[nema741]

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[maz_636]

Hats off to you sir, well done.

I am so jealous right now !! Glad you're enjoying it though, I've still been looking every day for a crash damaged 250 but they're not exactly common in the UK so it's proving difficult....but I'm also in no major rush so i'll wait for one to pop up rather than spending money modding my stock engine.

 

[dubSolo]

Hats off to you sir, well done.

Agreed! That looks Sweet, Nema you did not waist anytime on top of being what sounds like an Awesome Dad. Congrats on the Success of your Build ride safe

 

[Paultergeist]

Wow......just wow.....I am so impressed.

When this engine swap was first described, I thought that the final outcome was going to look like a garishly-oversized motor sticking awkwardly out of an obviously too-small frame.....but that proved not to be the case at all. Based on your most-recent photo, the bike looks pretty well-proportioned, with a more-muscular, beefy look to the engine area. It works. It looks good. And importantly, you brought this ambitious task to a fruitful completion, where many others might have gotten stuck along the way and never finished. I extend my highest compliments to you.

 

[phillybuilt]

Wow......just wow.....I am so impressed.

When this engine swap was first described, I thought that the final outcome was going to look like a garishly-oversized motor sticking awkwardly out of an obviously too-small frame.....but that proved not to be the case at all. Based on your most-recent photo, the bike looks pretty well-proportioned, with a more-muscular, beefy look to the engine area. It works. It looks good. And importantly, you brought this ambitious task to a fruitful completion, where many others might have gotten stuck along the way and never finished. I extend my highest compliments to you.

What Paul said x100000... didn't think it would come out so clean!

Would be a fun little stunt bike for the street only problem would be the cage. I bet you can do some sick rolling burnouts on that thing... Slay tire for miles!

 

[nema741]

Thanks for all the comments! I am still blown away at just how fun this thing is now, First time I took the highway all the way to work this morning. When I had the BBK I would occasionally use the highway but use to dip off about 1/2 way and take the back roads. Today I cruised in at 80-85mph effortlessly. I still can't get use to not starring down at the temp gage, its very nice knowing having the liquid cooled. I love how the center of gravity feels very low and keeps the bike stable.

 

[Dutch-MG]

Looking so good nema741! But I have a question for you that isn't really clear to me yet. What are the total costs that you spend on this whole project? Because it's a really interesting mod that makes the Grom so much more mature and usable.

I think finding a used 250cc or 300cc Honda engine is the most difficult and expensive part. How difficult would you rate this mod on a scale of 1 (total mechanic noob) to 10 (true mechanic jesus)?

Looking forward to more pics and info!

 

[nema741]

Looking so good nema741! But I have a question for you that isn't really clear to me yet. What are the total costs that you spend on this whole project? Because it's a really interesting mod that makes the Grom so much more mature and usable.

I think finding a used 250cc or 300cc Honda engine is the most difficult and expensive part. How difficult would you rate this mod on a scale of 1 (total mechanic noob) to 10 (true mechanic jesus)?

Looking forward to more pics and info!

$678.89 w/hondagrom.net discount for the engine mount kit, chain, rear sprocket, header pipe, shift lever, (Ordered from Steady Garage)
$250 Engine, Radiator, Throttle body (local sale, right time right place, got very lucky) but expect to pay about $750
30$ CBR250r Wire Harness off ebay.
12$ CBR250r Coil & plug wire off ebay.
22$ CBR250 Cooling Fan for radiator off ebay.
9$ CBR250 Injector hold down cap off ebay. (plastic fuel adapter that holds the injector in the TB, engine owner couldn't find it)
Approx 8 hours of my time from the strip down to the complete build. Minus "3" things that I have not completely finished yet. Final mount for exhaust, license plate & radiator mount.

All in all $1,002.00 but most likely will easily cost you 1500-1800 depending on deals I also sold my BBK & other accessories that I had which paid for the bulk of this swap. I still have my koso DB-03 cluster, entire stock grom motor, stock cluster, grom sprockets to sell which will more than cover the cost of my entire swap.

Also, I bought a CBR250 fuel line which I was going to change out my smaller line from the grom, however the clips that hold the fuel line to the throttle body and underside of the tank didn't come with the line I got off ebay. Interestingly enough I'm using the stock grom fuel line with the CBR250 and have ZERO fuel delivery issues. Even know it is significantly smaller. Starting to think this entire "larger" fuel line conversations really are not necessary. My BBK ran just fine with the stock line as well......

 

[nema741]

Almost forgot about the "rating" for difficulty. This is a tough one (sorta). If you have common sense, are decent with tools (and have tools lol), do all of the research before beginning the job(pre-planning will save you on down time), learn how to do basic soldering than I will put this someplace at a 6 or a 7. The wiring is easy especially with the guide that I made, it's just time consuming. You also have to remove a few links from the new chain which is not hard. If I had another swap to do, i'm confident with saying it would be very easy to accomplish it in one day and back out riding. Now knowing exactly what wires I lengthened and such I would probably just work on the wire harness's sitting on the bench which would easily cut the time down on soldering / heat shrinking and wrapping all the new connections. Also i'm available to anyone that has questions or starts the swap and just needs some advice.

 

[CiscoSanJose]

thanks again for the cool write up and pic

 

[3sexy5u]

Yup, that's ALOT less than my 170 4V build. I think I'm close to ~2K in so far (99% done), and that's not even counting the Aracer gear. Honestly it's probably a good thing I don't know the exact number. All those supporting mods add up!

Love how the end result looks!! Beefy as hell.

I wonder what a tuned 170 4V and a 250 swap would look like drag racing. Power numbers between them are similar, but one is a bone stock Honda engine, and the other is a grenade I assembled in my living room...

 

[Dutch-MG]

$678.89 w/hondagrom.net discount for the engine mount kit, chain, rear sprocket, header pipe, shift lever, (Ordered from Steady Garage)
$250 Engine, Radiator, Throttle body (local sale, right time right place, got very lucky)
30$ CBR250r Wire Harness off ebay.
12$ CBR250r Coil & plug wire off ebay.
22$ CBR250 Cooling Fan for radiator off ebay.
9$ CBR250 Injector hold down cap off ebay. (plastic fuel adapter that holds the injector in the TB, engine owner couldn't find it)
Approx 8 hours of my time from the strip down to the complete build. Minus "3" things that I have not completely finished yet. Final mount for exhaust, license plate & radiator mount.

All in all $1,002.00 I also sold my BBK & other accessories that I had which paid for the bulk of this swap. I still have my koso DB-03 cluster, entire stock grom motor, stock cluster, grom sprockets to sell which will more than cover the cost of my entire swap.

Also, I bought a CBR250 fuel line which I was going to change out my smaller line from the grom, however the clips that hold the fuel line to the throttle body and underside of the tank didn't come with the line I got off ebay. Interestingly enough I'm using the stock grom fuel line with the CBR250 and have ZERO fuel delivery issues. Even know it is significantly smaller. Starting to think this entire "larger" fuel line conversations really are not necessary. My BBK ran just fine with the stock line as well......

Thanks for the write up man! Really appreciate it.

I'm going to be on the lookout here in The Netherlands for a 250/300cc motor. Until then I'm going to learn to do some more maintenance stuff and practice soldering.
Would appreciate the PDF file once it's finished

 

[CiscoSanJose]

Yup, that's ALOT less than my 170 4V build. I think I'm close to ~2K in so far (99% done), and that's not even counting the Aracer gear. Honestly it's probably a good thing I don't know the exact number. All those supporting mods add up!

Love how the end result looks!! Beefy as hell.

I wonder what a tuned 170 4V and a 250 swap would look like drag racing. Power numbers between them are similar, but one is a bone stock Honda engine, and the other is a grenade I assembled in my living room...

My friend has a 204-4v grom using the Koso 4v head and he has beaten most of the 250-300cc transplant grom around here in the Bay Area and only lost to the new Honda rebel 500 by a bike length.

Here's his bike with 13" wheels, his waiting for his custom CNC 241cc engine that will be coming from Kenny "GromFatherZ", using a Hoedar-Fujin technology standalone ECM

 

[pwr2wh8]

a well tuned 200+ 4v setup will givve a 250-300 stock swap a run for the money and probably surpass it. however, for the long haul/endurance, the 250-300 swap is the way to go. you are pushing the limits of with the 200+ 4v bbk setups so reliability over the long haul will obviously drop. with that said, i'm still up in the air going 4v or 250-300 swap. both have the pro's and con's. when riding at a spirited pace in the canyons/track, i might prefer a high revving lower torque setup so it's less likely to break the rear loose coming out of a turn.

 

[jeremiah420]

i want a 250 or 300 grom. the bad thing i have no room and prob cant be without it for a long period of time so i would prob have to pay someone to do it.. i cant even find used cbr 250 for super cheap.. and have no clue where to get brand new engine from. so not really sure how much a overall price would be to do it. though i would have to do suspension also.
but ya its two things i want to do to my grom eventually. have you done swaps before?
i never have. how long does it even take? for a first time.. to also someone who has done it before.. ?
not sure how much a good price would be to even pay someone to do it if i already had all the parts.
gl with it man.. groms should have came 6 speed 250s... to me the industry is a joke. they can make 1000 and more cc rockets
but not a 250cc minbike..

pwr2wh8 the swaps are gonna be where its at. wait till they start and big bore a swap. the revving and torque to me can be adjusted with sprockets and set up to how you want it.. the engine on other hand more gears engine running cooler. being able to legally go on freeway in cali since 250 is minimum legally. ect.. is also a big draw. and then also if you can haul ass and are lightweight on a grom big bored or not the 250 will just be that much better. a lot of bike racing is also rider.. the guy owning others with similiar set ups could be all his shifting and his weight over just the bike set up. and yes big bikes tend to try to go all out for a sec when i beat them off the line with my grom. lol

 

[CiscoSanJose]

a well tuned 200+ 4v setup will givve a 250-300 stock swap a run for the money and probably surpass it. however, for the long haul/endurance, the 250-300 swap is the way to go. you are pushing the limits of with the 200+ 4v bbk setups so reliability over the long haul will obviously drop. with that said, i'm still up in the air going 4v or 250-300 swap. both have the pro's and con's. when riding at a spirited pace in the canyons/track, i might prefer a high revving lower torque setup so it's less likely to break the rear loose coming out of a turn.

By the time everyone switches to 250-300cc water cooled,6 speed groms, honda will come out with there OEM water cooled units or even a new gen grom with 13" wheels water cooled 6 speed sort of like their proto type

something like this and if they don't build it than someone like KTM or maybe Suzuki might "little Busa"

 

[Mr. Thompson]

i want a 250 or 300 grom. the bad thing i have no room and prob cant be without it for a long period of time so i would prob have to pay someone to do it.. i cant even find used cbr 250 for super cheap.. and have no clue where to get brand new engine from. so not really sure how much a overall price would be to do it. though i would have to do suspension also.
but ya its two things i want to do to my grom eventually. have you done swaps before?
i never have. how long does it even take? for a first time.. to also someone who has done it before.. ?
not sure how much a good price would be to even pay someone to do it if i already had all the parts.
gl with it man.. groms should have came 6 speed 250s... to me the industry is a joke. they can make 1000 and more cc rockets
but not a 250cc minbike..

My $9k Grom was totaled and this is something I have put a lot of thought into over the last seven weeks as I plan the replacement.

In college while studying mechanical engineering in the late 70s I maintained a souped up MGB/GT which was my transportation and my autocross car. I still have the car, the rotary files purchased at the local True Value Hardware store and Black & Decker drill I used to port the head. I could change a head gasket overnight (blown racing around Woodward Park after the park closed at 10 PM) and have the car ready in the morning with a little bit of sleep. Over the years my skills have improved, with the exception of a pair of Prius (plural has yet to be decided upon and they do have rear sway bars) none of our vehicles are touched by anyone but me. I would not attempt a swap other than the Chimera kit without help. If you depend on your Grom for daily transportation think about this before doing any mods. Not trying to scare you away but the fabrication skills for an engine swap are a lot more complicated than just hopping your bike up or maintaining it.

You will need suspension upgrades, the stock Grom suspension is a marginal marshmallow at best. MNNTHBX's Galfer promo will give you all the brakes you need, simply stunning for the money.

If you want to pursue this I would suggest that you contact Scott's Steering Dampers. Ask them if they can provide the contact information for their machinist. He lives in Castaic and as I understand commutes on a Grom because it's a hoot, improves his smooth and lowers his lap times on the track. While I don't know if this fellow would be willing to do the job I suspect he will know who would be best in your area to do the conversion.

Edit: Re-read your post after typing this. Space challenged folks work on Groms indoors. Think small and use your imagination.

 

[nema741]

Opus - That was the only thing I really was unhappy with my BBK. The high rev's kept me always thinking "when" is it going to finally let go. Unlike the reliability of a stock motor that is not being pushed to its ever loving limits which also offered more torque and similar power to the Koso 170 4v setup that I had. Down low the CBR250 swap is excellent! It pulls very well up to speed. Where my koso setup seriously came alive at 6k+ rpm's... Other than the fact the CBR is able to take me at faster speeds then I was getting with my koso setup the overall high rev area of the koso was better. Example: I feel like if I were cruising at 50mph with the koso setup and nailed it until redline might be a touch faster than the cbr250 (not sure on the cbr300). But from a dead stop my CBR250 gets me up to speed very quickly but tends to "fall off" after 7k rpms. But the positive side to that is the engine sounds so relaxed verse my koso setup was just "screaming along" you could feel the RPMS coming up through the foot pegs lol... I think depending on the tune of a koso setup would determine the outcome vs a cbr250. I know that when I had my koso I originally tuned it to 13.0 AFR and got 19hp from it. Then I decided to up the AFR to 13.3 and re-did my map. The bike certainly had a REALLY good increase in power. Unfortunately I never put it back on the dyno to verify the numbers but from what I've seen people have gotten close to the 23-24hp mark on a koso setup. Also I never messed with my rev limiter. The 4v setup is capable of lifting the redline which I wasn't willing to do, because I Wanted my "grenade" to last a bit longer. So all in all, I'd agree that a koso with a 13.3AFR or leaner w/increased rev limit could take a CBR250 "stock" in a drag race assuming the riders were similar weight & skill.

Dutch - Send me a PM with your email and i'll send you what I currently have on the PDF.

Cisco - I've been considering those 13" wheels... Time for researching where I can get a set!!

Pwr2w8 - Agreed, although a properly geared 250 swap IMO would be amazing on track/canyons. I have a very steep/long incline here by me, and with my 230lb self with koso 170 4v setup I had to approach the climb at the right RPMS and jamming out shifting from 3rd to 4th at the absolute perfect time where 1/2 way up the hill had a slight reprieve from the incline, otherwise I had to down shift back to 3rd to keep speed all the way to the top. With the CBR I'm able to just "torque" through the entire incline without the effort of having all the stars aligned to make it lol.

Mr Thompson - I am very happy with the chimera kit, and would not go any other way to complete this swap as of now. I wanted nothing to do with modifying my frame as that is outside the scope of "fabrication" work that I have a facility to work with. Also very similar to work you have done, I have done quite a few engine swaps, builds etc to some of my prior vehicles.

 

[3sexy5u]

All that makes sense! I really appreciate the thorough feedback about the two setups. I can already tell the Koso really likes the revs, but like you I am keeping the revs limited for longevity. I think there's alot to be said about the capability of the standalone tuners we have available for our BBKs today.

Being 140 geared up is my true advantage, lol.

What kind of exhaust are you going to go with? I really like the look of the center exit Yoshis, I think you can use an aftermarket can off a CBR600RR, they have undertail exhausts.

 

[AvR]

Thanks for the write up man! Really appreciate it.

I'm going to be on the lookout here in The Netherlands for a 250/300cc motor. Until then I'm going to learn to do some more maintenance stuff and practice soldering.
Would appreciate the PDF file once it's finished

@Dutch-MG: I was already looking on the Dutch marketplace for an engine:
Engine 750 euro and 250 euro for ECU complete with keys and Hiss, the tacho cluster was damaged.

Think it's really hard to find this engine cheap in The Netherlands, think we need to extend our search to the whole of EU.