Fork oil weights – what is the difference

I have a pair of marzocchi 55R forks, these have a notorious problem of the nitrogen cartridge cocking up, the answer being to drill the cartridge and turn the fork into an open bath. I’ve done all this and all seems good except for having no control over rebound anymore. I’ve flushed the old oil from the fork and replaced with new to the levels that windwave (Marzocchi service centre) have recommended. The only thing I can think of is that I have used a 10w oil (it was all I could get at short notice) rather than recommended 7.5w. I don’t really have any knowledge on this sort of thing but would the oil weight effect rebound?

Found lots of info on different weights and viscosity of various oils but not a simple explanation of what the implication of different weights is.

Any help much appreciated.

Simon

Usually higher weight = more damping.If you’re above average weight,then 10wt should be fine,if you’re a lightweight,it may feel over damped,you need to ride it and see what you think.Also one firm’s 10wt can be lighter than another’s 5 wt.There’s a comparison chart and good advice here http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

Have you charged the damper with oil? It can be tricky to find but there is a “how to” video somewhere. Had the same issue working on a pair of cr for a friend.

Heavier weight oil, ie bigger numbers, are thicker. Thicker oils will need more force to squeeze through a certain size hole or for the same force will go through more slowly. Hence the heavier oil will provide more damping than a lighter oil.

Thanks for replies.

Onzadog – not as such, topped up oil with fork compressed, will look into that though

So If I wanted to achieve a slower rebound I need to use a heavier weight oil? That chart is useful although the figures are all over the place!

The oil manufacturers blend their own blends,they’re all different.MTB fork manufacturers usually use an oil from a set manufacturer,but I haven’t had a marzocchi fork for years,so I don’t know what they’re using now.

I did the same thing first time and had no rebound control at all. charge the cartridge and all was fine.

UKBIKESTORE are showing shell oil under the marzocchi oil

How did you go about charging the cartridge?

I seem to remember filling a bowl with oil and cycling the cartridge up and down and then putting it all part in a certain order.

I’d assumed that using the fork in an oil bath would do it through use but it seems that’s not the case.