Reliant Regal Pistons?

[Chris KC]

Hepolite 17229 pistons are - as far as I can tell - identical to A7 pistons except for the gudgeon pin diameter, which was increased from 1/2" to 9/16" (I *think* these were applied to late OHV Regal 600cc engines).

I have often seen side valve Regal rods reamed oversize to take the larger gudgeon pins - the small end bush has (barely) enough bronze to accommodate them.

My question is, has anyone successfully fitted them to A7 rods with 1/2" pins?

A7 rods are, I think, too slender to accommodate the 9/16" pin. However logic suggests the piston might plausibly be bushed undersize.

Someone, somewhere must have tried...?

[Parazine]

I think the other difference is that the oil control rings are a different width, compression rings are the same. I have a set of these in the Autojumble pile.....

[Chris KC]

My set had an oil control ring missing, I replaced it with one of Jamie's - as far as I can tell they are identical.
I may have a set of Regal pistons with A7 rings on I suppose - but the clearances seem about right.

My Googling suggests some modern makers now use bronze bushings in aluminium pistons (e.g. VW). 
I also found a supplier of bronze 'repair' bushings for worn Scott Motorcycle pistons.

No takers?

[Alan]

With the new slipper pistons currently available, why would you?

[Chris KC]

Alan, let me put that another way - I have a new set of Hepolite pistons & rings sitting in front of me and a block which is already bored the right size for them, if there is a proven way to adapt the pin sizes why wouldn't I?

[Hedd_Jones]

Is there not a suitable rod you could use?, bushed or reamed to utilize the Regal sized gudgeon pin. Not that I have ever used them, though I did recently pass a set on, are R4 rods not for 16mm gudgeon pins?. Be a doddle to bush one, assuming the end fits in the piston ok.

If you had access to a nice CNC mill, you could carve yourself 4 suitable conrods out of solid. Assuming you were happy to 'design' them also.

But I have to agree, buying pistons to fit would be the easiest way. I've still got to do a similar process here. But I do not have pistons (unless the ones still in the engine are ok).

[Chris KC]

Hedd my 'other' A7 engines use SV Reliant Regal conrods and based on the number of them I've seen reamed out to 9/16" I reckon you can probably get away with it. So what I might do is just put these away until I need the relevant oversize for one of those. 

The engine I'm building though will use standard A7 rods and I'm not really wanting a fundamental change of plan at this stage.

How I wish I had the kit to machine my own rods! Though I love the idea. As it happens I'm half way through designing a rod for another application and it would be too much to take on right now.

Likewise I don't have the means to machine the pistons and bush them myself. I've just been talking with my local engine recon shop and they have seen this many times, though not done it themselves. They would take on the job but it would be something like £40/ piston, which - as per Alan's observation - isn't really worth it under present circumstances.

[Alan]

With Renault 4 set up, the rods are shorter and the piston has a higher crown to compensate. So a combination of R4 rods and Austin sized pistons doesn’t work. It would be nice to find another off the shelf (aka out of the scrapyard) rod that would fit.

[Chris KC]

It would Alan - as you probably know, the Reliant SV rods are 1/8" longer, so you can use an A7 piston but need a spacer under the block. Not much use on a 2-bearing due to the offset.

[Hedd_Jones]

How much shorter are the R4 rods? Could make eccentric little end bush, also white metal the big end and bore offset.