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Aluminum Pistons Better Than Iron?


MochetVelo
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From what I've read, it's a good idea to replace iron pistons with aluminum in pre-war cars for more power and less crankshaft/bearing wear. My old-timer mechanic friend is giving me static, however, saying I should keep the engine original. Any thoughts on this?

Phil

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From what I've read, it's a good idea to replace iron pistons with aluminum in pre-war cars for more power and less crankshaft/bearing wear. My old-timer mechanic friend is giving me static, however, saying I should keep the engine original. Any thoughts on this?

Phil

Pre which war? My 1933 came from the factory with cam ground aluminum pistons...

The less the reciprocating mass the lower the bearing load. So it should help bearing life. But aluminum has different expansion with heat so they would need to be fitted different than iron pistons.

Should make no difference on power as you aren't changing the stoke or compression ratio. Might help on responsiveness as there is less mass to speed up/slow down when you change the accelerator position.

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Keep it original. If you are lucky enough that the pistons and cylinders are not worn out.

Your engine was designed and built with a certain balance factor in mind. If you change the weight of any moving part in the crankshaft, connecting rods or pistons you change the balance factor. This will introduce vibration problems unless you rebalance the whole crank train.

This is a common problem on old cars. Replacement pistons that are not the same weight as the originals can introduce bad vibration problems in cars that ran smooth when new.

In many cases the "one size fits all" or "Chinatown special" pistons are heavier than the originals and of inferior quality as well.

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Iron pistons are better than aluminum. They expand at the same rate as the cylinders, so are less prone to piston slap and loss of compression. And they wear like iron more durable than soft aluminum.

The only drawback is the weight and, as explained above, this is part of the original design and not a problem if you stay within the original speed limitations.

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The original iron pistons are best for engines that came with iron pistons.

Aluminum pistons became popular because they are lighter in weight and transfer heat readily. This gives a performance increase.

But, aluminum pistons did not become popular right away. At first they had severe development problems like melting, burning, seizing in the bores due to expansion, or slapping and flopping around if made small enough not to seize up. And of course they wore faster than iron.

All these problems were solved more than 50 years ago. You would not put iron pistons in today's engines because aluminum is better - today.

But for engines that came with iron pistons there is nothing to be gained by changing to aluminum. Unless the old pistons are worn out, then you don't have much choice because aluminum is all they make today.

Or, if you were building a hot rod 1913 Metz or a racing 1913 Metz it would make sense to change pistons. But that is so absurd I don't even consider it.

In general I am against trying to improve an old design. Usually any improvement you make, causes problems somewhere else.

In the case of an old engine, it may be possible to improve power and performance but at the cost of spoiling the smoothness and sweet running that was built in, and possibly shortening the life of the engine by overstraining the other parts.

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To look at it from another angle aluminum pistons do give more power and less crankshaft/bearing wear but only in motors designed for aluminum pistons.

If you were forced to put aluminum pistons in your motor you would have to make them the same weight as the originals to prevent severe imbalance and vibration problems. This would negate any advantage of light weight.

The only alternative would be to use light weight pistons and rebalance the motor from scratch. This too is a trial and error process like what 1910 anon describes because the same balance factor does not work best for all motors.

The best thing is to keep the original pistons if possible. Second best, aluminum pistons of the same weight as the originals.

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I'd like to offer a dissenting opinion. Take it for what its worth.

True, aluminum pistons have a different expansion rate. If your mechanic does not take that into account, the engine runs the risk of seizing the first time it warms up. At the very least it may ruin the bores. However, if he knows his stuff, he will know what clearances to account for.

Aluminum pistons reduce reciprocating mass, because you've got less mass flying up and down in the bores and therefore less stress on the crank, rods, and bearings. Vibration will be less because there is less mass moving up and down in the bores. Counterbalanced cranks were not used until well into the 1920's.

The reason that they only make aluminum pistons today, even reproductions for our early cars, is because they are much better than iron pistons. The reason they didn't use aluminum originally is because they didn't have the technology back then. There's a world of difference between an aluminum casting from 1913 and 2010.

On the other hand, I've also had early cars that still had their iron pistons and they were still running fine. But these were low mileage engines. When I've had an engine rebuilt, I use aluminum pistons for the above reasons.

If you do decide to go with aluminum pistons, I'd suggest Arias:

Arias Pistons

On the other hand, if you want to save cost, there's no critical reason not to re-use the iron pistons if they are not worn.

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I am not aware of any rebuilders or resto shops today who do not use aluminum pistons except in the very rare instance where an original cast iron piston is still usable. We recently restored a '27 Kissel. Due to lack of availability from the usual sources we were forced to use very expensive forged aluminum "racing" pistons. The manufacturer told us what additional clearance was needed over standard cast pistons, no problem.

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Unless your Metz has a counterbalanced crankshaft (which I doubt, it probably looks more like a bent coat hanger), then aluminuim pistons will cause you no harm and only a world of good. If they match in all dimensions, you are good to go. There are machinists standards for clearancing alloy pistons that can be followed for fitment.

Modern rings, modern pistons...just no downside to this. Your main and rod bearings will love you for it! And oil consumption should drop too!

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That is correct that only engines with counterbalanced crankshafts are noticeably sensitive to change in piston mass, if you can notice it. From the change to the split-plane counterbalanced crank V63 in 1923, Cadillac were obsessive about piston mas to the extent of using different core size for oversizes. The Cadillac dealer in Melbourne in the 1920's and 30's told me that it was approved proceedure if necessary to rebore one bank only! The pistons would still be the same mass within close limits. However when I rebuilt my first car, a 1927 314B Cadillac under the wattle tree in the back yard in 1961, the bores were very worn and I used a set of Chrysler pistons I was able to find. I must say that I never detected any balance problem in that engine, and I really liked that car, which with the high axle ratio seldom needed resort to lower gears except for starting from lights on an incline in city traffic (and it commanded respect). I traded it and a V63 for a 1918 Mercer in 1967). The one thing about those pistons that was not perfect was that I should have made the skirts shorter to match the original pistons, because I was just learning at the time, and didn't know that the holes into the valve chambers from the bores were necessary for crankcase ventillation.

Now if you look at the 1913-14 4cylinder Cadillacs, the cast iron pistons metaphorically weigh as much as a brick. While originality of a car is an important consideration, recording what alterations you may feel obliged to make, and for what reasons is also important. And what you do is likely to be influenced by your type of use, that is whether you intend to drive or trailer it, et cetera. In about 1964 Ken Moss from Sydney shipped his 1912 Cadillac to California, and drove it with Joan and their three teenage daughters to Detroit and to Indy to watch the 500, then back to California with a side-trip to the top of Pikes Peak. Ken used aluminium alloy pistons and International Black Diamond conrods, to avoid trouble with those hinged Cadillac big end bearings in the splash lubricated engine.

If you want to use original pistons and the bores are a little worn, either hone them parallel slightly oversize with a rigid hone or get them ground on a Heald planetary grinder. Then built up the piston skirts by electroplating them with tin. About 6 thou coating thickness was normal proceedure. I have full details of the process in a Repco engine overhaul manual of the 1950's, and I can transcribe this if I cannot persuade my youngest son to scan it into my computer.

You get the smallest oversize rings, and carefully file the end gaps to suit the bores. I have instructions for this too. You can do all this at home yourself.

I make my own alloy pistons when I need them. You have to use correct low expansion alloy. Aluminium pistons are nearly as old as the motor car, but not quite. I once saw an aluminium piston from a 1908-9 4 cylinder Napier. W.O.Bently made light alloy piston before WW1 for the French DFP cars that he sold and raced with his brother. I think he used about 30% copper in his alloy. When the war got under way he talked so loudly about light pistons for aero engines that he was commissioned as an officer and effectively told to shut up and work on it. As you know he designed two sizes of superior rotary engines as were fashionable in aircraft at the time.(In as much as a rotary could ever be superior).

It is probably better to get a foundy to do your casting for you if they will do what you want. If necessary you can do all the machining your self on a small lathe, including reduction in diameter of the skirt across the pin axis to give cam relief for thermal expansion. It is of course much better to cam grind, and I would have workable parameters for about any antique engine if you need to know. Unfortunately I am to far away to do your cam grinding for you. In 1972 I saw Alan Lake in New Zealand cam-machining pistons on his bench lathe for his 8 litre ohc Hispano Suiza.

The other consideration some people might contemplate is change of crown shape and height, partcularly on a pre-Rickardo L-head engine for reduced flame travel and better resistance to combustion knock or "pinging". This can make a big improvement for many engines, and is a clear exception to F1 Repco Brabham engine designer Phil Irving's advice that "You can spend a lot of money and effort changing things, but to eventually find that the designer was right in the first place". And again, what the maker built originally has importance and value.

It is all a matter of balance, (quite apart from ensuring that all your pistons have the same mass within reasonable limits).

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So far, it is 5 to 1 in favor of aluminum pistons. I've checked the internet, and seen no discussions on this subject, though I'm sure there have been. In fact, I checked Google, and this thread was at the top of the list! I have a six or eight books on vintage car restoration, and none mention the subject except Matt Joseph in Collector Car Restoration Bible. He says (page 100) "When cast-steel or cast-iron pistons are encountered in an old engine, it is usually best to thank them for the years of faithful service that they have rendered, and put them in a nice, clean cardboard box and store them until you have the emotional resources to throw them away. Modern aluminum alloy pistons have better heat dissipation characteristics and are almost always lighter than old ferrous pistons. They are invariably tough enough to withstand any service conditions that they will encounter, and lighter pistons mean more power, so don't hesitate to make that replacement."

Phil

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It would be even better to throw away that crappy old 4 cylinder engine and put in a Chev 350.

I never said aluminum pistons aren't better. What I said is they are not original. Whether changing the operating characteristics of the engine is a good idea or not, depends on how much you respect the car as a piece of history. If you want a hot rod, go ahead and hot rod it.

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Your vote has been counted, Anon! I'm not sure if the aluminum piston counts as "hot rodding" or not. We also use paints, clutch materials, sealed bearings, vinyl, neoprene and other things that are not original to cars. I suppose the question is how far is too far!

Phil

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My vote would be to keep the original pistons if possible, if not, use good quality aluminum pistons that weigh the same as the original or less.

New pistons are not automatically lighter than the old ones. I know that some Model A pistons from overseas weigh nearly twice as much as the originals. I have ridden in Model As that were rebuilt with new pistons, and had bad vibration problems from 20 MPH up that were not there when the car was new.

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Your vote has been counted, Anon! I'm not sure if the aluminum piston counts as "hot rodding" or not. We also use paints, clutch materials, sealed bearings, vinyl, neoprene and other things that are not original to cars. I suppose the question is how far is too far!

Phil

Some people should maybe go to the artic, drill core samples, date the core samples, then save core sections that contain the appropriate year of trapped air, extract and compess the air...and STICK IT... :eek: ...in the tire of course. :D

When a person actually wants to save and get one of these very old cars back out where someone can enjoy them, why on earth do you say it's hotrodding?

By the way, the complainers rarely have a car of their own that they saved...or at least anything comparable.

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Guest DeSoto Frank

My two cents-worth...

If it's a trailer queen, that drives only from trailer to field and back, stay with the stock iron pistons.

If you plan on extensive touring, then quality Aluminum pistons, properly fitted and balanced, would make for a longer-lasting engine.

That's my humble opinion...

I guess if you're asking the question, your engine is worn to the point that it needs a rebore ?

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1910 I salute you. If everyone felt that way there would be a lot more old cars around, because over the years thousands have been chopped up and destroyed in an effort to "improve" them.

Next time you see a 1920s car with the wrong carburetor, seats, wheels or engine think how proud the owner was back in the fifties when he figured out how to get rid of that old junk for something "modern".

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How far you can change the characteristics of a 1913 car before you loose the experience of driving a 1913 car as a 1913 car is a valid point of discussion.

Anon; That is a very important thing, without question. Some fortunate owners of really early cars have places that they can still operate them on their favorite rural roads....and yes what would a Stanley be without all the noises and smells :) . Some of you are also fortunate to find cars that were very complete.

So, I agree completely with that statement!...but not on all years and makes/models.

I just get very upset about some viscious hate displayed by some AACA members on several different occasions awhile back. One was calling all rodders "ham fisted butchers". Do you think that kind of talk on THIS forum will attract more members to this website? I say that because other members here are also rodders; either street rodders or old time hot rodders. How'd you all like to get bashed like that. I can assure you that the old time rod site HAMB does not bash restorers...matter of fact if some person posts pics of a barn find complete car and then says they will rod it, most memberswill try to convince them to run it stock.

..and then just because of piston alloy, a restorer is jabbed with a hotrod statement??? Give me a break.

Some bashers don't put forth their own accomplishments..likely because they have never done a purist restore, never mind a very rough, incomplete obscure car that is not very popular with collectors. On the restorers side, I have seen so many antique cars that were ripped apart and mixed in with all the other cars he thought he'd tear apart to "restore" and then they are left to their heirs to figure out what goes with what basket case. You have too. Are they to be applauded?

The prewar hobby is dying...like it or not, that is a fact.

All of us who live and breath prewar need to encourage any potential new prewar guys to "do the best you can to get that car back out where people can enjoy it" There are so many prewar models and body styles out there that nobody will ever repair do to lack of proper parts...and these cars are the ones where there is no hope of barely getting started without exceeding the finished value of the car. It these cases, I'd rather see it saved and back on the road even if the owner has to use a motor that may be a year or two wrong for the car. Nobody should be bothered by that situation, if a car is saved, and we end up with another prewar hobbiest. No I am not saying to rod it, but if some components or parts are incorrect and it was saved, I am happy.

There are also a few people here that think this website is supposed to be completely centered around "Hershey level" "Senoir winners". The senoir competion crowd does not represent the entire hobby; they are a distinct minority by percentage numbers....and yes, for decades I enjoyed looking at the best of the best at Hershey, and applauld those owners for their efforts.

my thought? .."Do the best you can, and don't worry about the haters"

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Back to the question about lighter pistons on the Metz...

I don't know if lighter pistons would help, or not, on an issue with my former 1912 Metz. These early 2 passenger Metz cars were ultra light cars sitting on very flexible full-elliptical springs without shocks. If I parked the car and ran the throttle up a bit, there was a point where the whole car would start to bounce up and down on it's springs.

These cars have a very light flywheel that is permanently connected by a driveshaft, to a aluminum friction plate 1/4" thick reinforced with a few wood spokes. There just isn't much mass in the driveline to absorb what the motor does. Compound that to the lack of weight in the car and things do happen that would not be as noticable in a conventional car of that era.

So I wonder if lighter pistons would help in the case of the hopping, or is it more a case of the power strokes?

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That's what they call "character" or, if it happened on a new car, a "recall" or possibly a "class action suit" LOL.

:) Rusty, that little 1912 Metz had "better" things to call character. One feature I liked to show others were the unique wheel hubs it had: These ancient cars used rough roads with "wagon ruts". The wagons built in northern USA had different track widths compared to the southern USA, just like the difference in narrow and wide gauge railroads of the day. Metz made a 2 piece hub with a simple cross bolt which allowed you to turn the wheel around backwards, which changed your track to fit either width of wagon ruts! I have never heard of that feature on any other car.

Speaking of Metz AND hotrods in the same paragraph: 30 years ago when I had that Metz, I spoke with an elderly woman who told me that when she was 14 years old, she borrowed her familys 1917 Metz and drove from CT to Mass to visit relatives. I had a nice talk with her about driving Metx cars back in the day. Three years ago, I read about a somewhat well known "East Coast hot rod history book" that featured cars built just after WW2 and the 50's. I was very surprized to read that the son of the elderly lady with the Metz, had built a famous Model A coupe hotrod back then, and his car and name are in that history book. :cool:

Another old rod history tidbit; I enjoyed reading about the late Bill Harrah's first car as a teenager, a souped up early Model A with 1928 Chrysler wire wheels....and late in life he decided to recreate his old car. The story mentions Harrah at Hershey haggling with a vendor to get a cheap price on the 28 Chrysler wheels he needed. It was said that Harrah was proud of the fact he got the guy down on price :D

It's all about history and enjoyment.

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Standard track width was 4'8" or 56". I don't know how long ago it became standard, but the ruts worn in the streets of Pompeii are that far apart.

The first railroads adopted this measurement from the wagon makers so a standard gauge railroad is also 4'8".

I don't know why but in the south 60" track was used.

Other makes had reversible wheels for this reason.I don't recall the details but Model Ts could be adapted somehow, or maybe they offered a wide track model.

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Guest Bob Call

I have heard that the 4' 8" guage or track goes back to the Roman Empire and is the average width of a two horse hitch. So, the standard guage rail road is two horses asses wide.

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  • 6 years later...

I HAVE A 1912 MODEL F BRUSH AND IT HAS AN ALUMINUM PISTON IN IT WITH A SLIGHTLY GREATER COMPRESSION DISTANCE.  I HAVE DRIVEN IT AROUND 17,000 MILES  INCLUDING 15 GLIDDEN TOURS.  IT RUN COOLER AND HAS SLIGHTLY BETTER.  ALSO WITH THE BETTER RINGS IT USES NO OIL. THE PISTON IS A STANDARD 4 INCH BORE IN A STANDARD 4 IN BORE CYLINDER.  IT DOES NOT OVER HEAT AS MUCH AS IT DID PRIOR TO PUTTING IN THE ALUMINUM PISTON. i WOULD NEVER GO BACK TO A CI PISTON.

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Interesting feedback. I am trying to imagine the original 1913 Metz. As built it had a top speed of 45MPH and a cruising speed of 25 - 30 MPH. The original bores are good, and the owner has the option of putting it back together with new rings for another 100 years.

 

Instead he opts to bore it out and install custom made aluminum pistons for an extra $500. These are made of the best material, using the newest technology, by a company that supplies 200MPH Porsches and race cars.

 

They raise the top speed of the Metz to 48MPH. Comfortable cruising speed stays the same due to the limitations of 1913 suspension, steering, brakes, tires etc.

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If the bores on the OP's Metz are really so close to the original size that the iron pistons fit properly, I'd think that pretty remarkable. Every brass engine I've had apart – which I admit isn't a huge number – showed severe bore wear from running on dusty dirt roads without an air cleaner. The bores in my own car, a 1910 Mitchell T, measured perfectly at the base but had to be bored .085 over in order to get the taper out.

 

I've had some experience with aluminum pistons that didn't help much... on the only engine I ever sent out to have the work done by an "expert." He used White diesel truck pistons that weighed almost as much as the iron ones and actually lowered the compression ratio. I also once owned a 1902 Panhard engine that was, unbelievably, "NOS"... with a part number painted on the crankcase and absolutely no indication it had ever run at all. If I still had that engine, I'd have certainly kept the iron pistons.

 

But, regardless of whether its original or not, I would not purposely put an engine together using some of the slipshod methods I've seen in originals. Dynamic balancing machines weren't even invented in the brass era. The best they could do was try to get the individual components close in weight. Very expensive cars used machined-all-over cranks cut from big slabs of steel. They certainly understood the value of balance and their solution was to machine the crank to exacting tolerances... if this was done, they were automatically very close to being balanced. For relatively inexpensive cars, like my Mitchell and more so the Metz, they didn't even try very hard. I'm making my own pistons and rods... though I admit that isn't an option for most people. I don't expect to raise the top speed of the Mitchell (at 2000 rpm it will be doing 63 MPH) but I would like to get it to the point it will run at 45 without feeling excessive stress. I think that the key to this is balance and reciprocating weight, both of which should be addressed in engine rebuilding.

 

One of the odd things, to me, about old car restoration is that there is a certain amount of hypocrisy involved. Is anyone brush painting their car? That's how all of these brass cars were painted and yet it's taken for granted that the latest and greatest epoxy finishes are perfectly acceptable. Does anyone really think they put a mirror polish every brass bit... more often than not, they painted the brass black (special paint was sold for the purpose) to avoid polishing it but does anyone do that in a restoration? I just bought a nice Gray & Davis dash mounted amp gage that still has it's original black finish on it. I'm not replacing my shackle bolts with the grade X, soft carriage bolts the original factory used. We readily accept all sorts of minor adaptations to modern conditions.

 

F&J made a very good point earlier, that many of the critics have never wrestled with the problems of bringing a really early car back from an incomplete pile of parts. There simply is no valid comparison with restoring any post-war car or even most cars made after the mid-1920s

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On 9/18/2016 at 10:42 AM, JV Puleo said:

If the bores on the OP's Metz are really so close to the original size that the iron pistons fit properly, I'd think that pretty remarkable. Every brass engine I've had apart – which I admit isn't a huge number – showed severe bore wear from running on dusty dirt roads without an air cleaner. The bores in my own car, a 1910 Mitchell T, measured perfectly at the base but had to be bored .085 over in order to get the taper out.

 

I've had some experience with aluminum pistons that didn't help much... on the only engine I ever sent out to have the work done by an "expert." He used White diesel truck pistons that weighed almost as much as the iron ones and actually lowered the compression ratio. I also once owned a 1902 Panhard engine that was, unbelievably, "NOS"... with a part number painted on the crankcase and absolutely no indication it had ever run at all. If I still had that engine, I'd have certainly kept the iron pistons.

 

But, regardless of whether its original or not, I would not purposely put an engine together using some of the slipshod methods I've seen in originals. Dynamic balancing machines weren't even invented in the brass era. The best they could do was try to get the individual components close in weight. Very expensive cars used machined-all-over cranks cut from big slabs of steel. They certainly understood the value of balance and their solution was to machine the crank to exacting tolerances... if this was done, they were automatically very close to being balanced. For relatively inexpensive cars, like my Mitchell and more so the Metz, they didn't even try very hard. I'm making my own pistons and rods... though I admit that isn't an option for most people. I don't expect to raise the top speed of the Mitchell (at 2000 rpm it will be doing 63 MPH) but I would like to get it to the point it will run at 45 without feeling excessive stress. I think that the key to this is balance and reciprocating weight, both of which should be addressed in engine rebuilding.

 

One of the odd things, to me, about old car restoration is that there is a certain amount of hypocrisy involved. Is anyone brush painting their car? That's how all of these brass cars were painted and yet it's taken for granted that the latest and greatest epoxy finishes are perfectly acceptable. Does anyone really think they put a mirror polish every brass bit... more often than not, they painted the brass black (special paint was sold for the purpose) to avoid polishing it but does anyone do that in a restoration? I just bought a nice Gray & Davis dash mounted amp gage that still has it's original black finish on it. I'm not replacing my shackle bolts with the grade X, soft carriage bolts the original factory used. We readily accept all sorts of minor adaptations to modern conditions.

 

F&J made a very good point earlier, that many of the critics have never wrestled with the problems of bringing a really early car back from an incomplete pile of parts. There simply is no valid comparison with restoring any post-war car or even most cars made after the mid-1920s

I fully agree with JV on this topic.

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