V-Spec OS

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OS V-Spec 07/08 : How to make a good engine better

First Impressions:

One of the most popular .21 Offroad Race Engines currently available and it is easy to understand why. Although not without its weak points the OS V-Spec is manufactured to above industry standards. Fit and finish are excellent and performance is proven with countless wins in International and US offroad competition.

The carburetor, excluding the insulator, should be the industry standard and is almost dumbass proof. If you can't tune an OS its either broken or you should be running electric cars :-)

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Carburetor

Replacing the slide boot

The carb boot on the V-Spec is a little too soft and leaks fuel more than it should. It also gets damaged fairly easy. We replaced it with the black, more durable boot from the Speed Tuned version of this engine. This part is availabe via any OS Dealer or from Great Plane i.e. Tower.

As mentioned above, the carburetor insulating sleeve is made from some kind of epoxy which swells somewhat on the bottom edge below the o-ring in the crankcase. After being installed in the engine for any length of time it is virtually impossible to remove the carburetor without damaging the insulator or separating it from the carburetor which leaves it stuck in the crankcase. Extreme caution is advised when removing the stuck sleeve from the case as not to scratch the bore because it will cause an air leak even with a seemingly small scratch. Been there, done that. I am currently testing different materials to make some insulators that don't get stuck and last longer.

Crankcase

	After removing all components from the case we inspect it for any flaws and check the bore for the sleeve and the bearings.The exhaust port is enlarged a small amount to match up to the manifold size that is going to be used on this engine. After the finish sanding the block is chemically cleaned to remove any particles and oils. This case is well designed but can crack during hard landings or crashes that occur during racing. I recommend using a one piece engine mount design as well as leveling the mount and block bolted together before mounting the assembly onto the chassis. I hope OS takes the hint of the Mugen guys choosing the stronger XZ case for their new line and changes the cases for 09.
	In 90% of the engines I rework I replace at least the main bearing with a TKO Ceramic Engine Bearing. They are of superior quality for a good price. The factory bearings are not as good as their European counter parts and the upgrade to the ceramics is worth a few rpms.The front bearing could be replaced with the new double front NovaRossi seal but they are still stupid money.Of course i signed the cases, to go with the trend and serve my ego as well. Hey, if it blows up my name is still on there:-)

Rear Engine Cover

BTW, the orange background in the pictures is my brand new Pit Mat from Upgrade RC. It catches wrist pin clips too.

Here is something i wanted to do for some time and i finally included it in this engine rework. Racers are always threatening to use some kind of goo or other crap to "reseal" their engine. I added one more o-ring groove. If this leaks, better look for a crack. It will catch on as soon as somebody with the last name "Rossi" "invents" this on their engines. It will be good either way.

Crankshaft

For this project i wanted to try some DLC ( Diamond Like Coating) on the crankshafts especially the crank pins. This type of coating is found on almost all of the high end engines and , as far as i know, was used first by JP Racing for their modified engines.So I set out to educate myself what exactly it is, who provides this service, and what are the specifications of this type of coating. The idea is to reduce friction of the crank pin and increase the durability and therefore the lifespan of the crankshaft. The cool looks and corrosion protection are a bonus.

	The picture on the left shows a Nova Rossi crankshaft bored out past the intake window and the picture on the right is a finished RB Xenon crank for a Drag Racing Engine i was building at the same time as the V-Spec project. During the process of DLC coating several different type of cranks I learned that this is not a totally predictable process.The coating will adhere perfectly to any fine finished, ground to size, surface.However, being only 1.5 to 2 microns thick, it will show any machining markings unless the area is polished before coating. Also any press fit pieces, like the balancing copper slug in the Xenon crank can retain impurities that get drawn out during the heating/vacuum part of the process. I actually had to remove the coating from the front of the crank face on the RB piece due to uneven adhesion.
However, the crank pin and the rest came out superb. The advertised friction coefficient is 0.10 and the hardness is 8000-9000HV. Operating temperature range is up to 750 deg. Farenheit. I think the engine will give out before the coating in this case. The DLC type used for this first project involving any type of coating is Titankote C10 DLC. I am not big on "secrets" and have no problems sharing this kind of thing, but they will not coat just a single piece either. The process is fairly expensive as it is charged by the size of the vacuum chamber and the use of its capacity. i.e. per coating run.

	Back to the V-Spec crankshafts. I bored them out to a slightly larger diameter and a lot deeper in order to remove as much weight as possible. After finish honing they were sent off to be coated. The crank face was not altered because the opening has an efficient transition design already. Intake timing also remains stock since it is already in the 220 degree range. I had checked the balance of the V-Spec components during an earlier engine i worked on and found it to be quite good as designed.
I would just prefer the weight a little more "advanced" counterclockwise. This would require to add a pressed in slug of copper or tungsten or to remove material from the crank where there is very little or none already. Besides, i was going to still remove weight from the connecting rod and the piston. Once the parts returned from coating, they were degreased and the area that was bored out past the intake window was filled with self leveling "top secret" silicone to act as filler and to form a nice "ramp".

I have been boring and filling crankshafts for a while now and spent a considerable amount of time to find the right silicone for the job.Funny thing was that the people i know overseas don't use any in their engines, so i was on my own for this one. Anyway, i now have two at my disposal that will work perfectly. The silicone in the pictures is a clear type which is also used in the OS Speed version of the V-Spec engine. The other type is RED in color and available from Reid R/C Performance to anyone who needs or wants to use it.( See NEWS page). After filling with the silicone the crankshafts just sit in the holder to cure for about a week.

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Crankcase with TKO ceramic bearings, reworked DLC coated crankshaft and double seal rear cover.

Piston and Sleeve

Before any work had begun I had measured the port heights and con rod center distances on all the engines i was working on, as well as measuring the volume of the headbuttons.All this information is entered into a spread sheet on my PC and it displays all the timing numbers and height measurements.Once I can see the actual timing numbers of the engines I will decide which numbers will be changed. Engines for different purposes run slightly different timing numbers and set ups that have bearing on torque, top speed etc.Sometimes I read statements like " i had my engines modded but he didn't do anything" just because nothing is polished or ground off and visually everything looks like the stock engine. Looks can be deceiving and measuring is better than guessing.Since all the timing numbers except the crankshaft duration are pretty conservative I wanted to boost all the numbers a little.

(No, i am not posting what my final numbers are since it took several projects to find the number that works well with this engine.) There are two ways to increase all port timing numbers at the same time almost the same amount. One is to raise the sleeve, which also moves the taper upwards and therefore, to me, is not desirable since i want the factory taper right where it belongs by design. The second method is to shorten the piston by cutting a few thousands off the piston crown, this also removes weight from the piston. In most cases when the piston is shortened the head insert will have to be cut by the same amount to insure it reaches deep enough to allow a normal range of squishband adjustment via the headshims supplied with the engine. For another small weight savings of the reciprocating mass the wrist pins are

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replaced with lighter Nova Rossi pins. I have recently checked some wrist pins from Sirio Engines which are even lighter and top quality material.The V-Spec connecting rods are milled on both sides with a ball end mill as the pic on the right. Contrary to popular believe , even though the oil hole for the lower bushing is in the crankshaft, there is a right and a wrong way to install the con rod.There is a chamfer in the bronce bushing on the convex shaped side of the con rod (left rod pictured on the right), this side is to face the crankshaft and allows space on the radius from crank to crank pin.The other side (as the rod shown on the right) should face the rear cover when the engine is assembled. All parts are cleaned in an ultra sonic parts cleaner and degreased.

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Final Assembly and Set Up

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All pieces involved are laid out and the basic engine is assembled making liberal use of assembly lube. The crank pin and rod bushings deserve a little extra attention since initial lubrication at the first start up is critical. Once the basic engine is together the head clearence/squisband clearence is set using a depth micrometer, not a piece of shit solder :-) ) The V-Spec comes set from the factory with two shims installed one of which is 0.008 and the other is 0.004. Plus one extra shim in the box which measures 0.004. I found the factory clearence out of the box to be 0.017 of an inch on just about every V-Spec i ever checked, give or take half a thousands.For 30% nitro fuel most manufacturers will recommend clearence of 0.021 but the stock OS V-Spec runs strong and without detonation with the two shims right out of the box.

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I am expecting a few more rpms, to say the least, out of the modified version here and set the final clearence to 0.019. Shims are available down to one thousands of an inch which makes it easy to adjust the clearence exactly as desired. Finally the cooling head is installed and torqued. Yes, with a torque wrench, to ensure everything stays square and can expand and contract without distortion.Almost done.

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After final assembly I installed a Speed 2.5 racing clutch from our good friends at Reckward Modell Vertrieb (RMV) on the V-Spec I am keeping for myself. Hey, i like to play too.

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Final thought, aaahh.......oh yes, dremel this, bitches ;-)

Cheers, Good Racing

Rich Reid

For questions or comments please e- mail me at rich@reidrc.com