ATE fork question

[Rob Farmer]

Got a strange one that I'm hoping somebody can shed some light on.

Just rebuilt my R100RS and have started to get a few miles in and steadily ironing out all the little details that crop up after an extensive rebuild.

The fork action seems a little harsh so I thought I'd take a look. There's a new set of genuine RS springs in there but the bike appears to sit low at the front. I've taken a few measurements from the bottom of the bellows on the bottom of the leg (the one that seals the gap between the fairing and the fork legs) and the top of the rubber seal protector on the slider.

Front wheel off the floor - 200mm
Static sag - 80mm
Dynamic sag - 105mm

I would have expected more like
Static - 15mm
Dynamic - 66mm

I took the new springs out and fitted the originals - the measurements are virtually identical so it's not the springs. All the internals are in place and I have the correct top nuts are fitted.

what am I missing?

 

[DrFarkoff]

I took the new springs out and fitted the originals - the measurements are virtually identical so it's not the springs. All the internals are in place and I have the correct top nuts are fitted.

what am I missing?

Ehm a Lighter Rider :-D
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[Rob Farmer]

Thats you off the christmas card list

 

[DrFarkoff]

Thats you off the christmas card list

At least I didn;t ask had you any oil in them

I presume you have an exploded diagram?

Linkies?

 

[Rob Farmer]

There's got to be something missing in that stack below the spring. Looks like the whole lots coming out again

Strangely I have another front end and the springs sit at exactly the same height in those

 

[Kenny]

Long time since I played with one of these...part 18 the intermediate ring is ( IIRC ) 10mm..have you this in situ?

 

[bustupbiker]

My 90s had plastic blocks in the bottom about 20mm thick
or were they in the top
When i got the new ( to me ) left leg, i fitted it and did not look to
see if it had the block in it. It did'nt I did look after i took it off the centre stand and the bike dropped like a stone

 

[Rob Farmer]

hmm! everything appears to be there according to the diagram

A couple of preload spacers will probably sort it out, using original parts I'd have expected it to be pretty much spot on without having to frig anything.

 

[Rob Farmer]

Long time since I played with one of these...part 18 the intermediate ring is ( IIRC ) 10mm..have you this in situ?

thats on the later forks kenny. Part 18 is a ball bearing in the ATE forks. I should have mentioned that the bikes a 78

 

[Flipfly]

Rob, are you being to technical?

I would have thought in the late 70's the measurements would be

Static sag - aye, that'll do

Dynamic sag - Ya best stop eatin them meat pies lad or aye, that'll do



Have you checked you have that ball bearing, it could make all the difference

 

[Rob Farmer]

You'll not rev me up like that flip


You can't put the bike on it's side stand without leaning it to the right slightly and even then it's almost vertical and the ride is too harsh.

Everythings in there that should be so I guess it's a case of making a couple of 1inch preload spacers. Very odd

 

[Rob Farmer]

Had a call from the old fa....Proff this morning he's got exactly the same problem with his R90S and has had a couple of spacers made up, Aparently theres an awfull lot of ATE front ended bikes running about with soggy forks.

 

[Flipfly]

Had a call from the old fa....Proff this morning he's got exactly the same problem with his R90S and has had a couple of spacers made up, Aparently theres an awfull lot of ATE front ended bikes running about with soggy forks.

He's not a bad bloke for a grumpy old Bstard is he

Best not mention his name though, you may get the mod police on ya

 

[Kenny]

Now you mention it, I think I fitted 10mm spacers at the top

 

[Beemerboff]

You didnt mention how much preload there was on the spring when you assembled the forks , but most forks seem to have around 20 mm.

That is, the spring is just being compressed when the first thread on the top nut catches and the preload is the depth of the thread.

I have found that things feel best when the front rider sag is around 10% more than the rear - so that would be a good spot to start from too..

 

[(RIP) pastyman]

Yeah, I recon most airhead tossers have about 10% more sag at the front end. probbly a lot more in some cases.

 

[Rob Farmer]

You didnt mention how much preload there was on the spring when you assembled the forks , but most forks seem to have around 20 mm.

One snigger from you Kenny and there'll be trouble..

Fork springs with no tension on them

Static sag - this eats up 80mm of the travel. Should be 15mm to 25mm

Dynamic sag - takes up 105mm of the available travel. It should be around 66mm

You can see how little travels left to cope with bumps.

 

[Rob Farmer]

20mm spacer fitted. Static sag is now 56mm so 28% of the available travel. I'm not expecting miracles just something that doesn't clash my teeth together when I hit a bump.

 

[fayeslane]

Yeah, I recon most airhead tossers have about 10% more sag at the front end. probbly a lot more in some cases.

- yep that's me