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So my stock cranks is broken and will be replaced with a forged one with the new 186 kit .... so should be ready in 3 days
Hi Adam, just wondering, did you blew your hc piston engine becoz of the crank? What's the RPM limit of your bike and did you have 4th bearing installed on the crank? Thanks.
 

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Discussion Starter · #22 ·
Hi Adam, just wondering, did you blew your hc piston engine becoz of the crank? What's the RPM limit of your bike and did you have 4th bearing installed on the crank? Thanks.
It was only the crank that broke the piston and all DHM parts are actually fine
 

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It was only the crank that broke the piston and all DHM parts are actually fine
Thanks for the reply Adam. I can see where it breaks from your photo. I was expecting the connecting rod. Wondering if i should look for reinforced crank for stock hc piston. Seems like monkey father sells them.

Anyway, i'm planning to get DHM HC piston and head. I'm still waiting for his reply to some of my questions. Otherwise, might go for kitaco neo.

Just wondering, if we stays at stock rev limits, will we see much improvement in top speed with HC piston?
 

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Discussion Starter · #31 ·
I do believe the reason my crank snapped was earlier in the year I was T-bones an an intersection and my bike was repaired. I do believe this is the source of the issue with the crank for this is the side I got hit on. I am still very happy with the DHM stage III and if I didn’t make the decision to go to 186 I’d be keeping it. To answer your questions though at 125 I don’t think a Forge crank is necessary
 

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Discussion Starter · #32 ·
Got the bike today !

Only issues is the stock clutch can not Handel the power !
Ordered koso lifter plate and spring kit and clutch plate
 

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Did you consider the SMR 6 disk kit? A lot of people including myself like it.
 

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I do believe the reason my crank snapped was earlier in the year I was T-bones an an intersection and my bike was repaired. I do believe this is the source of the issue with the crank for this is the side I got hit on. I am still very happy with the DHM stage III and if I didn’t make the decision to go to 186 I’d be keeping it. To answer your questions though at 125 I don’t think a Forge crank is necessary
Maybe the t-bone accident had something to do with it, but the Grom SF has a known problem with the crankshaft snapping at the flywheel. Every broken crank I’ve seen, looked just like yours. They all break in the same spot and in the same way, with the crankshaft sheared off at an angle. Some people have suggested that the crankshafts have a casting flaw. I don’t know if that is what the problem is or not, but it’s safe to say that there is a known problem with them. There seems to be a pattern here.

The crankshaft and connecting rod are the only two parts in my engine that I worry about failing. With that said, some people have put really high mileage on their Grom SF and the crankshaft is still holding up. The problem seems to be hit or miss. I installed the Takegawa 4th crankshaft support bearing in my engine, but I read once where someone suggested that it didn’t seem to make a difference, they still snap. Time will tell, I guess. Fingers crossed. Good luck with your new build.
 
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Discussion Starter · #35 ·
Maybe the t-bone accident had something to do with it, but the Grom SF has a known problem with the crankshaft snapping at the flywheel. Every broken crank I’ve seen, looked just like yours. They all break in the same spot and in the same way, with the crankshaft sheared off at an angle. Some people have suggested that the crankshafts have a casting flaw. I don’t know if that is what the problem is or not, but it’s safe to say that there is a known problem with them. There seems to be a pattern here.

The crankshaft and connecting rod are the only two parts in my engine that I worry about failing. With that said, some people have put really high mileage on their Grom SF and the crankshaft is still holding up. The problem seems to be hit or miss. I installed the Takegawa 4th crankshaft support bearing in my engine, but I read once where someone suggested that it didn’t seem to make a difference, they still snap. Time will tell, I guess. Fingers crossed. Good luck with your new build.
oh I didn’t know that there was a known issue. if that is the case then I would definitely recommend replacing it :)
 

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Discussion Starter · #37 ·
I purchased rear sets that will be put on with the clutch and springs ... nemoto ... pictures to come
 

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Maybe the t-bone accident had something to do with it, but the Grom SF has a known problem with the crankshaft snapping at the flywheel. Every broken crank I’ve seen, looked just like yours. They all break in the same spot and in the same way, with the crankshaft sheared off at an angle. Some people have suggested that the crankshafts have a casting flaw. I don’t know if that is what the problem is or not, but it’s safe to say that there is a known problem with them. There seems to be a pattern here.

The crankshaft and connecting rod are the only two parts in my engine that I worry about failing. With that said, some people have put really high mileage on their Grom SF and the crankshaft is still holding up. The problem seems to be hit or miss. I installed the Takegawa 4th crankshaft support bearing in my engine, but I read once where someone suggested that it didn’t seem to make a difference, they still snap. Time will tell, I guess. Fingers crossed. Good luck with your new build.
I've definitely seen SF with 4th support bearing still snapping of stock SF cranks. But from what I've seen is that it's more comon if you go big bore. It's recommended to do the forge crankshaft on a SF if going big bore

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