I am wondering if I can fit an Ohlins HO206 shock made for the MC21 to an MC18. I see that nine16 has fit one but he didn't remember the specifics. I have read quite a few threads on shock replacement for the MC18 but none address this specific combination. The MC18 rear shock length is 285mm. The Ohlins unit is 302mm and is adjustable -4 mm so the shortest length is 298mm. The difference being 13mm too long. As I am also changing to a 17" rear wheel. So I want to lower the swingarm 1/2" too. In addition my suspension expert says I could/should lower the swingarm slightly more to improve the geometry. Can I not just fit the Ohlins shock, position the swingarm to the desired height and measure and fabricate new linkage plates accordingly? Will this be detrimental to the function/performance of the overall rear suspension? Thanks.
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MC21R9N track
MC18R2J track
CBR954
CR250

The 17" rear lowers the back end and the Ohlins shock raises it...probably slightly more, after the linkage ratio (lengthening a shock by 1 cm raises the rear more than 1 cm). The bike feels great. Fabricating custom triangle linkage plates would allow you to get the height exactly where you wanted. However, it's not quite that simple. You have to account for the leverage ratio too. If you screw that up, spring rates and damping could be way off. Springs would be easy enough to correct, but damping is another matter.

By the way, my bike is an '89 r5k. Many differences from the r2j, but I'm not sure what suspension/geometry changes were made.

Hello all. Just found thread which is helpful as I am doing this conversion. Have the Ohlin's shock built for MC21. 302mm eye to eye with shock length adjusted to minimum. I am finding the swingarm downward angle is excessive so that the chain will not clear the top of the swingarm with the stock MC18 link plates. Also the lower eye of the shock is touching or very nearly touching the link arm without rider.

I also bought aftermarket plates designed for adaptation of the MC18 for 17" rear. They seem to increase the ride height even further when installed with the long sides of the plates pointing down (i have seen a picture showing it oriented with the long end horizontal). which way should they go? seems horizontal orientation will greatly increase the rising rate.

My question is whether to try MC21 link plates and link. If they leave the back end too low i can always adjust the length of the shock. the other option is to shorten the shock by about 5mm with an internal spacer.

Appreciate any direction here.

YSS rear shock

https://www.ebay.co.uk/itm/303465609174?epid=2169756709&hash=item46a7f5b7d6:g:-YoAAOSw60NbNgmm
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Why do things simply when you can complicate them

Thanks for the note about the YSS shock. I did see those on ebay but I need something with full compression and rebound damping suitable for club racing and track days. I was supplied an Ohlins when nobody realized the differences between an MC18 and MC21 (we almost never see NSR's here). Turns out Ohlins only supplies a shock for the MC18. The Ohlins shock will not fit the MC18 with the stock plates, HRC type plates (unless they are installed with the long end down which results in too extreme a downward angle in the swingarm) nor with MC21 plates and link. The bottom eye of the shock jams up against the dogleg link. Looking at a custom built Ohlins shock for MC18 but i understand there are significant obstacles due to the shorter spring length required. I am also making inquiries with Nitron. The other possible option is a link kit from T2 Racing supplied by Webike Japan which seems to be designed to fit the MC21 shock into the MC18 frame and swingarm but it is difficult to get confirmation it will work due to language and other issues. I'll advise of the results in case anyone is interested.

For anyone who is interested, it turns out Nitron Japan has a line of off the shelf shocks for the MC18. that includes their R1, R2, R3 and RacePro models. They are built to order and there is a special order fee over and above their standard pricing (i am waiting for a quote on that cost). This was the result of inquiries i made to Fast Bike Industries in North Caroline USA. I have been dealing with Burch Waller in sales and he could not have been more helpful. Highly recommended. Here is the contact info:

Burch Wadewitz
Sales Manager

Fast Bike Industries
211 Duncan Hill Road
Hendersonville, NC 28792
(828) 435-0125
Website

Fast Bike Industries
Nitron Suspension USA
Andreani Group USA

Hi all.
I have a yss shock on my r5k and its a vast improvement over stock its adjustable for length and i found 2 turns longer on the top eye makes turn in just a tad sharper.
Also have yss cartridge emulaters fitted which totally transformed the forks, i highly recomend yss products.

Apologies in advance to the O.P for the thread highjack

FIL250 wrote:Hi all.
I have a YSS shock on my r5k and its a vast improvement over stock its adjustable for length and i found 2 turns longer on the top eye makes turn in just a tad sharper.
Also have YSS cartridge emulators fitted which totally transformed the forks, i highly recommend YSS products.

Phil
Couple of questions - just spent the past hour watching you tube video on fork emulators and can see why they would make such a massive improvement over stock

did you drill the extra holes for the oil and fit the emulators yourself - if so, is it as simple as the online videos or did you require additional (shorter) shims above the spring for setting the spring preload

have you got any pics of your YSS shock* as I've still got the OEM one on mine and its going to be pants after 30+ years, its in great shape externally and doubt it can be reworked etc so on the look out for something else - I'm assuming as its on an R5K you have the posher remote reservoir version on your MC18

* the sellers pic in Robs link shows what they call a Generic/stock image
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Nick

Rebuild project NSR250 MC18 R4J

Would be interested to see what price they come back with - Like the US the UK supplier here only lists MC21 & MC28 hence the need for a special order I guess

https://www.nitron.co.uk/buy-online/motorcycles/honda/nsr250r

tleighbell wrote:For anyone who is interested, it turns out Nitron Japan has a line of off the shelf shocks for the MC18. that includes their R1, R2, R3 and RacePro models. They are built to order and there is a special order fee over and above their standard pricing (i am waiting for a quote on that cost). This was the result of inquiries I made to Fast Bike Industries in North Caroline USA. I have been dealing with Burch Waller in sales and he could not have been more helpful. Highly recommended. Here is the contact info:

Burch Wadewitz
Sales Manager

Fast Bike Industries
211 Duncan Hill Road
Hendersonville, NC 28792
(828) 435-0125
Website

Fast Bike Industries
Nitron Suspension USA
Andreani Group USA

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Nick

Rebuild project NSR250 MC18 R4J

Hi all.
Fitting cartridge emulators is easy enough the yss instructions are comprehensive.
You do need to drill out all the holes in the damper rod and also drill more holes so the damper rod is completely redundant.
The long shims/tubes over the spring have to be shortened and properly squared off so it all sits nice.
the emulators have adjustable damping but you have to remove them to adjust which is a pain i had to do it twice, I also played with oil height but cant remember what i settled on.
The improvement over damper rod is massive, much less dive and nicely controlled damping, also no bumping off the stop springs at full braking force.
The rear shock is not remote res on r5k that is only on r6k.
I dont have a pic handy and you cant see much of it when fitted to the bike to be able to get one.
The build quality is fantastic at such a low price point, the rebound adjustment is effective and consistent. There is no adjustment for compression but also as standard i have felt no need to adjust compression it is set very well from the factory.

YSS are a Thai company. It may be worth messaging Paul/Matt at TYGA Performance about MC18 shocks.
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Andy.
NSR-WORLD.COM

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Wayne, I'll post any info when available. Not sure if shock would come direct from Japan or through the US/UK distributor.