Best of NX250 / AX1 / XL250 Degree built

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scrambler
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Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » Sa Nov 23, 2019 8:22 am

As well known, our MD21 engine was used in three models, the NX250, the AX1 (sold only in Japan) and the XL250 Degree (sold only in Japan and Oceania). Each has its pros and cons and quite for some time I was dreaming of a best of built, using only parts that I like best from each type.

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Having said this my built kicks off with a second best – the frame. My first choice would have been a second generation XL250 frame, because it’s sturdier and more off-road oriented. And second generation because it got a rear disc brake. But chances of getting a Degree frame with good paperwork are close to nil. And the year of build (1995) would prevent having it legalized, due to emissions laws.

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So the second choice is a 1988 NX250 frame, because it’s available. And due to its year of built I won’t have to worry about emission laws – they were introduced a year later in Germany.
Ok, I can’t have a Degree frame but at least I already got a Degree gas tank. I like the colour combination of blue tank and silver frame – I guess I keep it.

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But of course the frame needs new paint. After decades of dedicated services the NX250 frames are often in really bad condition. Before sandblasting I checked and if necessary recut the threads. The threads were then closed with old screws.

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And I pushed in new steering bearing shells before sandblasting because this process would otherwise easily damage the new paint. Of course the shells were then taped and sealed with two large washers and a bolt.

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Something else to consider before sandblasting a NX250 frame: it consists of two welded together, pressed steel plates, forming a large cavity. If sand from the blasting will get into that cavity it will bind moisture and the frames will rust through from the inside. So all holes were sealed with old bolts.

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Ready for blasting. The chassis number must not be sand blasted or it won’t be visible after re-painting. For the same reason I would avoid any kind of grinding in that area to remove the old paint.

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scrambler
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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » Sa Nov 30, 2019 7:22 am

The frame is off to sand-blasting, but with another frame I fitted the XL Degree engine bars to the NX250 frame. The geometry of the degree frame differs somewhat viewtopic.php?f=20&t=1610

The front bracket of the bars had to be cut off and re-welded in a different angle. Ok, I can’t really weld, I still have to practise.

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Next: let’s see if the XL Degree rear fender can be fitted to the NX250 frame.

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scrambler
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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » Mi Dez 04, 2019 7:02 am

The NX250 rear fender is made of brittle ABS plastic – good for being painted but bad for durability viewtopic.php?f=20&t=351.
The Degree fender is made of a more flexible material (polypropylene?) and thus almost unbreakable. However it’s not easy to paint, so I’m stuck with the white color.

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The front mounts of the Degree fender bracket fit without changes, for the rear mounts extensions are necessary. Could be easily made of steel plates. The XL250 does not have a tool compartment under the rear fender, likely because the large 18’’ wheel needs more space.

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So if I choose this option I would have to find a new place for the tools. Another disadvantage: no rear carrier – they are hard to find.

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But I guess I like the NX aluminium carrier better anyway - what do you think ;) ?

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With that option the tool compartment would be possible but I have to check if the clearance for the larger wheel is sufficient. But I haven't decided yet if I go for the 16/19'' or 18/21'' option.

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The upper mounts of the fender need a bracket for attaching to the carrier though.

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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » Sa Dez 14, 2019 8:22 am

Most used NX mufflers are rusted through beyond repair under that fancy stainless steel cover http://nx650.nx250.de/albums/userpics/1 ... fflers.JPG. The stainless steel literally eats up the normal steel of the canister – well done, Honda :shock: . The US mufflers are more durable, since the endcap is not directly welded on and the cover is made of chromed steel.

There is only one aftermarket exhaust with DOT approval, the MSR/Marving – which I don’t like because of its lame sound and poor performance viewtopic.php?f=20&t=376. Some years ago I modified an Arrow NX650 muffler to fit the NX250. But it’s way too noisy, despite my efforts to dampen it to a bearable level viewtopic.php?f=7&t=430&hilit=arrow

The muffler I like best is the one from the AX1 – a bit better sound. From the outside it looks like the EU stuff, the only difference is the missing “E1” after the “KW3”. That specimen I got from Japan doesn’t look too bad, but the problem zones are below the cover – so it has to go.

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First step of stripping the muffler is to grind the welding points in the rear. Be careful not to grind into the canister, it’s made of very thin steel and easily punctuated.

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I was lucky – rust as usual, but it’s not rusted through.

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Now the endcap - also stainless steel – has to go, too. Again, careful – I can’t weld steel that thin.

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Done – now the muffler can be send to sand-blasting and aluminium flame spraying. I’m using this technique for more than 15 years now, because on salty roads stock muffler and manifold will rust through in no time. The NX mufflers are well coated inside and they won’t rust from the inside - at least if they are not rusted through from the outside. So with the aluminium coat they will probably survive the rest of the bike. And it’s not expensive at all – sandblasting/coating a muffler/manifold is about 80€ by that company https://www.metallspritztechnik.de/?loc ... 22&lang=de

The muffler in the rear was already coated – and I have to find a way to re-attach the endcap (for no particular reason other than it looks nicer) after the coating without welding or using screws. I guess I will try to clue it with JB-Weld or the like https://www.ebay.de/itm/JB-WELD-HighHea ... SwxX1Z1gaH

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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » So Dez 22, 2019 9:03 am

Some years ago the frame of my own Nixie urgently needed new paint https://www.nx250.de/mediapool/143/1434 ... 00-682.jpg – thanks to extensive winter driving. Powder coating (even a good one with a zinc base) does not withstand driving in wet conditions for a long time so I was looking for something more durable. Since aluminium flame spraying of the muffler showed excellent results I decided to give it a shot at the frame, too. With success – after five more winters there is no rust whatsoever at the frame viewtopic.php?f=6&t=37&start=10

So the frame of the best of built got an aluminium cover, too. At Berolina I paid only 150€ for sand-blasting and flame-spraying – a good powder coating would have been more expensive.

The aluminium coat has a very rough surface, so don’t touch it with greasy fins – it soaks up everything. But it’s an excellent base and makes it easy to paint, even for a lousy painter like me.
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The rough surface needs a thick spray-on body filler for smoothing – and I would let the chassis number out.

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After drying the surface is lightly grinded with fine sand paper, when it’s still bumpy it needs another layer of spray-on body filler.

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After repeating that 2-4 times the surface is finally smooth enough for the paint.

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scrambler
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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » So Dez 29, 2019 11:41 am

After the primer the frame got the NH146M acurate silver topcoat. The original frame colour has a satin finish, which I like better than a high-glossy. This time I’ve tried the brand Tristar Color. It turned out that Tristar did not get the acurate silver right, it`s noticeable brighter (note the swingarm for comparison). The RH paint I used for my own nixie is a closer match, but very expensive https://www.ebay.de/itm/RH-Basislack-Sp ... Sw6UlcmA3w.

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And I finally got the fork parts back from glass bead blasting. This is ideal to remove corrosion and dirt, however the fresh aluminium surface is then sensitive to corrosion and gets easily stained by grease or the like (which is then hardly to remove). But there is a trick: after a dishwasher bath with a cleaning tab (I don’t know if all tab brands will work) the aluminium surface gets evenly oxidized (and a bit darker), similar to anodization.

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That coat prevents corrosion and stains pretty effective. I treated the engine covers of my NX650 that way some years ago and they still look good http://nx650.nx250.de/albums/userpics/1 ... _offen.jpg. For winter driving an additional clear coat would be probably better though.

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Looks like new. These are XL600R parts, the 41mm fork is more stable. The steering stem of the XL600R triple tree is however longer, so the stems have to be swapped. Which is easier said than done, you need a hydraulic press and the stems are still very hard to remove. That’s why I usually use XR250L triple trees, which got the same length.

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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » Do Jan 02, 2020 9:38 am

Stronger is not always better, but for my best of built I want the strongest engine available. That’s why the XL250 degree engine (leave alone where to get one) is out of the question – I do not know how many horse powers Honda claimed but I felt that my Degree had noticeable less ponies than my NX250. I guess the degree has something around 20 hp.
Of course a 29 hp AX1 engine would be a dream – but it’s only a myth, since engine and carb are identical to the NX250 MD21 viewtopic.php?f=20&t=927

The MD21 with 26 hp was replaced in 1991 with the 239cc MD25 with only 23 hp left – so a good MD21 engine is a very desirable thing around here and hence very rare. Also for another reason – the 1988 engines had some problems with the crankshaft bearings, so Honda changed the crankshaft four (!) times within one year (https://www.cmsnl.com/honda-nx250-domin ... g2fVvx7mcw). From engine number MD21-1011503 the latest crankshaft is installed, which is presumably the most durable.

That MD21 engine is a special one – because it was built in 1993. For some reason Honda sold a very few hundred MD21 in 1993 as “European direct sales” (download/file.php?id=2546&mode=view). Maybe Honda wanted to get rid of a few leftover MD21 engines? We’ll never know. In any case it has the last crankshaft version.

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The 1993 MD21 was never officially sold in Germany, but I was able to buy one from Luxenburg with only 24.000km on the clock a few years ago. Unfortunately, the dealer did not provide the vehicle documents, so a registration in Germany proved impossible viewtopic.php?f=7&t=361 .

Even though my heart was bleeding I had no choice than to slaughter it and sell in parts – except for the engine, of course. I used it in my own Nixie for a year and 1000km (when I was overhauling the original engine viewtopic.php?f=20&t=270) and found it as strong and powerful as a MD21 engine should be.
And ever since the engine was waiting in my barn and is now married with the 1988 frame.

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The XL600R triple trees were mounted with tapered roller bearings. Those type of bearings require a different adjustment procedure than given in the NX250 manual, which refers to the original ball-bearings.

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For my own Nixe I used NX650 fork legs viewtopic.php?f=11&t=110 but for this time I want something shorter for a lower seat height. After all, I’m not getting any younger. XL600V fork tubes are 4cm shorter.

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Since I want my built registered I need a steering/ignition lock. Luckily, concerning the mounts the locks of XL600R and NX250 are identical (the wiring is different), so a NX250 lock is plug and play in XL600R and XR250L fork bridges. The German lock that is – all other countries have different locks that won’t fit.

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Now I only have to screw a bracket to the frame for a working steering lock. Note that the chassis number is clearly visible, another must for a successful registration.

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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » Fr Jan 03, 2020 8:47 am

For getting the front fork lower I need XL600V Transalp fork legs as donors. The Transalp lower tubes can’t be used with a XL600R or NX250 front wheel since the brake callipers have different mounts.

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So the fork tubes and the inner pipes have to be swapped. The pipe length determines the way of travel, the Transalp has a bit less than the NX250. I could have used the XL600R pipes but that would have made the fork legs longer.

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Done. XL600R lower tube and XL600V Transalp tube and pipe.

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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » Mo Jan 06, 2020 8:18 am

Mission accomplished – the XL600 hybrid fork leg is 5 cm shorter than a NX650 and 1cm shorter than a NX250. I would have liked an even shorter fork, but the 700mm Transalp tube is the shortest I know of.

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Additionally, the tubes will be pushed 1-2cm through the triple trees for more lowering.

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Re: Best of NX250 / AX1 / XL250 Degree built

Beitrag von scrambler » Mi Jan 15, 2020 7:28 am

Moving on– since NX250 88 and AX1 (29 HP wannabe) carbs are identical I took one from the former. It had to be disassembled and ultra-sonic cleaned viewtopic.php?f=4&t=1673 (in German, though - if you have questions, don't hesitate to ask).

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Ready to go. That carb was likely already cleaned by the previous owner with an acidic detergent, because the surface appears to be rough and corroded. I hope that carb will run ok, otherwise I have a spare in my barn.

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In the rear I rely on a new YSS shock. I ordered it 1cm shorter (with 1cm less way of travel) to counteract the larger rear wheel. The XL250 degree shock is bytheway also 1cm shorter than the NX250 shock.

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And something I always wanted is the aluminium swingarm of the AX1. It bolts plug and play to the NX250 frame, but the main problem is adapting a spoke wheel. I found a solution with a KTM 620/640 rear wheel, that requires doable mods and got a way better cush drive than the original AX1 cast wheel viewtopic.php?f=20&t=1572

The front parts of the linkages are identical, but the rear parts are different. The NX250 has a fork-like iron cast piece whereas the AX1 has two aluminium plates. So for a conversion like this you need at least part of the AX1 linkages.

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What a sight – an aluminium swingarm on a NX250. The AX-1 chain slider is out of stock like the NX250 one (viewtopic.php?f=20&t=1421) – but there are Chinese duplicates available https://www.ebay.com/itm/Chain-Slider-R ... 4468634149 They are made of pretty soft rubber, so we’ll see about the durability.

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