# Built up crankshafts



## Brian Rupnow (Oct 19, 2010)

School me, my brothers. I made a mistake while machining the crankshaft for the small Hit and Miss engine I am building, rendering the finished product unusable. I am now leaning towards a built up crankshaft. I plan on drilling, reaming, and cross pinning all the joints, before cutting out the main shaft. All of my reamers are for sliding fits, not interferance fits. I don't trust my boring skills enough to bore interferance fits, and I'm not sure that is necessary anyways. My gut feeling is to silver solder everything before cutting the main shaft away. I have read of some people having success using only loctite to hold everything together, but I'm not sure I trust doing that. I have had a silver solderd joint on a crankshaft which was not pinned fail on one of my early steam engine builds.---Advice please----Brian.


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## Blogwitch (Oct 19, 2010)

Brian,

For the crank you are building there is no need for super strength.

If I was doing it, I would build it up by pinning, and for your pins, use normal soft nails. They swell nicely into close fitting holes and you can always use a belt and braces technique and put a but of loctite on them before forming.

After rivetting up, they can be filed flush until they disappear, then cut the main crank shaft away.

To get an interferance fit for your main shafts on assembly, you can always knurl them where they fit thru the side cheek plates before drilling and rivetting.


Bogs


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## kcmillin (Oct 19, 2010)

Brian, thus far all of my crankshafts have been built up. I have found that if the interference fit is too tight you may risk bending the crank when pressing it together. I go for an even fit with the same size reamer as the shaft that goes in. Sometimes I solder it then pin it, other times I have locktited then pinned. I also put locktite in the pin hole. If you have square crank webs then the crank can be held nicely in the vice when pinning. 

I should note that these cranks are 3/16" and 1/4" diameter, so quite small, but I have built a 3/8" shaft crank using the pin method.

Kel

Ah, Bogs beat me to it, but I will post anyway :big:


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## Jasonb (Oct 19, 2010)

I've just done one for the IHC Famous and silversolderd it then pinned with 1/16 pins before shaping the webs and cutting the middle out. I have also used this method on another Hit & miss and the Minnie in my avitar with no problems.

The shaft is 7/16" Bright MS, the holes were drilled 1/4, 3/8 and then a slot drill used to open them up to 7/16" which left just enough for the solder to flow.

Jason


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## jpeter (Oct 19, 2010)

Silver soldered a number of them. All held. Leave room for solder to wick in. Its hard to get parts aligned because of the sloppy fits need to allow room for solder to wick. Jig it up. Use lots of flux. Silver solder will only run where flux has been brushed on. I've sometimes drilled flux relief only part way through to help with alignment. Don't have an oversized reamer, try this. Take a piece of correct sized drill rod, punch it with a cold chisel a couple of times to cut a raised tooth so to speak. Heat treat it and use it to ream the reamed hole oversize a couple of thou. Works well for bearing clearance too. A long piece will linebore bearings. Try it.


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## Brian Rupnow (Oct 19, 2010)

Thanks fellows, for all the input. I will probably silver solder and pin it as well before cutting out the main shaft. Since I have the silver solder and paste anyways, it isn't an added expense.---Brian


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## kuhncw (Oct 19, 2010)

I have a built up crank in my 1/4 scale Galloway that has given no problems over three years. I used Loctite 609 (green) and tapered steel pins to assemble the crank. I built an alignment fixture for assembly and made the joints a slip fit. This is a hit and miss engine with 1.312 inch bore, 2.53 inch stroke, and 7.65 inch dia flywheels. I suspect the crank does see some load when the engine fires as the flywheels are fairly heavy.

Silver solder should work fine as well. 

Regards,

Chuck Kuhn


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## Brian Rupnow (Oct 19, 2010)

I am building a built up crankshaft over here http://www.homemodelenginemachinist.com/index.php?topic=10831.msg121730;topicseen#new if anybody wants to watch.


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## Captain Jerry (Oct 19, 2010)

Just a note on built up crankshafts. One of the longest engine design life cycle (pre WWII into the 1970's) belongs to the 
Gravely built, one cylinder 4 stroke engine used on the Gravely Model L, two wheel tractor. Early models were rated at 6.6hp and later models were rated at 7.6 HP. *This engine used a built up crankshaft.* The crank webs (called flywheels in gravely manuals) looked like 10 lb barbell weights and were pressed onto the crankshaft stubs at the factory. The crank pin was a field replaceable/service item and the connecting rod was a one piece item. The pin could be pressed out and replaced with a manual arbor press. To remove and service the con rod bushing, the webs were separated at the crank pin and the rod removed. The crank pin was hollow and a through bolt (called a spreader bolt in the manuals) had a shallow cone shaped shoulder and there was a beveled washer under the nut which fitted recesses in the webs. Reassembly required pressing the assembly together, eyeballing the alignment of the oil ports in the web with the oil hole in the crank pin and eyeballing the alignment of the crank webs. The bolt was inserted through the crank pin and torqued to about 45 ft/lbs. The assembly was then supported by the outer ends of the stub shafts between centers and trued to within .005" TIR by whacking on the flywheels (webs). No cross pining, no locktite, no heat/freeze. Just a manual arbor press. And these things seemed to run forever. Maybe pins, locktite, and silver solder are overkill?

Jerry


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## jpeter (Oct 21, 2010)

A friend tried pressing a few small cranks together without the aid of silver solder. They all failed. appears to me throws made from CRS in cranks small as we make just don't have enough beef to hold the press . Maybe heat treated tool steel could hold up but I doubt it. It'd be fun to try one. I've observed built up cranks in say weed wacker engines have really thick throws generally laminated from several thin plates and the metal for the throws is really hard stuff. Motorcycle engines often have pressed together cranks too and like before, the throws are really thick. I vote for silversolder.

Easy as it seems to build up and silver solder a crank, the few I've built have been difficult to keep straight. when cutting out the center section built in tension has warped the thing. Some bending has straightened them out so long as the shafts aren't made of drill rod. 

Anyway you do it, crankshafts are a chore.


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## Troutsqueezer (Oct 21, 2010)

I just built a 5/16 crankshaft for my upshur. I was sure to bevel the outsides of the cheeks to give the solder a trough. I made sure to flux the hole and shaft. I considered reaming at first but didn't possess a 5/16 reamer so I test-drilled a hole in some brass and the drill rod (shaft) fit nicely. As drill bits tend to do, this one drilled the hole just slightly larger than 5/16ths so it worked out well having the space for the silver solder to get into the fitting. I had quite a bit of cleanup on the bottom side of the joint so I know the joint was well heated. 

I didn't bother to pin it. I think it would be overkill, IMHO. 

http://www.homemodelenginemachinist.com/index.php?topic=10555.15


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## MachineTom (Oct 21, 2010)

With the price of reamers so cheap I am shocked you guys won't buy what you need. For $15 from MSC not the cheapest source, you can get say for a .375 pin a .373, .374,.3745 are available. At .0005 undersize a heat shrink fit would be easy to do. A shrink fit is 7 times stronger than a press fit (so says MHB). A good way to pin a cheek to a journal would be a tapered pin, you need a matching reamer, this is how the many machine tools builders handled those type connections.


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## Troutsqueezer (Oct 21, 2010)

For me, it's actually quite a bit more than $15. The reason being, if I only order a single reamer, I'll pay shipping. To make the shipping cost effective, I need to purchase more tools per order and that's when the cost really starts going up. If it was a matter of running down to the local store (there isn't any around here) I wouldn't hesitate to buy them as I need them. 

I figure if I really really need one and can't use a boring tool, I'll just make one but that need hasn't arrived yet.


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## jpeter (Oct 22, 2010)

Its not about fit its about the amount of metal outside the pin. The crank throw generally is not big enough around to provide enough metal between the outside of the pin and outside of the throw to keep the pin hole from stretching during the press/shrink. Pins can be pressed into large disks but not into disks only a pin diameter larger than the stroke.


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## tel (Oct 22, 2010)

> Pins can be pressed into large disks but not into disks only a pin diameter larger than the stroke



Yes they can (and are all the time) it's just that the amount of interference becomes more critical - too little and it won't hold, too much and it stretches the hole.


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