Holden Piston Rings

[DougT]

Hi All, does anyone know if original Holden type piston ring sets are still available? I have just pulled down a J series motor that has 0.040 oversize Holden pistons (P/N 7406474) fitted that I would like to re-use if possible. As a point of interest, the pistons only have the part number on the crown and a cast hole (dimple) to indicate the front of the piston, no other markings to indicate oversize. The engine also had one Repco piston fitted in pot six, interestingly it had the same Holden rings fitted not Repco rings, this piston has no markings on the crown and has a cast notch to indicate the front. The inside of the skirt has castings Repco, ACL and the number 319.

[ardiesse]

Yes, you can get rings for grey motor pistons, but they can take a bit of finding.

Firstly, I'd be inclined to weigh both the Repco piston and a Holden piston, with gudgeon, but without rings.  If they're not within a few grams of each other, your engine will be out of balance, and a rebore to 3-1/8" would be your best option.

Try Nornda in Adelaide (a.k.a. JP Pistons).  They sell grey motor rings in single-cylinder sets at about $30/cyl.  Otherwise, Auto Surplus in Melbourne, or Nason or Precision International.  Or if you have an engine reconditioner nearby who's familiar with grey motors, they'll be able to source rings for you.

Rob

[DougT]

Thanks Rob, let the search begin.

[my8thholden]

Doug ..You can carefully drill material out of the piston pin bosses to make all your pistons same weight as the lightest . all con rods should be same weight when assembled ,again very carefull grinding of material to reduce weight to the lightest ,they should be same weight when original , but reality is they often are not and can be mixed over time as you have noted .The crank will have been balanced in factory and if reground should be ok ..Vern

[DougT]

I have done as Rob suggested and, as Muphy's Law would have it, the Repco piston is 20 grams lighter so will need to lighten the other five if I can get away with just honing the bores.

[ardiesse]

20 grams is a lot of material to remove.  At this point, it might be worthwhile talking to an engine shop.

Rob

[my8thholden]

Doug .Was there any difference between the other 5 ?  Pity its not other way around only need to lighten one ..Is there a lip at top of the bore you can catch your finger nail on , if so thats wear , I would put a good worn ring in each bore say about 1'' down from deck pushing it in with piston upside down , so its square in bore , measure end gap, if its excessive then obviously rings are worn themselves but so is bore ..Time for a internal micrometer ..Also put each piston in bore till the oil control ring land is in bore ,hold the top ring lands with piston in correct alignment ..ie pin front to back ..and rock it side to side and feel for " slap " ,turn each piston around 90 deg so pin hole is now across the engine ,rock the piston now front to back along the engine , if the " slap " is less ,then there is wear in the skirt of the piston and bore ...micrometers tell the true picture..Vern 

[DougT]

Hi Vern,

I have weighed the holden pistons and they are all within six grams, I also weighed the conrods and they were within a nine gram range. There is no discernible ring ridge but I have decided to go with all new pistons and rings. The size will depend on the machine shop once they have run the micrometer over it. Doug 

[my8thholden]

Doug ..Doing a rebore and new pistons and rings is the guarantee of a new life for the old girl ..Vern