Forza head bearings and fork oil seals sizes

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Dave L
Posts: 93
Joined: Mon May 14, 2018 10:31 am
Location: Mallorca

Forza head bearings and fork oil seals sizes

Postby Dave L » Sun Dec 22, 2019 8:02 am

Can anyone tell the correct head bearing size for a 78 Forza and also the fork oil seal size.The forks are the disc brake type.
Also I'm having trouble compressing the valve springs.They seem to be extra strong compared to other bikes I've worked on.Is this the case or am I doing something wrong?

Jon Pegler
Posts: 459
Joined: Sun May 16, 2010 6:19 pm

Re: Forza head bearings and fork oil seals sizes

Postby Jon Pegler » Sun Dec 22, 2019 11:21 am

You have to be careful with Forza, Strada and Vento head races and oil seals as Mototrans fitted different sizes, almost at random.
If you have the late Strada forks with discs, the fork seals should be 47 35 7 in size. The earlier forks used 45 35 7. This is the size for a 78 Forza with the composite steel slider with the cast on aluminium caliper brackets.

Most of the head races use a size of taper roller bearing 25 52 16.25, which is sold as 30205.
I have come across some taper roller head bearings 26 52 16.25, so be sure to measure the diameter of the steering stem or the underside of the top adjusting nut to determine which size you need, before you buy your bearings.
When fitting the new taper roller head bearings it is necessary to remove the old outer races in the frame. The is a particularly difficult task as it is very hard to get a tool behind the old race to drive it out with a hammer. I made a special curved and shaped cold chisel to get the races out and it was still not easy.
Do not be tempted to fit new taper bearing races into the old outers. Apart from being bad practice, engineering wise, the taper of a new bearing will almost certainly not be the same angle of the old race, causing extremely high loadings at the point of contact.

Jon

Dave L
Posts: 93
Joined: Mon May 14, 2018 10:31 am
Location: Mallorca

Re: Forza head bearings and fork oil seals sizes

Postby Dave L » Tue Dec 24, 2019 10:34 am

Thanks Jon.I broke the bearing cups on my Strada with a Dremmel! That seemed to be the easiest route.Ill take a closer look at the forks to determine the correct size.
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