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2020 Honda Grom
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You sure you don't want a 300 swap? Now would be the time.
 
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Neo kit would probably be very reliable. I was turned off by what David from France and another former member had to say about some weird noise the Neo kit made.

I started leaning toward a big valve ported stock head, Koso 170 piston and cylinder, Kitaco forged crank and rod, along with the Takegawa 5-speed.
 
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Too much weight with the 300 swaps. I like it lean.
I agree 100%. Those things look pregnant or bloated to me. I mean, they’re neat, but I’d stay with the Grom engine.
 

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What was tuning it? Wonder if it was rich and washing the cylinder walls of any lubrication? Usually there is a nice carbon ring around the top of the cylinder and judging by the scoring on the cylinder... jk that thing is too far gone to say what any scoring was from.
 

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I went back and watched the video again. I’m not sure what bothers me more, the destruction of the engine or the fact that Pard is riding in the rain getting all that filthy water all over the bike.

With my OCD, I was like oooh, yuuuck. I was having all kinds of anxiety wondering how on earth I would ever get that thing clean if it was mine. lol...you think I’m kidding...

Throw in a blown up motor...talk about a bad day. Upgrayedd would be looking for a sedative dose of Klonopin.
 

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Just finished installing my 186 kit....
I hope it lasts a long time and never gives you any trouble. I remember reading another post where someone ran a 186cc kit and eventually the crankshaft snapped. If I remember correctly the 186cc kit lasted several thousand miles before meeting its end like Pard’s. I think they rebuilt the engine with another type of big bore kit, along with every supporting mod imaginable, including the Kitaco forged rod and crank. It was a thread about the bike not running correctly, but the guy gave the whole backstory.

It is so tempting to install one of the many big bore kits available and skip the forged rod and crank. It is a lot more work to split the case, and you have the additional expense of purchasing the forged rod and crank. I personally believe it is worth the extra labor and costs, though.
 
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I'm still going to run it, just obviously know what to look for. The piston isn't significantly much more weight, but the rod does seem to be the weak link. I have no problem splitting cases, but would rather not. Maybe I'll squirrel away some more money and when it comes winter time and I can't ride I'll add the forged one in. @Pard I see you like lightweight, perhaps a kx500 motor? Haha
 

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I guess the increased compression plays a role too, in a couple of ways. All of the BBKs are running increased compression. I imagine this puts more physical stress on the rod and crank, but also introduces more heat into the mix.

Yeah, next winter add the forged rod and crank if you can. You would be good to go then.
 
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Discussion Starter · #32 ·
Went ahead and ordered 2 new crankcase halves and the Neo 181 kit plus the tools required to get the job done. About $1700 all in. Not inexpensive.

Removed the engine from the bike and got a better look at the failure. That piston rod was the culprit.

I would not even consider running a BBK with a stock rod after seeing what happens.


89856
89855
89857
 

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Wow. It blew the whole bottom of the case out. That’s crazy.

Sounds like you are going to have a nice setup with the Neo kit. The bike will be even faster too. It’s a lot of money, but you are doing it the right way.

Two of my favorite sayings:

Good judgment comes from bad experience, and most of that, comes from bad judgement.

Experience is a hard teacher, she gives the test first, and the lesson later.
 

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This has happened to me many of times, where you located? maybe i can sell you what i have
 
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Discussion Starter · #35 ·
This has happened to me many of times, where you located? maybe i can sell you what i have
Feel free to PM me what you have to sell. I ordered a Kitaco NEO kit and new crankcases already, but may be interested in a complete motor ready to bolt in.

Thanks!
 

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EPIC damage, holy tits.
 
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2020 Honda Grom
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Lol, I'd swap spark plug brands. That one doesn't look too good.
what top 2 brand of spark plugs you recommend for the grom? I have a stock engine with only ecu w/Dino; air intake, yoshimura rs mini full exhaust with over 1100 miles on it.
 

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Wow. It blew the whole bottom of the case out. That’s crazy.

Sounds like you are going to have a nice setup with the Neo kit. The bike will be even faster too. It’s a lot of money, but you are doing it the right way.

Two of my favorite sayings:

Good judgment comes from bad experience, and most of that, comes from bad judgement.

Experience is a hard teacher, she gives the test first, and the lesson later.
i go by the quote ...”Experience is the BEST Teacher”.
 

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Yeah, keep us updated. I always appreciate your contributions to the forum.

If you plan to keep running a 186cc kit, it might be a good time to install the Kitaco forged rod and crankshaft. It looks like the rod broke to me.

The connecting rod and crankshaft are two of the weakest links on these engines.
noob here.....so since you said connecting rod and crankshaft are 2 of the weakest links on the grom engines is that after you install a big bore kit or stock engine or both? Reason I’m asking cause I was just thinking of replacing those 2 items you said on my stock grom since you posted those 2 are the weakest links BUT I wanted to ask you 1st.
 

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noob here.....so since you said connecting rod and crankshaft are 2 of the weakest links on the grom engines is that after you install a big bore kit or stock engine or both? Reason I’m asking cause I was just thinking of replacing those 2 items you said on my stock grom since you posted those 2 are the weakest links BUT I wanted to ask you 1st.
I feel that it is definitely the weakest link after installing a big bore kit with the typical supporting mods. Super oil pump, stiffer clutch springs, billet clutch lifter plate, better cam chain tensioner, delrin tensioner button, oil cooler, 4th crank bearing, etc. There is not much left to break after all of those items are upgraded to superior parts.

I run all of those mods and my bike is stock bore. I still push my bike hard. I feel that those parts only increase reliability. Horsepower is probably increased by around 50%. Increased from 8hp, up closer to 12hp now, is what I estimate. It runs at very high rpms for long periods on every ride.

These mods are pretty common on big bore kit bikes. People often skip the forged crank and rod, though. It is a lot more work to install them by splitting the case and adds significant expense. Some feel that it is not necessary. A basic big bore kit is pretty cheap, and not very difficult to install, so plenty of people want to just throw one on and enjoy the increased performance. The DHM 186 kit is extra tempting, because you can get an ECU flash for that kit, eliminating all of the tuning with a fuel controller or aftermarket ECU.

I’ve seen the crankshaft snap on stock bikes. Some people say it is due to a casting flaw, but I’m not sure. I won’t say it is super common though, but it has happened. They snap at the flywheel. All the ones I’ve seen, appeared to have broken in the exact same place. Someone suggested the Grom OG crank was more durable than the Grom SF crank. I have no idea if there is any truth to that.

On the other hand Ninelives17 has a ton of miles on his Grom. He has plenty of mods, but no big bore kit, and his stock crank and rod are still intact.

I will not personally install a big bore kit, without the forged rod and crank. I am of the opinion that it is only a matter of time before either the rod or crank breaks. Some people have put a lot of miles on a big bore kit without a failure. It’s just not a risk I’m willing to take.
 
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