John Builds Kerzel Hit & Miss

[Brian Rupnow]

Based on experience, I do not recommend silver soldering or brazing the crankshaft. Too much heat distortion. On a built up steel crankshaft, I put a bit of mig weld on both ends of the crank throws to hold them together, then drill and ream them both at the same time so you absolutely know that the holes are aligned. use an "on size" reamer. Cold rolled steel shafting is actually about 0.0005" undersize (drill rod is not). I do not recommend using drill rod. Cut two pieces of cold rolled crankshaft material. One piece is cut to the total length of the crankshaft, and one is cut to the overall dimension outside to outside of the crankthrows. Assemble with loctite #638. Let it set for 24 hours. Then cross-drill and ream .094" in four places and use 3/32" steel cold rolled steel for cross pins. Let set for 24 hours. Next step is very very important---Cut out the bit of shaft between the crank throws. You can hacksaw, band-saw or mill it away. BE SURE TO CUT THE CORRECT SHAFT.

 

[simister]

OK, what you say makes good sense. Do you think I could use Bright Mild Steel for the shafts instead of Cold Rolled Steel?

 

[Brian Rupnow]

I'm not sure where you are in the world, but Bright Mild steel is (I think} a United Kingdom designation. I don't know what it's properties are, but I kind of think it is similar to out 01 steel which is drill rod.

 

[minh-thanh]

Minh-thanh,

What method did you use to join the pieces together. I have oxy gear but I am concerned about distorting the shaft.

simister !

With several times I welded the pieces together, I couldn't make an almost straight crankshaft
So, I solve the problem:
when I need a 10mm diameter crankshaft, I will make an 11 mm shaft ( I just need exact tolerances around the crank - the rest of the shaft I normally make the diameter smaller - which makes it easier to bring the crank into the shaft )
, then assemble it all together and fix them with pins, then I solder the silver.
Then I mounted the crankshaft on the lathe and turned out on both sides to 10 mm
then cut the bit of shaft between the crank

 

[simister]

Ok, thanks Brian. I have decided to go with the multiple piece crankshaft.

 

[simister]

minh-thanh, that sounds like a good idea. However, I am going to go with the multiple piece crankshaft and see how that goes. I have already ordered the cold rolled steel. thanks John

 

[simister]

I have finished the main bearings in sintered bronze and the cylinder liner. All I have to do now is lap the cylinder to size. The Acro Laps arrived today so I can get started on that. The main bearings need to be machined to a fine finish but I will do that when I have finished the crankshaft and ready to assemble.

The cylinder liner is a tight fit but I can slide it in and out without much effort.

 

[johwen]

I am about to start the crankshaft. I notice that some people have made it as per the plans from 1 piece and others made it from multiple pieces. I notice that Brian made it from 1 piece and also made it up from steel rod. Any suggestions on the best method for this part?

John

Johwen here I have made many shafts using both methods Machining from the solid one piece is tricky as distortion is usually the problem and can be slow in machining compared with a built up shaft. For single cylinder long stroke engines I use the built up shaft method. Machine the two crank plates locktite together drill and ream the crank pin and main shaft holes, separate the plates and locate them on the full length main shaft and place the crank pin cut to correct over all length. You need a good flat surface to avoid any slight twist. When you are happy with this separate and clean all joints and use locktite 620 High strength. Leave set for a couple of hours and the drill through each joint and ream with a tapered reamer to a set depth and press in a tapered pin with some locktite and when set machine of the extra length leave for twenty four hours and then mill, saw and file the piece of main shat away and you now have a strait and true crankshaft. I've never had one fail nor any alignment problems using this method and is very time saving. On larger engines I have lightened the big end by drilling it and you can use a harder material. You can also do all your drilling before assembly of the big end an then case harden sme then locktite pin and assemble your big end. Hope this gives you some ideas that have worked for me John.

 

[L98fiero]

Cold rolled steel shafting is actually about 0.0005" undersize (drill rod is not).

Based on 40 years of machining, cold rolled steel may be .0005 undersize or not but it also may not be round either, depending on how the draw dies wore. Take the piece you want to use and indicate it as you roll it in a vee block, you might be surprised how far out of round they are. Ryerson in Canada lists tolerances of -.002 up to 1.625 diameter and KV Steel in the UK says -.07mm to 18mm diameter. Experience has shown it's usually closer to -.0005 but I'd check before making an assumption on size.

According to the Atlas Steel (Australia) site "Bright steel bar is usually a carbon steel alloy which has had the surface condition improved by drawing, peeling or grinding over the hot rolled finish supplied by the steel mill." I think our "drill rod" is their "silver steel" or it used to be in the old Model Engineer magazines that got me into the hobby.

 

[awake]

I'm not sure where you are in the world, but Bright Mild steel is (I think} a United Kingdom designation. I don't know what it's properties are, but I kind of think it is similar to out 01 steel which is drill rod.

Hmm, I wouldn't think anything labeled "mild steel" is likely to be a high-carbon steel - ?? I'd guess "Bright Mild steel" is equivalent to our "cold rolled steel" - bright as opposed to the dark color of hot-rolled steel.

 

[simister]

John,

Thanks for your help. Yes, that is basically the method I will use to make the crankshaft. Brian, has also used a similar method. I was originally going to make it as per the Kerzel plans but I was concerned of trying to keep it true on the lathe. Making the crankshaft by not silver soldering thereby "no heat distortion" seems to be the way to go. John

 

[simister]

I have just finished machining the piston for a slide fit into the cylinder liner. I had originally intended to use Viton rings of which I have now received.

The piston is still in the lathe ready for the grooves to be cut for the Viton rings. However, the slide fit of the cylinder onto to piston seems to have compression without rings. If I slide the cylinder liner onto the piston - block the other end, then pull the cylinder liner off quickly it "pops" from the suction.

I am not sure if the compression that is there without any rings, is sufficient to not go ahead with the grooves for the Viton rings. I understand if the compression is good enough then I am better without any rings for this hit and miss engine.

My question is: should I still go ahead and cut the grooves for the Viton rings just in case it does not have sufficient compression or would that compromise the piston if it is grooved without any rings?

John

 

[xpylonracer]

With such a close fitting piston you may find with heat from running it expands and seizes in the bore, I would add the grooves whilst set up in the lathe.

xpylonracer

 

[Brian Rupnow]

If you have that good a fit, then don't use rings. This is a "try it and see" world. If it doesn't have enough compression to run, then add the groove and the ring later.

 

[simister]

OK, thanks for the advice. I will try first and see how it goes.

 

[L98fiero]

If you have that good a fit, then don't use rings. This is a "try it and see" world. If it doesn't have enough compression to run, then add the groove and the ring later.

I'm not speaking from experience, just asking, if you have a good fit anyway, would the grooves not act as a labyrinth seal and be of benefit even if there are no rings installed?

 

[Brian Rupnow]

The grooves, as originally shown on the drawings, are oil retention grooves. The engine using a piston like this must have an external oiler fitted to the cylinder which drips oil directly into the cylinder. The grooves in the piston pick this oil up, and distributes it along the i.d. of the cylinder. It helps the piston to hold compression and lubricates the piston and cylinder.

 

[simister]

With regards to the Wrist Pin for piston. What is meant by Teflon end caps?

John

 

[Sprocket]

Like this but in Teflon.
If I remember correctly, this one is 3/16" diameter. The end caps are "t" shaped, or I should say, have a small peg in the middle which goes into a hole in the wrist pin.

Doug

 

[simister]

OK, What type of supplier sells Teflon caps?