It should be stressed that this page is entirely opinion based on things read and researched. I have an old set of HCI plans for the five cylinder so any references to the plans should be taken in this context. The newer sets of plans may have had changes. Currently I'm building a seven cylinder radial which loosely fits the design description of HCI's engines.
One could get away with making an engine by the plans but attention to certain details will result in what I think would be a better product. The stock HCI design is simple, light and has a low parts count. If you should undertake any redesign you will quickly appreciate this.
Starting from the front...
The prop flange should obviously be machined while bolted to the crank shaft prior to drilling bolt holes. This means that you'll have to machine the tapered bore on the flange first. (duh) The male and female tapers should be ground. Getting the tapers to match should prove interesting! The tapered hole has a keyway which is made using a broach and a special jig/collar for the broach. The surface where the front seal rides should get a speedi sleeve for maximum seal life. There are Ra and hardness requirements for surfaces which seals ride on. (Click on the highlighted text to go to files)
Tony Bilgelis' book FIREWALL FORWARD page 267 has some pics of the different bolt hole patterns you might want to use.
The bearing carrier (integral on cast crankcases but shown separately above) needs special attention. Ideally the all crankshaft bearings from front case to back case should have bores aligned within .001" from centerline. If the engine were using plain bearings (shell type) the alignment could be a bit sloppier. Obviously one would want to machine things so as to line bore the case and have the cylinder decks parallel to the centerline also. Using a dial indicator graduated in .0001" increments is a must when centering each bore. The way I did this was to bolt and dowel the case together, dial in the finished bearing carrier and make rough bores in the center and rear bearing registers. The case was separated and the center and end bores were centered within .0001" and bored to finish ID.
The tapered roller bearing cups used in the carrier need to have a certain degree of interference fit. (.001" per 1" dia interference) The HCI "5" video showed a crush sleeve in use for the loose fitting cones. (Cones refers to the part that rides on the shaft) The tightness or looseness of fit alters the installed height of a tapered roller assembly. What this means is that you can't count on tables or pre-installation measured height in determining bearing preload. The HCI video describes how to attain the proper bearing preload. Timkens website also has a few articles about setting preload. As a final note, be sure to mill some slots for removal of the bearing cups. These are not shown in the plans.
As mentioned above, the bearing bore centerline for the entire case should deviate less than .001". (Per Machinery's Handbook) Make sure that the cylinder bores have a few thousandths slop to accomodate warpage of your VW cylinder jugs. It is wise to have the VW jugs in hand before machining your cylinder bores.
If the HCI 5 plans have not changed have a look at how much meat is around the lifter bores... Not enough in my opinion. My case will be using bronze liners and deeper lifter bores as well as pressure lubrication for all moving valve-gear.
CAMSHAFT
HCI plans show an outline drawing of the cam but no hard data for making one. HCI will provide you G-code if you request it. For testing cam profiles HCI has used CNC milled 7075 aluminum which gives them about ten hours of run time. The plate cam for non testing purposes is made of hardened steel. HCI has mentioned some minor problems with their cam profile. It seems that the lobes exhibit mushrooming even though they were heat treated tool steel. I think this is because the ramps aren't designed right and the cam diameter could be enlarged. My camshaft will be ground using a standard auto cam as the master profile. Although this is a less than perfect way of making a cam for our purpose it should cure the mushrooming problem. From what I've read a cam should be ground from a real master cam and there is quite a bit of math involved in designing a cam. Since I don't have access to a CNC grinder, mathmetician, cam software or a cam grinding machine I'm making my own cam grinding machine and copying a cam with the approximate values.
After making my own foundry and castings I've realized that HCI's casting kit is quite a deal. When you consider the risk of injury, time involved and the cost of heat treating your own parts the only thing to be gained by casting your own parts is satisfaction and spares! (As an added bonus you gain a new hobby I suppose.)
Arrows show ramps mentioned earlier. Cam design is really for the experts. Here is a book which might be of interest...
CAM DESIGN AND MANUFACTURING HANDBOOK
By Robert L. Norton, P.E.
2001, 7 3/8 x 9 1/4, Hard, Illustrated, 640 pages
Includes CD
ISBN: (0-8311-) 3122-5
As far as alloys for the plate cam go I'm still looking. Part of the problem is finding something readily available in small quantity. For my initial cam I'll try casehardened 1020. If I could find alloy 8620 in .375" plate I'd be all over it but it looks like 4140 will have to do. The 8620 would be the best because can be casehardenedwhile retaining a soft core. HCI has their cams heat treated in a stack so as to keep warpage down. With 4140 I suppose you could grind the profile/ drill mounting holes then heat treat and regrind the profile and finish grind the sides.
One other possible cause of mushrooming may be the way the HCI cam is mounted. To this end, I've come up with a tapered roller bearing cam hub. Ball bearings don't handle shock as well as tapered roller bearings do. The pain of making the tapered rollers work on the tailshaft is coming up with a way of securing the assembly. Yet another whacky twist for my engine! Real radials use large bronze bearings on which a cam "drum" rides.
MASTER ROD/ LINK RODS
Where do I start? All pins should be hardened with the proper Ra (Surface finish) The pins should be sent to an engine shop for polishing as they are more familiar with proper polishing. It is possible to over polish the pins. If you had to do it at home 3M offers microfinishing film which can be used. Pin to bore clearance should be .001" per inch diameter. (According to CFT's book) To save myself the problems of making pins I'll just buy piston pins from Flatlander racing and cut them to size. The open end of the pin will get a teflon plug. If you buy prehardened material try not to get through hardened stuff as this will make drilling holes VERY interesting. Get case hardened material instead. Things will be interesting enough when you try to drill the hard stuff.
Make sure that any holes you drill in a shaft or pin are peened. Simply take a ball from a used bearing, place it over the hole and tap it with a hammer. (Post heat treat) This reduces the possiblity of a cracking due to compressed material surrounding the hole.
The master rod link pin bores should have one end +/- 0 and the other -.001". This will allow the pin to be pressed in to a warm master rod and once cooled should help keep the pins from rotating in the MR. HCI has noted the the piston end of the link rods shows little wear but the master rod ends DO wear. For this reason they have started using bronze inserts on the link rods. Have an engine shop install your bronze bushings because they have the tools to do this. Yes, you could get away with simply pressing in your own and reaming them but the bushings should be roller burnished in place to nest them properly.
IMPORTANT When you make your master/link rods leave about .005" extra material for final sanding and polishing. You are going to want a snug fit between the master rod and link rods. As for the inner track of the master rod HCI has used a split design due to chatter when machining the deep recesses. You can use a one piece master rod if you go with a smaller end mill for making those deep recesses. I used 3/8" followed by a 7/16" end mill with the appropriate radiused end and multiple passes. The 1/2" ball mill cut the beam troughs and using those I lined up for my final passes. The final passes were done full depth with about .005" material removed while climb milling. When finished, interior faces were sanded with progressively finer grades of paper.
I made one master rod using my rotary table and two more using my newly purchased DRO. What a difference using the digital readout made! By then I had things down to a science. After pilot drilling I used a large drill of the right size followed by the undersize reamer.(.749") After the rod was out of the machine I used a hand reamer to enlarge one sides holes to the pin diameter.(.750")
Although I have not heard of any trouble I feel the little end caps on the master rod and link rod could be thicker than my "5" plans called for. Manley billet performance rods have .25"-.36" cap thickness on their billet 7075 con rods.
GEARS FOR CAMSHAFT/REAR SECTION
The early HCI "5" used a chain drive system but I've heard they switched to gears. Make sure that your gears are not subject to undercut. When you have a small pinion driving a large gear you will have undercut. One way around this is to enlarge the pinion's diameter and reduce the driven gears diameter. (Assuming you want to keep the standard center to center distance. See Machinery's Handbook regarding this matter. Cam gears are not heavily loaded so one might be able to get away with no heat treat. The small pinion gear should probably be heat treated though. My distributor drive will be on a separate gear/shaft which are both made of nylon. I don't like the idea of having the oil pump share the same shaft as the distributor.
OIL PUMP
I went off the deep end and made a three section pump for my engine since the lubrication needs are different. One thing I would like to see the HCI oil pump use is an SAE O-ring boss as a plumbing attachment. I didn't see pipe threads used in the plans but don't even think about using them on an aircraft engine.
For oil input seals Chicago Rawhide's CRWAR5 series is good up to 50-60 psi. Make sure you have one in hand before making your oil input assembly. There are sometimes availabilty issues. Shaft tolerances and surface finish are important when using a seal for this purpose. Below are some files regarding seal surface requirements.
