Vintage Dirt Bike Q & A

Hello I was wondering if anyone would beable to tell me how much fork oil to put in my 78 cr250? The guy at the store I bought the oil from (30w by the way) said about 4 ounces in each? Thought I would check here first to doublecheck. And after that what should I set the air pressure at in them. Any help would be appreciated! Thanks!

If you drain the forks then re-fill with 205 c.c. (6.9 oz) If you completely dis-assemble them then re-build with 275 c.c. (9.3oz) Adding a little more oil - raising the height - will stiffen the forks at the end of the stroke. Less oil will have the opposite effect. The manual recommends 5 weight oil but I have heard of 2 weight oil being used. There are suspension people who will drill an extra hole in the damping rod to make the forks more supple. I recommend you start with 5 weight at the stock height and work from there. Normally the air cap is used to bleed out air pressure created when the forks get warmed up. However you can use a little air pressure - say 5 lbs - to again make a stiffer air spring that will resist bottoming (if you have after-market air caps). Don't use air pressure to over-come sacked out springs. The springs should be at least 41mm and 517.5mm respectively.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

So this 30w oil he sold me wont work then? There is a big difference between 5w and 30w. What bikes would use a 30w fork oil? just curious

thanks for the help!

Maybe Travis Pastrana's bike.

I think I read somewhere recently that the fastest Supercross Pros are using oil that heavy in their modern works forks, but us mortals should be ok with 5,7 or 10 wt.

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

Ok when I go back into the city I am gona trade the 30w in for a bottle of 5w or maybe 10w what do you think? How much stiffer would 10w be over 5w? And I was wondering if in the meantime until I get to the city (I live quite aways away) if using 5w30 engine oil would work in the forks just for about 4 days or is that just a stupid idea?


thanks!

Bad Idea! Totally different type of fluid.

I remember reading in old Dirt Bike mags that they often used GM transmission fuild (ATF) in there forks, so maybe that would be an alternative until you can get back into town.

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

I think ATF is about 10 weight and it would get you by....

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF