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Discussion Starter #1
When I disassembled the engine on my 1948 6C 2500SS it had two different types of lock washers under most of the bolts and nuts. They used split lock washers in some places and star washers in other places. Does anyone know if the engine originally used both types? My friend thinks star washers are too modern to be authentic for this car. This engine had been previously overhauled in Europe.
 

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I look forward to an expert reply for the 6C, which mine is not.

However, I've worked with Alfa engines built back into the mid-50s, and they never used either split or star lock washers. Depending upon the application, they used high quality flat washers, curved "wavy" washers, and "paugh-nuts" (aka "palnuts").

Sometimes they used bend-over lock tabs, safety wire, and cotter pins for security.

I have found some split lock washers in chassis applications, but never on or in an engine.
 

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I'm certainly no expert on the 6C 2500 so I took a look through a number of parts manuals to see what, if anything, they could offer.

In particular, 6C 2500 parts manual #4912 dated 10/49, and the Normaizzati (Hardware) manual dated 5/72 (no publication number shown). The washers listed in 4912 are shown in the hardware manual as being either flat or split locks. However, not all washers in 4912 are shown in the hardware manual. This includes internal and external tooth washers. So the documents I have can't say whether or not tooth washers were used on the 6C 2500 engine.

Further research in other parts books shows the first documented use of wave washers was with the 1900 series while tooth washers first appeared on the Giuliettas. For the Giulietta, the tooth washers were not used on the engine proper but on the chassis side of the engine mounts.

From personal experience with countless 105/115 engines, I do not recall the use of tooth washers anywhere; only flats, split locks and waves.
 

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Papajam's comment adds to my own, in that the earliest engine I'm familiar with is the 1900. Perhaps there was a change in technique after the 6C, even though that engine and the 1900 somewhat over lapped in production dates.

I might suggest that sensible techniques are best followed where you won't harm the historical value. Inside an engine, I would favor whatever was original, unless a newer technique had been developed that improved on the original. Outside in visible areas, I would try to retain the original.

I never use split washers inside an engine, and can't recall ever using a star washer inside. I don't trust springy things to retain the critical tensions. Generally, a precision ground washer and correct torquing does a better job. In some cases, a drop of Loctite is smart.
 

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Papajam beat me to the punch with looking up 6C 2500 manuals.

It appears star lock washers (both inside and outside), and the method to produce them, were first patented in US patent 2234194, filed in 1938 and issued in 1941.

I think, based on this information, we can safely assume that (a) no prewar cars had star lock washers, and that, (b) until this patent expired in about 1958, Alfa would have had to buy them from a licensed source. Since the 6C 2500 is, in essence, a prewar design, it is unlikely that Alfa changed components or materials unless they were known to fail. When new designs came about in the 1950s with the 1900 and Giulietta models, it made sense to use the latest technology, if such technology provided an affordable improvement.

By comparison, it appears a patent for wave lock washers was first applied for in 1921 and granted in 1922 und US patent 1427194. I found no patents regarding the split ring or compression spring washer, but some people on the Internet say it was invented in 1901 by a blacksmith by the name of Morris Landry, for the purpose of holding railroad ties in place. US patent 1709933, filed in 1928 and granted in 1929, seems to improve on the idea by varying the slot design, and US patent 2277852, filed in 1939 and granted in 1942, adds a washer that prevents the split washer from sliding off the bolt.

However, it should be noted that the idea of the star lock washer was not entirely new 1937. US patent 1427807, applied for in 1918 and grated in 1922, was also for an outside star washer, but this design relied on a keyed groove or a flattened surface on the bolt to improve friction by preventing the washer from turning against the bolt. Also, US patent 1878425, filed in 1930 and granted in 1932, seems to be a combination between an inside star washer and a wave washer.

US2234194-0 (cropped and resized).png
 

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Since the inside of the engine isn't seen by a judge, I would consider items that would provide a strong installation. The rods were known to fail and throw out through the side of the block usually because the babbitt failing from lack of lubrication. Hence many 6c2500's were side lined for this reason. It wasn't beyond imagination to see a substitute engine put in it's place to keep the car on the road. IMHO, s split lock tab holding two sides of a rod bolt nut, would be a safer bet than a star washer or split (lock) washer. The 1300 used bolts/nuts with cotter pins. The later 1750 used a single sided lock tab that locked in the space under the nut. I never pulled the pan on my 6c2500 Ss engine to know what the factory put in to be honest.
 

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I recommend against using any washer on a rod bolt other than a precision ground, hardened steel flat washer.

The quickest way for a tension fastener to fail is to loosen. Soft, cheap split washers allow movement in a couple of directions, leading to reduced tension.

It's common to find rod bolts with NO washer, or a simple flat one.
 

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Discussion Starter #8
Rod nut locks

When I reassembled the bottom end of the engine in my 6C 2500 I used the original method of locking the rods and main bearings. They used a castle nut and cotter pin on each bolt or stud. There are flat washers under each main bearing cap nut but no washers on the rod nuts. I replaced all the cotter pins and flat washers with new high quality parts. Also I managed to buy some used castle nuts for the rods to improve their quality and add more choices for reassembly. The hard part of the task is applying the torque and having the hole for each cotter pin line up with a slot in the castle nut. The whole process took me about a full day, but I was able to do it. The trial and error process involves moving the nuts and washers from one position to another while gradually reducing the number of remaining changes. The last few nuts are the most difficult because the choices are more limited. I used 40 ft-lb of torque on each fastener, which matched the torque needed to remove each nut during disassembly. The factory workshop manual does not specify any torques. Probably there was a lack of torque wrenches back in the day.

I found the original castle nuts were match marked for location by the factory. Unfortunately all the nuts were mixed up during a previous overhaul and some marks were not possible to read. The original flat washers were also not high quality so once they were replaced the original marks were useless. The workshop manual has instructions and illustrations regarding the marks on the nuts, but no torque values. I am very happy this tedious job is over.

My original question refers to the lock washers on the outside of the engine where they are visible. Based on information provided I think the use of star washers on this 1948 engine is not correct. I still have input coming from a friend in Europe who has lots of experience working on these cars.
 

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Fred,

Although I've never played with a 6C2500, in general main bearing fasteners end up being torqued to around 60 - 70 ft pounds, with good threads and lubrication. While your engine may work with a 40 lb torque, I seriously doubt that was the original spec back in the day. The torque to release is not indicative of the torque to tension.

For amusement...

The French Renault engines in the Stampe aircraft (see my avatar) were not provided with any torque specs at all. The connecting rods were aluminum, as well. We just use the same specs as might be found on a modern day engine, and it works fine. However, the tools provided by the factory included wrenches with fairly short handles, all of which had a sharpish-leading edge. We decided that the original tightening spec was to pull until the pain in your fingers couldn't take it.

I assume the block on the 6C is iron? We would not use a star or split washer on aluminum, although with steel it is somewhat common now. On an aircraft aluminum engine we will use a high quality flat washer with a star washer stacked on top of that.
 

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Lots of stuff here right on..Firstly I would not put too much value on aligning castellated nuts with cotter pins. They did it in the 50's on Giulietta Veloce engines but when re-assembled for what ever reason (rebuild) the builders I know just don't bother with alignment. There is a stretch factor on the bolt that is not repeatable if you mix the nuts.

Star washers are one time only technically and not for the inside of a motor... hardened flat washers yes.

Split washers were never intended to be an anti release feature. I learned that in research.

Torque is usually determined by the size of the bolt/nut combination and the thread pitch and the type of metal of the bolt and nut... ( ref. pages of tables) go with that, IMO

All of this is really IMO....I would never assemble the lower end of a 6C 2500 without turning it over to an expert machine shop who knows all the rules of machines. It's all in the knowledge of the application and most of us don't know it.
 

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The little Continental 4-cylinder aircraft engines used cotter keys in the rod bolt ends. I never opened one up that still had them in place. They were always somewhere in the bottom of the sump.

When building the Renault engines we used safety wire across the main bearing saddles. It would stay in place. The technique was to torque the big nuts to around 75#, then go whatever more was required to line up the safety wire holes. The absolute perfection of "torque" is far less critical than most people think. Essentially, the tightness of the nut (or bolt) should be just at or short of the point at which the fastener begins to go plastic. Of course, you won't know that unless you've gone too far. So - we all rely upon the manufacturer's torque recommendation. Well.... The 200HP Lycoming in my Mooney uses a "stretch bolt", that is precision ground to a specific length. You measure them before tightening, and keep going until they've stretched to a specified value.

But - as I said - I doubt any large engine (ie, not a lawn mower or weed wacker) would use a main or rod bearing torque setting as low as 40 ft lbs. I recommend you find out the diameters of the main bearing studs and the rod bolts and use the torque recommendation for a similar engine. I'd bet you a very fine bottle of wine that there are other Alfa engines with the same diameters, and you'd be OK to use those settings.
 

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Discussion Starter #12
Lock washer decision

Thanks for the input from everyone. Also I have good input from a long time expert restorer of similar Alfas. For originality I decided to replace all the star washers I found on this engine with split lock washers. I will also refer to the illustrations in the factory parts manual which shows every lock and flat washer.

The torque I used on the lower end was based on many comments received several years ago from 6C 2500 restorers. Modern engines have little application to this near original Alfa because of the soft materials used on the fasteners. The torque needs to be low to avoid yielding of the material. The engine is only 110 hp and will be used gently for tours and shows. The redline will be below 4500 rpm and thus the stress on the lower end will be modest. Remember back in the day these cars were raced in long events such as the Mille Miglia and Mexican Road Race. That results in many more load cycles and much higher loads.
 
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