Fork oil - '72 Honda XL250 Motosport

[Colin Jay]

Hi all,

I would like some advice regarding what oil to put into the fork on the 72 XL250 that I am building up for next years reliability trial series. I have fitted a set of XL350 fork to the bike as the fork tube on the original 250 forks were to badly pitted to use.  My manual say to use 170cc of ATF to refill them from dry after stipping.

Back in the 70's before the general availability of purpose made fork oils, ATF was what I used to use, and I alway believed that ATF was about the equivelant of a 20W oil, but one of the mates reckons it is about a 30W.  Now that you can buy oils made specifically for forks I would like some advice from other Honda owners and suspension gurus on what weight of oil to use in place of the ATF and if there is any improvments to be had by using a different amount of oil.

By the way, I weigh in at about 120kg fully kitted out in riding gear, so the the suspension has a far bit of weight to handle.

CJ

[MX?]

G'day CJ, don't have an answer unfortunately, but will be interested in any replies you get! Just doing one up myself and have just sent my forks in to have emulators fitted. I know there are a couple (at least) of XL exponents here......so let's hope they chime in. 

[LWC82PE]

Heres an extract I saved off the Progressive Suspension website sometime ago on ATF

Most motorcycle manufacturers recommend ATF (automatic transmission fluid) for fork oil. This has excellent lubricating and cleaning quailities but we do now recommend ATF oil for one main reason. When it is manufactured it has no viscosity specification other than it must fall between 5 weight and 17 weight. One time you buy ATF it might be 5 weight and the next time it could be 17 weight. We do not feel that this is acceptable for motorcycle forks. Therefore we recommend most major brands of fork motorcycle fork oil. As a general recommendation 10 weight works well for most motorcycles.

The main reason its was specified a long time ago was because fork oils were not common back then. I hardly use it much in forks except for a very few old bikes that they specify the use of ATF. I mainly only use it in old triumphs. Why? Well fork oil is just so much better these days so why not use that? ATF is ment for auto transmissions, not in motorcycle suspensions. That’s what we have fork/shock oils for now, they are so much better suited and are designed for suspensions.

you might have to do some experimenting. i reckon you might want to try 20 W but if its too harsh, then go back to 15 and raise level and spring preload. it will take some mucking around to get them set of for your use they way you like.

another option is air fork caps. they would be a good idea for your weight on that old bike (ive got 2 pairs of aftermarket ones but dont want to sell them as they are for a XL project in the future) and chances are the springs are sagged a little if they are originals. that will stiffen them up a bit more and then you can use a oil lighter than 20 W. also try some preload spacers on top of the springs.eg large washers or PVC pipe.

this ebay seller in NZ makes air fork caps. he has made and sold them for early XL 250s before.

http://cgi.ebay.com/ebaymotors/YAMAHA-TT500-SUZUKI-PE-175-250-400-AIR-FORK-CAPS_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1205Q7c66Q3a2Q7c65Q3a12Q7c39Q3a1Q7c240Q3a1318Q7c301Q3a1Q7c293Q3a1Q7c294Q3a50QQ_trksidZp3286Q2ec0Q2em14QQhashZitem270313691162QQitemZ270313691162QQptZMotorcyclesQ5fPartsQ5fAccessories

he is a good guy. if you have any trouble contactign him i do have his email address.

[holeshot buddy]

i run atf in my honda forks and i weigh 90kg
and i ride her hard 
i have found the heavier oil does not work as well in these forks
i have been racing the honda for about 10 years
and i have found this the best
you will need 19mm spacers in the top above springs
then just ride her like she is a cheap hooker

[211kawasaki]

been running ATF for 30 years, works fine for me.

211

[VMX247]

For MX application I tried 15W with high pre-load on the springs and found that for flat type tracks it was pretty good. But on really rough stuff the dampening effect and spring rate was way too much.
I would recon for reliabity trials you would want a firm suspension but with feel. With the standard springs, I would try 15 weight. A bit of preload on the springs and maybe 2lb of air in each leg. If its bottoming out run the oil level a couple of mm (5mm) higher. If it seems a bit harsh next time yo do the oil change try the 10 weight. Be mind full of how much sag you have on the front end. The couple of lb of air helps to keep the front up a bit and compensates for old and sagging springs. Sometimes a new set of springs can go a long way to a good front end.
Steven

[Colin Jay]

Thanks guys, I have so 15w in the shed and I will put that in. One of the sets of forks I have have home made air caps, they look rough, but, I will fit them so I can play with air pressure when I get her going

CJ.

[LWC82PE]

yeah its simple just to screw in a schrader valve, i didnt think of that. just make sure they dont leak. you probably know this but you need a special pump with special no loss valve connection to accuratly gauge and fill the forks with zero air loss.

i will be interested to hear what you do with the alternator/lighting. in stock form i know the best you can do is 60W @12 V and use a 60/55 H4 but the brake light will dim a little when you press the brake when at low revs but if you change to LED tail light that would fix that. i got a Baja article on the 350 i think and they use some sort of honda road bike alternator. i havent asked Beta bikes what they can rewind the stock one to.

if you havent already done this, fit a XL 350 rear hub. they are heaps better.

[VMX247]

LWC3077 is right about the "no air Loss" bit. Over the years I have worked out that a couple of stokes of the pushy pump equals 4 or 5 pound then each application of the low air pressure gauge drops it a lb or so. You get used to how much each instrument effects the air pressure.
Cheers Steven

[LWC82PE]

and theres plenty of cheap pumps around too. the ones for modern bicycle shock/forks are good. Fox usa makes a good pump.

[Colin Jay]

I still have a LINKO air fork pump from my days in the 80's when I worked as a bike mechanic, these pumps are basicaly a large sryinge with an air bleed valve fitted and were all the go back then when everything was fitted with air caps, hopefully it still works ok and the seal hasn't gone. I knew keeping all my special tools would come in handy one day.

As for lighting, I was going to get in touch with Beta bikes once I had the old girl up and running and descided if she was going to be a better bike than the MkII version of my XT500 that I am also building up. But, since you mentioned about the road bike alternators, I might have to check out the couple of SL350 (twin) engines that are laying in the corner of the shed and see it the alternators form either of them will fit into the XL cases with out to much work.

I have fitted the XL350 swingarm, but when I initially looked I couldn't pick any differences between the rear wheels, what is the difference?

CJ

[LWC82PE]

yeah it was SL electrics. i will try and find that article. i think the XL350 has cush drive hub and has better sprocket mountings, i cant remember exactly and its been ages sinc ive looked at it, something used to break on them. but thats what everyone did. thats what my dads 250 had done to it. ive got the old 250 hub somewhere. im going to fit a 350 swing arm to it sometime aswell.

[MX?]

CJ, What length rear shocks did you use with the 350 swingarm? I've just fitted a 350 swingarm to my project and have been trying to decide whether or not to increase the length of the shocks seeing as how the 350 mounts sit a bit further back than the stock 250 arm.

[Colin Jay]

LWC3077
If you can find the article about the electrics I would be interested in having a look. The rear wheel that I am currently plaing with is from the XL350 chassis and does have a cushdrie sprocket carrier. Both the hub and carrier assemblies  are badly worn through never having been grease. In the new year, I am going to have a look and see if I can mount the bits in the lathe at work and repair/rebush the hub and carrier. I will have to get into the shed and check the actual wheel that came from the 250 frame.

MX?
I currently have one of the std XL350 shocks fitted just to keep it from falling over. I was actually going to ask about the best length of reart shock once I got it up and going and them probably buy a pair of YSS shocks.

CJ

[LWC82PE]

ok Colin, i will dig out that article again. i know where it is and its not too hard to find. just allow me a day or 2.