Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
I haven't used the Rcexl yet, but my impression was that the shielding is just shielding, not a ground. so just cutting it off short and splicing an appropriate wire would be all that is needed. The shielding would be to protect the radio receiver function in an RC airplane.
Their plug connectors are big and ugly anyway. (IMO)
Doug
 
I miss you guys too Mr. John V.
Doug, you are nearly correct but the braided shielding IS THE GROUND for the spark plug/CDI. I did this on an older unit but have not had time to do it on a newer Rcexl but am 99% sure we are good to go. You can cut both the braided shield and the spark plug wire off. On the old systems you could get to those items inside the box, not so on the newer units ( these are marked DC 6 to 12 volts). Cut the shielded cable about 1" from the box and cut the spark plug wire about 3" from the box. Solder on a #20-22 wire to got to engine ground and then any spark plug wire to the large Rcexl wire. Make sure to insulate the spark plug wire very well, I'd use at least 3 layers of heat shrink.
The braided shield was both a ground to the SS spark plug cap and EMI protection for the radio gear. Keep in mind that all of the Rcexl CDI's have a delay built into them for hand starting aircraft engines. I don't think it will be a problem but until I get a chance to look at a newer Rcexl unit on the scope and timing light I won't know exactly where the "retard timing" is and when it ends.
 
I miss you guys too Mr. John V.
Doug, you are nearly correct but the braided shielding IS THE GROUND for the spark plug/CDI. I did this on an older unit but have not had time to do it on a newer Rcexl but am 99% sure we are good to go. You can cut both the braided shield and the spark plug wire off. On the old systems you could get to those items inside the box, not so on the newer units ( these are marked DC 6 to 12 volts). Cut the shielded cable about 1" from the box and cut the spark plug wire about 3" from the box. Solder on a #20-22 wire to got to engine ground and then any spark plug wire to the large Rcexl wire. Make sure to insulate the spark plug wire very well, I'd use at least 3 layers of heat shrink.
The braided shield was both a ground to the SS spark plug cap and EMI protection for the radio gear. Keep in mind that all of the Rcexl CDI's have a delay built into them for hand starting aircraft engines. I don't think it will be a problem but until I get a chance to look at a newer Rcexl unit on the scope and timing light I won't know exactly where the "retard timing" is and when it ends.


Thank you for the very good advice and tips on how to shorten the spark plug leads
I found this version online for a very reasonable cost. Good to sort this out ahead of time... :rolleyes:

https://www.amazon.com/dp/B08MZG85Q...JY7OLC1J&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it
 
Thank you for the ignition help and compliments and likes. Glad to have the company for this build.

Cylinder Sleeves

I set up and started to center drill the various 10,000 holes in the top of the cylinder and had to stop when I noticed how close they would be to breaking through into the cylinder sleeve. Way too much time invested thus far to snap a tap or drill in one of these parts.

Time to make the sleeves. I recently discovered some really nice carbide inserts that are also pretty inexpensive. They are made by CDBPT tools and are black on top and gold on the sides. I'm thinking the black is some kind of Nitride coating? They last far longer than the other affordable ones so far. I used them on the bore of the leaded steel liners and am thrilled with the finish.
CDBPT Inserts.jpgsleeve finish.jpg


Boring 0.010" depth of cut at 400 RPM with 3.25" stick-out on a import boring bar. At first I was measuring 0.017" taper and was able to reduce it to 0.008" taper by blowing compressed air in and reversing the direction of feed by hand cranking out each time. Final pass of 0.003 and several "spring passes" really nailed the dimension of 1.000". I lapped them with 240 grit compound using a previously made lap and 120 thru 320 grit flex-hones.


Flexhone.jpg
Honing sleeves.jpgShop lap.jpg

Then the 2 sleeves were chucked up on the same lapping mandrel and the OD reduced to an easy press into the cylinders. Well it ended up being a somewhat sloppy fit because I think I egg shaped the cylinders when clamping the valve bodies and brazing them. It looks like about 0.002" of distortion. I could take a chance soldering them in, but I believe Loctite would be a better choice at this point.

Before I do either, I thought I would drill the coolant holes so I don't BOZO up the thin liners. The plans call for 0-80 screws and I can only drill and tap about 0.150" depth without breaking through the cooling jacket. Seemed like a good place to take a break.

20231028_165231.jpg
 
Last edited:
raveny: Do you plan on making your own gears? I am in the process of gathering parts & materials together for the Nash 25 and have not been able to find the part # called out. H 3240 & H3280 Boston Gear. Both do not come up on Boston Gear catalogue or Mc Master Carr. I plan on cutting my own gears but would have liked the dimension of the hub width not called out on the drawing page 45 .I plan on making mine pretty much the way you are going. Thanks for the inspiration!
Colin
 
raveny: Do you plan on making your own gears? I am in the process of gathering parts & materials together for the Nash 25 and have not been able to find the part # called out. H 3240 & H3280 Boston Gear. Both do not come up on Boston Gear catalogue or Mc Master Carr. I plan on cutting my own gears but would have liked the dimension of the hub width not called out on the drawing page 45 .I plan on making mine pretty much the way you are going. Thanks for the inspiration!
Colin

Hi Colin,

yes I will be making my own. I have a full set of shop made 48DP gear cutters so I will likely have to modify dimensions to suit. Miss google-search told me that the H3280 hub projection is 0.38" (likely 0.375"). They are listed at well over $100 :oops::oops::oops:

please keep me posted on your progress

H3280 gear.png
 
cylinder fabrication continued

I was very concerned about snapping a small tap or drill bit off in the cylinders and used copious amounts of slippery tap magic. All was going very well and I was deburring the holes and smoothing over the edges when the assembly slipped out of my hands and struck the concrete floor breaking the brazed joint of the valve block to water jacket.
ream valve cages.jpgdarn it.jpg

It must have been a cold joint but it really looked just like the other one from outside. No experience with this ribbon solder stuff....damn. Should have done some trials on parts that weren't that critical.

Several of the head stud tappings are tangent to the cylinder liner OD and these were used to reposition the valve block and re-braze it together. I removed the screws after most of the brazing was complete so I wouldn't loose the hole. The cylinder sleeve came out and needed to be cleaned up and re-Loctited and honed again. The tappings were re-tapped. The top sealing surface needed a third and fourth brazing with lower temperature silver so it was all flush again and no gaps present. The mounting pads also mshifted with the multiple re-heatings and needed to be repositioned using a lower heat solder.
rebrazed.jpgboth drrilled and flush.jpg
I am fairly confident this mishap is recovered now, and proceeded to drill out the other cylinder. I also drilled the flanges and bolted together the top and bottom crankcase.

Still have valve cages and the intake/exhaust passageways to machine before I call them complete. I am guessing these cylinders are the most challenging part of the build, but we'll see.
 
Still have valve cages and the intake/exhaust passageways to machine before I call them complete. I am guessing these cylinders are the most challenging part of the build, but we'll see.
I think you're right about the cylinders. They are pretty involved. The heads are a little less, but still a lot of processes. I found I needed a little extra space in the head recess at the corners over the valves.
Doug
 
Last edited:
I think you're right about the cylinders. They are pretty involved. The heads are a little less, but still a lot of processes. I found I needed a little extra space in the head recess at the corners over the valves.
Doug
Thank you for the "HEADs up" :p
would not have caught that myself unless I laid it out using CAD. I'm going to change the radius from 0.5 to 0.516 and the 1.219 to 1.235 so the valves don't hit.

Did you purchase the spark plugs, or make your own?
 
Raveney,
I bought my spark plugs from Roy Sholl when I bought the ignition system, but that was in 2021. They came from
You Fount it! - World Famous Rimfire Spark Plugs Distributed by Roland Morrison and those are still available, but fairly expensive. Steve Hucks makes a 10-40 plug miniaturesparkplugs.com .
I have made a plug before, and while do-able, it wasn't easy (for me) and these were even smaller, so I just bought them.
oldengineguy,
Silver brazing isn't all that difficult but takes prep and practice. I don't know what you are using for heat, but I had no luck when I tried propane. maybe very small parts were OK. I use oxy-acetylene, it sounds like raveney is using acetylene-air. Sufficient heat is a key part of having the braze work.
I got ribbon braze from Brownell's and it worked great. Also, there are different alloys of silver braze. I use a 56% silver, which is the lowest melting point
of those alloys I believe. www.brownells.com/tools-cleaning/general-gunsmith-tools/adhesives-solder/silvaloy-355-silver-solder/ . It says it is 56% silver, melts at 1145 degrees, flows at 1205 degrees. Something the mass of one of those valve blocks will take some time to heat.
Good luck with your build. I learned a lot from mine. (See "25 HP Nash" below)
Doug
 
Gear Calculations

my plan is to make the cam and crank gears using a set of 48 diametral pitch (DP) cutters that I already made. Over coffee I did some "maths" and could use a peer check please. All dimensions are inches.

Doug Kelley's plan uses Boston Gear set: 32DP, 80T with 2.5 PD and 32dP 40T with 1.25 PD
so the critical center to center dimension is (2.5+1.25)/2=1.875
this matches the critical dimensions called out for boring the crank and camshaft bearing centers

calculations
N/48 +2N/48 = 3.75 where N is number of teeth needed and the 3.75 is the sum of the pitch diameters (PD)
solving for N; N=60, so 60T for the crank gear and 120T for the cam gear
the outside diameter of the gear blanks are (N+2)/DP, so 1.292 for the crank and 2.542 for the cam
depth of cut should be 2.25/DP, or 0.047

do these numbers make sense? I was expecting to wind up having to alter the center to center dimensions of the gears because of some crazy odd number of teeth. Seems like that happened to me when I built the Panther Pup engine years ago...maybe I just screwed up back then?

thank you in advance for your replies
 
I did find 1214L for the sleeve, and a stick of 1-1/2" SCH 80 steel seamless pipe I could use. Revised the plan to accommodate this. Basically the outer water jacket will be brazed to a top and bottom spacer leaving a cooling passage as intended, but all carbon steel. This also eliminated the stepped boring operation inside the jacket as I would needed to make that cutter.
Enjoying your build, especially the brazing business. I just wanted to confirm, it looks like you had no adverse issues brazing the 12L14? The picture looks like a nice joint. I was under the impression the lead content was a problem in this regard. But maybe I misunderstood & it only pertains to welding?
 
I just wanted to confirm, it looks like you had no adverse issues brazing the 12L14

I did not attempt to braze the cylinder sleeve which is the only 1214L part. The sleeve is held in the cylinder jacket with green Loctite. All of the parts I brazed are regular carbon steel. 1018 CRS for the crankcases and A106 B seamless pipe for the cylinder jackets. The valve block was hot rolled A36. Nothing really planned about these choices, it's what I had in my scrap bin except for the 1018 cold rolled steel plate purchased for the crankcases.
 
thank you for the comments and questions

Before I could call the cylinders complete, I though I should make the bronze valve cages and drill the remaining holes and tappings. I chose to make the valve cages in one setup to maintain concentricity to the valve guide. I liked how the plan called out a depth of the chamfer, and this was accomplished with my 1" dial indicator and mighty magnet setup instead of advancing the compound. Nicer finish I believe.
20231111_145243.jpg20231111_141310.jpg20231111_165130.jpg
instead of pressing them into the valve block I made them a snug fit and relied on sister Loctite again. I bead-blasted the assemblies after cross-drilling the intake ports and plugging the visible passage way. The intake manifold connects to the bottom.

lastly the chamfer on the bottom of the cylinder sleeve was done and the head sealing surface wet sanded atop my granite surface block.

Crankcase Bearings

It was nice to do some simple mill and lathe work on aluminum for the bearing housings. This engine uses sealed ball bearings at each end and a bronze split bearing in the center. I built the parts per plan including the 4-40 flat head counter sunk screws that hold the bearing covers to the crankcase. I never realized that standard thread screws were 82 degree included angle and not 90 degree like metric ones. Luckily one of my hand held deburring tools is a zero flute 82 degree countersink. All the other bits are 60 and 90 degrees.

Started by drilling all the holes with the DRO and boring head in the mill vise. Then I indicated the rough cut square blanks on an expandable arbor and made them round.

20231112_100618.jpg20231112_103122.jpg

Had to hold them on the outer diameter and dial in again to bore the bearing recesses and finish to depth. The bearings are a snug fit inside the holders.


20231112_130947.jpg


Now it is finally time to bore the journals in the two crankcase halves. I had previously run a 1/8 ball end mill down each half to establish the centerline when I was milling the flanges and decking the mating surfaces. Used a heavy duty "angle plate" to secure everything directly on the mill table so I would have Z axis room to use my longest boring bar. Indicated on the 1/8 center witness point using magnification and a wiggler. Verified everything was square and plumb with respect to the mill axis'. I was able to reach both the end and center web of the crankcase. I also drilled the camshaft and rocker arm pivots in this setup. Lastly I reduced the cruddy looking extra roundy end of the camshaft support and it looks a lot better compared to the other end. I left extra because of the perceived inaccuracy brazing these on the crankcase. Still have to repeat on the other side of the crankcase.

20231112_150647.jpg20231112_161357.jpg

Quit early so I could order some 4-40 x 1/4 flat head screws and share this weekend's work.

Happy Veterans Day weekend to all that have served this great country!👏👏👏
 
Crankcase

Continued machining the crankcase assembly by boring the opposite side crankshaft bearing support. Then flipped the part to drill and bore the cylinder sleeves. I have gotten fairly complacent touching off each end and using the DRO's centering function instead of doing the math with a pencil and paper.

good catch.jpg


Nearly BOZO'd this up as can be seen by the red arrows pointing to center drill spots that are exactly 0.100" off. It didn't look right and I stopped and realized that I touched off the angle plate and the outer edge as the blue double-headed arrow shows. My Mitutoyo edge finder is 0.200" so that is the error. May have not realized it if I used the Starret wiggler which would have given 0.050" error. 🥸

Rounded over the upper top edges and filed a bit more before grit blasting and scrubbing clean again.
For securing the cylinders to the crankcase I chose to attempt to pay tribute to Jason B and make studs with scale size XH hex nuts. Even chamfered the stud tips.
cylinder studs.jpgAssembly 11-17-23.jpg

the logical sequence to follow in my mind is to try making the crankshaft. I have enough drill rod for one attempt and am a little hesitant to braze everything because I thought the drill rod would harden and grow a bit making it very difficult to fit into the ball bearings that are used on each end. I have fabricated a few steam/hot air engine cranks by cross-pinning and loctiting the journals. All of the higher power IC engines have been one piece. Good learning opportunity.....

Maybe I can cover the part immediately with ceramic fiber insulation after brazing and/or retemper in the oven at 600 F?
 
Back
Top