Honda Grom Engine Swap: Twice the Engine for Twice the Price - CBR 250cc / 300cc How-To

The Honda Grom doesn't really solve any problems. It's fun but limited to nine horsepower of fun even on my relatively short commute to work where there are no speed limits over forty-five miles per hour. I usually go full throttle. from stoplight to stoplight with its little

engine

screaming like an angry leaf blower there's something to be said about riding fast on a slow bike and this is a slow bike that's fun to ride fast but it needs to be a little faster, it needs a little more big The motor needs a 250, the ground needs more power, but just a little, maybe we go from nine to, I don't know, 25, maybe 30.

Some people go even bigger by launching 400, 500 or 700 CC motors in these things, some guy went to the max. Crazy and I put a 205 horsepower Ducati

engine

in it and one of those things that doesn't really work, it would share the rear axle and wrinkle the swingarm like a used tissue, but I digress a little more power, what you need is 250 or 300 DC. engine specifically a Honda CBR 250r or 300 R or 300 F or even a rebel 300 engine. I'm going to use it 250 because I found a good and cheap one essentially, it's the same process for any of the Honda NC 51 or MC 41 engines, so Yes you're doing this with a 300, every time I say 250 just pretend I'm saying 300, it may be tempting to save some money and just buy the engine but you really need so many 250 parts that you should buy. entire donor bike, you will need the engine, radiator, radiator fan, throttle body wiring harness, a bunch of sub harnesses like headlight and battery relay, ECU, handlebar controls, ignition boot, etc., so it is easier and cheaper if you buy. the complete bike basically all the other things you need you can buy from a company called Steady Garage some of the things you can make yourself and save money but most of it is worth buying this is what I bought if You don't have one. welder, you may also want to get the radiator and exhaust.

I have done a few other engine

swap

s and while this is not trivial, it is by far the easiest I have done, requiring no special tools. There's no fabrication you need to do if you've done a few engine

swap

s before you can do this half drunk, which is pretty much how I did it, okay here are the basic steps, pretty simple, okay let's break them down into a few more discreet steps. It seems like a lot, but it's all pretty easy and pretty quick. The only thing that really takes time is putting the wiring harness in and plugging everything in, so the first thing I did was take the 250 apart, it was super easy and I did it in just a few seconds.

As you can see, the only thing that was a headache is that it was a little difficult to get to the electrical connector under the fuel tank. I ended up just cutting that connector off, which was nice because when you shift it to the ground, I actually need the length on that connector anyway, we'll get to that later, but feel free to cut the connector off when removing the fuel tank, drain the coolant, unplug all connectors, remove the engine bolts, lower the engine with a jack or simply with force. it's not that heavy, the next step is to do the same with a Grom, this is also easy, especially with power tools and a friend again removes the plastics, connectors, chain motor mounts and coolant hoses.

Just kidding, there are no coolant hoses, don't forget to bring the chain. There's probably a master link for this, but I have these bolt cutters that I never use, so I'll use them. This is also a good time to replace the front sprocket with the new one that is secured with this small plate. The plate is bolted to the sprocket and has some teeth that engage the groove in the countershaft. It's probably a good time to change the rear sprocket as well. You will need to remove the wheel and make sure to tighten these four bolts down. to specify or just use it again if you're feeling lucky this is where I did something a little stupid.

I put the 250 on before removing the Grom harness. This is a problem because the 250 captures the wiring harness and then I got really lazy and instead of pulling the engine out to get the wiring harness I just cut it off which is really stupid because if I want to use this engine again on someone else crazy project I'll have to buy another wiring harness so it's just where you need to remove the harness before putting the motor in to put the motor in the Grom. You will need a support. You can probably make one yourself, but I recommend spending money on this.

I'm generally a big fan. build it instead of buying it, but this bracket is worth the hundred and eighty dollars, the spacers are kind of important so keep an eye on where they are when you take it out of the box because that's how they go into the engine, take the spacers out of the middle. and put them on the Grom first, they should be tight so you may need a hammer to tap them in, they will stay in place while you install the motor. The short spacers all go on the right side except the really short one which goes on the left side between the frame and the bearings one of the frame plates will go here between the spacers here and here is a welded sleeve that goes here the other side of the frame just goes out to get the With the engine running, you will have to completely remove the right rear assembly and loosen the left rear assembly.

There is a bolt that goes through it that holds both rear assemblies and also holds the swing arm, so make sure you don't pull on the bolt all the time. outlet, otherwise you will lose the swing arm, then simply lift the motor, line up the top center bolt hole and put a bolt through it, put in the rest of the bolts and spacers. I left the bolts loose at this point and tightened them. Later, but if I were to do this again, I'd probably just tighten them now. It's much easier to get to them before placing all the other things.

There is a bolt that needs to be oriented in the correct direction. This is the correct one. Here, if you have it like I have it with a nut on the left side, the chain will rub. This is bad. I had to take everything apart after putting it together and it was a pain, so go ahead and install. it's the right way now you want the bolt head on the chain side and the nut on the other side you need to space out the right rear set you can do this with a couple of washers you also need to modify the brake lever to clear the motor I did this gently and carefully with a hammer.

You may have noticed that the engine won't start if you have the throttle body engaged. Maybe I should have mentioned that first you need to remove the throttle body between the engine and the throttle body you need to use this little elbow that comes with your bracket, this relocates the throttle body to the side and is really the only way to position the throttle body there without seriously modifying its frame, it has some drawbacks, the fuel injector is not in the correct location and we will talk about that later if you remember the previous video. I tried installing the engine with the elbow and throttle body attached, it's kind of a paint job, he has to do that, so I just take it off.

Place a paper towel in the intake port to prevent things from getting in there, install it and then place the elbow on the throttle body on the rubber elbow, it's a bit of a crude way to attach the throttle body to the engine, so which I recommend making some type. of strap to attach it to the frame or motor, only the filter for this KNN has a working capsule filter, this is the part number. You can also do it, if you feel dangerous, just use a screen filter, install and adjust the clutch cable. It will fit completely on both the motor side and the lever side.

It barely fits, but it does fit. Install the throttle cables again. You will have to adjust the cables completely. Now it's time to attach the 250 wiring harness. This is the only part that's really time consuming. I started in the middle of the throttle body. I reconnect all the spark plugs to the engine. The only two I had to extend are the fuel tank spark plug and the ignition coil wires, you need to install the spark plug. rips from the 250 to the Grom ignition coil, you can just unscrew the one from the Grom and then screw the one from the 250 on.

You can also swap the entire coil and wire assembly if you want, it's the same coil between the two. Bikes stuff excess wires into the glove box and behind the headlight and anywhere else where everything needs to be zip-tied, you will also need to purchase the headlight adapter for 2017 and newer Grom to use the factory headlight. I used the left side handlebar. controls from the CBR because the Grom pigtail was not long enough and for the right side I just took the controls apart and looked at what each of the cables did and then took the one from the CBR and looked at what those cables did and then I just made cables from bridge between the two to be able to use the Grom's controls.

If I were to do this again I would probably use the handlebar controls on either side of the CBR, it's much easier. I definitely recommend you do it. that if you have a CBR 300 F, the Grom board will connect directly to your harness if you don't have it and want to use the Grom; you will have to cut the plug from the wiring harness and rewire it. I found this wiring pen I looked for it online to help with rewiring but I didn't use it so I can't verify it's correct. I only used the 250 board, it's a bit ugly.

I'll probably change it eventually, but it works for now. I made a stand. Clipping it to the bike and just plugging it into this dash is also nice because it has a temperature gauge and also provides the correct RPM up to the redline which the Grom dash doesn't do. Some of you are wondering what it has to do with the fuel system, do you take the pump out of the CBR and put it in the Grom somehow? Well, it turns out you don't actually need the bomb in the Grom. It's totally fine for 250 or 300. It's a little strange. the bike makes 9 horsepower, but the pump can handle up to 30, that's okay, it's easier for us, all we have to do is extend that plug on the 250 harness and extend the fuel line, extension of the Fuel line requires a little work, but it's something like that.

Easy, basically you need to remove the ends of the 250 fuel line, just cut the little metal clamps that are there and remove the fuel line, then you will need to go to your auto parts store and get some 5/ fuel 16 inch. The line is technically 8 millimeters, but 5/16 is almost exactly 8 millimeters and is much easier to find, cut it to the right length, attach the 250 ends, put some hose clamps on it and you're done, for some reason. The Grom key has two switches, but you only need one, so take two of these wires and ignore the other two.

You will need a wire on a Zener diode. I don't think you need to do this if you're running an aftermarket ECU, but I'm not sure the diode needs to be about three point nine volts. You can search this part number and purchase it. Make sure you have the diode facing the correct direction. I'm not sure why this diode is needed in some safety feature apparently the radiator. I use the 250 radiator and welded on some new brackets. This is easy enough if you have a soldering iron and can inflate them, if not, don't worry, this is another thing you can do.

Just throw money at a stable garage will sell you a radiator with the correct brackets already in place, the plastics can be trimmed a bit to fit better but I only cut out a small area for the filler cap and the rest just moves out of the way. You may be able to modify the CVR hoses to make them work if you cut them and fit them and maybe use some unions, but I just bought the preformed hoses, it's much easier. I recommend that now seems like a good time to test starting the engines. to make sure everything is connected there is no escaping so it will sound like a robot fragmenting the 250 uses a 520 chain which is recommended because the

grom

s 420 chain is a small weak chain with a new chain that will need new sprockets and since the wheel sizes are different you will need a new ratio.

I did some calculations on a spreadsheet and determined that I arrived at the same relationship that the CVR has. You will need a 15 tooth front sprocket and a 32 to 3r sprocket. It gives you the same top speed as a CBR with a correct speed reading on your dash. If you are not using this gear ratio, you will need to get a speedometer correction. You can get them for about $75 and they are really easy to set up. This is another thing you may not need if you are using an aftermarket ECU EGR block off plate. You can buy one of these for about $30, but I decided to be smart and modify the existing one by tapping the outlet and plugging it in. with an NPT plugTurns out it's actually not a great idea because it's too tall and interferes with the radiator fan.

I guess I'm not that smart. I ended up making a flat one out of some aluminum I had lying around. You need a new exhaust, you can buy a custom or working header for this and just put on your own muffler. You can only do this if you don't live in California, they will not ship to California addresses. I guess if you have a friend out of state you can send it through them. I live in California, but it's okay because I have a welder, so I just cut and soldered a temporary exhaust to get everything working.

I know it looks like total garbage, it's also too low. I scraped it. I first took the bike out, I'll find out more later, but it works for now. Before you put the body back on, you'll want to remember to tighten all those engine mount bolts you left loose. In fact, just check every bolt, now it's time for a test drive, get in, turn the key on, okay, dash lights up, everything's okay, push the start button, give some gas, this one Things don't like to be inactive, especially in a minute. go ahead and shift into first and ahh, did you forget to put the shift in? shifter, idiot, you can't ride without a shifter, okay, no big deal, put the shifter in real quick, let's try that again and If everything was put together everything should be fine, you will notice a whine when I let off the throttle, that is normal, they are those roller bearings that come with a kit, the bearings are there to prevent the chain from writing on the frame, now we have to put the rest back together, the intake will need a small hole cut in the body I just lifted the body up about where it was supposed to be marked, the center of the throttle body I cut a hole a little smaller than I needed, then turned it back to put on and I finished it off with a dremel and before we put the glue on there is one more thing we need to do, so the last thing is the ECU, the ECU needs to be readjusted.

I haven't done this. I'm still using the stock tune, it's not great, there's definitely more power than the Grom, but there's so much left in there that it's kind of a full video anyway, so I'll just say that maybe you want to tune your ECU or maybe you want to be lazy like me and write it like this for a while, an extra one. The thing is that the fuel injector, the location of the fuel injector is not ideal. Remember when I told you this doesn't idle very well with that curve in the intake between the throttle body and the engine, the fuel doesn't atomize properly at low rpm and the bike just stinks below about 4500 rpm.

I solve this by designing a metal angle that replaces the silicone tube that comes with the kit. This places the injector close to the engine so it can spray directly behind the intake valves. It doesn't look much better, but that could simply be because I haven't tuned the ECU yet. You need a very tight bend. I got mine from a stainless steel donut. You will need a three-quarter inch outside diameter bend with a maximum bend radius. from one and three quarters of an inch cut a ninety from the donut omit a nozzle boss solder some thread make a small dent there to clear the frame wow buddy, I thought you said this didn't require any fabrication, what is this? getting out and soldering well good news about the time I was finishing mine someone started selling this stuff.

I can't speak to their products specifically, but it's probably worth buying if you're trying to get the most power out of your engine, that's all. Have a Groomzilla go to your local DMV Get your custom

grom

s and a license plate Take it out on a nice drive along the coast Enjoy the beautiful sunset and the feeling of a job well done Do you like your automotive ideas half-baked and questionably Well if so hit the subscribe button because I have a lot of them, enjoy the video, give it a like and thanks for watching.