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Cylinder bores


Being both poor and mean, but needing a good engine, I've set about building one from the remains of six or seven incomplete units, most of which have been scrap since the 1950s.

The best of the blocks has very straight and consistent bores, which I reckon have a diameter of 2.257". I've given it a very light honing to get rid of light surface rust.

The best set of pistons, from another engine, are +060" and without rings slip quite easily down the bores.

The question is, am I likely to run into problems using +060" pistons in a block that appears to have been bored to +057"?

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

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Re: Cylinder bores

How are you measuring the bores Martin? I think its possible you may have made an error on the bore size, you could also check the clearance between the piston and bore with a couple of sets of feeler gauges.

Location: NZ

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Re: Cylinder bores

My past experience of skimping on building an engine,a 1275 mini,reringing a tired engine was taking it out again after 10k miles to do it properly.
For less than £300 I would bore it and fit a good set of pistons and enjoy the extra bit of power from the lack of blow by from the pistons and some confidence that I won't have to pull it to pieces again.

Location: Channel Islands

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Re: Cylinder bores

I'm with the Shed on this one

Location: Oakley hants

Re: Cylinder bores

+1

Re: Cylinder bores

hi martin,

im with shed,

but.

if you dont try, you dont learn.

good luck tony

Location: huncote on the pig

Re: Cylinder bores

I'm sure that you of all Austineers must be aware that you need every ounce of power you can get Martin.
Old pistons and doubtful bores are not generally conducive to acquiring matchstick breaking acceleration.
Do it once and do it right saves a great deal of hassle and expense.

Location: Bristol

Re: Cylinder bores

Save yourself grief, do it right, do it once is the best way.

Location: Centre of the Universe

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Re: Cylinder bores

Where has all this "impecunious enthusiasm " gone? I thought Austin Seven enthusiasts liked the tinkering aspect of owning one. 💣

Location: Sheffield

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Re: Cylinder bores

Quote: Dave Wortley
Where has all this "impecunious enthusiasm " gone? I thought Austin Seven enthusiasts liked the tinkering aspect of owning one. 💣



At Last, a man after my own heart! This sort of makeshift, shoestring engineering idiocy was what Austin Seven owning was all about when I started playing with them 45 years ago!

I should have explained that the reason for building this engine on the cheap (my budget is £100)is that the RP's engine now has about 80,000 miles on it since its last major overhaul and is starting to rumble a bit. As this is the original unit that was fitted when the car left Longbridge I want retain it and do a proper job on it. I need a temporary engine to keep the car on the road, but my previous spare suffered a crankshaft failure and was knackered anyway. The cheapo project is a replacement for this.

I have built up a couple of engines this way in the past. My only problem with this one is that the available parts are far less worn than in previous exercises and I'm concerned that the pistons may be a bit tight for the bores. I have a set of +040" pistons, but they're much too loose.

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

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Re: Cylinder bores

What kind of honing tool do you have Martin?

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Re: Cylinder bores

Martin , I am with the others as regards to rebore and new piston if you want to be sure your rebuild will be ok first time. However if you are like me and do not take your time and effort into account go ahead the most you can loose is the time of doing it all again together with the cost of rebore and new Pistons together with a few new gaskets.
As to your bore measurements over size normally go +2. +4.+6. Try measuring more than one bore and measure top bottom and centre of the bores. Also measure different diameters as worn bores tend to go oval in shape.
Following that assemble your block and piston ( with rings) together with rods to the crank and crankcase well lubricate bearings,big ends and bores and see how it turns. It should turn very freely as there is no compression.

John Mason

Location: Nottinghamshire

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Re: Cylinder bores

Martin

Mr Dunfords question in pointed.

We made the bores on my traction engine which were 80tho barrelled, both round and parallel using a 3 armed lorry honing tool and much time and measiring. Took a set of new stones mind.

3tho should be 10mins work

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Re: Cylinder bores

Martin

What we dont know is what size the +60 pistons are in reality

Just been reading an old book here.

It says cast ali pistons need 1.5 to 2 tho clearance per inch diameter. As a general rule.

Lets say 2. This suggests 5 tho clearance needed give or take max.

You can easily measure this with feeler gauge. Measure top. Middle bottom.

5 is a nice easy number.

4 is in the range. 3 is too tight.

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Re: Cylinder bores

Courting controversy and with the greatest of respect to the other contributors on this thread I say why not. It appears that Martin is well aware of the limitations when going down this route, and as anyone who has been around Austin sevens for any length of time will know nice loose clearances make for a quick engine. I have on more than one occasion gone down this route on a budget engine rebuild with success. So IF the bores are round and parallel why not, sure the life of the engine will be reduced but as long as you accept this whats the problem. I disagree that it will reduce performance in fact I suggest it may actually improve performance, my quickest race engine ran with quite large clearances, and those who know me will appreciate just how quick that engine was.

Location: NZ

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Re: Cylinder bores

Ruairidh - it's a basic, new 3-arm honing tool. I've run it through just enough to clean off some very light surface rusting.

John, as I mentioned above, this is meant to be a cheap stopgap so I can spend some real money on the RP's original engine. I simply can't afford a full job on two engines.

I've measured all four bores top and bottom, side-to-side and fore-and-aft using a vernier caliper. 13 out of 16 measurements were 2.257", the remaining three, all on the rear cylinder, are 2.260" to 2.261". I've checked for lips and barelling with a back-illuminated steel rule and the bores appear to be straight.

I have standard, +020", +040" and +060" pistons to hand. The +060" are a good fit and slide comfortably with light resistance when fitted with rings.

Given that the valves and seats are clean and in perfect condition, I'm pretty confident that I have a reconditioned nominally +060" block with close to zero miles on it.

I'm not worried about potential lack of compression; it's whether the apparently slightly undersize bores will cause trouble, but Hedd's response probably addresses that.

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

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Re: Cylinder bores

I would hone it a little more and suggest it will be fine for your stated purpose.

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Re: Cylinder bores

Quote: Ruairidh Dunford
I would hone it a little more and suggest it will be fine for your stated purpose.






Like Mr Trump, Ruairidh, I'll hire and fire experts until they give me the answer I wanted in the first place!

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

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Re: Cylinder bores

Like Mr Trump, Martin, you missed out loads of facts when you asked the opening question!

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Re: Cylinder bores

Since I'm not an expert I'm in no danger of being hired or fired. The Austin 7 engine is a simple robust device which is why so many have survived despite being worked on by people like me. I learned everything from the Austin Seven Companion book which is full of advice for the impecunious or mean. Have a go, it's all good fun, and it will probably work.

Location: Isle of Wight

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Re: Cylinder bores

Quote: Martin Prior
Ruairidh - it's a basic, new 3-arm honing tool. I've run it through just enough to clean off some very light surface rusting.
.


Hi Martin,

Have you bought a honing tool, or a deglaze bar.

A £30 deglaze bar from machine mart. Will not be man enough to hone.

It would probably brake the three grinding stones of there glued basses before you can take 3 thou out. And would probably take six weeks to do it.

A deglaze will help the rings bed in. But if you have 3 thou variation I doubt the bores were done with an experienced hand. So would expect there to be plenty of gaps for the rings to run over.

Although for what you need this won't really matter.

Location: Huncote on the pig

Re: Cylinder bores

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.

Re: Cylinder bores

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

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Re: Cylinder bores

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

Re: Cylinder bores

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

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Re: Cylinder bores

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

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Re: Cylinder bores

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.

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Re: Cylinder bores

Quote: Tony betts
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.


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.

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Re: Cylinder bores


Thanks Hedd. I've only had the chance to check one bore so far, but on that I can get a 0.0015" feeler in on both sides of the piston all the way down. 0.002" won't fit at any point, so that appears to confirm my suspicion that the bores are a little tight.

I'll have a gentle go at it with the three-armed thing (hone or not?) and will see what happens.

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

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Re: Cylinder bores

Quote: Mark Dymond
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...



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".

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Re: Cylinder bores

2.200" converts to 55.88mm

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

Ian Mc.

Location: Shropshire

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Re: Cylinder bores

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.

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Re: Cylinder bores

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

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Re: Cylinder bores


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".

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Re: Cylinder bores

Quote: Austin in the shed
My past experience of skimping on building an engine,a 1275 mini,reringing a tired engine was taking it out again after 10k miles to do it properly.
For less than £300 I would bore it and fit a good set of pistons and enjoy the extra bit of power from the lack of blow by from the pistons and some confidence that I won't have to pull it to pieces again.

Oh, forgot about the engine in my box saloon, cost £20 or £30,its that long ago.Built by a Rolls Royce engine build fitter,It looked lovely ,shiny aluminium all well painted.Put it in the box while I recond the slow original,20 miles later it had oiled the plugs up,then a rusty line appeared about 1/2" down from the top,that was the frost crack.

Location: Channel Islands

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Re: Cylinder bores

I built an engine about 50 years
ago entirely from scrapped second hand parts in the shed.I had no money at all.
It ran even more slowly and noisily than usual but lasted for about two years and tewnty thousand odd miles.
I measured nothing and hoped for the best.
Ignore my advice above and go for it Martin.
If your pistons move up and down in the bloc what more could we need.

Location: Bristol

Re: Cylinder bores

Oh dear, oh dear, what a little ray of sunshine you are, Austin-in-the shed!

Where's everyone's reckless spirit of adventure? Doom and gloom and "that'll never work" everywhere! This is not what built the British Empire.

Come on, chaps, you're only young (or 58) once! This is a challenge,and is FUN, which is what I thought A7s were all about.

If this works, I will have a serviceable spare engine that has cost me almost nothing. If it doesn't, I shall be sadder and wiser and worse off to the tune of 20 or 30 mis-spent hours.

I shall keep you posted on progress - or not, if it's a disaster!


EDIT: Thank you, Mr Dunford Snr!

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

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Re: Cylinder bores

Martin,

I've watched this thread with interest. I can understand the 'do it right, do it once' opinion, there's increased certainty of a good result. And barring duff quality parts or assembly **** ups that should give you a good engine. I don't think it's been mentioned above in this thread - that it would also give you a good spare run in engine for the future as well.

However; I got into A7's in the 1970's and being an engineer, straight into specials after reading Bill Williams' and Pat Stephens' books from front to back. Then I discovered the Special Builders Guide (there was no interweb or Amazon in those days!) with the Jack French writings through the Simplicity build. In this he built an engine seemingly from used bits including main bearings and big ends. It worked well for him in Simplicity. At some point he used +1/32" pistons into worn +30 bores. My Opal has pitting marks in number 4 bore where it stood for 50 years - the valves must have been open on that bore. I glaze bust it and reringing has worked for me; it doesn't blow by nor smoke the exhaust. In honesty and for balance, I don't always get it right - and had some things that haven't worked for me.

You seem to know what to look out for when selecting good viable bits. If you spend time rather than money getting the parts fitting together well you should get a running engine. It may blow/smoke and rattle a little more than a 'new' one but you can probably live with that for a reasonably short period.

To size the bores try putting a ring down and measuring the gap. Don't get too hung up on bore and skirt absolute dimensions - it's the acceptable difference between the two that matters. A good ring gap all the way down is a good indication of that. There was a thread recently about piston clearances that had the Hepolite sizing chart.

Have a go; I sense you're going to anyway. I hope it works for you.

Dave

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Re: Cylinder bores

Martin, just do it!
In 1965 I broke the crank of my Special. It was also my daily driver, by the way, so a quick fix was necessary. I had some of the bits of what became my good engine, but need something in a hurry. So bought a 55 Standard 10, quite the worst car I ever owned, put the blown up engine into the boot and went to see my father.
In one evening he and I built an engine from used parts. It had more than generous bore clearances, timing gears were not a matched pair but spun and meshed freely,and one rod had to be straightened by old-fashioned methods, but did check out for straightness and twist when done. I took that engine back home, put it in the special, and ran it for over a year. It won autocross and driving test (autotest) awards, used a lot of oil it's true, but served it's purpose well. The only thing wrong with it was that we'd fitted a shaved and modified 37 head, which oiled plugs easily. I fitted a Speedex head to cure that.

This, by the way was a 2-bearing, 1 5/16", 34-ish engine.

Good luck!

Location: Richmond, Texas, USA

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Re: Cylinder bores

This reminds me that we used to cure oiling up plugs by putting in stepped inserts which allowed us to dispense with 18mm plugs for 14mm.
This worked to quite a while .
I wonder if they are still available.
Or necessary..

Location: Bristol

Re: Cylinder bores

Still available. I use them on my 9E head so I can use 14mm plugs.

Re: Cylinder bores

Quote: Dave Armstrong
Martin,

To size the bores try putting a ring down and measuring the gap. Don't get too hung up on bore and skirt absolute dimensions - it's the acceptable difference between the two that matters. A good ring gap all the way down is a good indication of that. There was a thread recently about piston clearances that had the Hepolite sizing chart.

Have a go; I sense you're going to anyway. I hope it works for you.

Dave


Follow Dave's advice above and I think you'll be OK.


Steve V.

Location: Polegate, East Sussex, United Kingdom

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Re: Cylinder bores

Internal diameters are notoriously difficult to measure accurately with basic equipment, and there is often a lot more 'plus or minus' than we like to imagine.

Many years ago 'Super Accessories' in Bromley published their guide for Austin 7 Special builders, including the following words.

'There is no other car in the world that could stand the amount of mis-use, poor assembly, and "first-time-ever" efforts, and yet still give faithful, lively service for years to come.'

Best wishes!

Location: Northumberland

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Re: Cylinder bores

Quote: David Heywood


'There is no other car in the world that could stand the amount of mis-use, poor assembly, and "first-time-ever" efforts, and yet still give faithful, lively service for years to come.'

Best wishes!



That says it all, David!

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

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Re: Cylinder bores

One of the best engines I ever built was a pure bitsa. I snapped a crank on a trial so went into dads loft to see what I could find, slung it all together without much care as I needed it for the following weekend. The engine was amazing and lasted a good few years of hard trials abuse.
So I'm all for building engines out of left over parts Martin.

Location: New Forest

Re: Cylinder bores

The '29 Saloon engine was built around 10 years ago using similar methods (and an 1 1/8" crank) Stuart - imminent destruction is always anticipated!

Last month an engine came in for some minor work which I completed - on testing I was alarmed to note it had no oil pressure whatsoever. I checked all the usual suspects and replaced many parts to attempt a cure - eventually I discovered that an early type rear camshaft bush had been fitted, this left an 1/8" gap for oil and pressure to escape!

According to the owner the engine had run like this for at least 8 years...

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Re: Cylinder bores

Quote: Ruairidh Dunford
The '29 Saloon engine was built around 10 years ago using similar methods (and an 1 1/8" crank) Stuart - imminent destruction is always anticipated!

Last month an engine came in for some minor work which I completed - on testing I was alarmed to note it had no oil pressure whatsoever. I checked all the usual suspects and replaced many parts to attempt a cure - eventually I discovered that an early type rear camshaft bush had been fitted, this left an 1/8" gap for oil and pressure to escape!

According to the owner the engine had run like this for at least 8 years...


I had a similar experience with a 2brg Ruby engine also fitted with the wrong rear camshaft bearing, no oil pressure but apparently it had run for years with no obvious issues!

Location: NZ

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Re: Cylinder bores

Fault finding in that case was excruciating Ian!

After several fruitless attempts to find and remedy the cause I resorted to (desperately) removing the entire oil pump with the block and crank/rods still installed. The swap was successful, if incredibly fiddly, but did not cure the problem. The engine was also giving false tappet clearance readings, which I now know to be caused by the bush moving in the hole!

It was a very frustrating experience which was, happily, resolved in the end.

How the engine was properly lubricated in this state I really don't know!

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Re: Cylinder bores


The penny-pinching engine build continues.

The hone (or de-glazer) took out a couple of thou quite easily. I'm hoping to borrow a bore micrometer next week to check my crude measurements.

I still think that the bores may be a little tight. With a piston half way up the cylinder I poured in about 1/8" of paraffin and in all four this took several hours to leak away.

 photo IMG_2245_zpsvc28n2p1.jpg
 photo IMG_2247_zpsbxon0eem.jpg

I've sorted out the best of my crankshafts and have checked it with a crack-detecting spray kit. All seems OK and it rings with a nice note!

I've spent the afternoon fettling a set of con rods from another engine (parts will come from at least eight motors) and these now seem to be a good fit.

The only thing that I know I'm short of at the moment is a decent filter gauze. Does anyone have one they'd be willing to part with at modest cost?

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

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Re: Cylinder bores

Quote: Martin Prior
The only thing that I know I'm short of at the moment is a decent filter gauze. Does anyone have one they'd be willing to part with at modest cost?


Happy to help - email me your address again...

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Re: Cylinder bores

Hi Martin

As previous, if used split skirt, esp important that adequate clearance across gudgeon maintained. Even the original solid Austin pistons were circular only immediately above the gudgeon, with increased clearance below in the gudgeon area. A set of new split skirt I have allows .006

I am a bit sceptical of the non magnetic penetrant tests. Have you got a few steering arms as reference? Not long ago I acquired a stack of cranks “on appro” but with just my primitive magnet found all cracked. The seller was miffed and set to with a non magnetic dye kit (admittedly time expired) and it was only after some persistence that the cracks were apparent. Start at the flywheel journal and work forward. The internal radii are the primary suspects. Based on Seven and other makes, arms and cranks, I don’t think ringing test prove anything until hugely fractured.
Based on the number of cranks which test cracked, moderately driven unmodified cars must run for quite a large percentage of life with detectable cracks.

I dunno about the leak down test. If with rings it would depend how the ring chanced to be seated or not, and on the gap. Without rings would only work with original round pistons with oil drillings below gudgeon. Perfect fitting slipper pistons would leak instantly.
(Remarkably some models new were drilled behind the 2nd ring eliminating it as a compression ring! With a Seven any reduction in ring friction is welcome!)

External mikes tend to be more available than internal and size can be accurately transferred with fitted wires or some simple telescope device, minimising additive errors.
Some knack is required to measure internal diameters with a basic two contact point gauge.

One virtue of solid big ends is the fitting options. By careful filing of faces, thick shims, and scraping I have got thousands of miles out of very bedraggled sets. Colleagues associated Ford 10s regularly adapt random used rods.

One difficulty with major fitting is a tendency to drift the b.e out of parallel with the gudgeon; for those without lathes to make jigs not simple to detect. Any corrective bending should be near end of rod, and not by means of the dents customarily inflicted by “mechanics” in the past. Pieces of plate glass make useful reference planes.

Older letters in Motor and the like correct oval cranks with oilstones, emery cloth etc. Serious textbooks describe a hand operated G clamp cutter for correcting big end crankpins in place!

Provided joints are rigid, head and nut seat fully, and threads do not run out, locking devices on bes. not necessary.

Location: Auckland, NZ

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