More power! It's the mantra many of us in the hobby seem to live by. While the age old question regarding whether there is such as thing as too much power remains, many of us (especially racers) will certainly respond with a resounding yes. After all, there is a fine balance of stuffing power into a platform, but yet still not upsetting the overall balance.

With that in mind, O.S. Max introduced the 18TM line of motors targeted towards the Revo and T-Maxx. Knowing that on the track most owners want to stay in the production class which requires a .18ci or smaller motor, they decided to set about providing a powerful motor platform targeted just for this specific purpose. Anything more would move an owner up to the unlimited classes, be much tougher to control, and add additional weight to the truck. After all the low weight and agility of the Maxx and Revo are two of their strongest points.

So how does the 18TM fare when dropped into a Revo? After all, the 2.5 is no slouch when it comes to power. So any performance gains need to be substantial for the motor to be a worthwhile investment. Does the 18TM also retain the tuning ease that is commonly associated with the O.S. lineup? I certainly hope so, and I'm certainly ready to find out!

The version of the 18TM I received, and reviewed, was for the Traxxas Revo. If you're interested in dropping this motor into a T-Maxx, you'll want O.S. part number 11930. It comes ready to drop into the T-Maxx. The motor internals are the same for both motor combinations however.

The 18TM is a direct drop-in motor for the Revo, and you'll receive several items along with it to help you with the swap. The most notable of these items is the header. While you'll retain the use of the stock pipe, the header provided with the 18TM has a slightly larger diameter, and will allow for a greater exhaust flow.

In addition to the header, you'll also receive a big block style spring that secures the header to the motor. This differs from the 2.5mm screws that are used on the factory setup, but has the advantage of being removed much quicker than the method used with the Traxxas 2.5R. A header gasket accompanies the spring, and it provides the seal between the header and the engine block.

As you would expect, you're also provided a glow plug. The included plug is an O.S. LC3, and is the recommended plug for use with 10-20% nitro fuels. While O.S. mentions the 18TM can be used with higher content nitro fuels such as 30%, I would use a colder plug in those scenarios. Information such as this is contained in the well documented manual as well, as it provides you tuning instructions as well as a break-in procedure. You will also find a walkthrough of the installation procedure.

The motor itself looks very sharp and distinctive with its blue anodized head. It retains the same overall foot print as the Traxxas 2.5R, which helps it obtain its direct drop-in status. In case there was any doubt as to who made this motor, or what it is, the O.S. Max 18TM emblazoned on the side of the motor will put any questions to rest.

The motor's head sports some distinctive detail as well. While the blue anodized finish usually tips one off that the motor is probably an O.S., all doubt is removed once you see the top of the head. O.S. 18TM is etched into the blue finish on the top of the head, while the surrounding flames add a nice decorative touch. You've got to hand it to O.S., as they can certainly produce one sweet looking motor.

Since the 18TM is a direct drop in, the rear of the motor must mate to the various starting methods that a Revo may be equipped with. In most cases this will probably be the factory-equipped EZ-Start. However there will be some that have made the swap to a pullstart. Regardless of what method you use, the backplate and shaft of the 18TM is ready for you to swap the starting items of your choosing onto. I should also mention that if you're currently using a starter box with your 2.5R, and wish to go that route with your 18TM, O.S. offers a replacement backplate (part # 21917000), although you'll have to grind off the nub on the crankshaft.

The motor head itself uses a replaceable button to retain the glow plug. This method is one that I prefer to see used with a motor. Should the glow plug threads become damaged, the button itself can be replaced cheaper than replacing the entire head. It's not uncommon to see a newcomer over-tighten or cross-thread a plug and the replaceable button helps tremendously in this regard.

The main components of the 18TM are what you'd typically expect to make up a nitro-powered motor. First of all is the motor block, which is a direct drop-in replacement for the Traxxas 2.5R. The bigger motor doesn't necessarily require, or result in, a bigger block. The block itself is approximately the same size as the stock motor, although the castings themselves will appear slightly different.

Most of the rest of the motor's components reside inside the block itself. These parts consist of the crankshaft, the piston assembly, and the sleeve. We'll cover these items in a little more detail a little further down in the review. However, rest assured that the components use ABC construction, providing parts that are made of what's considered the best material combination to date.

The fuel and air mixture is handled by an aluminum slide carburetor. The aluminum body is durable and rugged. The carburetor is an integral component which helps provide an O.S. motor such as this with its well known ability to tune easily. I certainly wouldn't expect anything less than an easy to tune motor, given O.S. motor experiences I've had in the past. However, ease of tuning isn't all that O.S. was focused on providing. They also wanted the carburetor to be as adjustable as possible. So the carburetor also provides a mixture adjustment as well. The mixture adjustment is often referred to as "the third needle", and provides you with the ability to tailor the transition between the low speed and high speed needles.

Many manufacturers are now turning to composite plastic carburetors, and that's not without a valid reason. As a metal carburetor warms up, it can sometimes become a victim to the fuel boiling in its throat. However this potential problem wasn't lost on the part of O.S., as they have equipped the 18TM's carburetor with a plastic sleeve to insulate the aluminum-bodies carburetor from the motor's heat.

Since the 18TM is a direct drop in, it needs to be compatible with the Revo's factory EZ-Start, or any other factory compatible starting system that the owner may be using. This is accomplished by the motor backplate that O.S. equips the motor with. While the backplate itself is slightly different from the one on the Traxxas 2.5, the shaft exiting through it is the same diameter. The backplate itself is also made so that any 2.5 compatible starting system will attach directly to it as well.

The block of the O.S. 18TM is aluminum, and designed to drop into the same space occupied by the stock 2.5R motor. Fins all along the outside of the block help to dissipate heat and contribute to a cooler motor. Inside the motor large bearings provide the crankshaft the ability to spin at high speeds with minimal resistance. The porting inside the block matches up perfectly with the sleeve, and is focused on providing optimum velocity of the fuel and air.

The piston and reciprocating rod assembly are machined from top grade aluminum, providing the skirted piston a solid fit with the sleeve while the motor is running. A single groove at the top of the piston provides oil retention for lubrication purposes. The rod itself has a knife-edged cut, which helps to reduce weight and crankcase drag. This contributes to more useable power when compared to motors that skip this detail. An oil hole on the front side of the rod provides lubrication for the rod bushing.

The large diameter crankshaft, of the 18TM, provides the motor with its 15mm stroke. When combined with the 16mm bore, this gives the O.S. its 3.0cc (.18ci) displacement. The large inner bore of the crankshaft is focused on providing a large amount of fuel and better dispersion of it as well. This helps to boost the power when it comes time to out-muscle other similar motors. The nub at the rear of the crankshaft is designed for the motor's backplate. This allows the use of the factory EZ-Start, or other similar starting methods such as a pullstart.

The sleeve for the 18TM is a rear-exhaust, four port design. It matches the crankcase extremely well, providing plenty of oxygen and fuel into the motor. The rear exhaust design ensures that the spent gases can exit the motor as easily as they exited it. The chrome plated sleeve provides a very tight fit to the piston, which in turn provides excellent seal and compression. Chrome plated sleeves also provide a much better lifespan than the older nickel-plated sleeves.

While swapping the motor may at first seem like a frighteningly complicated task, you shouldn't worry. Due to the fact that the O.S. 18TM is a direct drop-in, there is no major work to do when dropping it onto the chassis. All you'll need to do is to swap a few components from your 2.5R to the new motor. You can see just how easy the swap is by following the steps I used for my installation.

The first thing you'll want to do is to remove the air filter, as it will help give you a little room to work. You can also remove the rollbar for some more room if you wish, but I found that it's far from being necessary. You might want to go ahead and remove your fuel lines at this stage as well.

There are four screws that secure the motor to the motor mount. They are placed in pairs, with each pair located on opposite sides of the motor. Use a 2.5mm hex driver to remove the screws, and then move to the hanger screw on the tuned pipe. You may notice that the rear end of my Revo differs from the stock configuration. This is due to the rear buggy wing I have installed, which will not change any aspect of the installation from what you would encounter with a stock Revo.

The screw on the tuned pipe will require you to use a 2.0mm hex driver. Loosen it slightly, as removal is not necessary, and then the motor should be completely loosened from the chassis. Pull the back of the motor up first, and then slide the carburetor's lever out of the throttle bellcrank to free the motor. You should note that if you are using the EZ-Start, you'll need to remove the wiring harness plug from the rear body mount or disconnect the wires from the motor. Either method should be self explanatory and easily accomplished.

With the motor removed you can easily access the components you'll need to move to the O.S. 18TM. Take a close look at the throttle bellcrank and motor mount now that the engine has been removed. You'll see another hole for the throttle bellcrank further out on the mount. Keep this option in mind. With some radio configurations, it may prove beneficial to use this alternate position for the bellcrank. I found that this was the case with my JR XS3.

Now that the motor is removed, it's time to start removing the parts of the motor we'll want to swap to the 18TM. I started by removing the pullstart and tuned pipe. Keep in mind that if you are using the factory EZ-Start it removes in the same fashion. All that' needed is for you to remove a few 2.0mm screws that hold the starter to the motor. The pullstart uses four screws, but the EZ-Start will only have three screws installed. Pay close attention to the one-way bearing that rides on the motor's starter shaft. If it doesn't slide off with the starter, make sure you don't reverse its orientation. The lettering on the bearing should face the motor.

The header will not be needed, but the tuned pipe will. Since you are removing the pipe, now would be a good time to remove both the wire ties that hold the coupler in place. Even though you'll only need to remove one, it doesn't hurt to perform a little more preventative maintenance. In case you noticed, I'm not running the factory exhaust coupler, but instead one from GS Racing. It has proved to be more durable for my needs than the factory coupler.

The front of the motor requires a little more disassembly, but it's still all basic nitro motor knowledge and nothing to be worried about. If you are fairly new to nitro powerplants, I suggest you place the items in a logical order as you remove them. You'll need to reverse the disassembly procedure on the O.S., and knowing what order everything goes back on will help tremendously.

Removal of the clutch bell and clutch shoes is rather simple. All you'll need to do is to pop the e-clip off and then slide the items off as you come to them. Once you reach the flywheel though, you may start to encounter some minor difficulties in holding the flywheel still while trying to remove the flywheel nut. You can purchase a flywheel tool to help you hold the crankshaft and flywheel still while loosening the nut. Alternatively, if you're on a budget, you can use a pair of channel locks to hold the flywheel still as well. You'll just want to avoid scratching up the edges of the flywheel, especially if you plan on using a starter box in the future. The burrs and scratches on the flywheels edges could cause premature wear on the box's starter wheel.

Once the nut is removed, you'll need to slide the flywheel off of the crankshaft. Most of the time, it will be stuck and difficult to remove. If this is the case, tap the flywheel off gently with a hammer. The beveled cone should slide off easily once the flywheel has been removed.

From this point, we'll be focusing on the O.S. motor, as removing what we need off of the 2.5R is now complete. The first thing you'll need to do is to install the flywheel, clutch shoes, and clutch bell onto the new motor. All of the components you removed are used, and installed in the reverse order. When working with the flywheel and beveled cone, you don't need to tap it into place with a hammer. Simply push it as far as it will go, and then when you tighten the flywheel nut it will lock onto the crankshaft.

The pullstart, or EZ-Start, will slide into place on the rear of the O.S. in the same manner as it slid onto the stock motor. I would advocate the use of threadlock on the screws that hold the starter to the motor. Otherwise the screws may loosen up and fall out once you run your truck.

The 18TM uses a different diameter header than the factory motor does. Therefore it also comes with its own silicone exhaust gasket. Install this gasket on the motor's exhaust port in preparation for the header installation.

Once the header gasket is in place, slide the header onto the motor making sure it is oriented as shown. O.S. supplies you with a big-block style header spring to secure the header onto the block. Fasten one side to the header, wrap the spring around the motor and then hook the other end into the opposite side of the header. You'll need to use an exhaust spring tool, or needle nose pliers, to help you accomplish this.

Next slide the tuned pipe and coupler onto the O.S. supplied header and secure the components with a couple of wire ties. Exact orientation of the pipe isn't critical, as the pipe can be rotated once the motor is installed.

Now all that's left to do is to drop the motor onto the chassis. Slide the front end of the motor into place first, making sure the carburetor's lever is in the bellcrank, and then lower the back end into position. Secure the motor to the mount using the four screws that were removed earlier. Once the motor is taken care of, secure the pipe to the exhaust hanger. Rotate the pipe if you find it is needed. It would also be a good idea to verify the gap between your clutch bell and spur gear, although I didn't see the need to make an adjustment after my installation.

With the motor in place, the final steps you'll need are to reinstall the air filter and fuel lines. If you are using the EZ-Start, make sure you install the wiring harness back as well. Once all that's done, you're ready to rock!

Once I had the O.S. Max 18TM installed in my Revo, I was anxious to get started and see what kind of performance improvement there was to be seen over the stock motor. The manual addresses break-in, however I chose to deviate from what it laid out as the break-in procedure. Normally I follow the manual to the letter with box-stock motors but with a high performance motor, such as the 18 TM, I like to follow the heat-cycling route myself. You can find more information on this break-in method here. Keep in mind though, that if you're new to nitro, I'd recommend sticking with the procedure in the manual.

During the break-in procedure, I found it necessary to lean the high speed needle some to get the motor up to a satisfactory operating temperature. More specifically, I was shooting to see temperatures break the 200° mark so I could ensure that the piston and sleeve were properly expanded during the break-in process. When the motor is completely cooled, the piston and sleeve fit is very tight. So I would recommend that you have a hair dryer or heat gun handy to warm up the motor before you attempt to start it. Not only will this make starting easier, but it will help prevent any premature wear due to the motor being operated at a low temperature for the first few seconds of operation.

The motor break-in process went without a hitch for me, and soon I was ready to tune the motor for optimum performance. While the high-speed and low-speed needles were easily reached, I did run across a snag with the idle adjustment screw being rather difficult to reach. To counteract this problem I changed the angle of the carburetor by loosening the cinch nut, which holds it in place, and then rotated the carburetor counter-clockwise slightly. This provided me better access to the idle screw, and made adjusting the idle much easier. I had noticed that prior to this the slide felt a little sticky, but once the carburetor angle was changed I found that it operated very smoothly.

Once the motor was tuned, I saw normal temps in the 220-240° range and gobs of low-end power. I was running the stock Revo Talon tires, and the 18TM just forced them to spin in the dry dusty conditions in the backyard. Top-end speeds with the stock gearing seemed to be on par with the stock 2.5R motor. However the low-end grunt of the O.S. gets it up to top speed in a hurry. Without adequate rubber at the four corners of the truck, the motor can easily overpower the wheels and bring the rear of the truck around catching you off-guard.

If you're after more top-end speed, the incredible low-end power of the 18TM will allow you to change your gearing to increase your top end speed. Seeing this ability, I made a mental note to pick up a 16-tooth clutch bell the next time I was at the hobby store. I figured that once I mounted a set of good racing tires to the Revo I would have problems keeping the front end down. Going up in clutch bell sizes would tame the low-end power some, and give me a little more speed for the straightaway.

Even with the stock Talon tires not gripping the dusty ground well, I could still manage to pick the front end of the truck up and ride out a wheelie if I did manage to get some traction. Wheelies in the grass, or on pavement, were no problem at all. However the ones that proved the most fun to watch were when the front end would lift, after getting back on the throttle, when landing a jump. The landing would firmly plant the tires in the ground and provide the Talon tires a good solid amount of grip.

At the track, and with a gearing of 16/38, the O.S. 18TM proved to be a perfect match for my local off-road track. Top-end speeds seemed to increase by around 4-5 MPH, and even with the higher gearing, there was no lack of ability to pull the Revo over the jumps as it made its way around the track. One pair of jumps that had previously caused me much grief with the stock motor was easily doubled with the grunt of the O.S. powerplant. The stock 2.5R just didn't allow me to build up enough speed from the time I exited the corner before it until I hit the first of the jumps. The O.S did this in stride, and that alone helped cut my lap times down. Further along the track the tabletops fell prey to the O.S. as well, as it showed I didn't need to use their back-slope. Instead the O.S.-powered Revo took to the air clearing the tabletop completely, landing back on level ground beyond them.

Even with my rather heavy Panther Pythons holding the Revo to the track, the 18TM was certainly providing me the punch I need to get around the track in a hurry. While the stock 2.5R is certainly no slouch at all, the O.S. simply blows it away in useable power throughout the RPM range.

The O.S. has also proven itself to be easily tuned as well. It has required very few adjustments in the times I've taken it out for runs in at the track, or even just bashing. At the track, it's easy to predict any adjustment that may be necessary as the weather changes with the O.S. 18TM. I found myself adjusting it much less than I normally would, had I been using the stock 2.5R during a day at the track. This is certainly another welcome benefit of the O.S., as it allowed me to focus on other aspects of my truck instead.

The O.S. 18TM is one mean and powerful motor. It's a perfect choice for those looking to replace the motor in a monster truck such as the Revo, because of the hefty amount of low-end power it provides. With heavier four-wheel drive trucks, there can never seem to be too much low end grunt helping it get up and over the jumps.

However there's more to the 18TM than just low end power. It has the sharp looks that will turn heads in the pits, thanks to the blue anodized head. Also, thankfully, the 18TM retains the easy tuning characteristics that many look to the O.S. Max line of motors for. This means less time tuning, and more time running, which is always a welcome benefit. While I have heard through the grapevine that some people seemed to have problems with the slide carburetor sticking, I found that moving the throttle bellcrank out on the mount and changing the carburetor angle eliminated any problems that I saw. So any issues anyone else may have seen were likely related to this as well, as the angle of the carburetor is very important to proper operation. That is simply part of fine tuning the motor for the application, and is certainly no fault with the motor or carburetor itself.

If you're racing, then the 18TM is certainly one of the top contenders you should be considering. Its size provides you with the largest motor you can run in most production classes, giving you the power you need to push your truck around the track. However, even bashers will be pleased at the amount of power the 18TM provides, giving them a solid choice that doesn't require a big block motor that sticks up and is susceptible to becoming damaged. The O.S. 18TM is a winner on all fronts!

O.S. Engines
Distributed Exclusively By
Great Planes Model Distributors
P.O. Box 9021
Champaign, IL 61826-9021 USA
Phone: (800) 637-6050
Website: www.osengines.com

Trinity Products, Inc.
36 Meridian Road
Edison, NJ 08820 USA
Phone: (800) 848-9411
Fax: (732) 635-1640
Website: www.teamtrinity.com
Products used: Monster Horsepower Fuel (20%), After Run Oil