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Fitting Bultaco Sherpa Fork Oil Seals

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#1 hightown



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Posted 02 June 2009 - 06:46 PM

Hi All

Any advice on fitting the bultaco oil seals would be appreciated especially unscrewing the nut at the bottom of the fork leg.

Regards Eddie/

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#2 bultaco49


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Posted 02 June 2009 - 07:35 PM

Hi - the nut on the bottom of the fork leg should be an allen head. If it is turning and not loosening, screw a long m5 setscrew gently into the fork oil drain screw hole to trap the base of the fork rod. Be careful doing this as if too much pressure is applied it will damage the rod. There are o-ring seals at the base of the leg and around allen screw. Replace them or fork oil will find its way past the screw. I also paste a little silicone around the scrw threads at the socket head.

Its not the fitting of the seals that is a problem - its getting the old ones out! I always gently heat the fork leg around the top oil seals until the residual oil boils then use a fork removing tool (available from http://www.frost.co....e_catalogue.asp or ebay). The top seal comes out easy but be careful removing base seal. If too much pressure is applied the fork ally will split. If it refuses to budge use a dremel with small grinder to cut the metal seal band. Even if a little alloy is removed it is better than a split seal housing. Can be fixed with locktight bearing seal or even some filler. Clean out the swarf!

When replacing the seals lips face to the bottom. Heat the fork leg, lubricate seal and insert one at a time, preferably with a drift.

#3 monoped



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Posted 02 June 2009 - 07:40 PM

Hello Eddie,

Try sitting the leg in some penetrating oil overnight, then pour a kettle of boiling water over the area around the securing bolt. I would not recommend using direct heat from a blow lamp etc on the alloy. However the relatively low heat of boiling water being poured over the alloy should allow the alloy to expand slightly, without damage. Likewise when re-fitting new seals heat the top of the lower leg with boiling water then drift the new seal in using a close fitting socket (one with approximately the same external diameter as the internal daimeter on the recess that the seal fits into) and rubber mallet.

#4 swooshdave


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Posted 02 June 2009 - 08:43 PM

I think I used an impact wrench on the allen head bolt to get it loose. I think that you can also use a really long screwdriver to help hold the damper rod.

I used a regular seal puller. If they are extra corroded I'm sure it will be more challenging. I had one set of forks which were just horrid but I don't recall the seals being any problem.

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#5 nigel dabster

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Posted 03 June 2009 - 05:15 AM

we always just wrecked the old seal by carefully tapping in with a screw driver. the outer edge of the seal can withstand a bit of damage anyway.

#6 sherpa325


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Posted 03 June 2009 - 01:11 PM

Hi , I have always found the easiest way to undo and tighten the allen screw on the bottom of the forks is to compress the forks. Use your tie downs to pull the forks down as far as possible- the screw should be able to be undone without any problems.
Cheers greg

#7 sherpa325


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Posted 08 June 2009 - 09:38 AM

Hi Eddie glad to hear you undone the bolts and replaced the seals without any problems, the forks take 180cc of oil, as the forks were made 30 odd years ago you will find that todays lightweight oils dont work that well in them, so you need at least 10w I would think, I have used ATF in mine with no problems, you may have to add some longer alloy spacers to the top of the fork spring [25mm on my bike] as the springs are soft and tend to sag over time
Cheers Greg

#8 seakayaker


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Posted 10 January 2014 - 08:47 PM

January 2014,
Just read Bultaco 49's advice on removing fork oil seals.
Great advice.
I did use a dremel to cut the old seals.
I am now sure that the seals that i have just removed were the originals: almost 40 years of service, and really well embedded in the fork ally. So very good advice.
many thanks,

Sea Kayaker
Bultaco Alpina #213

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