My girder & frame project - Anything blatantly wrong?

[Nero]

Ok guys, I was finally able to came away with the solution showed below for my frame and its front end.
The frame will accomodate a 4 in-line, 600cc Yamaha unit engine (I will have to replace the airbox with some filter cones to avoid interference with the backbone, but that shouldn't be a problem... )
The wheels are stolen from a Kawasazi ZX 12-R (200/50 rear tyre).
The girder's shock is a rear shock from an Honda Rebel 250.

General dimensions (in millimeters, I've already converted them below for you imperial guys and for blonde, sweet girls off course... ) :

Choppa 2 Dimensions.JPG (163.06 KiB) Viewed 6267 times

Rake: 40°
Trail: 77.88mm [3.06"]
Neck Height (measured from the right end of the lower cup, as in Gary's drawing): 642.03mm [25.27"]
Ground clearence: 108.64mm [4.27"]
Front axle height: 300mm [11.81"]
Rear axle height: 315mm [12.40"]
Wheel base: 1796.94 [70.74"]

Girder length: 750mm [29.52"]
Girder links length from center to center: 110mm [4.3"]


Some girder's shots:

Girder - Top 1.JPG (129.18 KiB) Viewed 6267 times

Girder - Top 2.JPG (129.1 KiB) Viewed 6267 times

Girder - Top 3.JPG (156.64 KiB) Viewed 6267 times

Girder - Bottom 2.JPG (131.63 KiB) Viewed 6267 times

As you can see the girder is a little bit on the stubby side, but I had to make it much shorter (8.5") compared to Gary's one to get an acceptable positive trail, while maintaining the links at a reasonable angle with the ground (between 10°-12°).
I've checked for interferences and I shouldn't have problems; the rest of the measurment are all in the recommended ranges, I suppose.

My only question is about the lower shock mounts position: is it ok to have them pointing up as you can see in the last two pictures, or do they need to be at right angle with the girder's front (straight) leg?

Many thanks and feel free to let me know if you see something that seems wrong in the whole assembly..

[gww25]

It looks good to me. The angle of the shock is oaky as well but from an appearance standpoint it might look better if it was parallel with the angle of the front legs as long as there is no clearance issues.

[Nero]

I could make the shock sit almost parallel to the neck and the girder's front leg by shortening the lower mounts:

Girder Shock Parallel.JPG (165.67 KiB) Viewed 6262 times

I didn't do that for 2 reasons, the first is that doing this way the mounts would point even more upwards, and I wasn't sure if this would have been a problem (it seems it isn't, if I understand correctly...):

Girder Shock Parallel 2.JPG (114.9 KiB) Viewed 6262 times

and the second one is that in this configuration the mount is long 30mm (1.18") center-to-center, and in your plans you called for 1.375" min for this distance (yes, I got all your stuff from Bitter End Choppers and went through it I don't know how many times now.. ); but maybe even this shouldn't be an issue, because probably your recomendation was specifically conceived for that particular girder, isn't it?

In this case I will go with this second configuration for sure...

[railroad bob]

In my opinion, Gary is the ultimate authority here, but just a quick comment for clarity.

The lower shock mount connects to the fork member between the front attachment points of the lower links.
The movement of the lower links (and the member between them) provides the force that actuates the shock.
It follows that the lower mount attached to the cross member moves the same as they do.
For that reason, the position of the lower mount does not affect the function, only the looks.
If there were no interference, it could be on the bottom, and make no difference in the function.

This is my view of it, but if someone sees something wrong with my description, by all means, chime in

[Nero]

That seems reasonable, my only doubt was about some "binding" situation that could occur in some particular configuration.. but maybe I'm just overthinking it all.. :P

[Nero]

Couple more questions about the girder:

1) is it ok to use brass to machine the bushing from, instead of bronze?
2) considering the fact that I have no idea about how much the shock will compress under the bike's weight, do you think that it should be a wieser choice to build the fork a little longer? (I was planning to build the fork fisrt, and then the frame...)

As always, many thanks..

[concrete guy]

I would build the frame first.
Most likely you need a counter bore on the top of the upper yoke for the stem nut.
You will need a counter bore on the underside of the top yoke for the preload nut.
Why would you not want to use oil lite bushings?

Just for reference...My bike sits 3.25" off the ground, 42* neck, 4" up in the down tubes, my girder is 36" long.

I wish I had your computer skills.....8)

Scott

[Nero]

I've seen using the stem nut for preloading also, so I was thinking about using just one nut... sounds too risky?
I will still need the counterbore on top of the upper yoke however..
I've no problems with oil lite bushing, aside from finding them..

Oh, and I wish I had your fab skills.. :P it was after seeing your bike in the "how to build girder forks" cd that I realised how cool a girder fork could be, and that I wanted one..

[concrete guy]

I am humbled by your kind words. I never knew there were pics of my forks on the CD.

McMaster Carr is a good source for online oil lite bushings. I would recomend when you make your links to drill the holes undersize and then ream to size for a press fit. If you have problems getting the oil lites let me know and I will send you some.

On the preload nut, I would recomend the one that is a nut & dust cap in one. It has a very slim profile. I suppose you run without a preload nut. I couldn't give you an honest answer on the results. I guess I would just worry about it loosening up with time. I figured why reinvent the wheel from seeing previous practices. Your design looks great and I look forward to seeing more. I will tell you that I had to build two to get it right. My first one was over an 1" to short. I sat at the drawing board for quite awhile to get it right or atleast what I thought was right, LOL. It was a good exercise for me and I learned a lot from it. Polishing all your parts before bending and welding is nicer than after the fact....8)

Keep us udpated when you can......................Scott

[Maxthegardener]

McMaster Carr wont post outside the us...or at least to the UK anyway...Try http://simplybearings.co.uk/shop/advanc ... rds=oilite

[Maz]

A really nice design, but just a couple of points - the girder links should sit parallel to the ground under load ie when you are riding and therefore should incline downwards at the fork end when not under load (the bike will sit very slightly nose up when you are not sat on it!) otherwise there is a risk of bottoming out when you are riding under normal conditions....
With the bike at rest and on the side-stand it should sit more like this....

Niccy28 002.jpg (197.28 KiB) Viewed 6156 times

You should use Oilite bushes and not plain brass, the material is actually phosphor-bronze that has been impregnated with oil....the main world wide manufacturer is American and there are a couple of outlets here in the UK, don't know about the rest of the world....

Otherwise I think you've nailed it dude

Oh by the way, this blonde sweet girl is happy to work in either metric or imperial but thanks for the thought

Maz xx

[Nero]

Ok, I'll buy the bushings from the shop posted by Maxthegardener (thanks man ): they have the size I need, the prices are reasonable and the experience tells me that, thanks to the Royal Mail, I will recieve them before I get the "SKF equivalent" from one of the town shops (if they are able to find them in the first place.. )

At the online shop however they do not sell oilite thrust washers, so I'm afraid that I will have to resort to something different for those.. could teflon work or it's not though enough? Otherwise I still have that brass...

Last but not least, I'm a bit confused by the first part of Maz post... Shouldn't that be the position of the fork with the shock fully extended?

Shock Ext.png (48.53 KiB) Viewed 6147 times

I was planning to tack weld the girder together, and then wait for frame's completion to finally weld in position the shock mounting tabs, as per Gary's suggestion:

"you set the shock mounts so that the links are exactly parallel with the ground when the shock is fully extended and there is no load on the forks. In other words take the weight off of the forks by sitting the front of the bikes frame on a block about 1-inch higher than normal ride height and then prop up the girder until the links are level with the ground and then mark where you need to weld in the shock mounting tabs to install the shock when it is fully extended."


Please don't get this wrong, I'm not trying to be an a$$hole, I'm just trying to understand the differences and the subtle nuances in the methods that every builder adopts to build his girders.. (and probably you are just saying the exact same thing, and it's just my "newbiness" that keeps me from getting it.. :P )

[curt]

sounds like your gettin it to me but im on my first one too

[Maz]

They shock should be at full extension when you tack the mounts but just under that when at rest with minimal load on the forks....hope that makes sense, in my pic the bike is leaning onto the side stand so there is very little load on the forks....

maz xx

[concrete guy]

My only other thoughts on your sequence of building is tack welding the girder and then letting it sit for awhile. Some rust will accumulate at your joints. For tig welding this sucks but if your are stick or flux core welding it may not be as much of an issue.............Scott