Monza Jr. fork seals

[DucMonzter]

Hello. I’m currently in the process of restoring a round tank Monza Jr. 160 that’s been in my family since the 1960s. The project has had several major ups and downs over the past few years but I’m finally getting close to completing it. Most recently, I've been working on the front forks.

Although they didn’t seem to be leaking when I disassembled them, it would seem reasonable to replace the 50 year-old fork seals out of principle. After extensive searching, I’ve been unable to locate a replacement set for this bike. The original flange-type seals measure 30 x 42 x 7 mm. Does anyone know of a source for these? One person recommended trimming down the O.D. of seals for the 125/175 models (which are available). Does anyone have experience with this? As a possible alternative, I’m curious to know if anyone has a recommendation for a method to recondition the old seals. Any assistance on this would be greatly appreciated. Thank you.

[Rick]

I believe the Monza Jr used the same forks as a Bronco- if you're in the USA, you can get the 30mm or 31.5mm seals here:
http://guzzino.com/du12foseseea.html
I'm surprised that you can't find a 30mm seal at a bearing supplier.
Rick

[amartina75]

Like Rick said check with your local bearing supplier.
They should have a suitable seal, for a few dollars instead of
$30. If you google the seal size 30x42x7 oil seal
You will get a lot of results so it is a common size.
Also you might be able to use a thicker seal like 10mm
I'm not familiar with those forks but like on my 450 scrambler I used
A 10 mm double lip seal instead of two single lip 7mm seals. If there is
Room to use a taller double lip seal it's better, but again
I don't know with your forks what will fit

[DucMonzter]

Thank you for your replies. I brought my old fork seal to a local bearing supplier but they were unable to match it. Although the salesperson was also a trained motorcycle mechanic, he had never seen one like this. He spent quite a bit of time looking through his resources but nothing even came close. His conclusion was that this seal was specially made for the particular application.

The seals that Rick pointed out (from Guzzino) are specifically designated for early model (1950s), 125/175 singles. My bike was manufactured in the mid-‘60s so they probably wouldn’t be a direct fit. However, I was once told that these might be adapted to work since they’re sized for 30mm fork tubes. I’m curious to know if anyone has tried this and how to accurately cut the seals to size. I’m open to any other suggestions, as well.

Thanks again for your help,
Jeff

[amartina75]

Im surprised they couldn't find anything that would work for you. did you take in just the seal or the fork leg itself. you don't need to match the seal exactly, you need a seal that will fit in the leg and seal against the tube. I looked at the monza jr parts book but i cant tell what the seal and washer assembly looks like. It looks like there are a couple washers, the seal and maybe a dust guard.
surely there is some play in all that as to what "exact" size seal you can use.
search on ebay, 30x42x8 fork seal they are available, also 30x42x10.5 are available

[DucMonzter]

I brought only the seal to the bearing shop. As I understand it, the complication may be that the fork seal seems to serve two purposes: 1.) it functions as a wiper against the fork tube and 2.) it has a flange that seals between the upper bushing and a washer within the dust cover. None of the other seals the salesman showed me had the flange. Also, most seemed to have a metal casing around them. Mine is all rubber with a metal spring running circumferencially. I've attached a few photos to help clarify my description. Is it possible that a standard wiper seal would fit inside the bushing and that a separate rubber gasket could be used between the bushing and dust cover? Thanks again for your help.

- Jeff

[amartina75]

I see the problem now. And I'm surprised this hasn't been covered before it seems like someone else surely has run into this before. That seal is exactly the same shape as the ones in my NC Scrambler shocks. I was also not able to find anything like it. In order to rebuild them my brother machined out the seat to fit a standard seal that I was able to buy locally. It worked perfectly. I guess that is an option for you. If you can find a seal that will fit down inside the bushing and use a seperate washer that would definetly work. If you can't find a seal to fit you'd be stuck machining it for a new seal.
Good luck hopefully someone on here has solved this problem before and can chime in

[joe46ho]

Jeff, There is more than one solution to your problem... First off the seal that was originally used on these forks is outdated and will not seal as good as a modern double lip seal. As Aaron said, some of the rear Marzocchi shocks used this type of seal too, and i recommend converting those over to modern seals as well, like I did on his... You can actually still buy that type of seal (at a hydraulic cylinder shop) I know because at my old job i had to overhaul old forklift steering, tilt, and lift cylinders all the time, and modifying them for different seals was not an option... So if you measure your upper cap/seal retainer you will find the i.d. is 37.5mm and the depth down to the "fingers" that are meant for the factory spanner tool is almost 5mm. If you wanted to modify the caps as little as possible this is the seal i would recommend:
30mm x 38mm x 4mm

http://www.ebay.com/itm/like/161113943990?lpid=82

With this seal you will still need to removed a small amount of material to enlarge the i.d. of the caps. (on a lathe)
However this seal will not hold up quite as good as an even better alternative which is a

30mm x 38mm x 7mm

http://www.ultimateindustrial.com/metri ... ouble-lip/

Obviously with this seal you will need to remove a little more metal (to enlarge the i.d. and the depth)
This is the best option in my opinion. And you can actually use a 8mm thick seal also if thats easier to find.

also with a seal conversion like this you will not need any additional seal between the spring seat washer and seal retainer. You may want to use a paper or fiber washer between these pieces (just as the Ducati/Marzocchi 31.5mm forks do)

One last note the earlier seals (125/175) you are looking at pictures of are 30 x 40 x 7 and while i suppose you could machine the caps to fit these seals i would not recommend it because the caps o.d. is only 42mm so you would be left with a very thin wall (and that wall is what the spring is supported by)
Hope this answers all your questions, and if you do not have access to a lathe, or know a machinist. I could machine the caps for you easily, but you would have to send them to me, and unless your in the usa, that could be kind of expensive for shipping them both ways...

Also if anyone needs a set of the early 125/175 seals, buy them from this guy on ebay (he has them listed wrong he says they are 250 forks seals, they are not though, i have bought 2 sets from him, they are the early seals they come with headlamp ear grommets, and are $5.00 cheaper than guzzino.com and shipping is free)

http://www.ebay.com/itm/Ducati-250-350- ... 14&vxp=mtr

Joe

[DucMonzter]

Thank you for your recommendations on fork seal options and for the offer to machine the bushings. Fortunately, I have access to a lathe at work so I can handle whichever bushing modifications are necessary. My approach will probably be to use the seals that require the least amount of material removal first and see if it works. I'll then be able to remove more material and progress to a larger seal if necessary. It's good to know there are several viable options to rebuild these forks.

Thanks again,
Jeff