Use Motor Oil for Fork Oil?

I'm ready to replace a bent fork on my 1979 KZ400 LTD and the manual says use 5W20 fork oil. Nobody around stocks it. Will straight 20 weight high detergent motor oil work in place of 5W20 fork oil, or is fork oil a completly fifferent beast all together?

Any advice would be appreciated.

Ridge Runner wrote:

I'm ready to replace a bent fork on my 1979 KZ400 LTD and the manual says use 5W20 fork oil. Nobody around stocks it. Will straight 20 weight high detergent motor oil work in place of 5W20 fork oil, or is fork oil a completly fifferent beast all together?

Any advice would be appreciated.

Whoa! , motor oil is not hydraulic and way too heavy anyway.

Use Automatic transmission fluid if only nothing else is available.
Otherwise use the straight 20wt .

5W20 oil is actually a 5W oil that lubricates as well as 20w oil when it is hot, or so Mobil oil taught us. If you can't get the fork oil, use the ATF. Straight 20w would prduce quite a rough ride. Just my $0.02.
Ride safe,
Les

NAPA should have hydraulic fluid. If what you want is not in stock, they can order it just like they order a 1983 Volvo ATE rear caliper rebuild kit. If the guy tells you they can't, ask to talk to 'the old guy'.

I agree, your best bet if fork oil or 5w20 motor oil is not available, would be ATF. It will lubricate, is a hydraulic fluid and keeps seals healthy.

For me (at 235 lbs) and my riding style, I have found that 1/2 10 wt and 1/2 15 wt ( guess that makes it 12 1/2 wt) fork oil has worked best in the 79, 80, 82, 750 twins, 79, 80, KZ650's, and 82 KZ1000M. If you weigh less or ride less aggressively then straight 10 wt would probably be best. ATF is generally somewhere near 10 wt, although I have been unable to find any manufacturer that lists the wt of ATF.
You could order fork oil online and have it in 2-3 days.

Post edited by: steell, at: 2006/04/14 00:29

steell wrote:

ATF is generally somewhere near 10 wt, although I have been unable to find any manufacturer that lists the wt of ATF.

Just to clarify, ATF=Automatic Transmission Fluid, right?
Scott

correct!!! ATF = auto tranny fluid.

Great! that stuff is easy to find.

Thanks for all the info. You guys probably saved me a set of fork seals at the very least. I suspected motor oil wasn’t the stuff to use but when I read “SAE 5W20” in the manual it sure sounded like a motor oil designation to me.

I have plenty of ATF on hand. Since it’s a fairly simple procedure to change the fluid in these things I think I’ll experiment and see what works best.

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“Ships are save in a harbor, but then that’s not what ships are made for, is it?”

Motor oil will work fine. We're not rocket science here. 140wt gear lube is not the thing to use of course but any light weight motor oil won't hurt a thing and I'd bet no body could tell 2 cents worth of difference.

That was my initial thought as well Ron. In fact I had already purchased a quart of SAE 20 motor oil just prior to posting my question. My background is in auto parts but I have almost no experience with motorcycles, which is why I sought advice from you guys.

I’ve leapt without looking before and paid the price. One doesn’t put brake fluid in a power steering pump or motor oil in an automatic transmission.

So to clarify, you have used motor oil in forks with no problems? I just want to be sure. Thanks for the input.