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Can anyone tell me what the stroke measurement was on the 3rd series single six engine from 1925/6 ? I believe that it was 5" - the same as the earlier engine. The crank assembly/bottom end which we used in rebuilding the engine on my 1st series car was from engine number 68644, which I think is a 3rd series and the stroke is 5". However, I have been told that the 3rd series six had a longer stroke and that the number 68644 is from a 2nd series. I would appreciate it if someone could clarify this for me.

It was the bore that was increased (from 3-3/8 to 3-1/2) for the 3rd series Six, not the stroke; the stroke remained the same at 5 inches. Motor # 68644 is a 3rd Series Six motor.

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Thank you very much for that very useful information. It confirms what we thought. Notably, the crank is MUCH heavier than in the original engine and the rebuilt unit runs much more smoothly. We used a 1st series block, bored out slightly to 87mm, a 1st series head and 3rd series cam and roller followers. We also fitted new 87mm alloy pistons designed for a British Ferguson 35 petrol tractor. The result gives great power and torque and the engine runs very well indeed.
Richard

I'm delighted to advise members that, after many false dawns, we have finally got the engine in my 1922 1sr Series Single Six back to full health. It has had new pistons and rings, a rebore, new valves and springs, replacement block and (just recently, as the replacement 1st series proved to be cracked!)) a 3rd series "squish" head, complete re-white metalling/line boring of all main and con-rod bearings, new wrist pins etc etc etc.......the list goes on and on! Last problem after reassembling with a brand new cylinder head gasket, was water pouring down the distributor drive into the oil - cause was found to be the hard copper used to make the new gasket, so the old original "Packard" one was re-annealed, cleaned up like new and recoated with liquid shellac before refitting. Result is perfect and the car runs silently and sweetly as new. Needless to say, this has all cost a bomb, but it's worth it to have such a beautiful and rare car back in full operational order.

Latest news on my car is that the engine continues to improve as it beds in. The car is now a genuine delight to drive and pulls strongly and near-silently from tick-over, even in top gear, with the only faint sound that it is running coming from the timing chain. When the block was re-bored to 87mm (3.4252") it obviously increased the displacement slightly, to 276.5 cu.ins.(4535cc) from the original 268 cu.ins.(4395cc) and this obviously helps the power and torque to a small extent, but I guess that the 3rd series head runs a higher compression ratio than the original 1st Series item Can anyone tell me the ratio?) and the "squish" design, with the combustion chamber over the valves, provides for more efficient combustion than the 1st Series system, where the piston crown partially entered the combustion chamber which was directly above the cylinder. I am so impressed with the Packard that it has become a firm favourite in our small collection of veteran and vintage cars. My only regret is that, being made in 1922, it is 4 years too young to be used in the Veteran Car Club events in which my wife and I participate in our older cars. However, I consider myself lucky to own such a machine and I take great pleasure in hearing that silky smooth Packard engine start up and propel me along in better style than the equivalent Rolls Royce model from that era - "Ask the man who owns one"!!!!!!!

Nice! Ernie

Richard,
Great to hear that you are so pleased with the Packard.
I can't recall seeing compression ratio specs for these cars although 4.2 :1 keeps coming to mind, maybe someone can correct this . However, I have a friend who recently completed the restoration of his First Series six which he fitted with the later "Ricardo" head. His car has more power than mine with the original First Series head.
David

What is this 'squish'/'Ricardo' head?????

Although Wikipedia is a child of the internet and not always believable, this will help.

As well as this.

Maybe some photos?
Thanks!