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Discussion Starter #1
Background

I bought a Grom early this year and started racing it with friends. As bought, the bike has 7,000 miles and a header, pipe, PCV, tail tidy, LED signals kits, and a few other odds and ends. I installed Öhlins front and year, MNNTBX bronze swing arm bushing, sticky tires, and a few other odds & ends. Had a ball this summer racing and my bike is very evenly matched with my buddy's.

BUT

Last week while chasing each other around at high speeds (for Groms) my engine seized. Trailered home. Magnetic drain plug covered in shavings. No rattling when it went so I suspect bottom end. At this point I'm not sure whether the seized engine is worth rebuilding or if I should just go with a used engine (which I have a line on).

ANYWAY

My Grom friends and I have come to a gentleman's agreement that big bore kits aren't allowed. Max displacement is 125cc. Help me spend my money to make this track-focused Grom make more power.

Recap: Bike has header, pipe, PCV with unknown tune, and a seized engine. I upgraded the clutch this summer.

So, I'm looking at your various heads, pistons, cams, etc. My goal is the most power I can make with 125cc displacement without decreasing longevity too much. I look at all the options and I have a hard time deciding which would be the best combination of everything.


• Which head? Or OEM head with maybe some home porting?


• Is a 4 valve head possible? Is it even worth it?


• Which piston? Is a piston even necessary?


• Which crank? Or, stick with stock crank?


• Which cam? Or, stick with stock cam?


• Does converting to an oil pump add power to the rear tire because the oil spinner goes away, or is it just to improve lubrication, or both, or neither?


• With a higher output 125cc motor is an oil cooler a good idea? I don't want to add unnecessary weight, but will if it's functional.


• I see that heavier duty starters are offered. Necessary or good idea for 125cc built motor, or BBK only?


• Any other things I should be considering?


Again, I'm looking for a balanced package of upgrades to do to my Grom engine for power for road racing while keeping 125cc displacement.
 

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I can only offer my experience with building the original monkey engines up.
I haven't fully modded my 2018 monkey yet.
Only larger air intake and exhaust with Efie mod so far
115km/h indicated.

So if you want to modify the standard cylinder you want to increase your fueling, most accurate way would be with a power commander and an auto tune O2 sensor module, or go the cheaper way but not as accurate way with an Efie device.

Stick with the stock throttle body and injectors as they are enough for stock bore.
Bigger air intake and filter.
Free flow exhaust.
Upgraded cam, version 1 or 2 depends and where you want the power, and again brand will also effect this too.
High compression piston will help a fair amount too.
There are ported and bigger valve heads that would also make a good difference, but no point in trying to get a 4v head to fit with the stock bore.
The clutch case for removing the oil spinner is more of a convenience thing and adding the oil filter than anything else, though it might help the engine spin easier, can't say myself for sure on that.
There are a few little things you could do to but I guess that's the main things.

Oh and an oil cooler depends on your local climate and your type of riding, BBK would need them for the bigger kits, some people run the smaller bore kits without.
You can add one if you want and probably easier if you did change the clutch case, but not necessarily needed.
 

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• Which head? Or OEM head with maybe some home porting?
Ported stock head
• Is a 4 valve head possible? Is it even worth it?
Not on 125cc
• Which piston? Is a piston even necessary?
12:1 compression or greater - aim for 11.5:1 effective compression with your cam choice
• Which crank? Or, stick with stock crank?
Stock
• Which cam? Or, stick with stock cam?
Many good options, and none of them are the stock cam
• Does converting to an oil pump add power to the rear tire because the oil spinner goes away, or is it just to improve lubrication, or both, or neither?
Just get the Kitaco right-side cover and call it good
• With a higher output 125cc motor is an oil cooler a good idea? I don't want to add unnecessary weight, but will if it's functional.
A 3-row is a good idea if you run aggressive timing but in your area, it's not *needed*
• I see that heavier duty starters are offered. Necessary or good idea for 125cc built motor, or BBK only?
The Kitaco starter is a good idea with the high comp. piston
• Any other things I should be considering?
aRacer or Power Vision and a good tune, considering that's probably why you blew the first motor
High flow oil pump
Porting the throttle
5 speed kit and a set of sprockets

To be honest, I got bored pretty quickly with a 12.2:1 125cc motor and the TB cam. I have a 181cc NEO kit sitting in the garage; just waiting for my intake manifold to show up to have the head ported and matched to the manifold before I install it all.

 

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7K miles on the engine so I assume you bought a used grom from someone or you bought a 2018-19 grom new from a dealer and put on 7k miles.

First off drop the engine to inspect the broken parts, if engine stop working normally the piston went "lack of oil" or the stock OEM rod broke "lack of oil" or too many wheelies with out a modified oil pump with copper pipe extender.

split the case and check out the parts, it is EZ to rebuild on a stock 125cc.

Check out my posting on organizing your parts as you remove them from the crank.

If crank/rod failure you will have to buy a new rod kit, "cheap" on OEM parts.

Your stock head should be removed and inspected and if in good order do a head porting, valve cleaning and polishing and valve lapping. Open up your intake port to about 26-27mm and also your inlet tube for your throttle body to 26-27mm including your plastic spacer.

get rid of that PCV and get yourself a Arace mini2+ or mini5, this will get rid of you piggy back ECM unit.

Clean out the case after splitting and check for damage.

Get yourself a Kitaco clutch side cover to remove the oil spinner and get yourself a external oil cooler, lots of 5 fin ones on ebay from China.

Look up my old posting and read and re-read my post about organizing the parts being taken apart.

check the bearings for the crank and transmission to make sure the bearings spin freely with no lagging or ruff spots when spinning the wheel.

Use the correct assembly grease.

good luck
 

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I like the nature of the OP's thought-process regarding this idea, and I many times found myself thinking along similar lines: port the head, get a higher-compression piston, and add a cam -- all while still keeping it ridable and reliable and 125...…but it is the whole deep, dark, and confusing world of the fuel-controller requirement which leaves my head hurting and halts me in my tracks.

I will be really interested to see where this thread goes.
 

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Assuming stock sprockets and redline,
Let's say the 4 speed tops out at 45.7 mph at the top of 3rd gear. It's going to be at 5618 rpm when you shift into 4th, assuming you can shift instantly, which you can't but this is just an example.
The takegawa 5 speed is going to top out at 50.5 mph in 4th gear. It's going to be at 6208 rpm in 5th, again assuming instant shift time.
I think the 5 speed would usually give an advantage. You don't want to put it back together and then decide you want the 5 speed and take it all apart again.

Gearing commander doesn't have the takegawa 5 speed but I think the ratios are 35/15 32/19 28/22 26/25 24/26 if you want to plug those numbers in and check it out.
 

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Faster acceleration, if you're a good shifter, but the top speed remains the same, correct?
Takegawa kit has the same 5th gear ratio as the stock 4th.
Kitaco kit has a shorter 5th ratio (1.0) and will reduce top speed without considering sprocket changes.

Buy a full set of sprockets (34/35/36/37 and 14/15/16) and play with them until you're happy.

I'm running a 14-36 with the Takegawa 5 speed on my 125cc high-comp and it's pretty ideal for my riding and tops out at 72-ish (depending on redline). I am also running a fatter rear tire and a 428 chain so with the stock 420 chain, you can probably squeak a little more top end speed with a 15-37 or 15-36.
 

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Care to elaborate a bit? Not trying to argue, just curious on your thoughts.
Everything surrounding that company is drama and it stems from the owner. He's quite arrogant and he's got a chip on his shoulder. Anytime somebody questions his claims or even sometimes when a person is legitimately trying to learn he responds with a "how dare you question me!?" attitude. It's quite childish. And if there every came a time when you had an issue with his products or you needed help installing or troubleshooting you'd have to deal with that attitude.

Cameron, on the other hand, is a very nice guy and willing to help. I do not have any of his products, but we've chatted a couple of times and he's always very cool and helpful. And his products already have a great reputation.
 

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Everything surrounding that company is drama and it stems from the owner. He's quite arrogant and he's got a chip on his shoulder. Anytime somebody questions his claims or even sometimes when a person is legitimately trying to learn he responds with a "how dare you question me!?" attitude. It's quite childish. And if there every came a time when you had an issue with his products or you needed help installing or troubleshooting you'd have to deal with that attitude.

Cameron, on the other hand, is a very nice guy and willing to help. I do not have any of his products, but we've chatted a couple of times and he's always very cool and helpful. And his products already have a great reputation.
In life you will meet people that rub you the wrong way or their attitude sucks but if their products produces results that is all that matters to me. I've met a few of those type of people in life when buying surfing gear, diving gear, car/truck stuff, motorcycle stuff, gun stuff and the list goes on.

In my world of thinking if the product does it job and gets me the results I want that is all that matters.

Like I tell people it's your money spend it the way you want.

Most of the guys I run with that own groms use GFZ hardware, from his HD stud bolts, adjustable cam chain tensioner, cam breather cover, speed spacer and custom one of built cylinder/piston setup "241cc", and his stuff works.

Last of all no matter who you buy your hardware from shit happens, things fail, and such, bottom line is analyze the failure and improve on it and contact the seller stating what happened, most will make things right.

As for the real world, youtube posting of some of these fast Groms, you see the results if the run is good but you will never see the results when the engine goes Ka-boom, just remember that.

I've seen a few posting on youtube of grom wheelies causing engine failure and the poster has fixed the problem for his engine by putting in the modified oil pump with the extended copper tube, and most of these posters are non-seller people or vendors. In life if you are a vendor or sales person you never want to post or shout out your failures.

Ride safe
 

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In life you will meet people that rub you the wrong way or their attitude sucks but if their products produces results that is all that matters to me. I've met a few of those type of people in life when buying surfing gear, diving gear, car/truck stuff, motorcycle stuff, gun stuff and the list goes on.

In my world of thinking if the product does it job and gets me the results I want that is all that matters.

Like I tell people it's your money spend it the way you want.

Most of the guys I run with that own groms use GFZ hardware, from his HD stud bolts, adjustable cam chain tensioner, cam breather cover, speed spacer and custom one of built cylinder/piston setup "241cc", and his stuff works.

Last of all no matter who you buy your hardware from shit happens, things fail, and such, bottom line is analyze the failure and improve on it and contact the seller stating what happened, most will make things right.

As for the real world, youtube posting of some of these fast Groms, you see the results if the run is good but you will never see the results when the engine goes Ka-boom, just remember that.

I've seen a few posting on youtube of grom wheelies causing engine failure and the poster has fixed the problem for his engine by putting in the modified oil pump with the extended copper tube, and most of these posters are non-seller people or vendors. In life if you are a vendor or sales person you never want to post or shout out your failures.

Ride safe
I personally want to buy from a company that is going to support me even if I never need it rather than give me grief when I do need them to stand behind their products. I don't care if they have great products if the service sucks. But that's for everybody to decide on their own.
 
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