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M in sc, you are correct. Below is a comparison between the old SOHC CB 750 vs a F2 DOHC tensioners.





Te tensioner roller would fail on the SOHC motors much like it does on the Grom. The rubber would shred to pieces.
 

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SHIT! got one coming. Might just put it in my lathe and knock the teeth off then. still better than rubber on a bushing.
Give it a shot. I know, I have beaten on the rubber one for 2,000 hard miles on the 4V, but with the metal one, you will never have to worry about it again.
 

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Discussion Starter #44
Give it a shot. I know, I have beaten on the rubber one for 2,000 hard miles on the 4V, but with the metal one, you will never have to worry about it again.
exactly. that's why I made a brass button for the tensioner
 

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SHIT! got one coming. Might just put it in my lathe and knock the teeth off then. still better than rubber on a bushing.
I'd test a couple of your creations on both my groms since I ride everyday on the groms to the gym, costco, and just visiting friends and I'm WOT most of the time.

Just as long they are mounted on the OEM arm for the grom I will buy two for testing and abuse.
 

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Discussion Starter #46
thanks cisco, i'll leave the parts sales to the distributors. I really don't like making things for other people (don't really have time/my free time is worth a LOT (to me)than most will pay me for it) but what I find I will share with them all. Not always open on the forums but this on yes. I don't mind helping improve our hobby, even though i can be a word class dick about it. :D.
 

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I also made it a manual tensioner (fixed). The hydraulic (oil fed) puts too much tension when you run a high volume pump and 20/50 oil like I do.
the "hydraulic" tensioner on the groms / any horizontal honda motor with CCT of this kind is not pressurized by the oil pump. The tension is done by the long spring between the bottom case bolt and bottom of the tensioner rod. There is a floating check valve in the bottom of the rod that dampens the movement of the rod up and down as it sits in oil, but main tension is done by the spring.

If it was pressurized by the pump, there would be no provisions / instructions (like there are stock) to fill the tensioner rod area with 4cc's of oil after disassembly as the oil pump would VERY quickly fill that 4cc's. But when you rely on the movement up and down of the rod to pull oil into the area it takes MUCH longer.


That stated, thicker oil will increase dampening and provide more instantaneous tension on the chain.

How much stiffer are the springs of a 4v assembly by themselves compared to the original springs?
 

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Ok. So knocked the check valve out of the bottom of the tensioner with a drift, bought an M5 Allen bolt 30mm long, two flanged locking nuts and I had a nylon tube lying around to help center the assembly under the tensioner rod.
Assembled as pictured.
ImageUploadedByHondaGrom.net1468105600.927143.jpg
ImageUploadedByHondaGrom.net1468105626.103340.jpg
ImageUploadedByHondaGrom.net1468105639.979271.jpg
Adjust until free play is gone from chain when 14mm head bolt on bottom of crankcase is fully tightened, disassemble and lock both flange nuts together.
Note: you want chain free play gone at TDC, but you don't want any more tension on chain than that. You should be able to spin the smooth bottom chain guide wheel easily while the engine is at TDC, but not be able to skip teeth on the tensioner arm's toothed wheel.

Any bets on how long it will be till I see someone peddling this improvised manual tensioner setup on EBay?
 

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Another note- when pressing the new wheel onto the arm, note the oil hole. The small hole on the outside shows where the oil hole is on the inside. It should be on the bottom when the arm is mounted in the engine so the wheel bushing can get lubed with splashed oil.
ImageUploadedByHondaGrom.net1468107553.153836.jpg
 

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Ahhh. an oil hole. i wasnt sure what that was. i thought maybe that piece was actually threaded in and that was used as a spanner hole.
 

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Another note- when pressing the new wheel onto the arm, note the oil hole. The small hole on the outside shows where the oil hole is on the inside. It should be on the bottom when the arm is mounted in the engine so the wheel bushing can get lubed with splashed oil.
View attachment 28212
yep ordered my parts so I can mount the 1977 CT70 roller on to a new 2014 grom cam chain tensioner arm. Cost $10.86 for the roller and $16.30 for a grom arm which is a total of $27.26 plus bend over sales tax from Calif. It was cheaper than $55 for the FB brand
 

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....... It was cheaper than $55 for the FB brand
.

Damn Cisco.

Never thought we would see the day you would post a comment like this. ;-)


.
 

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I have another idea as well if the lower wheel turns into a weak point- order an xr50 arm and wheel, cut the arm bushing and use it as the bearing surface for the wheel, secure with a hardened washer and 10.9 m6 bolt. I'll supply pictures of that if the current setup grenades.
 

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Ahhh. an oil hole. i wasnt sure what that was. i thought maybe that piece was actually threaded in and that was used as a spanner hole.
Pressed in and expanded- that outside hole is for the assembler or machine to clock the bushing and the arm. The bushing likely won't sit flush in the press without that hole lined up with the pin on the press- keeps an assembler from making a whole lot of bad arms.
 

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Discussion Starter #59
now were talking. and yes, the 350 one pitch is wrong. HOWEVER one of the ct70's ones are a larger diameter AND metal toothed but needs lathe work. Good work fox, im going to get on mine this week. Qyestion: bow large an ID whee can fit on the tensioner? I havent even cracked mine open yet
 

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I think somewhere in the neighborhood of 10-15mm diameter larger than the crf50/ct70 wheel would be max unless you are willing to cut your tensioner rod- I am about to correct the manual tensioner bolt length to 30mm, 40mm won't hurt anything but no need for that long of a bolt, I double checked everything after 100 miles last night and found that I used the 30 instead of the 40.
 
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