John,
Sorry to be such an A-hole.....I am just feeling real bad today.......it was a knee jerk reaction to feeling so sxxxxy.......
Rod, Dave Richardson here - I don't usually get into discussions here on the web-
but- following along this on con rods, I will with info on the rods that I produced over the years-
history: first rods I made were for Vico 19, Ops 3.5, KB40(6.5), Ops 65 motors-
This was 1968 ?? onwards- rods were for marine & R/c car & pylon plane motors-
The KB 21 marine motors came along approx. 197-? - then KB7.5 motors- etcetc-
With a call from modeler with a new to market motor & the owner wanting a rod, I would make a rod for free for use of the motor to measure it, make a blueprint for my files & make the parts...
That worked well, as over the years I make rods for 280 different motors-
I went into RPM business in 1975 & retired in 2001-
I had help from good guys along the way: John Ackerman & Martin Davis (lots of testing), **** Mccoy (glow plugs& info), Don Donikowski (Revenge racing Fuels), Morgan Fuels (oils & good info). & others...
These are NO secrets to make a good conrod. Good design, materials, proper machining methods & precision sizing are needed.
I used a CNC milling machine & Sunnen Honing machine etcetc to produce my product-
with those tools (& more) & years of experience in the Aero space & computer industries, the rods were produced with consistent good quality that always worked well I think-
So... What sizes/ clearances were used on the bores of the rods?
3.5/21 motors (new parts) crankpin size+ .0015"
40/45/46 motors (new parts) Cp size + .002"
65/81 motors (new parts) Cp size + .0025"
90/91/ 1 cu motors (new parts) Cp size + .003"
Wrist pins bores sized to max. to +.0002"
Checking sizes was done with gage pins... made to the correct size by lapping each needed size-
Remember: a rod will run OK with too much clearance... (Stories on that from my own experiences)-
Not enough clearance & rod failure will be there...
Any (ALL) motors with new parts (conrod etc) need a few tanks full of fuel running to allow the parts to seat each other.
15/20 percent oil content in the fuel.
Over 55% nitro fuel needs synthetic oil made for nitro fuel.
Castro oil doesn't mix well with higher nitro percentages above that-
A good fuel is 50 nitro that needles well & produced good power & has some castor oil in the mix-
Oil holes: The hole on top at the base of the rod beam is an oil vent hole.
The two holes on the bottom are inlet pressure holes.
The rods are made to be installed in any direction - there is no front or back side of the rods.
The outer edges of the bottom bore need a chamfer to clear the inner corner of the C pin-
As the motor runs, the big end of the rod runs close to the case bottom bore, which pressures the fuel/ oil into the clearance space on the bottom of the rod / C pin.
the space is wedged shaped & the Cp rotation draws the mix into the top of the bushing, lubing it at the max pressure point.
Oil now is pushed out the top hole keeping that part of the rod lubed & cool, if not to lean a mixture is used.
The faces of the big end of the rod are machined with taper to them: this forms the important wedge shape that helps draw oil into the bushing also.
All the fixturing used for making the rods was pretty simple to use and was made for quick turn around
of setup for different types of rods.
At times I would run 4 or 5 different types of rods in the same production lot of parts.
Maybe this helps answer some of the points about the conrod questions here-
Maybe also more questions are brought up? I hope not too many...
Rod - Thanks for your knowledge & replies to all this... as I've told you before, we can't thank you guys that had some of your life taken away being a standup good citizen...
Be well my friend- KIT-
Dave Richardson
RPM Inc. (retired)
