XS650 C Fork oil

[jacksdad]

Hi guys, looking for some help once again!
My latest resto bike is a 1977 XS650C, imported from Daytona Beach.
I've stripped the forks, all looks good, but I'm unsure about replacing the fork oil
One leg was coated in oil, so has lost its original volume: got 85ml out.
The good leg had 100 ml of oil in it, which seems much too little oil!
The forks are 34mm, the early ones with disc brake, with lugs on them for front and rear mudguard brackets.
Anyone know the weight of oil, and quantity please?

 

[fredintoon]

Hi jackdad,
the answer is in Clymer's manual, order one from your local bookstore eh?
It sez the XS650C will need 155ccs (5.2 fl. oz.) in each fork leg.
Although it gets delightfully vague about what particular oil to use.
I quote:- "10, 20 or 30W motor oil or special fork oil"
I'd go for a fork oil, they have the seal lube additives the motor oil don't and I've mostly used 20W with good results.
And there's a sizeable minority using ATF instead of either.
Clymers also details how to change the bike's fork seals.

 

[jacksdad]

Thats great, thanks!
Our Haynes manuals are usually pretty good, but the XS650 book is full of mistakes, I think a Clymer would be a good investment! Just need to find one here in England.
I have had problems with my 650D as well, The forks bottom out very easily when braking hard. I've got 30W engine oil in this bike: would adding more oil help? I've also heard of people using 20/50 engine oil
Back to my C, I'll try 155 ml/cc of 30W and see what happens, thanks for the info...and if anyone has a Clymer they want to sell, let me know

 

[5twins]

Yes, more oil will help the '77 35mm forks. The factory spec is a little under 6 ounces per leg. Use about 7 ounces. The forks just plain work better with a bit more oil in them. It reduces the air volume above the oil and creates more of an "air spring" effect. The factory oil spec for the '77 forks is 20wt. All later forks spec 10wt. I don't know if this is because Yamaha discovered the 20 was too thick after the first year of 35mm fork production, or if it has something to do with the damper rods. The '77 rods differ from the later ones. They have the same amount and size of oil flow holes in them but the holes are beveled. An engineer buddy of mine told me beveled holes flow more.

 

[jacksdad]

Ok thanks, I'll refill my D 35mm's asap:
Back to my C 34mm...any idea on the best weight and volume of oil?

 

[XSLeo]

I have found that the 6 inches down method works well.
The 6 inches down method is to remove the springs, compress the forks fully. Add about 8 ounces of oil. I then pump the forks up and down to remove any air. With the forks fully collapsed, Then use a device that allows you to draw out the extra oil to 6 inches below the top of the tube.
I have piece of 3/16 inch clear hose. I put a zip tie around the hose, snug it down, nit so tight it can't move but snug. Now adjust the zip tie on the hose to get it 6 inches from the end of the hose. Now slip this end down into the fork.
You can use what ever method you choose to create a vacuum that can draw oil out of the fork. I use a Miti Vac tool, by mouth will work but oil tastes nasty.
This gives you a bit of air shock effect. Under normal riding they act as usual but under braking this smaller air space won't let the forks compress as far as they used to, limiting dive.
I have not tried a fork oil yet but have tried several other types of oil. The AFT I have in there works well.
Leo

 

[jacksdad]

I'm going for 20W oil, and the 6" method!
I've got a tool I made years ago, one of my bikes specified the oil height not volume (as per 6" method)
Its a small piece of wood about 2"sq and 1" thick, with a narrow alloy tube running through a hole in its centre, which you set to the required depth...6" from bottom of block.
Simply guess pouring in the oil, then with the block sitting central ontop of the leg, carefully suck out oil until no more comes out
I then added a length of clear plastic tube to the top of the alloy one...as fork oil tastes really really bad

 

[angus67]

if your a slight guy....10wt. if your a big guy....15wt. Mine don't bottom out any more with 15wt. Im 5'11" 250lbs.

 

[XS650D]

I have a 77D and have experimented quite a bit with all the info on here regarding oil weights,tried 10,15 and 20 with different levels and different sized shims for pre tension (with the original strait rate spring) and settled on 10 weight,6" from top off fork leg with a shim.sorry cant remember size I ended up with,but 1 inch comes to mind,Regardless its way better than it was BUT theres still room for improvement and next season I am going to either do the Minton mod or add the adjustable units that go in the bottom,cant recall the name rite now.

 

[angus67]

emulators.

 

[XS650D]

Yep,thats it.

 

[jacksdad]

My D 35mm forks bottom out often, so I'm going to try 20's...as I've already bought it! I have got some 5W from another bike, so I can mix n match
On the C 34mm (which I've got ridden, bought it in bits) there was no tension at all in the fork cap: I unscrewed it whilst holding down firmly...and it just came off, I can even refit the cap about 5mm before it hits the top sleeve, seems that the springs have collapsed, does anyone know what the free length is please?