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Discussion Starter · #1 ·
While riding the Grom this week, I noticed that the moment you start out, the forks have sagged about 3/4" to 1". So, that 25 degree steering head is now about 24 degrees with 12" wheels. No a good combination. My Ninja1000 has a 25 degree steering head & about the same sag, but it has 17" wheels, and a fair amount of trail.
So, this morning I decided to fix the problem, if I could and increase the fork dampening. Honda use's 10WT fork oil. I switched to 20WT, and the dampening is much better. This winter I'll put the forks on my shock dyno & play with fork oils up to 40WT. Could the fork use a stiffer spring, yes. But before I pull the lower casting off the chrome inner tubes, I'm going to purchase a spare set, and completely re-engineer the internal parts. Showa did not make the lowers to come off. If you noticed, the tubes had aluninum galling on the threads in the RaceTech photo's. The lower casting should be heated/expanded, before you try to twist it.
What I did was to raise the forks in the triple clamps .260", and add a machined spacer that was .825", for a net change of 9/16" increase in the front ride height.
The bike is more stable at speed, & feels planted to the road, with noticable better dampening.
Brian
I know the photo's are reversed, sorry about that.







 

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My buddy uses gear oil in his forks on his Zuma 125 so we might try that on my grom here in a few weeks. The photos look great and I think the spacer is a great idea.
 

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My buddy uses gear oil in his forks on his Zuma 125 so we might try that on my grom here in a few weeks. The photos look great and I think the spacer is a great idea.

Thicker fluid slows low speed damping but to thick can make high speed damping very harsh.

Preload and thicker fluid is a stop gap till some one makes different springs and damping.
 

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Discussion Starter · #5 ·
Fork Oil Viscosity

hrcnick11,

Actually, I agree with you. I don't think there is a need to go to really thick oils. When I get the forks on the dyno, the numbers will tell the story.

I think there is a cost of modificaton / time / result factor here with the Grom. The average rider may want certain changes, but is he really willing to pay for them. Dampening inserts, replacement fork springs, and the labor involved will run into the hundreds of dollars, could easily be about $400.00, how many Grom guys or gals will really do that? The fork tubes will need to be removed from the bike, shipped out to someone, worked on for a week or two, returned, and then remounted on the bike. Heck the shipping will be $75.00, because they don't fit in a flat rate box, being so long.

I'm riding the changes I made yesterday, today, but from what I felt riding the bike last night, the spring rate is not that bad, once the dampening rate was increased. The changes I made yesterday, could be done by anyone handy with tools, with or without my spacers. Good fork oil is about $12.00 / $14.00 a qt.

I'll post a note after the ride.

Brian S

PS, I purposely made the spacers a hair long, I can always shorten them.



 

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Nice the front suspension is getting some attention. Look forward to your findings.
Yellow FZR400 in the background! Whoohoo
 

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Discussion Starter · #8 ·
Grom Ride Height

minimotoman50,
The spacer changes the front ride height, not the preload tension of the spring. I raised the front to get it to settle when the rider is on it, in the original location. The forks have more movement, .825", but the total change is only .562", because I raised the tubes in the triple clamps as much as I could. I road the bike about 15 miles today, over all sorts of roads. Because the steering head angle is closer to the original number, 25 degrees, the bike is less nervious, it feels more like a big bike. The fork spring is locked in by a washer on the top. So it's not easy to change the preload tension. I think the 20wt fork oil is worth the effort to change out the 10wt. It's less spring rate & more the lack of dampening that is effecting the handling.
Brian S
 

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Discussion Starter · #11 ·
Assembly

Guys,
I replaced the OEM steel plated 8mm allens with stainless steel longer allens. I set the fluid level at 75mm, because it was too hard to try to get 221 cc of shock fluid into the fork tube. I'm guessing that there will always be some old oil left in the tubes, unless you do a complete disassembly. I used Spectro 20wt fork oil. I finished by using anti sieze on the steel end caps.
I changed the engine oil today, after 50 miles, just to get any assembly lube, and build junk out of the engine. The oil was fairly dark, but nothing in it. I'll do another oil change at 250 miles, and change over to Amsoil at 500miles.
I had to adjust the throttle cable, it had about a 1/8 turn of play from the factory.
Brian
 

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PS, I purposely made the spacers a hair long, I can always shorten them.



Hey Brian.
Can you please tell me the diameter of these spaces.
Are they made from normal machining alloy bar or some sort of bronze, it's not easy to tell on my tabby thing
I need to order some material and thought I would get some to make up a pair of these at the same time.
I'm only an amature machineist so your advice would be helpfull

Cheers Dog
 

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Hey Brian I swapped to 20wt oil already and found that I had to reinstall the cap and pump the fork in order to bleed them with out installing the cap I could not get the air bubbles out of the lower half. I measured what I drained and put the same back in it was 200cc. But It would not surprise me if there was 20-30cc still in the fork.
 
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