Welcome to the Austin Seven Friends web site and forum
As announced earlier, this forum with it's respective web address will go offline within the next days!
Please follow the link to our new forum
http://www.austinsevenfriends.co.uk/forum
and make sure, you readjust your link button to the new address!
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
Save yourself grief, do it right, do it once is the best way.
Location: Centre of the Universe
Where has all this "impecunious enthusiasm " gone? I thought Austin Seven enthusiasts liked the tinkering aspect of owning one. 💣
Location: Sheffield
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".
What kind of honing tool do you have Martin?
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
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
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.
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
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".
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".
Like Mr Trump, Martin, you missed out loads of facts when you asked the opening question!
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
.
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
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
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.
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.
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".
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".
Hi Bob.
Many thanks for the very helpful advice. with yours and everyone else's input, this should end up as a pretty bomb-proof engine!
M.
Location: Herefordshire, with an "E" not a "T".
OK. Feeling quite smug at the moment.
As suggested, I had the cylinder bores measured and was rather pleased with myself to be told that all of my primitive measurements were spot-on - well, within 3/10 of a thou, anyway.
I then got to work with the honing tool/deglazing bar (?) - cautiously, fortunately. It opened up the bores at about 1 thou every 30 seconds and the previously undersize bores are all now +.060" and appear to be within tolerances of +.0005", -0.
However, pride come before a fall and my sharp-eyed son brought me down to earth by pointing out a crack in one of the mounting lugs on the crankcase. It looks weldable, I've just got to find someone who'll do it.
Location: Herefordshire, with an "E" not a "T".
Hello Martin, when you find a welder could you let me know as my 1928 early coil crankcase is also cracked.
Regards
Stuart
Location: Staffordshire, the creative county.
Regards
Stuart
Yes, certainly, Stuart.
Location: Herefordshire, with an "E" not a "T".
I seem to remember from years ago people recommending only using 3 mounting bolts so the crankcase didn't attempt the impossible stopping the chassis flexing. There's your money saving alternative, don't use that mounting lug!
Location: Isle of Wight
Martin,
Well done with the dimensions and bore honing; one up for impecunisity. On that theme, if the crack isn't through to the oily side I wouldn't think about welding. Bolting all four up hard may have contributed to the crack. Just bolt the other three up with a spacer washer to lift the cracked foot away from the chassis?
Dave
Hi Martin
I am just going through the same process as you except being an Austin 7 virgin, I completely assembled the engine and installed it in the car before finding that it was too tight. I was assured by 'friends' that it would loosen up, but after trying to start it up, with no success, only a smoking starter motor, I am now in the process of stripping everything down so that I can hone the bores. Like you, I think I need to take out a couple of thou and I am encouraged that you seem to have managed this easily with a honing bar/deglazing tool
Location: About 40 km SW of Limoges
Hi Tony
If I can give you the benefit of my experience, check first of all before honong the bores that the tightness is in that area. I reassembled a 3 bearing engine 40 years ago only to find it was too tight, and altough I managed to get things moving as your 'friends' suggested, the real tightness turned out to be th big engds that wore very rapidly due to some previous 'enthusiast' filing the con rod caps - something that should NEVER be carried out with shell beaings. Honing the bores removes material, and you don't want to increase bore wear unneccessarily do you!
Good luck!
Bob
Location: St Tudy North Cornwall
Hi Tony and Bob.
Tony - the use of a cheap 3-arm hone seems to have worked for me, but as I mentioned, it removed metal a lot faster than some contributors suggested - about 30 seconds to take out a thou - so go carefully, and as Bob says, make sure that it is the bores that are the problem.
Bob - I quite agree about not filing the big ends. I did however pass the mating faces of the rods and caps over a flat, fine oilstone, which revealed and removed a few small burrs. I took care not to remove any material from the actual faces.
I now have three big ends that are a very nice fit on a crank that they didn't start life on. The fourth is going to need a little scraping. Deep breath..............
Location: Herefordshire, with an "E" not a "T".
Martin.
I guess the 4th is a little tight?
Scraping is fun. Do you have the relevant tooling? Its a bit too easy with white metal and very easy to remove too much.
May I suggest you invest in some 'timesaver' lapping compound. It will take the high spots off the white metal but it wears itself out so you dont need to be quite so carefull with cleanliness.
Another product used extensiveley on steamers. Look it up.
Location: not north wales any more
Hi Bob
Thanks for the tip. However my Phoenix crank and matching Austin conrods were supplied by a very well known Austin 7 engine builder and I know that they are OK. Like Martin, I cannot get more than a 2 thou feeler between the piston and the bore. I intend opening this out to 5 thou and see how the pistons slide in the bore.Also, due to inexperience I did not gap the rings. All these good things will be done when I re-build the engine for the second time.
Hedd, thanks for the tip about the Timesaver compound. Appears to be a great product. If my big ends are still a little tight, I will invest in some, probably the fine grade.
Location: About 40 km SW of Limoges
Hi Hedd. Yes, no.4 is too tight. Thanks for the "Timesaver" tip; that sounds just the job, as I know that the amount of white metal that I need to remove is minimal.
Location: Herefordshire, with an "E" not a "T".
In general lapping compounds, other abrasives, and white metal shouldbe kept far apart in case it embeds.
If not shell bearings it is no crime to accurately file caps.
I am much in favour of Martins activities; far more satisfying than just assembling expensive new and reconditioned parts.
But before many others get carried away it needs to be realised that judging from his woodwork efforts Martins abilities and standards are somewhat above the average!
(I have often noted that many of the more enterprising and meticulous restorers have a woodworking background)
When it comes to crankcase cracks a thorough inspection is necessary; the front lip, sides below the studs, cam bearing housing etc.
Whilst piston fit may prove too tight when running, it would be unlikely to render an engine difficult to turn. If that tight the pistons would not enter, except perhaps at the top if bores quite tapered. Big ends or 3rd bearing more suspect. Tales of mechanics towing cars to free them were common into the 1960s but such practices are diabolical. That marvellous fitting in the front with a brass handle has many diagnostic uses.
Location: Auckland, NZ
I agree with Bob about the lapping compound on white metal (it may be OK on harder bearing surfaces). It's an abrasive in a liquid suspension, the particles embed in the soft white metal and continuously lap the crank pin!
I follow Jack French's advice; the conrod should be able to fall under it's own weight when on the pin. If close a judicious tap with a mallet all round can help with the high spots. Being quite small it's hard to scrape the metal out without digging in and putting grooves in. I've a very small 3 sided scraper I use. Try slowly grinding the teeth off a short 3 sided file and sharpen the edges on an oil stone. You have to be patient scraping and not try to dig out too much, the scraper should just take a skin off. You may want to think about belling the ends a few thou as well to cope with crank whip and give plenty end clearance. I've seen big turbine bearings cleaned up with a Scotchbrite pad - the industrial equivalent of the washing up plastic scouring pad, it may be worth a try when you get close.
As Bob says if you over do it take a few thou off the faces and have another go!
Keep us updated.
Dave
Thanks, Dave! Yes, three rods glide down gracefully under their own weight, so I'm quite happy with those. I think that the fourth is a little too tight for the tap-with-a-mallet solution to work, so I'll pool all of the advice that everyone's kindly provided and just go very carefully with the metal removal.
Location: Herefordshire, with an "E" not a "T".
Bob and Dave. Please research the 'Timesaver' it does not embed or continue to lap.
So that when you are reading the guff. The term 'Babbit' is what the Americans term white metal.
Location: not north wales any more
So that when you are reading the guff. The term 'Babbit' is what the Americans term white metal.
I second that on Timesaver.
Not your text book lapping compound so the usual rules do not apply
C
Hi Hedd,
An entirely different possible use for this 'Timesaver Lapping Compound' - I want to gently remove a thin very old (1950's) top layer of paint to reveal the sign written paint layer below, as on a sign written van door. Any thoughts on whether you think this compound may have that desired effect on old paint ? It's probably going to be a case of me buying a tin and giving it a try. I see Craftmaster Steam Supplies sell it for £14.95 for a 3oz tin.
Jeff.
Location: Almost but not quite, the far North East of England
TIMESAVER LAPPING COMPOUNDS
order on line
add to cart
yellow can
PRECISION FINISH ON BEARING SURFACES
GUARANTEED NOT TO IMBED - WILL NOT CONTINUE TO CUT!
Please see Precision Finish Booklet (PDF)
Timesaver Lapping Compound does not contain emery, aluminum oxide, silicon-carbide or similar charging abrasives.
They are unconditionally guaranteed not to imbed into any metal surface.
Prepared in powder form, to be mixed with oil as used.
Timesaver first acts as an abrasive, then the particles diminish to a polish, and finally to inert material.
Directions for use in each can.
.........So hopefully does exactly what it says on the tin.....?
Location: Herefordshire, with an "E" not a "T".
Mine is not in a tin. Its in a plastic box
Location: not north wales any more
Hi Hedd,
Which grade of Timesaver would you suggest for Martin's job - there are 4 listed.
Regards,
Steve V.
Location: Polegate, East Sussex, United Kingdom
