What have I got here??

[Anubis]

Recently aquired 6/1 SOM (Solid Kidney hole flywheels). Clearly at some point the block has been replaced (It is a diferent colour) and it has been running like this for some time (the block is full of limescale and the piston crown had a healthy layer of coke) though I have not had it running myself. (The head had no compression due to knackererd valves and needs an overhaul/replacement)

The piston is an alloy one and only has 4 rings (3 compression and one oil scraper. The top compression ring is significantly thicker than the other two)

I was given to understand that these originally had cast iron pistons. and  had pistons with 5 rings.

So what do I have here??

And should I replace it with a 5 ring cast iron one (I would imagine that an iron piston would be heavier than the alloy one and having an incorrect piston would mean that the flywheel ballance would be wrong)

Sorry if these are Lister CS newby questions but that is exactly what I am! 

[potter]

Are you sure its a 6/1 the  8/1 used the alloy pistons due to the increased R.P.M.

[Bottleveg]

As Potter points out, the 8/1 had the alloy piston and the four-ring configuration. Does the engine plate have 650 rpm?  Sounds like you may have a 6/1 engine with an 8/1 cylinder and piston.

[Anubis]

As Potter points out, the 8/1 had the alloy piston and the four-ring configuration. Does the engine plate have 650 rpm?  Sounds like you may have a 6/1 engine with an 8/1 cylinder and piston.

It is definitely a 6/1 650RPM engine. So that sounds likely. As I said, the block has been replaced so it wouldn't be surprising if a "new" piston came with it. Appart from this the machine appears to be complete (IE all the various serial numbers match up with one another)

Would it be advisable to replace the piston with a 6/1 one?

[Combustor]

Hello Anubis,
                 I believe there were such things as 8/1 type engines de-rated to 6 hp at 650 rpm. If it is one of these it will not have the change over valve in the head, but
a square headed plug instead. In this case the alloy piston and 4 rings will be correct.  Indian Listeroid spares are available to fit most CS types, and quality is OK. It's the
assembly methods that is their main problem.  Hope you solve the mystery.  Try decoding the year of manufacture. Any digits following the 61 on the plate are added to
1950 to give the year. Change over valves were discontinued somewhere in the '50's, when the 8/1 was produced, so you may have a de-rated one of these,
                                                                                                                                                                  Regards,  Combustor.

[compig]

It may have had an Indian piston and cylinder fitted to replace the originals.

[Anubis]

Hello Anubis,
                 I believe there were such things as 8/1 type engines de-rated to 6 hp at 650 rpm. If it is one of these it will not have the change over valve in the head, but
a square headed plug instead. In this case the alloy piston and 4 rings will be correct.  Indian Listeroid spares are available to fit most CS types, and quality is OK. It's the
assembly methods that is their main problem.  Hope you solve the mystery.  Try decoding the year of manufacture. Any digits following the 61 on the plate are added to
1950 to give the year. Change over valves were discontinued somewhere in the '50's, when the 8/1 was produced, so you may have a de-rated one of these,
                                                                                                                                                                  Regards,  Combustor.

The engine number is 8158616 so I guess that would suggest 1956.

(The engine number and generator number each correspond to the plant plate on the cast iron base)

The head does have a change over valve and "Appears" to be the original one. It is only the cylinder block that is different (It is red (Primer?) instead of green) but the cylinder does not look like a new one, rather a S/H one of some age!

The cylinder and piston seem in good condition.

I have not had the engine running since I acquired it (Leaking exhaust valve) so I don't know to what extent balance might be an issue, But I would have thought that a cast iron piston would be heavier than an alloy one and that if an "Incorrect" piston has been fitted then the counterweighting on the flywheels will be wrong.

If nobody has a "Definitive" awnser then I suppose I could just put it back together again and see! it wouldn't take long after all.   

[Bottleveg]

Well my guess is your 6/1 has had a frosted cylinder at some time and it’s been replaced with one from an 8/1. As to how it will run, I don’t know, I’ve never tried it or found one with this mod, yet. See what happens and let us know, then, if it were me, I’d put it back to original.

[contaucreek]

8/1 cylinders had exposed cylinder studs and 600/650 rpm engines had the studs pass through the block.If using an alloy piston in a 6/1 then you need to use an 8/1 bump height (cylinder head clearance) re expansion of the piston when hot.

[Anubis]

8/1 cylinders had exposed cylinder studs and 600/650 rpm engines had the studs pass through the block.If using an alloy piston in a 6/1 then you need to use an 8/1 bump height (cylinder head clearance) re expansion of the piston when hot.

That sounds like it. The studs are visible along the body of the block passing through "Flanges" at the top and bottom (IYSWIM)

I have also done a little checking and conclude that the iron piston is several pounds heavier than the alloy one so a new piston might well be a good idea.

Unless anybody knows better. I cannot think of any particular reason to change the block. Some of the originals might have been chromed but I doubt if any of the Indian replacement ones are. (In fact the spares shop only offers a choice of "Old" 7 stud and "New" 5 stud) and it otherwise seems in good condition (There is the "slightest" of ridges at the top, barely noticable with the edge of a finger nail. Nothing a light honeing wont fix!)

[potter]

Whats the wattage of the gen head , perhaps it was run at 850 R.P.M. to boost H.P. for a larger head.

[Bottleveg]

Whats the wattage of the gen head , perhaps it was run at 850 R.P.M. to boost H.P. for a larger head.

Would the 8/1 governor weights also have to be fitted?
On the point of exposed cylinder studs. I believe this was done to reduce machining costs. I used to think this type of cylinder was confined to the 8/1 but I have 8’s and 6’s with both types of cylinder. Now whether each cylinder is original to each engine is another matter.

[Anubis]

Whats the wattage of the gen head , perhaps it was run at 850 R.P.M. to boost H.P. for a larger head.

It is a genuine SOM (IE with the built in starter etc) head rated at 2.5KVA, which is correct for the 6/1 application. It also has the correct part number for the chassis plate so I am sure that this is how it left the factory and hasn't been unduly messed with over the last  55 years or so (Well, appart from this odd cylinder/piston situation anyway   ).