My 5-Speed Manual Conversion / Tutorial

[ball_socket]

Summary
• I have a ‘22 JA55.
• This tutorial uses most of the original parts from the CT bottom end, with a few Grom/Monkey and aftermarket parts.
• My conversion is working but there are still some issues that need to be ironed out (see below).
• My apologies if this post is somewhat long-winded or if I come off as a smarty-pants cunt. That’s not my intention. I tend to get rather autistic when I write these kind of things and I error on the side of adding more detail so that somebody who wants to do this but maybe doesn’t have a lot of automotive or mechanical experience can do so.

My Story
My original plan was basically to break down a Grom bottom end, put an aftermarket 5-speed transmission in it, paint it silver, and swap the CT top end onto it. That way I could leave most of the original motor in tact if I ever wanted it or if I ran into some roadblock preventing the conversion from being completed. So I bought a blow Grom motor, tore it down, spent forever prepping it for paint, painted it, and found that the “Matte Crypton Silver Metallic” paint I purchased from automotivetouchup.com was way too dark (it’s more apparently in real life/in sunlight).


(Left: stock cover paint, "protector" ring painted with Scratches Happen, right: entire case painted with automotivetouchup.com)

I then tore down the CT bottom end. I found that other than the case paint color (the Grom case is black), there is only one difference between the Grom and CT cases: the right Grom case has two perches molded into it for attaching the “oil separator plate.”



When I discovered this I debated whether I should order a Monkey right case (because it’s silver and has the perches) but decided against it for three reasons: 1) It costs money 2) The semi auto bikes (CT and Super Cub) don’t have the oil separation plate, and 3) The newer motor design doesn’t have it. So how important can it be? Well it turns out it might actually be important; my clutch is dragging when pulled in all the way (make gear shifts crunchy and neutral hard to find at idle). I think there are several reasons for this: 1) I’m using an SMR 6-disk clutch, which will have less total separation between plates when fully disengauged compared to the stock Grom 5-disk plate. 2) My Magura clutch lever doesn’t have the same adjustability as a stock Grom lever/cable (I bought one and tried it), and 3) The lack of oil separation plate, I think, is causing drag between the plates and the basket due to oil circulation – I believe the separator plate’s purpose is to eliminate this drag. I realized that because I was reading a Grom forum where one member mentioned that he had failry bad clutch dragging issues with his Grom one time when he over-filled the engine oil, and after draining some oil the dragging went away (must have been spilling over the top of the separation plate?)

These are my theories… I will put a TB Parts 5-disk clutch in along with a Monkey right case and hopefully that will fix the clutch dragging.

Tools & Materials
”*” denotes items that are not strictly necessary or have some other special consideration.
• * ‘14-20 Grom 125A Service Manual from Helminc.com
• * ‘21 CT125A Service Manual from Helminc.com
• ‘13-20 Grom flywheel/stator puller tool (I used 150620/MP8 from Hard Racing)
• ‘13-20 Grom crankshaft assembly tool (I used Kitaco 674-1432700 from Hard Racing)
• ‘13-20 Grom clutch/oil spinner socket (I used a Chinese Special from eBay but if buying again would either try the one Drow sells or get the real Honda tool 07716-0020100)
• Tusk Crankcase Splitter 17-8668
• Clutch/flywheel holder tool (I bought PP2332 from Hard Racing but just use my hand and a small impact gun instead)
• * Small impact gun (I have a Makita XPH11ZB)
• A Penny (or Honda 2.5mm gear holder tool 07724-001A100)
• Dremel or file to notch out right side plastics to allow clearance for the clutch cable receiver, and to remove metal from the back of one of the right-side plastics mounts if using a Hymec (see below).
• A tube of Hondabond
• Blue threadlocker
• * Assembly lube
• A complete, or semi-complete gasket set including new exhaust doughnut (+ extras for oil changes -- see below) & Grom oil spinner gasket 15439-K26-901
• Honda Matte Crypton Silver Metallic (NH-A40M) paint. I had a bad experience with automotivetouchup.com, and used scratcheshappen.com paint (https://scratcheshappen.com/shop/touch-up-paint/honda-matte-crypton-silver-nh-a40m/) to paint the Monkey “right protector” – see “My Story” above. For the right case cover, inside the circular center portion of the protector, I used “Flat Black” High-Heat Rust-Oleum 248903.

Parts I'm Currently Using
• Stock top-end
• Stock 14/39 sprockets
• * CT left & right cases (see below)
• Grom crankshaft 13000-K26-B00
• Crankshaft bearing 91001-KWS-901
• Grom crankshaft drive hardware: 94303-03050, 15341-KPH-900, 23125-KPG-T00, 90741-KGH-900, primary drive gear “B” if using a new Monkey right case 23122-K26-900 (see below)
• Grom neutral switch 35759-K26-C01
• Grom clutch receiver & linkage parts: 22821-K26-900, 22810-K26-C00, 22815-166-000, 91305-K26-900, 22847-K26-900
• Grom oil spinner & hardware: 15431-K26-900 (I used a lightened spinner from Steady Garage), 90432-KPT-A00, 90231-087-010, (spinner gasket, mentioned above), 15441-K26-900, 3x bolts 95701-06014-00.
• CT gear shift spindle (I used the return spring from the Grom, which although looks beefier, actually had less tension than the one on the CT: 24651-K26-900)
• ‘19-21 Monkey right case cover, protector & hardware: 11330-K0F-T00, 11370-K0F-T00, 3x 19639-GBC-000, 3x 33715-GB0-900
• * Yuminashi 5-speed transmission for Grom/Monkey (see notes below about popping out of gear)
• * SMR 6-disk Grom clutch (see notes below about plate separation and clutch dragging)
• * +60% stiffer clutch springs (or whatever you want, my new TB Parts clutch came with its own springs)
• Hard Racing ‘13-22 Grom billet clutch lifter plate HR-BSP
• * Magura Hymec hydraulic clutch lever for Grom 2100004-20 (can use OEM Grom parts or an aftermarket cable clutch)
• * Male-side kickstand Sumitomo connector kit MTW-3 from Corsa-Technic (or you could ghetto-rig something for free)
• * Yuminashi oil pump (good time to upgrade)
• * Takegawa CT125 “crankshaft support adapter” 01-10-0145 + WickedGrom’s left crankcase cover mod

Parts I am going to try/would recommend starting with​

• ‘19-21 Monkey right case 11010-K0F-T00 (has perches for oil separator plate, unlike the CT right case)
• Grom/Monkey Oil Separator Plate 15661-K26-900 and 2x bolts 95701-06016-00
• OEM disks/plates (or TB Parts -- what I am trying next)
• * Hard Racing Shift Shaft Support Bracket (for the CT since you’re using the CT gearshift spindle). Some say these help with finding neutral, some say they do nothing.
• Takegawa or Kitaco 5-speed transmission (see notes about finding neutral and popping out of gear below)
• * KOSO Cam Chain Tensioner for ‘14-20 Grom (if you plan to do any power mods, this is a convenient time to replace the tensioner)

 

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Key Points / High-level Specifics​

• Because the stock CT’s ECU will not allow the starter motor to engage unless either the bike is in neutral, or the sidestand is up, you will probably want to close the sidestand circuit so that you can start the bike in any gear (up to you to pull the clutch in!). Originally I wired the Magura cltuch switch into the sidestand connector, but found that when you let the clutch out and applied throttle the ECU would either cut fuel or timing, making the bike stall – then the clutch was out the ECU though the sidestand was down so restricted acceleration. I used the male-side sidestand connector from Corsa-Technic (see “Parts I’m currently using” above).



• You need a Grom crankshaft, and crankshaft puller & installation tools (see above). The Grom crankshaft has a different spline configuration on the clutch side that facilitates the Grom/Monkey oil spinner.
• You will need to re-use your CT gear shift spindle. The Grom spindle is too short on the left side when it exists the case and won’t clear the foot pegs. However, the Monkey/Grom clutch covers have a hole in them that accepts the right side of the gear shift spindle, which is slightly longer on the Grom/Monkey spindle than the CT – the result if that without putting something in the back of that hole (I just compacted aluminum foil until it was the correct thickness) the CT gear shifter will slide ~1/8-1/4” left and right through the grease seal.



• Note that if you’re not using a fancy Magura hydraulic clutch lever, the stock Grom clutch cable is too sort. I also bought an XR cable that was way too long. You’re probably best of making your own cable.
• Because the CT shift pattern is 4-up, and the aftermarket 5-speeds are 1-down-4-up, you need a Grom neutral switch to properly sense when the transmission is in neutral.
• To make room for the clutch cable & receiver, you will need to notch out a section of the CT’s right frame-tube over. I used a Dremel.




• If you’re using the Magura Hymec lever, the slave cylinder is a tight fit and you need to bend one of the PCV hose hanger arms out of the way, and possibly remove some material from the back of the plastics hanger.




Actually Doing It
First off, if you’ve never pulled a motor apart don’t be afraid of it. If you have basic mechanical skills & tools (or even if this is your intro) it’s really not hard. The hardest part is getting the motor out and back into the frame.
Watch a few Grom tear-down and assembly videos. There are a bunch on YouTube. I like HunterTuned and WickedGrom.

You will need to remove the motor from the frame. You can follow the CT service manual or just start taking things off. I supported mine from below with one hand to soften its fall, but it’s pretty heavy and you might want to wratchet-strap it to the jack before removing the last of the 3 frame bolts.

Make sure to use Hondabond when re-sealing the case, and follow the application diagram in the service manual:



Turn the transmission input shaft and you slide the output shaft through the grease seal on the left case so avoid damaging the seal.
Riding Impressions
I love it. I feel much more connected with the bike having a manual clutch and it makes it much more enjoyable to ride for me. Maybe if I did more trail riding I would prefer the auto, but for a grocery-getter around the small town I live in the manual is way better.

Issues/Pitfalls
• No more kickstarter. I just barely care. Many new dirt bikes these days don’t even come with them anymore, and of the two newer KTMs I’ve owned I never missed it. Somebody on here also pointed out that the CT is very easy to bump start, which I have not tried, but it is probably even easier with a manual clutch.
• Removing the right case cover/cleaning the oil spinner is now a pain in the ass. You have to remove the left, top & right ftame tube plastics ,and the muffler, to allow access to the clutch cable receiver.
• Neutral is hard/impossible to get into when the bike isn’t rolling. I think this is a combination of the lack of clutch oil separator plate (see notes on Monkey vs CT right case) causing current in the oil to drag on the pressure plate, combined with the SMR 6-disk clutch having less total separation between each plate when fully disengaged, combined with a relative lack of travel of the Hymec slave cylinder vs. stock cable. See “My Story” above.
• My bike pops out of gear often when its under load which is super annoying. Maybe this is related to the clutch dragging but I suspect it’s the Yuminashi transmission’s fault. I will put a Kitaco transmission in and see if it solves the issue.
• My SMR clutch has started to develop some chatter while engauging after only 100 or so miles. The plates are likely glazing because of drag (see “My Story” above).

Other Thoughts
• This process is probably similar if you have a ‘23+ JA65, but you are lucky because you can use an OEM Honda 5-speed transmission from a ‘22+ Grom (or ‘22+ Monkey?)
• If you haven’t heard of how to remove a blind bearing using bread, check it out. I used buttermilk.
• If you use this information and find that something is incorrect or left out, please post here.

Even more thoughts I am too lazy to appropriately insert above
• Originally I used the Grom right/clutch cover but it has an aggressive styling that I’m not super into. Contrary to my initial assumption, the right cover “protectors” (the circular things with three bolts holding them to the cover) are all different sizes and not interchangeable. I decided to use a Monkey cover and paint the center of the protector matte black with high-temp Rust-Oleum to mimic the factory CT cover. I think it turned out well.

• The Magura Hymec clutch lever matches the CT styling perfectly (much better than a Grom lever, IMO)

 

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Images that exceeded the 10-image limit:

 

[m in sc]

nice way to do it. Me? id skip the hydraulic clutch, go cable. I don't think youre getting the throw you need. I ran into this when i put a 250 quad motor in my grom, but what I did there was shorten the throw arm out of the case (same basic setup) so that may be a solution to keep the hydraulic unit. .

IF i would have had a grom motor lower end laying around i would have done very similar to what you did, I even mentioned it in my thread when i did my manual conversion.

well done btw, i like seeing different solutions.

 

[Timmy6216]

A five speed is a slick idea for these little bikes. Out of curiosity, does it actually give you any better top end or any nicer low end?

 

[ball_socket]

nice way to do it. Me? id skip the hydraulic clutch, go cable. I don't think youre getting the throw you need. I ran into this when i put a 250 quad motor in my grom, but what I did there was shorten the throw arm out of the case (same basic setup) so that may be a solution to keep the hydraulic unit. .

IF i would have had a grom motor lower end laying around i would have done very similar to what you did, I even mentioned it in my thread when i did my manual conversion.

well done btw, i like seeing different solutions.

You may be right about the clutch lever. I'm still banking on it being an incompatibility with the aftermarket disks as that makes logical sense to me, and I know there are Grom people who love that clutch. We wi llsee!

 

[ball_socket]

A five speed is a slick idea for these little bikes. Out of curiosity, does it actually give you any better top end or any nicer low end?

The bike only had like 120 miles on it when I did the conversion so its hard to say for sure, but it does seem zippier. After all you're adding torque by effectively lowering the gearing. Top speed is the same.

 

[m in sc]

the discs themselves wont make a difference unless they are thinner,
what does matter is:
total travel from resting which is dependent on 1: slave cyl total travel 2: 'freeplay' between actuator and pressure plate 3: actuator arm geometry, and 4: fluid displacement at master.

I've done a bunch of hydraulic conversions over the years on other bikes, and i'm pretty sure the throw is the issue. another option is to 'back' up the slave cyl to try to increase total throw, OR if the'freeplay' in the motor is too great, shim the bearing out of the clutch pressure plate a bit to decrease it. ( i had to do this on the trail clutch using the grom cover) I used a grom cover on my trail bottom end, and the cover did sit further out from the hub than the grom one, but thats apples and oranges, but worth mentioning. .02

 

[ball_socket]

the discs themselves wont make a difference unless they are thinner,

The disks are actually slightly thicker on the OEM Grom clutch, but there is one less compared to the SMR clutch. The total height of the SMR stack is higher than stock Grom, and for the same through length on either disk set, the SMR will have less total separation between the plates so that could be causing some drag and exacerbating the Hymec's limited throw to begin with.

what does matter is:
total travel from resting which is dependent on 1: slave cyl total travel 2: 'freeplay' between actuator and pressure plate 3: actuator arm geometry, and 4: fluid displacement at master.

I've done a bunch of hydraulic conversions over the years on other bikes, and i'm pretty sure the throw is the issue. another option is to 'back' up the slave cyl to try to increase total throw, OR if the'freeplay' in the motor is too great, shim the bearing out of the clutch pressure plate a bit to decrease it.

There is no free pay as I shimmed the slave back a bit with washers
I do like your idea about shortening the actuator arm though!

( i had to do this on the trail clutch using the grom cover) I used a grom cover on my trail bottom end, and the cover did sit further out from the hub than the grom one, but thats apples and oranges, but worth mentioning. .02

Thank you, these are all good suggestions. I'm going to start with trying an OEM disk set. I think the hydraulic is really cool and the Hymec specifically aesthetically. But I may just have to bight the bullet and go cable. Do you happen to know a Honda model which has a clutch lever nicely matching the CT brake lever?

 

[ball_socket]

Another thing I've heard Grom guys say is that using a "shifter support bracket" (as in an external shift drum bracket on the left case) minimizes false neutrals.

I hope the Yuminashi gearbox is okay, I don't really want to spend $500-600 on a Takegawa or Kitaco tranny.

 

[m in sc]

yeah, i had to do lots of mechanical acrobatics to make the mechanical clutch work in the trail bottom end, mixing and matching plates also made the stack taller. I run into this a LOT on the older 2 strokes i have, mixing fz100 clutch frictions, banshee steels in old baskets designed to take 6 discs and then after this accepting 7. its a tricky balance but you'll get it.


for some reason ALL the pics when i did the clutch conversion on the trail went 'poof' on the server or id be able to show exactly what i did.

 

[ball_socket]

I put a TB Parts clutch disk set in (stock replacement) and things are improved. Still pops out of gear sometimes but a lot less often. Shifting is smoother. Neutral is now easy to find at idle/standing still. I removed the stack of washers on the clutch cable receiver @ the slave cylinder. I may put one washer back to allow it to disengage further. The extra disk on the SMR clutch definitely was not a good combo with the Hymec lever.

When I first put the new disks in I could adjust the lever at the handlebars so it would lock before the lever hit the bar -- good -- but after riding for a bit, even with the lever adjusted all the way out, I can now pull the lever all the way to the bar. Odd. don't know what's going on with that.