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Jim Allen

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About Jim Allen

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    National Racer
  • Birthday 01/30/1941

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    Graham, NC

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  1. Jim Allen


    "Jim- I must be missing something here... regardless of pinch, will not the rod still push the piston all the way to TDC?" I do not know what you're missing except that you DO NOT want to take any measurements at the point where the piston is stuck in the bore (pinch point). In the photo, the depth micrometer is reading .394" with the .200" gage block in place. .394" minus .200" gives .194". This number tells me the cylinder is at the correct height for the desired timing. .194" minus .185" (measured head button depth) gives .009" clearance. .009" plus .007" gives a .016" total deck clearance. Jim Allen
  2. Jim Allen


    Tom, You will want to measure at the maximum crunch point (TDC) of the piston in the cylinder. This becomes easy to do once the cylinder has been raised to eliminate the sticking of the piston at TDC. The posted photos show what is done to totally eliminate any sticking of the piston at TDC. Raising the cylinder a known amount, exactly .200" in this case, eliminates the sticking problem. Sometimes we use a gage block (shown in the photo) & sometimes we use a precisely machined ring that sits under the liners lip. We also check the measurement after any shims that may be necessary are included in the measurement. We use .001", .003", .005" & .008" shims to set the deck clearance & timing to exact numbers. Every part must be super clean to do this!! Jim Allen
  3. Jim Allen

    Hopper tanks

    My setup is similar to yours Mic. No problems with the pressurized fuel delivery even with the .4724" bore carb. JA
  4. Jim Allen

    Rudder Pins?

    Tony, I do not know what Speedmaster is using. However, I have used standard dowel pins, M-2 steel HHS blanks & piano wire, all 1/4' diameter. Never had any of these break even when shearing a 6-32 stainless steel rudder shear pin. I drill the 1/4" size pins with a 9/64" carbide drill to reduce the weight. JA
  5. Jim Allen

    Delrin question.

    Samuel, I do not care to get into an argument with anyone about machining or threading plastic materials such as delrin. After machining & threading thousands of delrin blocks as well as various plastics used in high speed airline ticket printers, the advice I can give is the following. Tools used for plastics need to be as sharp as possible, lower cutting speeds should be used to prevent heat build up & a recommended type of coolant should be used. "It should be noted that a tap cannot produce a class of thread, however it can produce a tapped hole within a specific product limit. Since the tap is used only in tapping a hole or producing a thread, a tap has no control over the fitting properties of the MATING EXTERNAL THREAD!! Tap limits refer to the various SIZES of taps manufactured. A tap should be selected which will produce an internal thread within the desired limit." Tap limits are designated as L3, L2, L1, H1, H2, H3,---------H7. Each designation is a different pitch diameter, with L3 as the lowest pitch diameter & H7 as the largest pitch diameter. Each designation can give a particular class of thread, (class 1B, 2B, 3B) with 3B as a very close tolerance when combined with a particular external thread. No spiral tap of any kind is needed for tapping delrin or aluminum in a non production environment! Jim Allen
  6. Jim Allen

    Delrin question.

    There are many grades of Dupont Delrin acetal homopolymer resins available. Some, such as Delrin 300CP NC010, give very high tensile strength, high impact strength, high fatigue resistance & high toughness. All of the Delrin acetal resins will exhibit some creep traits, even when machined with very sharp cutting tools. There are also some heat treatable grades that can be stabilized before machining. Jim Allen
  7. Jim Allen

    Engine Cooling

    Lohring, I found greater detonation resistance with toroidal type head designs could be achieved by cutting a deep trough adjacent to the plugs threads. JA
  8. Good job guys. Looks like all the photos & posts are back up. JA
  9. Jim Allen

    Worn out P/S?

    Bob, In the very early days of ABC & AAC engine building, a tight fit between the piston & sleeve, plus a course crosshatch honing pattern was used to compensate for the "out of round" (+ or - .0002") condition of the piston & sleeve. A roundness (+ or - .00005") of both parts is absolutely essential before anything works properly! We eventually discovered that the tight fit method does not correct "out of round" problems & it does not extend high RPM engine life! Some engine builders thought that higher amounts of silicon in aluminum alloys used for pistons would prevent piston scuffing or engine seizing. This is also untrue, as the answer to this problem involves the cylinder taper amount & the piston top taper amount. You are correct about what cold fit can & should be used with the many possible piston, cylinder alloy combinations that can be used. We have tested & used in production miniature racing engines the following piston alloys; A-390, Dispal 250, Mahle-138, RSA-431-T6 & RSA-444-T6. We have tested & used in production racing engines the following cylinder alloys; C 36000 brass, C 54400 phosphor bronze & 4032-T6 aluminum. All of these alloys require different cold fits! However, Nothing works properly until the involved parts, the piston & the sleeve, are properly machined & finished! The correct mechanical design of these parts is also absolutely necessary! Jim Allen
  10. Jim Allen

    Are radar guns accurate for boat speed?

    Stephen, I use a Stalker PRO radar gun. To get the most accurate reading possible the radar gun must be placed directly in line from the front or rear of the boat. We use a dedicated person stationed at the end of the lake with a TRC-236 transceiver which allows communication as each pass is made. Standing on the shore always produces a tangent error that is hard to calculate! We have also used this gun to check radar speed readings when compared to data logger speeds derived from a pylon racing plane. As long as the radar gun is in line with the object being tested, it will read correctly! The gun comes with a tuning fork for onsite calibration. Jim Allen
  11. Jim Allen

    Worn out P/S?

    "What are the symptoms of a worn out piston/sleeve? I have a 21 Nova DD with absolutely no pinch left at the top." Bob, A loose fitting ABC or AAC piston & sleeve, in a tuned piped engine, doesn't necessarily mean the engine in question is worn out! ABC or AAC tuned pipe engines can still run strong even when the piston has lost most of its "pinch" at the top of the stroke. It is a proven fact that a looser fitting ABC or AAC tuned pipe engine will run faster, but will not produce high torque amounts at low & mid-range RPM's. The lower torque amounts can easily be seen when attempting to pipe up a looser fitting engine that is under load. A much more important factor for ABC or AAC tuned piped engines is how round the piston, sleeve (within .0001" works best) combination are, as well as how round they remain at WOT temperatures & RPM's. Sound mechanical design of the piston, sleeve combination make this possible! Jim Allen
  12. Jim Allen

    new gas pipes under construction

    This information comes from Les Smith of Performance Unlimited. It speaks about the progress of the 32 cc to 35 cc Pipe R&D work. This tuned pipe's design follows from the research developed over the last year. "The R&D design and the testing of our new Stainless Steel Pipe is finally being finished....below is a synopsis of the R&D testing ... The final results are more than impressive to say the least. Ray's 20 lb 53'' Delta Force Annihilator Mono started out with a top speed of 51 mph with a modified 30.5 cc engine using a QD Hot Pipe. He upgraded the displacement to a 35 cc engine and tried the following pipes from QD, Insane and Zipp Kits with no better performance than the 30.5 cc using a QD Hot Pipe, the JB pipe gave a little improvement over the others and all running in the 17k-18,600 rpms, however...the Pro-Modified 35 cc engine was producing the same power as the 30.5 cc, since the same prop was turning the same rpm as the 30.5 cc and the 35 cc was also showing a lot of increasing engine heat from the CHT sensor readings were going above 205° and then the performance of the engine was sluggish and the top end power dropped off. We went through 7 different designs of the pipe as well as several different shapes, angles to mention a few and the performance of the 35 cc engine came alive and we kept testing in the direction of the performance increases and the CHT temps were monitored closely to insure no melt down will occur at WOT for an extended period of time that was way beyond any heat racing or marathon running time frame. The air temps in the 3 digits and altitude changes from sea level to Las Vegas did not hinder the performance gains with the new pipe. Rays heavy mono now has a speed of 65.6 turning a prop with more pitch and rpms around 20k-21,400 with no over-heating and plenty of bottom end to more the heavy hull. This pipe is not a spin off of a QD Pipe, Zipp Kits Pipe, Insane Pipe or a modified pipe from those on ebay as some have done to sell pipes by modifying them and claim this is the pipe for the 32-35 cc or to claim their pipe works on this size of engine. In the R/C hobby most pipes will work across several different engine displacements, however only a pipe that is specifically designed for the engine and its displacement will work even better. There are several guys that have been there when Ray first started the testing and have witnessed the performance improvements during the R&D testing and have visually seen the results of the pipes performance even during NAMBA District 9 races. We are pursuing to have this 4 stage pipe stamped out of Stainless Steel and we decided on this method, since the inside of the pipe is smoother than a bunch of welded stages and the angles are radius to the other areas along the pipes length, so the pipe will have the welds similar to a QD Hot Pipe and have the flared diffuser that you can see without the welded stages and of course be lighter in weight too. The 32-35 cc Pipe uses a 1" header All clamps are Stainless Steel Muffler on our pipe has an integral stinger Weight of the pipe with stinger & muffler is 17 ozs JB Pipe is 18.8 ozs and QD is 15.4 ozs Below are photos of the visual differences between the tuned length and / or the pipes shape and length of the QD, JB and our pipe. Top Pipe is Our Stainless Steel Pipe, Middle Pipe is a JB Pipe and the Bottom Pipe is a QD Hot Pipe."
  13. Jim Allen

    Glow plug torque specs?

    Hi John, I use 1/4" drive, 0 to 60 in/lb, Armstrong beam type torque wrenches for tightening plugs & head bolts. Standard 1/4-32 plug threads are tightened to 45 in/lbs & 11/32-32 tapered seat plugs are tightened to 48 in/lbs. #8 SHCS head bolts are tightened to 20 in/lbs & #4 SHCS are tightened to 10 in/lbs. No loosening or thread stripping problems of any kind found thus far. Jim Allen
  14. Jim Allen

    Charlotte, NC area?

    Thanks Much Don! JA
  15. Jim Allen

    Exhaust Gas Pressure inside Tuned Pipe?

    Okay Mike, Let us know what you find out. Keep in mind that any tuned pipe or magic muffler type device that has insufficient volume compared to the engine's displacement will "NOT" allow large changes to a stingers ID or length. JA