Tony,

It didnt take 6 weeks to take 80 tho out of the bore of my traction engine. That is 8 inches diameter.

I should know, I was paying by the hour.

A vernier is not accurate enough of checking bore diameters and I expect the sizes you have taken may be misleading, you would be safer checking clearances as Hedd suggested

Location: NZ

Hi hedd,

Thought you sed you used a honing tool.

A 3 finger deglaze bar from machine mart is not a honing tool.

It would take weeks to take out 3 thou,

Tony.

Location: Huncote on the pig

So the standard size for a Cylinder bore is 2.2" not 56mm, if its the latter they are probably .050 oversize. I'm sure this is common knowledge in these parts, but just checking...

Location: Fremantle Australia

While it might not stand accounting scrutiny of the time spent, cobbling up an engine from discarded bits can be very satisfying when successful and is in the Seven spirit of old. If things rust through or go bang from other causes the loss is less. And if your own labour not a big deal to repeat.

Vernier callipers tricky; the slightest pressure leads to errors. Difficult to assess cyl state without mikes, and then using separate internal and external mikes can accumulate errors. Bore size and wear can be established with lengths of nail, wire etc fitted to length or some simple telescoping gadget and measured with the same external device as used for pistons. The exact point of maximum wear can take some searching. Measuring change of ring gap gives an indication, although taper will be more than 1/3 the change. If an engine has genuinely parallel bores, seems a pity not to utilise. Mikes now very cheap, esp 2nd hand inch.

There are various reasons bore may not be a standard oversize. Split skirt pistons typically need and have at least .003 clearance across gudgeon and .0015 across faces. The skirt needs only collapse .0015 as prone to do and may enter .003 under bore. The diameter at gudgeon may be greater than skirts. Must not operate with small clearance across and near gudgeon axis. I don’t think Austin ever fitted split pistons and do not know what typical life of split pistons is; solid ones are everlasting. Inspect closely for worn grooves and cracks at the ends of the split. Significant collapse suggests high mileage.

Bores can be accurately expanded with a rigid hone but few have these. It is not good practice but if already parallel with care could expand bores .003 with a ring resurfacer hone, which you apparently have.(Not a ball hone!) These are used after rebores to finish and remove nearly this. A range of stones are available. An elaborate cleaning with soap and water after any honing is recommended.

My limited experience has been that with the original Austin wide rings satisfactory operation and oil consumption is obtainable with considerable wear, but I found low oil consumption elusive with modern narrow ring split pistons even after rebore. Using one piece oil rings.

I don’t know what piston clearance and bore taper is considered the tolerable max for ordinary Sevens. For cars in general .007 taper was often quoted as rebore limit, but now much less. I had an engine with bores .003 barrel shape, pistons generous clearance, and consumption was notably high.

Clearance across gudgeon diameter can be increased by hand. (Some aftermarket solid pistons were round and needed this treatment to match the original Austin ones)

The one oversize cyl is a puzzle. Reminds of a mechanic we knew who used to do rebores on owners premises using a coarse rigid hone. Said he went for afternoon tea, came out, and did a cylinder a second time! Perhaps that is why the block has been set aside.

Location: Auckland, NZ

If you must do it with the 3 stone springy job then do it lightly, fit the pistons and rings and push each piston 1" down the bore. Fill each bore to the brim with paraffin and see how quickly it leaks down.

Call it what you like. It was a 3 finger tool. But a commercial vehicle one, not a car one.

It took a bit of time. But nothing like the time you suggest. Done in situ with a large electric drill drive, but operated by a man.

Now there's an interesting bit of confusion to add!

I work in Imperial, so I'd cheerfully assumed that the original bore was 2.2" - it had never occurred to me that usually-quoted 56mm isn't an exact conversion.

So, can anyone confirm with absolute authority that a +060" rebore should finish at 2.260"?

Location: Herefordshire, with an "E" not a "T".

2.200" converts to 55.88mm

56mm converts to 2.2045" only 0.0045" ( 41/2 thou.) oversize from standard.

Ian Mc.

Location: Shropshire

I had always understood it to be 2.2 bore. 3 inch stroke.

This works out to be 747.48CC assuming pie to be 3.1415.

If you do it with 56mm and 76mm you get 748.73CC

That seems to confirm the imperial dimensions.

Martin,It seems a lot of interest in your project and although I agree with some of the opinions as to "doing it correctly" I understand your initial request for an economic rebuild option. There is obviously some confusion as to the measurements of both bore and piston diameters and their compatibility,there is really only one definitive answer and that is to get both measures professionally. I just googled Precision engineers in your locality and there would seem to be quite a selection. I'm sure one or two would measure the dimensions for you at a reasonable cost. Camcraft in Bishops Frome may be a good start. Once you have good compression, do you have a crank and rods good enough to take the load? Trouble is when the ball starts rolling nobody can say where it will stop. Best of luck.

Location: Piddle Valley

Thanks Peter.

I think that the excitement caused by bores and pistons is enough for one decade!

The full horror of what I'm doing with crank and conrods will remain a secret between me and my engineer's blue!

Location: Herefordshire, with an "E" not a "T".