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Hello All,

I'm working through my first build and after buying a custom frame and Ultima front-end I got a couple questions.

The stock fork cups, races and bearings don't work on this sort of setup right?

So what do "real" builders use? I thought I could take these aftermarket 1" cups down to a machinist friend and have him take a little off the top so to speak. But after looking at them I'm not sure that would be safe.

Thanks
Jw

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Im searching for a moment, did you purchase the frame & the frt end from the same supplier? If not your going to have to contact the frame builder & let them in on what your planning on doing & the direction of the build. If for some reason the frame will not accept the inverted frt end your going to have to make a decision. Is it the frame or the frt end you prefer.

If you cannot get ahold of the frame builder then there is only one choice. Your going to have to mic/measure the inside diameter of the frame neck where the race seats & measure the portion of the new race where it seats into the neck. It should be a tolerance fit so it cannot rotate once it is pressed into the neck. As for race height I have seen before where the races are taller & require a longer stem to get you through the triple trees & lock-nut. Onced you are certain its ready for assembly the races should be seated/pressed in with loctite applied to the mating surfaces.

Another consideration is triple tree rake, I am not talking where the offset of the top of the tree is varied or a different measurement of the lower triple tree plate. I am talking the trees that have offset brg races so that the tree stem increases trail not reduce it as a raked tree will do.
The design difference is the triple tree stem bolt is parrallel to the fork tubes but is actually angled inside the frame neck which when properly measured out will make for a more stable frt end than trees which are raked, keep in mind raked trees reduce trail


I hope this helps you out, good luck with the build.

Keep us posted


Dare
 

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Hello Dare,

Im searching for a moment, did you purchase the frame & the frt end from the same supplier? If not
...
Yeah I purchased them from the same supplier, DemonsCycle, but not straight from the manufacturer. The frame MSO says Straight Up Choppers and the Forks are Ultima 58mm Inverted 3° 4 over (these are close to what I have). I used the little RB Racing calculator and if I did everything right it's 5.25 of trail.

I'm pretty sure the forks will work on the frame cause the rollers on Demons and StraighUpChoppers have the same forks.

your going to have to contact the frame builder & let them in on what your planning on doing & the direction of the build. If for
Yeah that was the next step, see how Demons handled theirs and then contact StraightUp. Harry over at Demons has been great in responding in the past.

Your going to have to mic/measure the inside diameter of the frame neck where the race seats & measure the portion of the new race where it seats into the neck. It should be a tolerance fit so it cannot rotate once it is pressed into the neck.
I started doing that when I thought about using those fork cups for the frame. It's 7 1/8 on the neck and between the trees is 7 5/8. I don't have depth micrometer but the digital says the inside dimension on the neck is 1 31/32. The cups have an outside dimension of 2 15/64 so I think they can be taken down so they slip into the neck. I just need to get a more accurate depth measurement than my trusty Stanley tape measure :). My machinist friend might have other thoughts.

The issue is height since I only have about 1/2 to play with. The top cup has a height of 3/4 from where it would normally sit on a standard frame neck to bearing seal washer. The bottom cup is much taller 59/64.

Scratch all that, I just measured the inside diameter of the cups and they're 1 31/32 so I might be able to use standard races press them into place and use the bearings and seals from these cups. Then it's just a matter of spacers.

What do you think?

As for race height I have seen before where the races are taller & require a longer stem to get you through the triple trees & lock-nut. Onced you are certain its ready for assembly the races should be seated/pressed in with loctite applied to the mating surfaces.
Good to know, thanks.

I hope this helps you out, good luck with the build.

Keep us posted

Dare
I will...

Thanks for the reply and your insights...
Jw
 

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I would give Harry a call at Demons, I am more than sure he will get ya all the info you need.
In most cases aftermarket products are usually built to take / accept OEM parts. Oem is the standard by which alot of manufacturers base their tolerances on. Ya there are some out there that are just totally different altogether but when it comes to internals a manufacturer has to compete with the tolerances no different than the internals of aftermarket forks & triple trees.

I can't see it not being able to work, it may just take a different road or different approach.
Just remember sooner or later You are going to have to check your trail, its nice having a trail calculator which is good reference & a basis for your design BUT you simply have to be correct, you have to know to the 1/8" what your trail actually is & the only way is to do it manually. Last thing one would need to be faced with is a tank slapper & a resolution of I wish I hada checked it myself.


Dare
 

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I agree call Demons- they have a great tech staff.
Tell them what you have and they will let you know what should work.
Also other web sites might be very helpful to you at this point
Club Chopper and Chopper Compendium . Useful info and experienced builders there
to help.
 

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Eh JW ... was wondering how your making out with the build??
 
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