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Discussion Starter · #1 · (Edited)
I don't wanna hear any speculation, how many miles do YOU have on YOUR Koso cam chain tensioner? Feel free to elaborate about it, I just don't want any internet knowledge in this thread. Any failures? First hand experience only, if you prefer another brand, why? How many miles do you have on that brand? Thanks!
 

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I'm sure there are higher milage examples around, but mine has 3000km on it (bike has 9300km on it). No issues so far and I'm running the oem lower wheel and a yuminashi manual tensioner and brass button.

Mines also a ported takegawa 4v with a DCR regrind cam, so it sees 11.5k rpm pretty regularly
 

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I'm sure there are higher milage examples around, but mine has 3000km on it (bike has 9300km on it). No issues so far and I'm running the oem lower wheel and a yuminashi manual tensioner and brass button.

Mines also a ported takegawa 4v with a DCR regrind cam, so it sees 11.5k rpm pretty regularly
How’s the oem lower wheel holding up with the koso? My 186 2v build with humongous valves likes sending rubber tensioner wheels so I wanna make sure it’s solid

edit: how’s the manual tensioner as well? I want one as the spring one gives me no solace at high rpm haha
 

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How’s the oem lower wheel holding up with the koso? My 186 2v build with humongous valves likes sending rubber tensioner wheels so I wanna make sure it’s solid

edit: how’s the manual tensioner as well? I want one as the spring one gives me no solace at high rpm haha
OEM lower is fine. Yours probably eats them because the spring tensioner is bouncing too much at high rpm. The manual tensioner makes a big difference.

Btw, what size valves are you running in your 186?

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OEM lower is fine. Yours probably eats them because the spring tensioner is bouncing too much at high rpm. The manual tensioner makes a big difference.

Btw, what size valves are you running in your 186?

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That’s good the oem lower is holding well with the manual tensioner. That’s what I’ll do then and see if it remedies my issue. I’m running a 31mm IN and a 26mm EX valve config. It’s basically the finbro 183 head but better. Taps like a mofo and it gets better flow than a stock koso 4v head but it chews up my tensioner wheels haha
 

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That’s good the oem lower is holding well with the manual tensioner. That’s what I’ll do then and see if it remedies my issue. I’m running a 31mm IN and a 26mm EX valve config. It’s basically the finbro 183 head but better. Taps like a mofo and it gets better flow than a stock koso 4v head but it chews up my tensioner wheels haha
Did that require any alterations to the 186 piston valve reliefs or did it fit right up?

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Did that require any alterations to the 186 piston valve reliefs or did it fit right up?

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Surprisingly it all fit up with no issues. It does come deathly close though which worries me but so far no damage. Depending on how my new tune from dhm goes with this setup I might switch back to my 27.5IN 23.5EX head. The head porting is the major limiting factor right now as well as total cylinder compression. I get more compression but slightly worse total flow with the smaller valve setup. I think I can make more power that way hence why the new tune haha.
 

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The Koso cam chain tensioner that Ninelives17, the person that started this thread, was running failed and bad stuff happened. Pretty sure he is running the Takegawa tensioner now. There is a thread about the failure.
 

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Discussion Starter · #11 ·
I am running the Takegawa now, my Koso failed after about 600 miles. I am still convinced mine had a manufacturing defect. A lot of people run the Koso with no problems. I just couldn't bring myself to trust another one. That and swingarms has been the only problem with my bike.
 

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I am running the Takegawa now, my Koso failed after about 600 miles. I am still convinced mine had a manufacturing defect. A lot of people run the Koso with no problems. I just couldn't bring myself to trust another one. That and swingarms has been the only problem with my bike.
Was the koso arm on the spring or on a manual tensioner when it failed?

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Discussion Starter · #13 ·
On the spring, same as the stock one and the Takegawa which now has about 4,000 miles on it.
 

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I am running the Takegawa now, my Koso failed after about 600 miles. I am still convinced mine had a manufacturing defect. A lot of people run the Koso with no problems. I just couldn't bring myself to trust another one. That and swingarms has been the only problem with my bike.
I really wanna run the koso as it’s metal and my bbk eats rubber tensioner wheels but what setup are you running with the takegawa tensioner? Oh and did you ever run the extra washer between the case and the koso tensioner? It seems all the ones that fail didn’t have the washer

Forgot to add but how did it fail? Was it the metal lower tensioner wheel?
 

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Discussion Starter · #15 ·
I never installed the lower wheel because of reported failures with that part. The shim IS required on some installations depending on clearance, my particular engine had no binding at all without the shim. I looked at this in detail during install, absolutely no binding. The wheel itself sheared off of the arm, no warning at all. Bike was running great, had spent 30-45 minutes running 70+ mph that morning. It failed in town running 45mph or so.
20200806_091739.jpg
 

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Discussion Starter · #16 ·

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I never installed the lower wheel because of reported failures with that part. The shim IS required on some installations depending on clearance, my particular engine had no binding at all without the shim. I looked at this in detail during install, absolutely no binding. The wheel itself sheared off of the arm, no warning at all. Bike was running great, had spent 30-45 minutes running 70+ mph that morning. It failed in town running 45mph or so.
View attachment 89924
Oh wow. I’m kinda scared to use the koso tensioner now as I’ve put far too much money and time into my engine to risk it going boom. I think I’ll go takegawa haha. Thanks for the info! Also how is your tensioner guide wheel holding up in the cylinder? Mine never really lasted so I swapped to the yuminashi one hoping I’ll get better results. Also swapping to their tougher flat chain as it’s supposed to be more gentle on rubber tensioner wheels
 

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Discussion Starter · #18 ·
Oh wow. I’m kinda scared to use the koso tensioner now as I’ve put far too much money and time into my engine to risk it going boom. I think I’ll go takegawa haha. Thanks for the info! Also how is your tensioner guide wheel holding up in the cylinder? Mine never really lasted so I swapped to the yuminashi one hoping I’ll get better results. Also swapping to their tougher flat chain as it’s supposed to be more gentle on rubber tensioner wheels
I replaced that guide wheel at the same time, nearly 4000 miles ago. I have not been back in to that side to look, but I have not seen any rubber particles in my oil filter either. A lot of 9000+ rpm riding. We did a 440 mile day a few weeks back.
 

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I'm sure there are higher milage examples around, but mine has 3000km on it (bike has 9300km on it). No issues so far and I'm running the oem lower wheel and a yuminashi manual tensioner and brass button.

Mines also a ported takegawa 4v with a DCR regrind cam, so it sees 11.5k rpm pretty regularly
With the Yuminashi manual tensioner, do you use the rod with the spring or does the spring get left out?
 

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With the Yuminashi manual tensioner, do you use the rod with the spring or does the spring get left out?
The spring gets left out. On my setup, I'm using a brass button as well instead of the koso plastic one.

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