Gudgeon Pin Lubrication

[John3528]

I am currently stripping, cleaning and putting back together a 1932 engine that was rebuilt at least 15 years ago, possibly considerably more, and then hardly used before the car went into storage.

The car, a 4 seater tourer (AG or AH, I don't yet know which), is tuned to the extent that it is bored 60 thou and has a Ruby head but it will be a road car possibly used for the occasional trial.

The engine is fitted with BHB split-skirt pistons which I note have no lubrication holes in the gudgeon pin bosses, different from all the other miscellaneous used Austin Seven pistons that I have amongst my collection of junk.

My main question is whether the gudgeon pins in this car will receive sufficient lubrication or whether now is the moment to drill an oil hole in each of the piston bosses?

A secondary question is can anyone put a rough age on these BHB pistons?   My little research on the internet so far suggests that BHB pistons have not been around for some time.

Thirdly, and not directly relevant, is how does one distinguish an AG Tourer from an AH?  The chassis register shows it as an AG but this car was first registered on 1st September 1932, still with a 3 speed gearbox and front fuel tank. By my reckoning, it should be an AH.  If it is down to whether or not the body is pressed steel, what are the telltale signs to look for that define pressed steel?

Any advice or suggestions would be greatly appreciated.

John.

[Mike Costigan]

Thirdly, and not directly relevant, is how does one distinguish an AG Tourer from an AH?  

John.

Quite simply, 6"! The AG was the last of the short-chassis cars, so still had the small doors with angled read edge. The AH was the first of the cars on the 6'9" chassis, and had full depth square doors. There is no possibility of confusing the two.

[Chris KC]

I wonder if this helps you John?
   

BHB were at least around until 1956, their piston drawings are available from the archive, some show 'without' oil holes and this one shows 'with'. I'd venture that as long as a bit of metal is left to support the gudgeon pin drilling two wee holes is unlikely* (*all the usual caveats apply!) to cause you a problem. On the other hand it would appear they made plenty of pistons without them.

[Zetomagneto]

I have seen them with a small flat on the gudgeon pin to allow lubrication, do your pins have a flat

[John3528]

Mike - thank you for that very clear advice.  I shall have to advise the Chassis Register to correct their records.

Chris - thank you too for once again coming to my assistance.  I never realised quite how many features had to be machined and measured on a piston.  Interesting too that the what looks like a pre-war drawing uses a mix of metric and imperial units, clearly noting a 2.2" cylinder bore but showing piston dimensions in mm, apart from the gudgeon pin lubrication holes that are 1/8" dia!  I haven't actually compared the drawing with one of my pistons but, at first sight, they match.  I shall now mull over whether or not to drill the additional holes.

Zetomagneto - thanks for the suggestion but these gudgeon pins have no flats on them, which is an argument perhaps for going ahead and drilling the holes.

Regards,

John.

[Zetomagneto]

Definitely drill the holes

[Chris KC]

Whoever scanned the drawing cut the change history off, but as far as I can tell the holes were added in an update around 1935, suggesting that they were deemed an improvement. I would only worry about adding them if the boss looks insubstantial. Seven Workshop pistons have holes here and are completely dependable.

[Archivist]

As it happens, I am taking the opportunity of being confined to barracks to sort out all the engineering drawings and digital images. I am hopeful that a completely new resource of all we have will appear on the Archive web site in the next couple of weeks. This will include some important historic drawings that have not been published before.

Fortunately, the piston diagrams are some of the drawings I have at home at the moment, so have been able to take a close up of the missing information. The existing images will form the basis of the new resource, but will be re-digitised as time and resources permit, to replace the versions made some time ago with higher quality ones.. My apologies for the rather 'jaunty angle'..

Hope that all helps..

   

[John3528]

My thanks to Chris and the Archivist for their researches.  There's something rather special about being able to look back at working drawings from almost 90 years ago!

[David.H]

AG looks like a late Chummy with small doors...mine has it stamped on the transmission tunnel top near the gearbor. It is also 6ft 3 chassis.there are vertical raised seams at the back.