps,
                            Regards,
                                          Eddie.

[tck]

Continuing the Specialoid theme they were low expansion. On the Vincent when specialoid stopped production Ron Kemp had a batch made he called 'kempaloid' and they were low expansion as well.
I have had a high comp racing Vincent piston made in low expansion alloy by the USA firm Venolia they make one offs to your pattern and spec (I sent them an old piston with the crown made up in plastecine and bore size of a new barrel) the piston cost £120 (for comparison a stock piston costs £95) so I guess a set of smaller Douglas pistons would be less and if a batch was made up......

[NeilR]

Thanks for posting this tck, very interesting. I'll look into it.

Cheers,

Neil