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REPORTS ON A 1914 HUMBERETTE RESTORATION


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I see a couple of possibilities. One would be changing the connecting rods, something that is already under consideration. Another would be reducing the width of original rods, added to counterboring for the heads of the bolts and then facing the bolt heads off to a slightly lower profile. Was there a thrust washer on the inside? And yes, these problems can be real mind-benders. I have a love/hate relationship with this kind of problem. On the one hand I think they are a PIA - on the other hand I am drawn to them and derive satisfaction from solving them.

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Or... use flat head shoulder screws. I tried copying the link. It didn't work but they are made. You would just have to clean up the chamfers for the the rivets a little for the heads to fit perfectly. It would take a little calculation to get the depth just right but it looks to me like the best of both worlds.

 

jp

 

 

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Maybe we are overthinking this... how about regular grade 8 flat head socket cap screws with a fine thread? Holes measure just under 8mm so get the bolts and measure them. Then see if you can get an under size reamer that will allow about .001 clearance (I have no idea how that is measured in the metric system)... ream the holes and replace the screws one at the time. The bolts would be so much cheaper than the low profile shoulder screws that this is probably the less expensive alternative. Of course, this is dependent on clearance on the other side. Fine thread will allow a higher torque setting. I'd use Locktite too.

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20 hours ago, JV Puleo said:

Was there a thrust washer on the inside? And yes, these problems can be real mind-benders. I have a love/hate relationship with this kind of problem. On the one hand I think they are a PIA - on the other hand I am drawn to them and derive satisfaction from solving them.

 

There are no thrust washers to the insides of the flywheels to the big end of the conrod. There is only one thrust washer on the main shafts and that is to the rear flywheel, between the flywheel and the bronze bush on the rear engine casing. I agree with your sentiments completely 'PIA', but when overcome the problems successfully you do get a great sense of achievement.

 

20 hours ago, JV Puleo said:

Or... use flat head shoulder screws.

 

As you say these maybe the better option as the flange they fit into is only just over 5mm thick (0.203"). It would be best if I could find some with a short shoulder that would fit snugly into the 'flange' and a . I could then thread the flywheel to accept the screws. This was what I was thinking of:

 

s-l300a.jpg.522ceb3cde947a03d3680f536b8f6ac1.jpg

 

But were you thinking of this type?

 

Flat-Head-Hex-Socket-Shoulder-Screws.jpg.ded21363d8214ab3d7a1ba694e68508d.jpg

 

The only problem that I can foresee is that the existing hole in the cast iron flywheel is 7mm (0.276"). If I use 7mm as the tapping drill size the nearest thread size is M8 x 1. I may get away with M8 x 1.25, the tapping drill for this is 6.8mm.

 

Another possible problem, that I will have to check out, is the diameter of the heads and the diameter of the shoulders too large to fit OK into the flange?

 

20 hours ago, JV Puleo said:

Maybe we are overthinking this... how about regular grade 8 flat head socket cap screws with a fine thread? 

 

Yes, we are overthinking this problem! I should have read all your posts before I started replying to them!

 

If I can find something like this with a bit of a shoulder, more of a bolt rather than a screw, it should work OK.

 

producttech-din7991.jpg.5fabd2ffd4927f8366b054e0094a0aad.jpg

 

Thanks Joe, for all your help and thoughts.

 

I've heard nothing from Australia about the Humberette with the Harley conrods. I may try a 'general post' on this site to see if I can find someone who knows some details on the sizes of conrods they used.

 

1892.thumb.jpg.76445557b11281cbde7784af484b74f1.jpg

 

This is the front casing. There was no thrust washer on this side of the flywheel. Just the flange with the rivet heads? My measuring should find out if there is space for one and maybe, it had been left out when the engine was assembled?

 

You may not hear from me for a few days as I have an article, on the Poppy Flyers, to finish for a cycling mag. I have said to myself "I must finish it before I go out and 'play' in the garage!"

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I think we have a solution.

The hole size for a 5/16-18 screw, in cast iron, is .277. You wouldn't even have to ream the holes - just tap them. The only machining operation would be to enlarge the holes and clean up the countersink on the head end. I think it is a 60 degree taper and should be the same as metric.  See if they are available in the UK. If not, I can get them from McMaster Carr and send you a box along with a tap. It should be a perfect fix. McMaster won't ship out of the country - some years ago they were fined for selling nuts and bolts to a would-be terrorist. The fact that there was no way to find out if the party was on that list was apparently immaterial. Apparently, the list is a secret. Another example of government stupidity.

 

 

Edited by JV Puleo (see edit history)
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Hello Mike,  It appears that you have a good and solid modern engineered update for your stock riveted flywheel connection.  You should, by all accounts, end up with a solid connection that should not flex or move.  Have you contacted anyone, in the Harley Davidson world, to get some information on the V twin connecting rods used.  You should be able to get the dimensions you require to see if a retrofit is possible and if the eye to eye measurement will work depending upon your chosen CR and pistons available, (even if you have to go with custom pistons).  The Indian enthusiasts might also be a second good source for information on pistons and rods.  The fork and blade style rods may allow you to have a bit more room for the bolt up connection that is currently an issue for you.

Al

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I did some more figures last night and now see that 8mm may be just as good as 5/16. Just figure the hole for a coarse thread. You don't want to use fine threads in cast iron. When the SAE threads were agreed on the coarse pitches were intended for castings and the fine threads for strength in steel. Coarse threads are better in soft materials (which iron qualifies for even fhtough it really is hard). I'm guessing that when you finally do this you'll be saying "why did it take so long to figure this out"?

 

Good quality cast iron threads very easily so you can safely use a slightly smaller hole than is often recommended for ferrous metals. I'd probably use the fine thread hole size with a coarse thread tap.

 

By way of explanation, since you've see me using fine threads in aluminum, this is only on parts that are not intended to be taken apart.

Edited by JV Puleo (see edit history)
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Thanks for your posts and offers of help and assistance, I do appreciate it. I have spent this week trying to finish an article on our quest for the human power vehicle land speed record, with the 'Poppy Flyer' machines, that we designed and built. So far, I have written four episodes or chapters, but writing the fifth, and hopefully the last, is proving bloody hard. Trying to remember back to the early 1980's, and writing it up, seems even harder with attempting making it sound interesting. At present I have got to our record attempt at the American Air Base at Greenham Common, in the UK and then have to describe our trip to the Indianapolis 500 Speedway to compete there. When I get back in the workshop I'll check how much room I have for the screw heads. I'm trying to be strict with myself to finish the article before going back to the Humberette. Sometimes, like now, I wonder why I volunteered?

 

In the meantime here are some photos of the inline thermostat I bought to fit in the top radiator hose.

 

1834.thumb.jpg.e1c3d43032b31fe48f7a7520fe47f9ab.jpg

 

The large diameter that seals the rubber hose is 44mm.

 

1835.thumb.jpg.256c8f9a1d8b4a78635641e572acf760.jpg

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Joe, I have found these in the UK. Do you think they would be suitable? The company is ACCU

 

SSK-A2_md.jpg.77e6b3d25da010d6874abcc4ecc41ab4.jpg

https://www.accu.co.uk/1536-imperial-socket-countersunk-screws#elasticsearch_id_feature_710702=710702_1&id_elasticsearch_category=1536&orderby=ranking&orderway=asc

 

Hopefully, the link will work for you. I will need to buy a countersink drill, but before that I will need to find out the angle of the countersink from the ACCU. Is A2 stainless material OK to use for this application. My knowledge of materials is very limited. Thanking you again for your help and advice.

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I'd prefer grade 8 to stainless but I doubt the stress on that flywheel requires them. Remember, the original rivets were very soft. Yes. I think those will work. What length are your looking for?

Spinny... since they just go through the flange and thread into the flywheel I suspect they have to be fully threaded. They probably aren't going to be  1" long.

Edited by JV Puleo (see edit history)
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I thought I knew a fair bit about nuts and bolts, how wrong I was! I have been trying to find the head size of a 5/16 UNC countersunk socket head cap screw. Eventually, I found a BS2470 table of measurement's for UNC screws with all the details but no drawing, showing me what measurement was what. After some searching I have found a drawing. I now have all the information I need. The thing that concerned me was that the large diameter of the countersunk head would stick out slightly at the side of the flange outside diameter. It seems there is just enough room. Below is a photo of the conrod side of the main shaft flange.

 

1913.thumb.jpg.3605c609225a443dead3f4da4ad6a72e.jpg

 

Outside diameter of the flange 55mm (2.160")

PCD of the 6 x 7mm holes 40mm (1.575")

Maximum diameter of the head of the 5/16" UNC countersunk socket head screw 11.1mm (0.437")

Thickness of the main shaft flange 5mm (0.197")

Thickness of the cast iron flywheel where the screws will be threaded into 10mm (0.394")

Therefore, maximum outside diameter of heads of screws is PCD + 1 screw head 40mm + 11.1mm = 51.1mm (2.012")

Therefore amount of metal at the outside of the flange is (55mm - 51.1mm)/2 = 1.55mm (0.061") Which should be enough?

The length of the 5/16" UNC countersunk socket head cap screw need to be 5mm + 10mm = 15mm (0.591")

1/2" long screws are 12.7mm long therefore length of thread in flywheel will be  12.7mm - 5mm = 7.7mm (0.303")

 

I will have to be very careful drilling the holes and the countersink to match the screws. I think the angle is 82 degrees, am I correct? I had better buy a new countersink as the ones I have are very old and I don't know the angle of them. I do have 5/16 UNC taps.

 

As an aside, the thread on the main shaft is strange. It appears to be M19 x 1mm pitch. I have never come across M19 before. When I first measured it I thought it would have been 3/4 UNF but that should be 12 TPI it's more like 18 TPI.

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3/4-18 is a real size, just not commonly seen. None of the "standards" we use today were agreed upon in 1914 and there were many threads in use that we don't see much today. During WWI the US Army had huge logistical problems associated with fixing the large number of motorized vehicles it acquired. Part of the solution was to create mobile field machine shops. The British had the same problem and, more or less solved it by assigning each service a specific maker. Vauxhall supplied the Royal Flying Corp, Buick supplied the British Red Cross, Armored Cars were always either Rolls Royce or Lanchester etc. After the war the US informed the motor industry that they would have to agree on standard fasteners before the government would buy their products. That is when the SAE standardized their threads although none of the sizes were "new". Usually they were just the most popular. So, where you had 1/2-12, 1/2-13 & 1/2-14 you now had just 1/2-13. Some makers, like Cadillac, made many of their own fasteners - early Cadillacs use a 12 pitch thread everywhere they can regardless of diameter. This facilitated easy threading and kept them from having to alter the set up on their change-gear lathes for different pitches.

 

You can always turn the head down a little. I've done that. I've also ground them using a valve grinder to reduce diameter and thickness while preserving a nice sharp finish.

Edit: This is the reason threading is such an important skill when working on pre-1920 cars. Many of the fasteners and the parts were not made using currently, readily available thread sizes.

 

Yes. The countersink angle is 82 degrees.

Edited by JV Puleo (see edit history)
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Very interesting information re early thread details.

Cadillacs use a 12 pitch thread everywhere they can regardless of diameter

That is presumably why BS Bicycle threads were all 20 TPI. Most of my early motorcycles have lots of these threads.

 

Thanks for the information on the countersink angle.

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Yet more engine problems to overcome!

 

1916.thumb.jpg.bbc17e25a74e85b5cf2d8fd87aee40db.jpg

 

Because I was a little worried about the surface where the main shaft flange sits into, on the cast iron flywheel, I coated the flange face of the main shaft flange with engineers blue and rotated the flange in the hole. As you can see in the photo above virtually no blue transferred to the casting.

 

1917.thumb.jpg.ad5d8bf3acd81c0f9ff63eb64d8144fb.jpg

 

On rubbing my finger from the outside of the recessed part to the hole in the centre it was very uneven, with a lot of wear between the bolt holes. The centre around the hole in the middle was also raised a bit. Now to think how to machine this surface flat, when the flywheel is loo large a diameter to fit the chuck on my big lathe? With my newly gained knowledge from Joe's 1911 Michell posts, I sat down and drew out a jig that I hope will work to mount the flywheel, to enable me to machine the face flat. A lot of work just to take off a few thou off the flywheel.

 

1915.thumb.jpg.a5adf26ce84006e21614652739e89932.jpg

 

I am hoping this will do the trick. I can then bolt the flywheel onto the jig and machine the face flat again taking off just the minimum amount of metal.

 

1918.thumb.jpg.0c51686bc856630b28e24b503b218b87.jpg

 

The only relatively large diameter bar I have is rusty steel, saved from being sent for scrap. I got the bar as near as I could to running straight and turned it clean, so I could put that end in the lathe chuck.

 

1919.thumb.jpg.7160b811465c282b895ec387de76f352.jpg

 

Then started machining the other end which now was running only a few thou out. It would be nice to be able to leave this in the chuck until I have machined the flywheel, but that will be impossible, because I will have to drill the clearance holes for the socket head cap screws that will screw into the 5/16 UNC threaded holes that I will tap into the flywheel. I can have a think about this while I clean up the rusted surface of this bar.

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I think I'd try putting a little grinding paste between the two faces and turning the shaft against the flywheel under light pressure. The Idea would be to lap the tow surfaces into each other while removing the smallest amount of metal. It would have to be perfectly straight, maybe with the flywheel on  the table of a drill press and the quill gently pressing on the shaft. You'd have to make something to use as a handle to turn the shaft so as not to mark it up. I'd be tempted to use a lathe dog with a piece of brass or copper between the tightening bolt and the shaft. It would be slow going but guaranteed to give a true surface and you Can't accidentally remove too much material.

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Oops. I think I'm looking at this backwards. It looks like the heads of the attaching bolts are on the flat side...so in order to lap the faces you'd have to turn the shaft from that side. That's a little more complicated. I'd think in terms of a flange with a pin or pins to pick up the holes (but not go through) with some sort of extension to turn from. I'll draw it and post a picture. It's hard to describe.

 

jp

 

This is what I have in mind... You could turn it by hand with a brace. With really fussy fitting like this I prefer to use the old and slow methods, especially with original parts.. If they take more time they also preclude making a bad error. The pins don't have to fit the holes perfectly. They are only there to drive the flange under light pressure.

 

360741908_newwaterpump-4.jpg.b3ea87aa8c34f107980f622e6205e11e.jpg

Edited by JV Puleo (see edit history)
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I thought about this when I was using the engineers blue to see how flat the surface was in the flywheel. I tried rotating the shaft in the flywheel using the main shaft. I hadn't thought of making a tool to lap it in. The only worry I had was that the grinding paste may seep down the shaft and wear down the nice fit of the shaft, where it goes through the centre of the flywheel. If I put a little grease on the shaft it should help stop the grinding past going down the hole.

 

I will make a tool this morning and see how I get on. Many thanks for your suggestion and drawing.

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Just be judicious as to how much grinding paste you put on the surface. It will break down in any case so I doubt it will have any measurable effect on the center. You are just lapping a big flat valve. The grey color you'll get where the past cuts will tell you how well you are doing. I use 120 grit on the lapping plate.

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Making the tool that Joe suggested was an easy task. Not too much precision needed here. I cut section out of some 3/8" plate.

 

1920.thumb.jpg.a74e046e34a953074c4008c927eafcfc.jpg

 

The plate after drilling, tapping and before cleaning up on the linisher. I threaded the two outer holes at M6 x1 and the centre hole at M8 x 1.25.

 

1922.thumb.jpg.7e796b47ab48912e7928c6fb9974a92a.jpg

 

The into the two outer holes were screwed M6 set screws. The centre hole had a M8 set screw fitted along with a lock nut.

 

1921.thumb.jpg.3396941e513e7161b665979630e11363.jpg

 

I chose the length of the outer screws so that they would stick 4mm out into the holes in the main shaft flange. The only grinding paste I had, was valve grinding paste, so I used the FINE paste. Perhaps I should have started off with the coarse grit?

 

1924.thumb.jpg.41c9793e5ae44786a1144ea6d36ecba9.jpg

 

After using a 14mm socket and a socket brace, for half a hour or so, I cleaned the faces and used some engineers blue to see how the lapping in was going. Well, at least there is a bit more blue on the flywheel side this time.

 

1923.thumb.jpg.dc90f6c3598247cce8aadd4db1f9efc9.jpg

 

 As I had a 1/4" - 14mm drive socket I thought an easier method maybe to use my reversible battery drill on a low speed, switching it from clockwise to anticlockwise every 5 rotations. As well as putting some 'dab's' of grinding paste on the flywheel, I filled the old rivet holes in the flange with paste, and every 15-turns in both directions I moved the tool, I had made, around to the next pair of holes. That pushed a bit more grinding paste in between the two surfaces and alleviated having to push the shaft right out each time I wanted to put some more grinding paste in.

 

1925.thumb.jpg.d3c3f7593885c2761f49cc455fdfa43a.jpg

 

I think I am getting somewhere? The grease in between the shaft and the flywheel worked OK and kept most of the grinding paste away from this area.  By now it was lunchtime and I had had enough for the day, time for some food and an afternoon nap! I'll start again fresh tomorrow morning.

Edited by Mike Macartney
removed empty space at the bottom (see edit history)
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On 6/28/2019 at 11:27 AM, Mike Macartney said:

That is presumably why BS Bicycle threads were all 20 TPI. Most of my early motorcycles have lots of these threads.

 

 

You've given me an idea here. I think I'm going to use 20tpi for all the fittings that, under normal circumstances, should never have to come apart. The shallow thread allows greater flexibility regarding thickness and the drawback, that they are easily damaged, is relatively unimportant if the parts stay assembled. I have to make a 1-1/4 x 20 and 1-1/8 x 20 threading gages but I think I can avoid having to buy expensive taps.

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After yesterday morning, spending about 3-hours lapping the main shaft to the cast iron flywheel, I cleaned up the surfaces to see how the lapping was working.

 

1926.thumb.jpg.c40d03767f5fbfdc345d52275a214d2c.jpg

 

It looks as if I am getting somewhere.

 

1929.thumb.jpg.a344d1304c2308338cd6c6603f0c52e5.jpg

 

More fine grinding paste added and some grease around the shaft diameter to help stop the grinding paste getting onto the main shaft.

 

1930.thumb.jpg.770a5a9b789c1c692dc692981d3e6072.jpg

 

I'm getting there! Just a few bright spots left, mainly around the edge.

 

1933.thumb.jpg.cd809519f8d45ac9a119f77e4a1d9dbd.jpg

 

A couple more times I cleaned up and added more grinding paste. I now think that is good enough. Now for a good clean up in the degreasing tank and a clean up with cleaning thinners should do the trick. Although it has taken me another mornings work, I am sure lapping the surfaces, was quicker than making the jig for cleaning the surface up in the lathe. Thank you Joe for the suggestion.

 

I have bought this permanent thread lock to fix the screws in place. I hope hot oil doesn't destroy it - I better - RTFI (Read The 'Flipping' Instructions), or a word to that effect!

 

1934.thumb.jpg.671f13bd9b4e3f01bf9531db1d1f5845.jpg

 

The flat countersunk socket screws arrived just now. But I am still waiting for the countersink drills to arrive.

 

 

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That looks really good Mike. Even though it is time consuming,  I like lapping because it is so slow. It is almost impossible to remove too much metal, something that is extremely easy to do in the lathe or with any machine tool.

 

High strength Locktite is good up to about 400 degrees F...about 200C. I doubt oil ever gets that hot. If it did, the engine would be in serious trouble. I'd look up a torque table. That should give you the optimum torque for the bolts based on thread and diameter. The thread locker is just an extra safety feature. If they are tightened to the optimum torque they shouldn't come loose. The tough part may be finding a hex wrench adapter that works with the torque wrench.

Edited by JV Puleo (see edit history)
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Thanks Joe. I have lapped, or ground valves in before, but never lapped in anything as large as this before. I will be interested to see if it has improved the runout on the flywheel, it should do. I will check the runout, after bolting the main shaft to the flywheel.

.

I was considering taking a bit of weight off the flywheels.

 

1940.thumb.jpg.6cb12ebcfa0755cb4ca6b73fe3ce7d80.jpg

 

It will take just over an 1/8" off each side if I go down to where I have marked on the photo above. Did you think that would be worth doing?

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Tapping the flywheel for the 5/16 UNC countersunk socket head screws to replace the original loose rivets in the flywheel.

 

1936.thumb.jpg.3a3aabee2a38850d864ea2c2cd4aa974.jpg

 

The original holes in the cast iron flywheel were 7mm diameter so I put a 7mm drill in the chuck of the drill press to locate the hole in the flywheel that I am going to tap.

 

1935.thumb.jpg.de80781e9d9fbba8e992d0e1ceaf6c96.jpg

 

Although the flywheel is very heavy I thought it best to use a clamp to hold it to the bed of the drill/milling machine. (sorry about the pair of my old pants hanging out of my rag box!)

 

1937.thumb.jpg.b37dcabe09ecc497a52e3ee5ecb9351d.jpg

 

I then replaced the 7mm drill with the 5/16" taper tap. Wound the tap down to the flywheel and rotated it by hand and then with the key as a lever to start cutting the thread.

 

1938.thumb.jpg.a8adb8ea055a24e606aff9c61fac85ad.jpg

 

Undid the chuck, leaving the tap in the hole and tapped the hole using the tap wrench. As I tapped the holes I checked the screws would fit.

 

1939.thumb.jpg.4abab31f8604496fe4284cbf7957235e.jpg

 

I then gave the flywheel a good wash in the parts washer to make sure no grinding past, from the lapping process,

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I'd say that is exactly right. Clamping the part down is essential regardless of how heavy it is. If the tap has a center hole in the back end you can put something pointy in the chuck to press gently against it, moving the chuck down a tiny bit each time you move the tap but starting the tap straight is the most important part of the job.

 

The recommended torque for 5/16 coarse threads / grade 8 bolt / is 18 ft./lbs. For stainless bolts, it is 11 ft./lbs. I don't know what that is in metric but there must be a cart on the internet somewhere.

Edited by JV Puleo (see edit history)
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I doubt it needs much lightening...it isn't all that heavy to begin with. That said, in period fly wheels were almost always too heavy. It was a holdover from steam engineering and it took a long time to realize that the extremely heavy fly wheels weren't needed. If you have a cone clutch in the flywheel it may not be possible to remove much material. That's the problem I have with my Mitchell. The clutch probably runs on a bushing...that should be checked and made as perfect as possible. I think that about 90% of the "trouble" people have with cone clutches is that they need to run very true or they'll grab. Very few "restorers" pay much attention to mechanical details like that until things stop working altogether hence, the poor reputation cone clutches have. Usually, they are just worn and nothing has been done about it. RR Silver Ghosts had cone clutches and I've never seen one that was a problem - but they were extremely well made and all the components were as balanced as they could get them.

 

What is very important is that those iron discs the rods are sandwiched between should run true after the "crankshaft ends" (for lack of a better term) are bolted up. I'd put them back in the lathe and check for trueness. They will almost certainly be out a little - then face them off so that are perpendicular to the crank and turn the diameter until it is round and concentric with the crankshaft. It would probably be good to make sure they are the same diameter when finished so you'll have to match the smaller of the two. If you haven't turned cast iron before, it is quite different from steel. You engage the back gears to run the machine very slow, use a sharp cutting tool and no lubricant. The graphite in the iron provides all the lubrication you'd need. I think for this HSS is much better than carbide. I like working with cast iron but it isn't everyone's cup of tea.

 

In 1914 the value of dynamic balancing was understood but the machines that we have today for that had not been invented. Their solution (when a solution was attempted) was to machine all the surfaces identically. This is how things like cranks and rods were made for expensive cars. Cheap cars used rough forgings and didn't attempt to balance them but relied on de-tuning the engine to keep the RPMs down.

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8 hours ago, JV Puleo said:

The recommended torque for 5/16 coarse threads / grade 8 bolt / is 18 ft./lbs. For stainless bolts, it is 11 ft./lbs. I don't know what that is in metric but there must be a cart on the internet somewhere.

Is that when they are into cast iron? Surely the iron strength will govern, not the bolt strength?

 

How many threads are in each hole? i.e. is it a full nut's worth?

Edited by Spinneyhill (see edit history)
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Hi, Mike.

From this distance it appears that the area you suggested lightening is actually the counterweight. The arrow may be deceiving me, though. I would leave the weight as it is. The little engine might appreciate some flywheel, when it meets a hill.

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2 hours ago, Spinneyhill said:

Is that when they are into cast iron? Surely the iron strength will govern, not the bolt strength?

 

How many threads are in each hole? i.e. is it a full nut's worth?

 

You raise a good question. If I remember Mike's figures, the threaded length is within a few thousandths of the width of a nut. The SAE coarse threads were intended for use in cast iron but I have the 1927 SAE handbook at home so I'll see if it says anything about that. I won't have torque specs but it may address the tightness issue.

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A post in Practical Machinist says


"in general a course [coarse!] threaded screw grade 2 should be at least 1 dia threaded depth in cast iron. a grade 5 screw should be 1.5 dia depth and a grade 8 screw should be 2 dia threaded depth into cast iron for screw strength to match cast iron. "

Edited by Spinneyhill (see edit history)
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