2 3/4 engine questions

[Dave@NZ]

Hi
I have read on one post there is a ball bearing and spring which go up inside the crankshaft and are held in place by the drive gear retainer screw. I don’t have these parts so will have to find a bearing the correct size and light spring and been thinking of rewinding a pen spring to size mainly due it being light spring pressure.
I could imagine the bearing and spring would have an influence on the lubrication system.

Does the bearing go in first followed by the spring and screw or the there way around and any recommendations on springs length and pressure?

The next thing I have been searching for is details on what goes in the aft plug hole in the crankcase, is it a blanking bung?

Thanks in advance,
David.







 

[Chris]

Hi Dave
The spring and ball set is available from The London Douglas MCC Spares Scheme available to members. A pen spring would be much too strong and the spring is also tapered so that the small end which sits on the ball is of a smaller diameter than the outer end which corresponds with the diameter of the tapped bore in the crankshaft. From this it should be clear that the ball goes in first. The wire of the spring is very fine and care may be needed in entering the large headed screw to avoid getting the spring trapped in the thread. A word of advice in securing the large headed screw. Make sure that this is done up really tight and indeed a drop of loctite is advisable as this screw is noted for coming loose when it acts like a milling cutter with its slot boring a clean hole through the timing cover. The rear tapped hole on the top of the crankcase is filled with a "Bung". However, it is a nicely shaped hexagonal bung about 3/4" long waisted in the centre and domed on top. Chris.

[Dave@NZ]

Hi Chris,
Thanks for the advice, good to know that the bearing and spring is available from the club I will contact them this week.
Do you know if the crankcase bung is available from LDMCC ?
If the bung is not available new maybe someone could post a photo or link and I could have one made up or search for one for sale.

I will make sure loctite and a tap with the shock driver on the crank gear retaining screw, I have been looking at it and wondering how tight it should be.
Dave.

[Chris]

Hi again Dave.
The Blanking Plug or "Bung" is not available from LDMCC. I should have added that it is made from brass and is nickel plated as should be the non-return valve and all oil piping from the pump to the sight glass and from the sight glass to the non-return valve . The same plug is also often found at the base of the crankcase sealing the drain hole. I will try to photograph one and post as soon as possible. The LDMCC normally also holds the tiny parallel springs and discs used in the non-return valve and in the oil pump base. Chris.

[Chris]

Hi Dave
I have taken a photo of the plug and it should be loaded shortly. The across flats dimension is 0.525" and the height above the surface is 0.75".
Chris.

[Dave]

Photo added to Chris' post above.

[Hutch]

Hi Dave,
Here is a cross section of the air release valve (part 505) from the 1914 Working instructions for the 2 3/4.

Cheers

Ian

[Dave@NZ]

 Hi Chris, Ian and Dave
Thanks very much for taking the time to provide the detailed information and photos, know what to look for or make now and must admit if I was not up to date reading the posts I would have missed the tip off about the ball bearing and spring required in the crankshaft.

Cheers,
Dave.

[DJS]

Can anyone let me know what size the ball bearing is for the air release valve please?
I have the spring but no ball!

Thanks in anticipation.

David

[Hutch]

Hi David,

The ball supplied to me from the LDMCC is 1/4".

Cheers

Ian

[DJS]

Hi David,

The ball supplied to me from the LDMCC is 1/4".

Cheers

Ian

Thanks Ian.

Regards,

David

[Chris]

Hi all
It is now some years since the LDMCC was supplying aluminium pistons for 2.3/4 hp machines manufactured by J P Pistons in Australia. They were supplied in two sizes JP 0868 +20 and JP 0868 +40 thou. (thousands of an inch). As supplied they came in a box containing the piston with the gudgeon pin wrapped in corrugated cardboard with a small polythene bag containing two wire circlips and a separate small cardboard box containing two piston rings. One of these is a plain square section the other is similar but has small "scallops" around one surface. In 2019 while assembling one of these pistons new/old stock the question arose in my mind as to what order and orientation these rings should be placed on the piston. I contacted JP and received the information that the plain section ring should be placed in the top groove and the scalloped ring in the second groove with the scalloped face down. I also found that the rings as supplied and fitted in the re-bored cylinders needed gapping as they appeared to be precisely to size of the standard bore plus the oversize . I set them for .006" gap; slightly less than the generally accepted .003" per inch of diameter. While on the subject of these pistons I will repeat here the advice previously supplied on the Forum and on an advice slip supplied with the pistons by the LDMCC. In developing the pistons for the 2.3/4 which was a mutual exercise between JP and The LDMCC the design was changed because of the change from the original cast iron to aluminium alloy. The original piston had a very large difference between the internal shoulder widths supporting the gudgeon pin. To copy this was considered to give insufficient support in aluminium and the width of the narrow shoulder was increased. In installation this prevented the piston being centralised in the cylinder bore unless the conrod was modified. The advice was given that to fit these pistons it was necessary to remove metal from the short side of the conrod little end. 1 to 1.5mm is normally sufficient and it was suggested that this could be done quite easily using a junior hacksaw as it is quite soft. Finally, there was considerable experience gained in the first few uses of these pistons that the recommended bore clearance given on a leaflet by JP enclosed with the pistons of .004" was insufficient leading to seizing of the pistons. I personally on one of my first restorations using these had to re-hone the cylinders several times before getting the engine to run for more than a few minutes without "picking up". The advice subsequently given on the Forum and by the Club, although to my knowledge not changed by JP, was that the bore clearance should be .006". Some advice from an Australian member was that up to .008" might be necessary. I have not had problems with .006" clearance providing gentle running in is observed .
Hope this information is useful.
Regards   Chris.

[DJS]

Thanks Chris,

That’s really useful info for the future. Thankfully my cast iron pistons are ok at the moment!
Just out of interest, whilst I appreciate that the LDMCC spares service is currently suspended, do you know if they still have supplies of the JP pistons and rings?
Thinking of future proofing!

Regards,

David

[Chris]

Hi David
As I understand it the LDMCC Spares Scheme stocks of JP pistons for 2.3/4 hp machines were nominally exhausted some time ago apart from a possible remaining pair of odd size examples. At the time of procurement of new pistons from a UK manufacturer for the Mark models, preliminary work was done with the object of future procurement for the 2.3/4 hp models. Surprisingly there has not been a demand for pistons for some time and the procurement of new pistons for these early models has not yet been finalised. I am aware however that some pistons have been supplied by direct purchase from JP in Australia.
Regards  Chris. 

[DJS]

Thanks for the update a Chris.

Regards,

David