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+--- Thread: Piston type (/showthread.php?tid=1504)
Piston type - Andy Bennett - 27-07-2018
I am working slowly but surely through my new top end.
I am trying to do as much as possible to have a finished top end read to swap over so that I have minimal down time.
Learning as I go I shall be buying pistons and sending them with the block for rebore.
This leads me to my latest question.
Remembering that a little knowledge is dangerous my understanding is that pistons can come with pinch bolt or fully floating gudgeon pins, so I need to know which to order to go with my existing con rods.
From a previous head gasket faiure I took notes that my pistons are marked 11121 plus 40 thou (I did not make any notes as to an RS being present).
From what I can find referencing 11121, I have found.
Hepolite Pistons Application List:
Reliant Regent 8, 10 & 12 cwt three wheeler van 1948 - 52
Pistons: Alloy 2·20" Bore and 1·13/16" Length - Hepolite Ref. RS11121
Pins: 1/2" Diameter and 1·15/16" Length
Type: SC i.e. fully floating pin retained by SEEGER circlips
So my questions:
Does the 11121 reference therefore mean that I have the fully floating gudgeon pin type or can that reference be on either floating or pinch bolt types and if so is there any way for me to find out what type of pistons/rods I have without taking the sump off and looking up? .
Alternatively I guess I could take delivery of pistons minus gudgeon pins and have the pistons fitted etc and then take delivery of the pins once I have taken the engine apart.
Thanks as always
Andy B
RE: Piston type - Stuart Giles - 27-07-2018
Gudgeon pins on the Reliant SV pistons are the same size (1/2") as the Austin ones, so it's possible that the Reliant full floating pins have been swapped for the standard 7 pinchbolt style. Taking off the sump and the oil gauze will allow you to confirm what you have in there. Or buy one of the cheap endoscopes off ebay or similar if you want find out without stripping the motor. Should be possible to get a view up the bore if you remove the oil filler tube.
RE: Piston type - Andy Bennett - 27-07-2018
Thanks Stuart
So if understand correctly, basically the pins are interchangeable on the pistons, meaning that I could have either original A7 type split rod gudgeon pins or floating ones, as would have been standard on the 11121 pistons.
Just checking my understanding of what might then be obvious, con rods are not interchangeable (unless you put a slit in the floating type to accept a pinch bolt). Meaning that if I want to keep the existing con rods I basically need to buy pistons with the same gudgeon pins as I currently have and if I still have the original type con rods then they will be split pin type?
cheers
Andy
RE: Piston type - Zetomagneto - 28-07-2018
(27-07-2018, 09:06 PM)Andy Bennett Wrote: Thanks Stuart
So if understand correctly, basically the pins are interchangeable on the pistons, meaning that I could have either original A7 type split rod gudgeon pins or floating ones, as would have been standard on the 11121 pistons.
Just checking my understanding of what might then be obvious, con rods are not interchangeable (unless you put a slit in the floating type to accept a pinch bolt). Meaning that if I want to keep the existing con rods I basically need to buy pistons with the same gudgeon pins as I currently have and if I still have the original type con rods then they will be split pin type?
cheers
Andy
Any of our cherished suppliers do Pistons of the shelf for clamp type rods.
Tony Betts posted on here not long ago stating the available sizes he has, they are very nice low expansion 3 ring Pistons at a good price
If you already have the Reliant Pistons you can use them by buying a set of clamp type gudgeon pins from Jamie at Seven Workshop
RE: Piston type - Stuart Giles - 28-07-2018
(27-07-2018, 09:06 PM)Andy Bennett Wrote: Thanks Stuart
So if understand correctly, basically the pins are interchangeable on the pistons, meaning that I could have either original A7 type split rod gudgeon pins or floating ones, as would have been standard on the 11121 pistons.
cheers
Andy
Yes, the gudgeon pins are directly interchangable. So, it's highly likely that you have the original pinch bolt style rods in there. The SV Reliant rods can be made to fit a 3 bearing A7 motor along with the Reliant crank, but it is a quite a bit of work, and unless they are the very early Reliant rods, you would need to have a quite thick spacer between the block and crankcase as the Reliant rods are longer than the A7 ones -did this conversion many years ago, so can't remember the exact dimension now.
RE: Piston type - Andy Bennett - 28-07-2018
Thanks Stuart and Zeto
I think I am pretty safe going for pinch bolt, with the back up that I can get floating in the unlikely event that I need them.
my hope is to build up the new block and head (new pistons onto existing con rods) and then swap it over with the existing tired one to freshen up the top end of the engine.
I have been looking longingly at the one on ebay for £775 and thinking that's not a bad price when I add up all the work and bits I will be getting done. But then its more fun to do it yourself and I shall learn so much more in the process.
Andy