Hello all,

Im a Canadian who is looking to swap CBR power into Honda Groms. Trying to connect with some people who have experience with the CBR125R and the CBR150R. What major problems/tips do you have? I'm hoping to strike up some chats that will lead to accessing the classifieds. If someone can direct me to an importer who can get me used motors, that would be amazing too.

I can find lots of CBR125 donor bikes close-by, but what I really want is the 2002+ CBR150R motor from Thailand. It's the exact horsepower/transmission gearing/weight I'm looking for with factory Honda reliability. I really don't want to take a vacation to Thailand just to buy motors.

 

Hi ,as your aware they are manufactured in Thailand, so this is the closet link I've found, but I think there's a minimum amount to buy, but may help your search
https://www.alibaba.com/product-deta...41067deaTJOvBR

 

Hey that's awesome! You're the only one who's offered tangible help on any forum lol.

I'd much rather find somewhere that sells used motors or brand new honda parts so I can make my own...but I had a flare-up of my insomnia so I crunched the numbers on the CBR125R transmission. I've posted the ratios below. The 125 might be the way to go for my build, and I can swap the Grom motor into the CBR chassis to have 2 bikes whereas if I source out just a motor all I have is a spare motor. I cannot afford a whole CBR150 and import it lol, not even a used one. Importing a motorcycle has almost no taxation if it doesn't have wheels attached (I looked it up). Because I can get a running CBR125 used for under $1500...my mind might be made up. PLUS CHECK THE RESEARCH SPEAKS FOR ITSELF!

I adjusted the CBR gearing ratios to the wheel size on the Grom, and figured out a sprocket combo that felt suitable. Once I did that, I scowered the internet for the weight of all the stock drivetrain components from the CBR125 to do a curb weight and unsprung weight comparison.

Transmission Gear Ratios: Grom* is 16-tooth front, 32 rear. Grom** is 16-tooth front, 31 rear. Stock Grom wheel diameter is 12", CBR125 is 17, margin for error in ratios is tire profile.
CBR(stock) CBR(Grom*) CBR(Grom**) Grom(stock) Kitaco 5-speed
First: 4.86 (3.26) (3.12) [2.5] [2.571]
Second: 2.73 (1.83) (1.75) [1.550] [1.722]
Third: 2.04 (1.37) (1.31) [1.150] [1.33]
Fourth: 1.65 (1.11) (1.06) [0.923] [1.130]
Fifth: 1.47 (0.985) (0.944) [-----] [1.0]
Sixth: 1.3 (0.871) (0.85) [-----] [-----]

As you can see, I get both more acceleration and more top speed over both the stock 4-speed and the Kitaco aftermarket 5-speed. 5-speed conversions use narrower gears and are less reliable than OEM Honda parts.

I like the 16/31 ratio of the "Grom**" gear combo. A lightened 16-tooth is lighter than the stock 15 on the CBR, and the aluminum 31-sprocket I would use is half the weight of the steel 42-tooth on the stock CBR. The rear wheel on the grom weighs about 7 lbs but I'd probably go carbon-fiber on the back to save even more unsprung weight but the stock CBR wheel is 17-inches...can't find a weight for the wheel but Im guessing its closer to 10 lbs or more.

As far as weight goes, a grom weighs 225 lbs full of fuel but a CBR125 weighs 304. The motor in the CBR likely weighs about 10 lbs more with the rad full but I'll delete a ton of stuff to make space for the rad. I found a source for CBR150 rads so I'd use it because its likely bigger and brand new. Center of gravity will be basically the same as a stock grom and it should appear stock because it's a 125 Honda motor that allegedly bolts right in and even uses the same ECU.

With all that out of the way, I can look at the actual performance. With the airbox totally removed for the radiator, I'd throw on whatever intake I can make work that comes out the side. I would add an ignition upgrade but I wouldn't change the redline. I'd upgrade the clutch and springs because of the revving it'll do. Add a full exhaust so I can have a bung for an auto-tune to get it running before a pro tune on dyno to see what it does. I would also have a valve job done and send my transmission gears as well as piston/rod/crank to be WPC treated. Fuel injector is cheap if it needs it.

Stock Grom Specs: 9.7 HP/8.04 TQ Redline: 8000rpm
Stock CBR Specs: 13 HP/7.7 TQ Redline: 11,000RPM

What I'm Gaining:

• 3.3+ Horsepower (probably more)
• Higher RPM ceiling
• Better transmission/gearing combo(increased acceleration AND top speed over stock Grom)
• Better reliability than factory while maintaining factory appearance for inspections
• A second bike I can frankenstein together with the Grom Motor for fun or sell it
• No need to purchase aftermarket Clutch cover/oil cooler setup, or purchase/install unreliable aftermarket transmission
• No need for high-end performance parts or Big Bore kit to improve Grom performance, no need for oil cooler

Losses:

• 0.3 lbs/tq from the original motor but the intake/exhaust/ignition/valve job/injector will mostly likely bump that up
• a lot of time and effort
• unable to install oil cooler or turbo without custom machining the block
• ability to install Oil-spinner delete or standard oil filter
• no dry clutch available
• fuel economy...LOL...

Well that's what my insomnia came up with...I want a Grom I can ride for ages in the heat and actually do highway speeds without redlining all the time until it overheats. Big block kits and aftermarket transmissions have no guarantee of reliability. It needs to be a Grom though because it fits in my car. Because I'm canadian, exchange rate and shipping make the parts I'd need for a stock Grom actually cost a lot more than a used CBR125.

Eventually I'm taking it across canada, as well as set up a 125cc race series, so Im trying to get out in front of my potential issues. End of rant.

 

A Grom fits in your car? Does that mean this qualifies as a trunk bike?

I guess you can't shoehorn a 250 in though eh? That's probably getting a little greedy

 

Lol you might call it that yeah

actually a 250 has been done, alone with 300s (there are exhausts for them even), but I just need a little more speed not a lot more speed. It also costs too much to buy one used and I have a Honda Rebel 250 twin in my garage

there's a guy who made a 990 ducati grom and a guy who drag races a 450. I'm looking for reliable, driveable, smaller than a 250 but just as fast. I also want to be able to use the second bike with the grom engine and a 250 will be too big

 

Can see you have gone into this to the enth degree, hope it all works out and good luck, keep us updated with your progress and any pictures

 

That's pretty rad

It's interesting to me that the ECU would work on either engine. I guess so long as the engines are roughly similar all it would worry about is the air/fuel ratio. Wouldn't the rev limiter kick in at 8k still? I mean if you have a donor it would be a non-issue since you'd swap them anyway but still

Where in Canada?

 

I would have to flash the ECU with a new map for the cbr125 but it's not a tough job considering it needs a tune anyway


Near Ottawa, which is central to Montreal and Toronto so used bikes are dirt cheap