Hello all,

What prop size is used on the K&B for TQR, I have been told that a 8 x 8 is the size to use.

Thanks Bill,

Another question is what mods are done to the motor, as I read the rules there are none that can be done to crank, rod, piston, liner and the head.

Do I machine the exhaust stack off?

What mods do people talk about when saying a TQR modified motor. Are they saying the venturi only?

Lionel.

I heard that a rule of thumb for changing the closing timing was to take a .093 cut from the closing side and remove any square edges.  Another is to drill the crank out to 7/16 ID, but that gets into some pretty shaky thin wall cranks.  And last chamfer, radius, or counter sink the opening into the crankcase to improve flow around the conrod.

Hi Lionel

Delaying the crank closing timing by 8-10 degrees is about right. Total timing should be 205-210. The opening timing is fine. There is no reason to bore the gas passage larger, since we are restricted by the venturi Dia. anyway. Also the rear bearing/crank/housing area needs as much support as possible as the rear bearing housing only holds about 1/4 of the bearings depth. This is another reason to leave the crank bore alone. You should be able to machine the head to get the clearance down to around .012"-.013". As for the ring, make sure there's no metal shavings in the ring groove, especially underneath the ring as this can cause an almost complete loss of compression.

One last thing you can do, and this really helps, is to add an exhaust primer. I drill the back side of the exhaust stack, locating the hole inline with the outer edge of the cylinder liner and tap it 6x32 for the fuel fitting from the r/c carb that usually comes with these engines. I then insert and solder in place a piece of 1/32 brass tubing. The internal dia of the 1/32 brass tubing works out just about perfect. Add a "T" fitting into your uniflow vent (which is also your overflow vent) and hook up a piece of fuel tubing to connect to your exhaust primer. Filling through your tanks fastfill gives enough pressure to send some of the overflow to the primer. One last thing...If you don't wan't a nasty pit fire, close the piston on compression when filling/priming.

Hope this helps

best regards, Les

Tain't no such thing as "stock" in racing!  Just look at the National Association for STOCK Car Auto Racing!  When you try to define stock you end up like them. 

Hi Lionel

Here is a copy of my article I did for the NCLRA Torque Roll Magazine with some additions.

K&B 4011 setup

For some of the events that I currently compete in, I have only one good engine. TQR was one of those events.
I’m sure that most everyone who has competed in this event has bought one of the ready to go K&B 4011, or 8011 engines from Vic Garner. I was no different. With Vic deciding not to produce any more engines, I thought I’d take a run at trying to build an engine as good as my current example.
I wanted at least 2 more good engines, and through various transactions, I found myself with a brand new series ’71 Torpedo 40, and three 4011’s, two of them new and one used. Could I build two good engines from these four?

The first thing I did was disassemble each engine, keeping all of the parts from each engine together.
Next was a trip to a fellow modelers shop to borrow his dial bore gauge. This fine piece of equipment would allow to me to select the roundest two of the four liners I have. These were set aside. Interestingly, the roundest liner was from the series ’71 Torpedo 40!

The liners were carefully deburred so that the ring would not catch on horizontal edges of the port pickets.
The rings were carefully removed from the pistons, so as to not impart a twist into them. The bottoms of the rings were then carefully lapped on a fine, flat stone to remove the machining marks, but no more.
Feeler gauges were used to select the pistons with the tightest ring grooves.
I then made a lathe spud to fit the pistons onto so I could remove any burrs and polish out the scratches.
The rings were then re-installed, and lapped to the bottom of the ring groove with after run oil and a careful twisting motion by hand.
The pistons ring groove must be square to the piston sides for the ring to work properly and seal. If it is not, you could re-cut the bottom of the piston’s ring groove on a lathe, but be careful...you only want to remove enough to square the ring groove and not add too much unneccessary clearance.

The crankcases were selected by the process of fitting the liners. If the liner wouldn’t install and remove without force, that crankcase was rejected. The reasoning, was that the K&B liner is quite thin and too tight a fit into the crankcase may affect the roundness of the liner as it conforms to the crankcase. There really is a lot of variance in the machining here. Another area to check is the part of the crankcase where the front end bolts to. The front end should fit tightly into the crankcase recess, when using a 4011 front end, as a little more than 2/3 of the rear bearing is supported by the crankcase.
At this point I was not confident of the overall quality of K&B’s machining tolerances. The next logical step, if you really want to get crazy here, is to machine a mandrel that fits very closely into the liner hole, and rests on the bottom inside of the crankcase. Then you measure to the mandrel from each mounting flange, add half the mandrel diameter,then record this number. Next, measure up your front end (from machined face of mounting flange to mid point of crank pin) then you can determine if you have to add gaskets or remove metal to get the crankpin centered with the liner hole. Getting this correct will prevent much, although not all of the piston skirt scuffing.

The choosing of the front ends was rather easy. I wanted new. So, the used one was set aside for spare parts. Having already timed the cranks, I removed them and the front bearings from the housings, performed the modifications to the crankshaft timing windows, which was done on the closing side only(62~65 degrees), cleaned everything, and re-installed them into the housings. However, one of the new housings had the bearing saddles machined so large that both front and rear bearings were a push fit. Out came the spare front end housing; problem solved. The next step was to spot face the sides of the venturi housing so that the needle valve assemblies I was using would have the spraybar’s exit hole centered.
There are basically two versions of Front ends for the K&B 40 ringed engines. The 4011 series engines use the larger front end with bigger front bearing and is the way to go unless you want eventual front end problems. It's easier to do shaft timing changes on the 4011 front end as well since it uses a split collet on the prop driver. Also, since there is no "step" on the 4011 prop driver like the Torpedo/8011 series has, you don't have to ream your props to 5/16" diameter to fit.

Henry Nelson can supply a needle valve assembly that has enough length if you spot face the sides of the venturi boss. The Super Tigre units can also be used.

The heads were selected by measuring the plug depth, and the head depth. I managed to find two of the four that were the same, or nearly so, and they fit the liners acceptably.
Assemble the engine dry and check for any binds or rough spots. Now is the time to fix them if you are able.
One last modification was performed, and it is entirely optional. I reduced the depth of the exhaust stacks a bit, and I drilled and tapped the stacks on my engines for an exhaust prime. I use the fuel nipples that come with the original R/C carbs for this. You may have to experiment with the size of the hole until you obtain satisfactory results.

The Exhaust prime really helps the restarts on these engines especially when they get hot, and they do get hot! I have installed them on all my K&B 40's and they all work fabulously. I have the uniflow vent teed off for the exhaust prime about .75" from the pipes end. The primer nozzle is a K&B fuel nipple from the R/C carb that has a 1/32" diameter brass tube pushed into it to restrict the diameter. I drill and tap the back of C/Case exhaust port flange, positioning the primer nozzle so that it just lines up with the outside curvature of the liner. When priming the fuel will catch the edge of one of the liner pickets.

The restarting drill is as follows; when airplane comes in for a pit, turn the prop back against comp (like you would an F2C) open the shutoff, and fill the tank allowing at least a 3" stream to come out the uniflow pipe when full. Bring the prop around and flick hard. It should start 1st or 2nd flip every time.

If you design your own airplane, experience has shown that you need at least 100 sq. inches of wing area. Much less than this and the airplane has trouble during the pass, and tends to land short and hard.

I realise much of what is mentioned here may well be more than the average modeller can do. Do not worry, the only work you really need to do is get your cranks timing to total 205-210, get the proper size venturi and needle valve, try and find a head that allows around .012"-.015" head clearance, and add an exhaust prime. The rest of the work mostly adds longevity to the engine.

I run bench run my engines on an APC 8x7 sport prop, and my best engine will turn this prop a bit over 18k on 10% fuel.

Regards, Les