MNSBR: Super Grom Build - MNSBR

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Super Grom Build

#16 User is offline   POE Icon

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Posted 02 April 2018 - 09:50 AM

View PostJim Hubert, on 02 April 2018 - 09:26 AM, said:

I once tried to break a bead by using a vacuum pump -- it did not work. But that would get all the air, and any moisture, out.


:lol2:

I used 3 wood clamps to break the beads on the Grom tires :D
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Posted 18 April 2018 - 08:36 PM

How stable are Groms once you get past 65mph?
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Posted 19 April 2018 - 07:51 AM

View PostnOOb, on 18 April 2018 - 08:36 PM, said:

How stable are Groms once you get past 65mph?


Compared to a full sized bike, they're twitchy at any speed. But when I'm pegged at 60, it's confidently planted and you can still do the handle-bar-shake and get away with it fine. Even though it's planted, it's still a short wheel base that reacts quickly to small inputs. I can easily and quickly dip in and out of lanes with confidence.


Once I put suspension on, front and back, it's MUCH(!!!!!) better. I shouldn't have a problem with it holding higher speeds. If I had stock suspension, I would not be adding power. Stock suspension would be very dangerous maneuvering at high speeds. The faster you go, the more potential for higher forces on the suspension that stock is equipped to handle in the least. In a quick-brake scenario, the stock suspension is garbage and bottoms out immediately. If you hit a horizontal crack mid-corner, even at 30mph, the front and rear bounce and cause you to fade out. Stock suspension is very VERY shitty. For a competent rider, suspension should be one of the first upgrades. For plain jane commuting, stock will get you by.
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#19 User is offline   Kent Larson Icon

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Posted 19 April 2018 - 09:32 AM

View PostnOOb, on 18 April 2018 - 08:36 PM, said:

How stable are Groms once you get past 65mph?


Never had any concern at any speed the wife's Grom could manage.
A few times I've been in full tuck and drafting I-94 traffic at 70-75 indicated with everything feeling smooth.

Later,
Kent Larson in Woodbury
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Posted 19 April 2018 - 10:02 AM

70-75? That must not be stock gearing... what does a Grom top out at (redline in 4th gear)?
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Posted 19 April 2018 - 10:58 AM

View PostKent Larson, on 19 April 2018 - 09:32 AM, said:

Never had any concern at any speed the wife's Grom could manage.
A few times I've been in full tuck and drafting I-94 traffic at 70-75 indicated with everything feeling smooth.

Later,
Kent Larson in Woodbury


If you play the full tuck and draft game, stock gears will always be rev limited at 73 indicated. Which GPS would tell you about 70 or maybe 71mph

I'm geared from stock 15/34 down to 14/37 (-1/+3) which puts my rev limited max GPS speed at 61mph.

A stock Grom with no draft, wind, or hill can aerodynamically limit at about 60-62mph on stock gears. Since 99% of my riding does not put me in a draft or highway situation where I need speeds higher than 61mph, setting my gears at -1/+3 lets me use the entire rev range up to 9500rpm to get to top speed of 61 It's all the power the Grom can offer across the functional speed of the Grom. It's the ideal ratio for best top speed and acceleration, excluding scenarios with draft, wind and hills.

When I get my new ECU, I'll have an increased red line that goes from stock 9,500rpm to 12,500rpm. Not sure if I'll still be making power at 12k+, but we'll see I suppose. I'm going to stick with the gearing I have now and try it out with the new engine build. I'll be going from 8hp to ~15-16hp so these gears should be very very strong. I'm sure I'll end up going higher eventually, but I won't know till I try it.
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Posted 19 April 2018 - 12:13 PM

View PostPOE, on 19 April 2018 - 10:58 AM, said:

If you play the full tuck and draft game, stock gears will always be rev limited at 73 indicated. Which GPS would tell you about 70 or maybe 71mph


Stock gears.
It's been a while. I'm sure I saw 65 indicated. I think I saw 70 but 75 is probably an exaggeration. Sorry. Good that you called me on it.
I do know that I was able to keep up with traffic. Barely.

Later,
Kent Larson in Woodbury
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Posted 16 May 2018 - 02:48 AM

Any updates? I'm incredibly tempted to add this to the Grom.
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Posted 16 May 2018 - 07:31 AM

View PostnOOb, on 16 May 2018 - 02:48 AM, said:

Any updates? I'm incredibly tempted to add this to the Grom.


There was a supplier backorder on a couple of the parts from Koso, so the kit just shipped out yesterday. I'll start tear down this week or this weekend. It works out well because I think my rear tire doesn't have much life left in it. I have a new Pilot Pure SC ready to slap on there.

I'm also going to upgrade chain/sprockets to 428. The stock 420 chain stretches bad enough with the stock motor so adding more meat there should help. After looking into it a bit, 15/35 sprockets seem to be the recommended ratio for this HP goal. Will probably order chain/sprockets today.


Once I strip the stock motor I'l get the cylinder honed and be ready for kit delivery and assembly.
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Posted 21 May 2018 - 10:04 AM

I got the whole kit at home finally.

Now I just need to find time to tear down, get the cylinder honed and start slapping it back together for some break-in riding around the neighborhood.

Speaking of break-in... Does anyone have suggestions on how to break in a 125cc high-compression engine?

I also never knew exhausts should be broken in. The new Hindle I bought suggested a 15 minute idle for a warmup and then 15 minutes of cooling. I did that yesterday on my stock motor because I wasn't sure 15 minutes of idle is what I wanted to do on a brand spankin' new Super 125 build. The hindle is LOUD AS FUCK. But with the baffle in it, it's only just loud. I can live with it. I'll be curious how tame the baffle insert can keep it after the build.

I don't want to work on my garage floor for this build, so currently the Grom is just going to be suspended from the joists in my basement. It looks weird as hell, but it'll save my back and neck from working that much on the ground. I'll post a pic once it's fully lifted off the ground. Right now I only had time to get it an inch off the ground as a proof of concept.
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Posted 22 May 2018 - 07:28 AM

Didn't have a ton of time to work on it, but she's suspended like a kinky masochist and half stripped down. Everything that runs to the throttle body and head is disconnected and I'll have the head off tonight and ready for honing.

(FYI: ratchet straps are cheaper than a bike lift :thumbup: )

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Posted 22 May 2018 - 09:16 PM

Nice piņata
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Posted 22 May 2018 - 09:44 PM

That's a lot of confidence in that 12 bar....
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Posted 23 May 2018 - 07:22 AM

The bike is < 200lbs. WIth 3 points of suspension, it'll be just fine.
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Posted 25 May 2018 - 10:19 AM

Small update

Head and cylinder were removed a few days ago. There was some minor vertical scarring on the inside of the cylinder. Best guess is it has been getting too hot and expanding caused by long wheelies and starving the head for oil. I have a new oil pump with a pickup line so it can still get oil when at balance point. I also bought an oil cooler that will both keep things cooler and allow for more oil in the system.

I got the cylinder honed last night and started reassembly. I got stuck when I dug into stator cover to replace the cam chain tensioner and couldn't get the flywheel off. I'll be borrowing the correct tool tonight and hopefully finish the motor assembly tomorrow, if I can find the time. I likely won't have this driveable till next week sometime. Too many other things going on.
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