SU Oil Consumption

[Jetaway]

I have a 1972 with SU carbs. I've always used "3 In 1" Motor Oil which is a straight SAE 20 oil. I can't go much more than 350 -- 400 miles without having to refill the reservoir. Is this normal?

Chris

[jaltman]

No, there is an o-ring where the needle mates to the piston in the tube. Over time that o-ring will decay from the effects of the oil and need replacement. ATF is about the same weight as your 3-in-1 and will not decay the o-ring.

[Stanley]

Since doing the FSM dome & piston 6-monthly maintainance the first time a few weeks ago, noticed my SU's seem to be using more oil. Wondering if I did something wrong. Maybe the carb cleaner damaged the o-rings, or the all the gunk prevented oil leaking out. Anyway, thank you jaltman, looks like the fix is easy. Need a tune-up kit anyway, hope it's got the o-rings.

[Bruce Palmer]

Mmmmm, There is only one way oil can escape the inner tube that is attached to the piston and that is over the top of the tube. Fill the inner tube to the top of the tube, put the plunger in and the puck on the end will displace it's volume in oil and that where it will stay. So if you are pulling the damper out and looking down in the inner tube and it appears low (like a 1/2" down) that's the LEVEL it will run at forever. I add to mine mabe twice a year with a little plastic pipette and I think it's as much for me as it is for the carbs. I probably push overfill out the second the damper gets screwed down.....

[Diseazd]

Thanks Bruce for putting that to rest. Since it's only function is to damp the rise of the piston, I couldn't imagine why there would be an "0" ring involved with the resevoir.

[Arne]

I can't recall ever having to add to mine over 5 years unless I had them apart and dumped the old out.

[rcb280z]

What Jim said, Change the o-ring and use ATF. I did and it worked with no problems. When I was in Nevada I ran early su's on my 77 280 while I slowly collected all fuel injection(another story for another time) components and used ATF for the 3 years, trouble free.

[Bruce Palmer]

Okay then, so disregarding the facts as laid our herein, when you find that O-ring take a picture of it and post it here....... Just saying there ain't no O-ring!!

Like Arne said consumption of this oil should be "monster minimal" 'cause any that goes away will have to be sucked up over the top of the tube and with the tight fit between the tube and the barrel it runs uo and down in, 5 years could work too.

[Diseazd]

Bruce......I love it when you get pissed off! Nyuck...Nyuck...Nyuck!!!

[Captain Obvious]

I have a 1972 with SU carbs. I've always used "3 In 1" Motor Oil which is a straight SAE 20 oil. I can't go much more than 350 -- 400 miles without having to refill the reservoir. Is this normal?

No, it is not normal.

No, there are no O-rings involved.

If you are losing fluid out of the dampers, the first thing I would look at are the little brass jiggly bits on the end of the damper stalks.

Those jiggly bits are a one way "check valve" system that is supposed to impede the flow of oil when the suction piston is moving in the up direction, yet pass oil easily when the suction piston is moving in the down direction. This allows the suction pistons to rise slow, but fall fast. If those jiggly bits are stuck and not allowing the check valve to open properly as the piston is falling, then the oil will be lifted up and out of the top of the tube by the valve itself.

Some things to check to verify proper operation?

a) Pull the damper rods, fill the dampers to the appropriate level (should be a fill-to line on the damper rods), and re-install the damper rods.

Pull your air cleaner cover off and lift the pistons by hand. They should lift slow, but fall fast.

c) Lift and release the pistons a bunch of times and then recheck the oil level. The oil level should not have changed. If, during this test, you have lifted oil up and out of the tubes then something is wrong with your jiggly bits.

[Diseazd]

Z Therapy sells SU oil. If you have a doubt, use it. However, I used 3 in 1 oil for years with absolutely no problem.....you're just looking for enough viscosity to keep the piston from rising too fast. Jiggy bits don't wear out :stupid: ....and there are no more "0"rings in the bottom of the SU reservoir than in the bottom of a beer mug!

Edited August 10, 2012 by Diseazd

[Arne]

Also while we're in here - ATF is too light weight, allows the piston to move too quickly. The factory called for straight 20 wt. oil, easily found at most motorcycle shops as fork/shock oil. ATF is closer to 5 wt.