Bloo

Have a look at the shafts for wear too.....

Probably because no replacements were available? Does anyone make these? No matter, those are too shot to use. He should have stopped, contacted you, and either found better ones himself or asked you to. It should normally be possible for a machinist to regrind them. They cant be used the way they are. Those edges will catch on the tips of the new or reground valves. The ones in your pictures are worn clear through the pads, I don't think regrinding would fix them. There are 2 main issues here, valvetrain geometry and lifter preload. If the geometry is wrong, the rocker will try to scrub the valve sideways as it pushes it down. This will cause the guides to wear out too fast, and might even break stuff, its hard to say. The geometry needs to be checked by the guy rebuilding the heads. Most engines have a spec for valvestem height, and this is the reason. If the valves are a little worn, or reground, the stem will come up higher and the geometry will be wrong. The tips are ground to correct it. Note that when this happens, the valvespring retainer will also be a little bit too high, and the valve spring will have less tension. This is why there is also a spec for "valve spring installed height". When wrong, it is corrected with shims between the bottom of the spring and the head. When the rocker tips have severe wear like that, they need to be precision ground back to the correct contour. The loss of material also screws up the geometry, and depending on how much was removed, may cause the scrubbing sideways on the valvestems I mentioned above. Also it may cause the rockers to have too much angle, and that can put the pushrods in a bind, and even more so with a higher lift cam. It may also screw up the lifter preload. To correct this, a machinist could leave the valvestems a little too tall, but that isn't really advisable, or more likely would machine a tiny bit off the bottom of the rocker shaft support towers. None of this matters though, because those look way beyond regrinding to me. I think you are gonna have to find another set. Hopefully they wont need grinding at all. If they do, maybe they will need a lot less. Lifter preload is the distance the lifter piston is pushed down in it's bore when the lifter is on the base circle of the cam lobe. Grinding material off of the rocker tips also lessens the lifter preload, but lowering the shaft in relation to the head has the opposite effect. A reground cam affects it too, but often not enough to matter. I think you should always check the preload. It can be fixed with different pushrod lengths if wrong. The geometry needs to be right first.

File fit rings are checked way down in the un-worn part of the cylinder. They need to be pushed straight before measuring. An upside down piston can do this if they're flattop pistons, if not find something the same diameter. You want them as tight as possible at the bottom, because no matter what you do, when they are at the top, where it matters, and where the cylinder is worn, they will be too loose. You want them tight up there too, but its impossible because of the taper. You are only making it less bad. If you get them too tight, the ends will touch when they get hot, and the ring will break and destroy the piston and cylinder. In theory you would set them to the tight end of the acceptable range of gaps in the manual. In real life, leave them slightly looser than the minimum acceptable gap. You cant afford to have them touch.

SBC Connecting rods? I wouldn't. Those ones in the pictures look like custom aftermarket rods. You might be able to use them, but no advantage really that I can think of. Maybe get new rod bolts, ARP if theyre available. If you are going to spring for any custom parts in this (you shouldn't have to), get pistons! Arias or something. You would have to know the actual deck height and you would have to CC the heads, because they will ask. Then you could have any compression ratio you want. Pick your cam first, because if it has more overlap you might need more compression. You also might be able to get the pistons lighter than stock, and probably modern-design rings, maybe lighter pins, and any style of pin retention you want. I don't know if its worth it, but along with rebalancing it might make a difference you could actually notice. Fancy rods wont be noticed again once you put the oil pan on. If they're heavier, and they might be, its actually worse. Only use custom rods in engines that have weak rods that might break at random, or that run to crazy high rpm. The Buick rods look forged to me, and forged is what you want. I don't think nailheads had weak rods. I don't ever remember seeing one that broke a rod back in the day. Someone here will know for sure. And speaking of compression, its unwise to believe compression ratio numbers in books or piston catalogs. If you care about the compression ratio, measure! Many American engines will be found to have a higher deck than the book says they should, and this lowers compression. I'm not sure if its sloppiness or maybe the factory intentionally leaves a little more metal for future remachining of the deck. Maybe Buick didn't, but you wont know unless you check it. Know how far off it is (if at all) and take it into account when ordering pistons. The volume of the combustion chambers is also often bigger than the book says it should be. It also gets a little bigger with every valve grind. Measure, and take that into account as well. Most cars of the 50s used steel shim head gaskets. Thicker gaskets are supplied today usually, and that also lowers compression. The compression ratio in most factory service manuals is somewhere between optimism and an outright lie. I'll bet a majority of them are half a point or more below what the book says. And one more thing about compression, I HIGHLY recommend you build this with a compression ratio that will be happy on cheap 87 octane ethanol-tainted fuel. It really is necessary for a daily driver, unless you are independently wealthy and never take it out of town. I once tried to daily drive an 11.25:1 (allegedly) Cadillac 472. Of course I couldn't afford to feed it premium, which wasn't good enough anyway, let alone the aviation gas or race fuel it really needed. I set it up to burn 87 octane to get me to work. I ran the timing retarded and recurved the distributor. I had it running acceptably, and not rattling itself to death, at least if I kept my foot out of it, but it was WAY down on power, exhaust ran hot, etc. A little too much compression is way worse than too little. If its too high you will be doing the sort of stuff I was doing with that Cadillac. No fun in that. If the compression is perfect but right on the hairy edge, then every time you get a load of slightly worse gas, you will be running to the trunk for a distributor wrench to back it off a couple of degrees to stop the pinging before it destroys your new engine. If the compression is a little bit too low, then your horsepower will be a bit down over what it could be, but you get to run ideal timing and fuel curves, and probably wont have to mess around with things much once its initially sorted out, and it will run great. Choose wisely. So I take it those loose pins destroyed the cylinder bores, and is that a broken valvespring? Did it drop the valve? Full floating pins need some sort of retainer in a groove in the piston pin bore to keep them in position. I don't see that. Thats absolutely crazy if he built it that way. If the pins are retained by the rods there shouldn't be bushings. I know it looks horrible in there, but most of the other things are not out of the ordinary. When something goes wrong early in an engines life, and you have to open it, it looks horrible. Most people never see it because nothing went wrong. New engines that aren't broken in yet burn oil, and yes, there will be carbon. Hone marks are a sign of a young engine. It takes a while for a soft aluminum piston to wipe those off. Those bearings look fine to me in the pics, but if the machinist says they're bad, they're bad. He can measure them. Is the valvetrain adjustable? If its not you will most likely have to mix and match some pushrod lengths to get the lifter preload right. Of course the ball has to be the right size o_O . Keep after this, and always prioritize the Buick over the old machinist and what happened in the past. Don't let that distract you from your goals. You are absolutely on the right track by doing it yourself this time. You will have this done sooner than you think.

It doesn't work like that. I completely understand why you might want to get rid of all that high-current wiring under the dash, but you will lose ammeter function. What I don't understand is the "fire hazard". I drove mopars of that vintage most of my young life, running one of them to almost 400k miles, helped friends build more of them than I can count, and I have never heard of someone catching the car on fire because of an ammeter. There is a design issue though, sort of. Where the wires go through the firewall to the ammeter at the bulkhead connector the connections can overheat and burn up. They are just 1/4 spades. Burning plastic smell? Yes. Car wont run or wont charge? Yes. Fire? Call me a Doubting Thomas. This arises usually because of the size of the alternator. Originally most mopars of that vintage used 32 amp alternators for non-a/c cars, 42 amp for a/c cars, and 60 amp for police (there are some exceptions, not many). Usually there was no problem with the connector on 32 amp cars. 42 amp cars were on the hairy edge. Police 60 amp cars had a separate harness with huge wires running unbroken through the firewall, and a +-60 amp ammeter. In the 80s, parts store rebuilt alternators were usually 42 amp with a double pulley. This is really the a/c alternator, but "one size fits all". Later on 60 amp alternators started popping up all over the place. The connectors could barely handle 42 amps. They couldn't handle 60 amps when they were new. Another thing that causes trouble is draw from power-hungry accessories. It is tempting to connect them to the battery or the starter relay, but if you do that you are on the wrong side of both the ammeter and those spade lugs in the bulkhead. Two things will happen: 1) any current drawn by the accessory will register on the ammeter as "charge", which of course it isn't, and 2) All the current drawn by the accessory will flow through the ammeter wiring, the ammeter, and both connections at the bulkhead connector. Connecting accessories like that can overheat the bulkhead connections even with a 32 amp alternator, because they were never intended to handle a constant load originally. Battery charging current may go all the way to the full output of the alternator right after a start but usually tapers off pretty fast. Back to your question. I see no way to do what you want and still have the factory ammeter work. On some other makes there were ammeters that had a remote shunt out under the hood (literally part of the ammeter was under the hood). This resulted in small wires through the firewall. Chrysler may have also done this for a moment or 2 in the 70s. I doubt it would fit your cluster. Almost all mopar ammeters are real ammeters with an internal shunt. The current flows through them. All of it. You can shunt them to make them usable with more current, but you still need the charging circuit running under the dash. If you want the ammeter to actually work, here is what I suggest. Get a big thick grommet (with lots of protection for the wires) and run 2 big wires through the dash, #8 or #10 or so, like they did on the police car. Run one to the back of the alternator, and the other to the starter relay (unhooking and abandoning the old wires). I would fuselink this wherever Chrysler did, and probably at the other end as well. Proper fuselink size is 2 sizes (4 numbers) below the wire size. There may be a small wire crimped into one of the connectors where the charging circuit went through the firewall. You will have to cut that loose from the abandoned wires and reconnect it. It needs to connect on the same side of the ammeter it was before. I have also seen people shove the new wires through the holes in the bulkhead connector where the old spade lugs were. This saves drilling a hole, the only thing it prevents you from doing is ever completely unhooking the wire harness. It looks cleaner, too. Solder everything! This is high current wiring. any questionable connections are gonna get hot. Do not skip this. Insulate all the new terminals with heatshrink or something. Make sure all mechanical connections (like the stud connections at the back of the ammeter) are squeaky clean. Power hungry accessories should be connected to the back of the alternator. Period. The ammeter only has to be able to register the maximum output of the alternator. If its 45 amps or less the stock one should work as intended. If you have more charging capacity than that, or it goes too high, you can shunt it. That link has the right idea, but these ammeters generally don't have marked scales anyway (except police ones, that were marked 60 amps at full scale). You really don't need to calculate. So, do something to make the alternator go to full charge. My favorite method is run the engine at 2000-2500 rpm, and put a load tester on the battery. When you activate the load (just for an instant) how high does the ammeter go? If it doesn't go too high, you don't need to do anything. If it does, make a really short stick of copper wire, start small, maybe 20 gauge. Crimp and then solder ring terminals on it, and put it across the ammeter and try again. Too low now? get a smaller wire of the same short length. Too high? get a bigger wire of the same length. Keep doing this until full charge registers where you want it to be on the ammeter. If you don't need the ammeter to work, you can just run a big wire from the alternator to the starter relay (or the battery). Fuselink it. If there is a small wire crimped in with the ammeter wiring at the bulkhead (there probably is) you are gonna have to cut it loose and extend to your new circuit and connect it. The alternator is best as a connection point, but if your new wire is nice and big, the starter relay or the battery would be fine. Disconnect and abandon the old wires. If you do this you will have no charge indicator at all, as the mopar system does not support an idiot light. You could get an aftermarket voltmeter, as voltmeters use small low-current wires, and mount it under the dash. Best of luck.

I'm in Central Washington, former Seattle resident . I sent lots of stuff to Delta years ago, as did several of my friends. The prices were good and the quality excellent.

Delta cams in Tacoma will regrind a cam to original spec or whatever you specify. I have had good luck with them in the past.

I'm not sure that getting the sender back to the middle of the tank would be enough. These are a balanced coil type fuel gauge. They respond instantly to any input from the sender, unlike the thermal gauges you might find on a much newer car. The original sending units have a cork brake to minimize movement. Sometimes it takes a few good bumps to change the reading after filling up. They are a 0-30 ohm system, with 0 ohms at the empty end of the scale. The implication is that the grounds at both the gauge and the sender have to be perfect, or you will never get the gauge all the way to empty. The gauge wiring has to be perfect too. I would suggest finding someone to rebuild the original sender.

On a compression test its the balance that matters. The 20 percent usually means balance. In a perfect world cylinders would all be exactly the same, but with rough cast combustion chambers it just varies. Many shop manuals say 20 percent. On a new engine I would expect it to more or less meet that, but wouldn't suspect trouble if it barely missed. Random cars off the street could have 25 percent or maybe even a little more and not be broken. If your lowest was 100psi, 20 percent would be 120psi. Thats not far off from what you are seeing. Matching the absolute numbers in the book is another thing entirely. I have a pretty good compression gauge (snap-on), and have never duplicated another person's exact numbers. The balance will be the same as any other competent person gets. If there is a cylinder at 40psi (burned valve) it will still be super low when I test it. If cylinder 6 was the highest compression, it still will be. I ignore the absolute numbers entirely, unless its so far low or high that I suspect wrong valve timing. Compression testing is easy and quick, and can find stuff like burned valves (most common cause of a cylinder way lower than the others) or worn compression rings (by dry checking and then wet checking). Leakdown testing is more trouble but tells you a lot more. You have to bring each cylinder to exact TDC, then adjust a regulator on the tester. It tells you PERCENTAGE OF LEAKAGE. Again, like compression results vary with different people and different testers, but some average cars might have 20 percent. some tired but just fine ones might have even 35. A new engine, fully broken in, might have on the order of 5 if its really good. It might be 10. You want less. 2 would be nice, but if you have that, you probably spent hours in the machine shop nitpicking every last little detail of every detail of every detail. In the real world I doubt you will ever see it. Those numbers assume it is all ring leakage. While the tester is running listen for air. Figure out where the air is going. This is where the leakdown tester really shines. If an exhaust valve is burned, It will hiss out the exhaust pipe. If an intake valve is warped or burned (extremely rare) it will hiss out the intake (open the throttle and listen). A head gasket blown between cylinders would hiss out the adjacent cylinder. A head gasket blown into the water jacket blows bubbles in the radiator. It should only hiss through the crankcase (listen at oil cap), because the leakage should all be through the rings. One cylinder with a much higher leakage number might indicate a broken ring or holed piston or a scored cylinder. Have someone disconnect the air from tester for a moment while you listen to the various leak points, so you don't get fooled by the "sea shell" effect. The reason I thought of your PCV experiment was that I thought there wasn't an actual pcv port on the carb. If the port was out in a manifold runner I would expect the oil to go to one cylinder. Maybe 2. On a carbureted car, a tiny air leak at a vacuum connection on a manifold runner can cause a miss on one cylinder by making it too lean. I would expect oil vapor to follow the same path, and foul one plug.

You cant really tell much about static compression ratio with a compression gauge. Everyones gauge behaves a little differently, cranking speed affects the readings (condition of the battery, gear ratio of the starter drive, etc). The cam grind affects it too. Some people hold the throttle wide open while taking the reading, some do not. Readings can be dry (lower) or wet (with a drop or two of oil, higher). The main thing with a compression gauge is that the readings are fairly close to the same. yours are. I wouldn't have been upset at all about those readings on a 9:1 Mopar back in the day. On the other hand one of my friends was driving around a Buick Electra with a 401 Nailhead and couldn't get good enough gas for it. The compression ratio was just too high. It's way better for the static compression ratio to be too low than a teeny bit too high. You can tell a lot more about the condition of an engine with a leakdown test, but the static compression ratio generally has to be measured with the engine apart. Your plugs look mostly ok. Light tan is perfect (other colors are possible with the gas now). Too rich would be black, Too lean would be white, often combined with signs of overheating or detonation (little balls of metal). The one plug with the buildup is most likely oil burning. If these plugs were in when you were experimenting with PCV, it could have easily come from that. The oily ones could be oil burning, but probably aren't. They look too clean. Oil can come up the spark plug threads on an oil burning engine. I doubt it though. If theres any sign the oil could have come from the outside, like a leaking valve cover gasket or oil cap, then it probably did come from the outside.

Nearly all 904 (or 727) pan leaks are actually shift shaft leaks. Take the shift shaft and its concentric partner the kickdown lever off and replace the 2 seals. I drop the pan and remove the valve body usually to do this. I think its easier. Here is someone who changed them from the outside without even dropping the pan: https://www.vanning.com/threads/ubbthreads.php/topics/580264/torqflight_727_seals.html

Looks good! Rebuilding the originals is the way to go. I guess you could peel the edge back, but I never thought I could do it and then get it back together looking good. I always ground them apart like you did, and then silver soldered or brazed them back together. I didn't have access to TIG. For what its worth "Chore Girl" type scouring pads work well to replace the mesh, either the stainless or the copper. It also works for the draft tube filter in some cars.

The pushbutton shift wasn't electric on those cars. There should be 2 cables. One is for park, operated by a lever. The other one is for the pushbuttons, and selects reverse, neutral, drive. low. There should be a mechanical linkage, made of rods and bellcranks, going up to the carburetor. This linkage must be present for the transmission to work properly. It tells the transmission how hard and how late to shift. It also provides a kickdown to second gear. The transmission cannot survive long without it. Best of luck finding your parts, and welcome to the forum!

Matt Harwood: I have been following this saga for years as well, and can understand the frustration. After reading online somewhere that the Auburns were FINALLY here, I called. They said they had them in stock (6.00:16 only) and would have sold me a set that day. They are pretty expensive, but I might have done it if I had a second set of wheels ready to go (I don't). This took place about 2 months ago. I suppose its possible they could have other sizes in stock now, thats why I suggested calling, but I see you already have. To be clear for everyone else following along, the "Diamondback Auburn" is a designed-from-scratch radial that looks like a vintage bias tire, pie crust edge and everything. AFAIK it is only a 16 inch tire, I think it was supposed to (eventually) be available in 6.50:16 and 7.00:16 in addition to the 6.00:16. DIamondback tires in smaller rim sizes 15, 14 etc., as far as I know, are modern off the shelf radial tires that have a whitewall permanently vulcanized to the side.

Call them. Last I heard they had only 600:16. That was a while ago.

No The crank is out 180 degrees EVERY OTHER rotation, because it turns twice as fast as the cam. It's completely normal. It IS, however, possible for the distributor to be out 180 degrees with relation to the cam, because it turns the same speed as the cam. This is NOT your problem. If it were simply 180 degrees out, it could not run at all. Its impossible. I would double check the ignition timing again, and the firing order. Could the wires be put on the distributor incorrectly? See which way the distributor turns, put on #1, then follow the firing order around the distributor in the direction the rotor turns. To be clear, when you put the #1 wire on, the engine should be on top dead center of the COMPRESSION STROKE for cylinder #1. Remember this only happens EVERY OTHER turn of the crank. Put #1 on the post the rotor is pointing at. You may need to advance the timing a little bit to get it to start. To advance, turn the distributor SLIGHTLY in the OPPOSITE direction the rotor turns. If its kicking back while trying to start use less advance. If that doesn't help go back to the basics, and do a compression test and a leakdown test. Good luck!

That looks like a Delco solenoid to me. Is it? On a Chrysler? ALMOST everything on that solenoid is rebuildable. The adjustment on the front just sets the pinion depth. There should be a spec in the manual for that. The copper disc has a little spring so that it can bottom out on the copper bolts a little before the solenoid bottoms out. Copper discs if not available can often be taken off and turned upside down. Copper bolts often have half of the heads burned off. They can be replaced. If not available sometimes they can be turned around backwards to get the full height back around the side that contacts the disc. The only thing that cant be fixed is a bad winding. There are 2 windings, check continuity on each of the two windings. I would really need to see the manual to tell you more. Is there a relay inside the cover? If so, look for one winding to be from one of the relay contacts to one of the copper bolts on the solenoid. The other one should be from the same relay contact but to ground. If the windings are good, you can rebuild it. If not, its gonna be expensive. Good luck.

The first thing to do is to check if the gearing is ok. Gearing is a separate issue from speedometer calibration. Take it out and drive it 10 miles, while paying close attention odometer and to the mile makers. If you gained a tenth, the speedometer is geared 1% fast. If it gains a mile, thats 10% fast, etc. Gearing is fixed with the little set of speedometer drive gears in the transmission. The steps (for different gears) are usually around 5%. A different tire size can also make a correction. If the speeedometer still reads wrong, then it needs calibration. You could drive 60mph (one mile a minute) by the speedometer for 10 miles, and have a passenger time you with a stopwatch. It should be exactly 10 minutes. You can caluclate how much change you need to make from there. I don't know about the magnet. I usually get the gearing right and let a speedometer shop calibrate the head if it needs it (it usually doesnt).

For crankcase ventilation to work you need 2 things, 1) a way for air to get in and 2) a way for air to get out. The air coming in must be filtered or dirt will be sucked into your crankcase. On a draft tube system the way in is usually a breather cap and the filter is in it. The draft tube creates a suction when the car is moving, and air flows in the breather cap and out the draft tube, hopefully taking the crankcase vapors out with the air. Draft tube systems left to their own devices would suck oil out. There has to be a way to separate the oil from the air. I don't know how the nailhead accomplished this, but for example on a Chevrolet 283, there is a can shaped thing with a series of baffles that seperates the oil and drains it back into the lifter valley. On a Ford 352, there was a steel or copper mesh like the one used in the kitchen to scrub pots. It can cake up with carbon and plug. You need to get that draft tube unplugged, and the oil separator, if there is one, also unplugged. Just connecting a PCV valve isn't going to accomplish what you want. If the draft tube is unplugged, the pcv will try to suck dirt up the tube. If it's plugged, its gonna create a vacuum in the crankcase and probably interfere with ring sealing. If the engine has a lot of blowby, draft tube systems tend to smoke out the tube at stoplights. It might just be a little. On the other hand, if you have a lot of blowby it can look like the car is on fire. I had a Ford like that. Pcv can help. You still need a way for the air to get in, and a way for it to get out. The breather cap is the way for filtered air to come in, and the PCV valve is the way out. On older engines, this usually means putting the valve in the hole designed for the draft tube. More modern systems put the breather cap on one valve cover and the pcv on the other. Any leftover breather tube hole would need to be plugged. This ventilates the rocker areas better but tends to leak more oil on the outside of the valve covers. Now, about that oil scum around your breather cap. If your engine is not basically brand new, with perfectly sealing rings, its normal. Every old car I have owned with a breather cap did this. No pcv system EVER keeps up all the time. The manifold vacuum cannot support enough flow for that without making the engine run like crap. When it doesn't keep up, oil vapors will come out the breather cap. In the 80s, they plumbed the breather cap vent up to the air cleaner. That just got the oil all over the air cleaner. On systems that have the PCV valve in the opposite-side valve cover, there has to be a baffle under the hole to keep the oil from the rockers from getting sucked up the pcv valve. Some aftermarket valve covers omit the baffle. Without the baffle the oil consumption will be astonishingly high. I wouldn't get too concerned about the flow rating of the valve. If you have a smooth idling cam, Dynaflow, high rearend gears, etc. then one from any similar displacement smooth idling automatic will be fine. Probably even a Chevy 350 one will be fine. The spring isn't supposed to be strong enough to hold the valve shut. They basically rattle. They are open at idle. Its normal. Some early systems didn't have a valve at all, just an orofice to restrict flow. The downside is if the engine backfires, it can cause a crankcase explosion. The valve is supposed to slam shut and prevent the fire from getting to the crankcase vapors. Supplying vacuum to a PCV valve is the tricky part. It is a huge vacuum leak. The trick is not making the car run like it has a huge vacuum leak. First, you are limited by the engine itself in how much air you can let in (the flow rating of the valve determines how much actually gets in). Then you must mix the air in such a way that it does not screw up the fuel distribution. This is toughest at idle. Just hooking it to a power brake nipple or whatever will not work well, you will have a horribly lean cylinder or two. Almost all factory PCV systems mix the air with the fuel/air mixture coming out of the idle jets. The PCV port will split and come out right under them. Sometimes its built in to the throttle body of the carburetor, sometimes its a plate under, but in 99.9 percent of all cases, this is how its done. The other 0.1 percent don't work very well. If you cant mix the air in under the jets, you would be way better off with a draft tube. Good luck with the project!

Sounds good, but what route in a prewar car like the ones Brass Is Best posted? Who has done it and which way did you go? Assuming your prewar car is not a Buick Century or a supercharged Graham or something, are there slow enough roads today?

I have an excellent one that is branded "Pacific Power Batteries", but I suspect that is a regional brand. I'm in Washington State. I wouldn't convert it to 12v. Most 12v conversions I have seen are about 75%-90% working. There is always something that doesn't work right with the conversion, some gauge, or the radio, or a heater motor, etc, and then you open the hood and theres an alternator. I'm sure there are some bad designs out there, but generally speaking, the engineers designed these things to work on 6 volts and they did. They do crank slower, but this is by design. It just sounds odd today. At 6v, current is twice as high as it would be at 12v to do the same work, so clean connections a must, as is larger wire in the battery cables. Generally speaking, the ones sold at parts stores for 12v cars are not big enough. Why do you need it to crank for a few minutes? Most 12v cars cant do that.

No documentation would be needed in the US. In 1975 the only common wheel diameters for cars were 13" , 14" , and 15". Anything larger in diameter would have been for a very old car or a truck. Wider 15" (and 14" and 13") tires and wheels were readily available. You just bought them and put them on. No one had to approve a different size. It is still like this, but today the common sizes are 16" and larger.