Stuart 10v

[Steamchick]

That's what I envisaged...
But an expert machinist can tell me it won't work and I shall accept that.

K2

 

[lee webster]

I am far from being a machinist, expert or otherwise. But I do have some experience with Austin Seven engines. They have white metal big end bearings, and oil pressure measured in low single digits. When the big ends wear, and you can't afford to have them redone, it was (still is to some) the done thing to take a bit off the mating faces. Probably on a piece of emery. If you take too much off, or if you don't have the right size replacement rod, then thin brass shims can be made and put between rod and big end. I have taken a few engines apart where this has been done, and spoken with a very highly respected A7 owner who still does it. A7 engines have lasted for decades with this sort of mod. £750 for new white metal, or a few pence for some brass shim stock. We went for new white metal.

 

[swarf]

Lol I'm no machinist either.
I'm good at taking perfectly good material and turning it into scrap in a very short period of time.
I can lay metal in thou. As I'm a pipe welder by day and a wanna be model maker by night.

 

[Jasonb]

My only worry is trying to ream the "hole" as it is not complete there is a very high chance of it snagging and that is after you have done a pilot hole which would really have to be bored.

The gaps won't do much for keeping a good oil film thickness buy not really an issue for a model being run for display.

When My brother and I had an A7 Swallow we also got the rods re-metaled

To save taking metal of the cap faces what should really be done with white metal bearings is the shims should be put in place before the metal is poured then if you do get wear you only need take out a shim and not have to touch the caps/housing mating surfaces

 

[Steamchick]

Years ago I tinned some worn bearings and "wiped" them while the soft solder was liquid. This took up the worn couple of thou... which didn't need a lot of linishing and blueing to get a good fit.
Also on my Triumph motorcycle I tinned the timing side bronze bush with plumbers'lead solder, which when wiped improved the oil pressure considerably. (Main oil feed to the crankshaft is through this bearing). At the next strip down the bearing had lost a bit of solder, but mostly it was still there, and the oil pressure was still as it should be.
The surface of tin or lead acts as an anti- scuff soft surface, should the oil film break down, thus preventing seizures. It also resists corrosion from blow-by gas pollution of the oil in IC Engines. Brass bearings contain zinc, which can be dissolved sacrificially in IC engines, thus leaving a poor biscuit-like surface that is mostly copper. So use bronze bearings not brass in IC engines. Brass is OK in non- enclosed engines like old design steam engines with exposed cranks.
Hope some of this may be useful?
K2

 

[Steamchick]

A point on linishing "tinned" bearings to take up wear... A few thou of wear in cap bearings can be taken up with tinning, but the side generally have too little wear for this to work immediately. The bearing cap is too tight on the journal. Using Engineers' blue, identify where there is a hard contact and use a light touch with 400 grade wet and dry or emery paper to alleviate the high spots. As soon as there is a proper fit on the sides of the bearing, the cap can be tightened to the other half and the main thrust surfaces studied with blue. This is a bit easier that scraping new tinned metals, as I found I didn't get enough practice to be good at scraping! That was 55 years ago....
K2

 

[Steamchick]

Jason, I agree that a reamer could snag in a bearing with joint gaps either side. But if line-boring - say in the lathe, or miller - careful feed and fine cut should be OK. After all, cylinder-ported 2-stroke bores have bigger holes for the boring tool cut to cope with and regular cuts and feeds manage it without issues. A multi-fluted reamer may be OK if machine held and fed instead of hand-held. Especially if the reamer is held in the lathe chuck, with a dead centre at the tailstock, and the work-piece is mounted on the saddle/cross-slide and progressed using the saddle feed very carefully.while rotation the reamer quite slowly. A Con-rod set-up on the cross slide is one way to get the centres spaced accurately and the big- and little-end bores truly parallel, if you do not have a miller to use as a boring bar.
But a proper machinist will tell us the best way! (I hope!)
K2

 

[Jasonb]

Good in theory but these parts are a pig to hold to start with and now that the chucking piece has been removed even more so.

I'd start again from solid or if someone wanted to salvage it silver solder the tapered shaft complete with fork onto new material which would give you a good piece to hold

 

[Steamchick]

Can the big-end be clamped to a suitably made holder? E.g. gauge plate or machined angle plate with a hole just a tad bigger than the big-end?
K2

 

[Steamchick]

Dare I suggest it is a part of the hobby to solve difficult problems for setting parts and how to machine them properly? Any toolmakers or expert machinists like to tell me a better way? I would like to learn please.
K2

 

[Richard Hed]

My only worry is trying to ream the "hole" as it is not complete there is a very high chance of it snagging and that is after you have done a pilot hole which would really have to be bored.

The gaps won't do much for keeping a good oil film thickness buy not really an issue for a model being run for display.

When My brother and I had an A7 Swallow we also got the rods re-metaled

To save taking metal of the cap faces what should really be done with white metal bearings is the shims should be put in place before the metal is poured then if you do get wear you only need take out a shim and not have to touch the caps/housing mating surfaces

Did you consider one of the "reverse" cutter blade reamer? I know they have a proper name but the cutter blades are spiraled in reverse.

 

[Steamchick]

There is a mathematical relationship affecting all multi-edged cutters, like drills, reamers, milling cutters, etc. Where the odd number of cutting points can oscillate away from being exactly centred, such that the cutter with n cutting points creates a hole with n+1 "corners' and opposite curved radius equal to the effective diameter of the distance between 2 distant cutting points.
Sorry, difficult to describe. But it is used to 'drill' a 4-sided hole with a 3-point drill, or 6-sided hole with a 5- point drill, or can produce a 12-sided hole with an eleven point reamer, etc.
Curious, but real.
However, should the cutter be fixed securely on centre, this does not happen. E.g. as with a reamer held between chuck and tailstock centre. It can only happen when the cutter is not held securely on centre of the planned hole. E.g. a hand-held reamer in a hole in a part in the Engineer's vice.
Where an even numbered cutter is used, this centre oscillation almost cannot occur, so a even number of cutting edges on the reamer is recommended for this big-end reaming.
It does not matter if the reamer is straight-cut or reverse-helical cut, the significant issue is secure support of the reamer on centre.
Single cutter boring of the hole should not cause any problems if the boring bar is adequately stiff for the cut being taken.
In my experience. ... that is.
K2

 

[Jasonb]

Richard still likely to be problems due to uneven engagement so chances of getting a hole on size and round are slim.

Far easier to solder 50thou of material onto each face then you have solid material to drill and ream.

Maybe Pat can say how he would machine it a she suggested the shims, Oh no forgot he can't see things that small so only talks of making larger

 

[Steamchick]

Hi Jason, my knowledge of oil films, tribology and stuff is less than a good reply here. But. Here goes....
The "working" oil film - that prevents metal-to-metal contact inside a bearing or between any 2 sliding surfaces - is actually only 1 or a few molecules thick.... but oil molecules are BIG.
Under a scanning electron microscope, the surfaces of polished bearing metal looks like an aerial view of the Rockies, Alps, or Himalayas... etc. - deep valleys in sharpish mountain peaks. The oil collects in the valleys, and forms oil-peaks upon which the opposing flooded valleys can float in reverse.
The gaps - between peaks of metal - are therefore not huge but really only molecules apart.
In a split plain-bearing, on the macroscopic scale we may think that there is an edge to skim the oil off the surface of the journal, and there is, but only excess oil. Bearings have microscopic machined clearances, so when the bearing is dry there is a tiny amount of play, that forms a volume that opens and closes with the action of vibratory or oscillatory loads on the bearing. So oil applied at the edge gets sucked-in and pumped-out of the normal bearing clearance gap. This helps to refresh and circulate oil inside the bearing, as hot oil is expelled and cooler oil sucked-in. The high surface tension of oil forms a meniscus at the edge of the bearing so there is a reservoir to supply the reserve for the pumping of oil in and out of the bearing under piston loads.
In addition, the "drag" forces, from the surface tension of oil on metal when surfaces are sliding relative to each other, causes the oil to be part dragged in and part dragged out by the sliding motion. Again the new oil is from the meniscus reservoir at the edge.
So I do not worry about the split bearing affecting lubrication.
Old "splash-fed" crankshafts were used on engine cranks for a few decades, before fully- pumped oil circulation took over. And the real engineering of that was to cool the bearing by pumping oil through, as the oil inside non-pumped bearing was overheating and breaking down, with metal-to-metal contact, pick-up, wear, and seizures occurring. The oil is heated by the shear forces on the oil film under pressure from the bearing loading.
On a pumped oil crank bearing, the oil goes into the bearing at the "no load" point of the cycle - e.g. The side away from the piston at BDC - then the oil is pumped out of the bearing by the piston pressure during compression and firing/combustion stroke. Well most of the oil, leaving just the molecular film that is resisting being pumped out by the internal forces within the oil.
All I know from a very brief expansion from a Doctor of tribology.
What is correct is his, what is in error is my eroded memory....
K2

 

[swarf]

I recall the words "hydrodynamic wedge" being used explaining the film of oil between bearing and pins.

 

[swarf]

So gents here it is.
New connecting rod, big end machined to spec. This obviously is the top half of the rod.
The spec from center of big end to center of little end is 1 11/16". I have layed this out out on the little end and as you can see, not in the center.
I have a few ideas, what do you think?

 

[Jasonb]

Put it in the middle and make any adjustments to the crosshead/rod/piston assembly length

Probably a combination of having the reamed hole in the crosshead a bit closer to the top and the O/A length of the assembled parts a bit shorter so that the piston still moves centrally in the cylinder

 

[swarf]

I should have done that in the first place. Seriously thou, thanks for pointing out the obvious.
Live and learn.