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After looking some more, I think the new moto may be related to the 2019+ fuel injected crf110 motor, and not related to the OG/SF grom motor. That would mean max bore sizes of 56mm which gives a capacity of 155cc with the new stroke. Look at these comparison shots of the stator covers of the 21 grom and the 20 crf110. I could be wrong, but we'll have to wait and see.

View attachment 88574

View attachment 88575

crf 2021 engine still the old msx-monkey -cub-ct-wave .
 

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Discussion Starter #42
Here is a video of the new engine being dismantled. it's not in english but they show a lot :

 

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Here is a video of the new engine being dismantled. it's not in english but they show a lot :

Some things I noticed from watching the video. Please keep in mind that I can't speak Thai, so this is just visual.
  • Definitely looks to be based on new CRF110. Small stud spacing means limited big bore size as per my previous posts and aftermarket og/sf grom heads won't be compatible
  • Transmission no longer uses blind bearings on the output shaft, so easier to replace without special tools
  • Transmission ratios are super wide ratio (see picture)
  • Clutch looks to be the same as current grom, so there's still hope the new 5 speed will fit our cases
  • Tensioner unit looks quite different, but still spring+hydraulic. Appears to have a cam chain guide to prevent whipping against the top of the cylinder
  • Crank webs are massive which compensates for the loss of the spinner in the new engine (rotational inertia)
  • Connecting rod appears very similar, if not the same as the current grom connecting rod. May be opportunities to use the kitaco rod kit with this crank
  • Rod length appear the same as the current grom. With the new stroke, this would give a rod ratio of 1.47, which is even worse than the current motor (1.6) for high rpm's.
  • Clearance between piston skirt to crank webs is very small

Did I miss anything?

88750
 

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2020 Honda Monkey and others
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Close up of clutch cover and oil filter similar to the aftermarket clutch covers for current models:

89321


The new bike has 5 speed stock, 1.6 gallon tank, customization from Honda.

I think I'll end up getting one of these to make my mini off-roader and make my Monkey a cafe bike.

With the Grom I wouldn't do the 181 4V though.
 

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Has there been further coverage about the new Grom engine?

If it is based on the CRF110?

I won't mind if it is. My next build is going to be stock bore or 143cc max to avoid having crankcase pressure issues.
 
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