M900 Marzocchi fork Oil

[Nasher]

I need to change the fork seals in the Marzocchi adjustable forks on my M900, which I'm hoping to do tomorrow.

I have the oil level tool and spring compressor, I made both of them a while ago.

I also purchased ages ago a pair of seals and a Hyperpro spring kit which came with oil.

I've just been checking what air gap i need and have found a big difference between the recommendation in the Haynes manual and the Hypepro instructions.

Haynes says for the Marzocchi forks it should be:
90mm air gap and SAE 7.5 Oil

The Hyperpro instructions say:
110mm air gap and SAE 10 Oil, which has been supplied.

I know most people say the SAE 7.5 Oil works better in the M900 on Marzocchis, but I'm a little concerned about the significantly less amount of Oil Hyperpro are suggesting.

Can anyone suggest from experience which is correct?
Or does the lower Oil level counteract the Oil weight?

Thanks

Nasher.

[Flip]

Hey Nasher

Sorry I've only just seen this so don't know if you've already started the work.

I know there was a change in oil quantity for the Marzocchi forks which would obviously result in a different air gap.

I would assume that Hyperpro would have done some research with oil weights and air gaps so with that in mind I think I would go with their recommendations but a larger air gap would make them firmer from the outset but as you say the oil weight must been taken into account.

I am a little surprised they don't do something more clever as in standard form one fork leg is for compression and the other rebound damping which as we know is not ideal.

I never used a spring compressor tool when I messed about with the forks but simply filled them with the forks compressed with the required oil quantity and then measured the air gap.

[Rrawlings]

Most air gaps are spring out so will get a discrepancy if the spring is still there.

[Nasher]

Thanks Flip

I went with the Hyperpro data, thinking like you that they must have done some research.

I had a great day in the garage from mid-morning through to tea time, but did have lunch with Lady Nasher and the dog in the garden.

Changed both front fork seals, did a couple of other smaller jobs, but also gave the whole front end a deep clean whilst it was stripped down. The Brembos have come up like new.

It's sat there all back together, all I need to do now is test ride it, but that won't be for a while of course.

I find that a spring compressor for upside down forks, and Oil height syringe tool make life so much easier, and make the whole process far more controlled.
I did of course find that the plastic tubes in the Marzocchis are not drilled to use a clamp, but I drilled them once they were apart to make putting them back together much easier. I did check it won't effect oil flow.

Both of mine are home made, but faithful copies or very expensive professional kit. As much as I like buying tools, it's even better when you make them.

Nasher.

[Nasher]

As an aside on this job, a small warning to others contemplating changing their fork seals.

I've had for a few years a Sealey 41mm(inner) fork seal driver, the split type, and have used it on several pairs of forks to push the seal home.

I tried using it on my M900 Marzocchi forks in this thread and found the outer diameter was too big to fit inside the fork leg.
A split driver is not strictly necessary on them as the fork is apart when you push it home, but you should tap it home with a drift of the right diameter.

I was going to turn up a special driver to use, but couldn't find and bar of a large enough size in my garage or a big socket that would do the job, so ended up turning down the end of the Sealey driver in my lathe.



So the warning is: If you are doing this job and buy a Sealey 41mm inner diameter driver, please be aware the outer diameter is too big to fit down inside the hole!
I'm lucky enough to have a Lathe in my garage, you'd have to modify it with a file otherwise.

Another aside, I mentioned my homemade Fork Oil level setting tool and Spring Compressor.

Both make life a lot easier when working on forks.

The Oil level tool is used by overfilling the fork with oil, setting the adjustable tube to the depth required and sucking out the additional oil.





The Spring compressor compresses the spring and holds the fork securely whilst you remove the slotted washer and then releases the tension in a controlled way. then the opposite for reassembly.





Nasher

[Nasher]

I'm a little annoyed about this at the moment.

As mentioned I did this work back in April, but have only done @250 miles since.

Was out yesterday for a potter around following my lad on his 125, but when we stopped I noticed one of the new fork seals was leaking like a sieve.
It was fine when I looked after @100 miles.

I know the chrome isn't damaged, and that I put the new seal in correctly, so it must be an issue with the seal itself which came from Hyperpro with the springs.

I must have changed 30 or 40 fork seals over the years, and have never had one leak after so few miles.

better order another pair, and will do both again as i now don't trust the other Hyperpro one to last.

Nasher.

[mickj]

I used all balls seals in my Speed Triple and one of the m leaked after a week or so, all ball replaced the seals straight away with no problem, second set are perfect so I can recommend all balls racing seals.

[350TSS]

I get my fork seals from Simply Bearings - about £5 each and arrive in a couple of days - you obviously have the bother of measuring the fork leg and the diameter and depth of the place it sits. Never had a problem with them though