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Discussion Starter · #1 ·
New to the board. Working on my first Triumph project.
Looking for some feedback particularly the rear motor mounts.
Im not at all thin skinned, fire away.

--DC--


freshly reworked frame



semi mocked up. lots of bailing wire and tack welds but wanted to get an feel for it.


I know how most of you feel about forward controls, but I like em. I wanted to do something different. Forward enough to not feel like I'm sitting on my heels but still rearward enough to be able to put some weight on them. I also wanted them to look like the belonged there, not just HD controls made to fit.


Rear motor mounts Started with choppahead 63-70 mountsand started working in. 1" tube with 1/2-13 threaded bungs

Cut 2 plates with a 3" cut out for the OIF backbone. This was not easy as I dont have much of a machine shop. A drill press,cut of wheel and lot of filing.


My plan is to weld them in something like this and then box the ends. Im a little concerned about the relatively thin tubing on the backbone.

Anyone have any thoughts or advice?
 

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I don't have much OIF expericence, but I think I would find a section of 3" id tubing and fishplate the bottom 4 inches or so of the back of the downtube. Add 1 horizontal reinforcement centered on the tubing, taper it and extend it to each end of the tubing. The horizontal tubes need to be notched to fit regardless of how you choose to do it. Should be able to do all this with an angle grinder and cutoff wheel. Do you have access to a TIG? Somebody jump in if I am missing something on OIF.
 

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Discussion Starter · #5 ·
Thanks for the reply Gapwelder.

This is what I have pictured from your description.


I probably should have asked the question before I started. It took getting it together as far as I did to start questioning how i was going about it.
I have a couple of questions. How thick and wide should the horizontal reinforcement be? How far above the horizontal tube should the 3" ID plate go and should I tie it in to the bottom plate below the down tube?

I plan to tack it all in place with the MIG then have my local shop TIG it. I know my limitations. Also, Anyone have any thoughts on where to score 3" ID tubing. I doubt i would need more than 1'.

Thanks

--DC--
 

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Discussion Starter · #7 ·
3" hairpin springs and a custom seat pan is what I have in my head. Maybe 5" if thats what it takes to make it sit the way I want.
 

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Yes, that is what I was thinking. I think if dimension "?" is less than 1" I would go with 7ga (3/16) flat stock. Over 1" and I think 11ga (1/8). That may be a little overkill but it looks like that is standard 1" round tubing you are using and the heavier flat stock will allow you to hold the heat away from the round stock when welding.

It would definitely strengthen the assy. if you extended the reinforcement down to the bottom plate. My concern would be welding around the joint. I think that would be the highest risk for burn thru. It you could find some heavy wall tubing you could chamfer the inside bottom of the plate where it would clear the bead, then weld the outside of the reinforcement to the bottom plate. I don't think I would disturb the existing weld.
 

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Discussion Starter · #11 ·
Thanks for the advice. Im a big fan of overkill so ill probably run with the 1/8" reinforcement. All I can seem to find for 3"ID is 1020 DOM Structural Round Steel Tube3-1/2 OD x .250 wall x 3.00 ID. More overkill.

Where I already cut the bottom off the down tube (I plan to run an external filter for better filtration and increased oil capacity) I was thinking of grinding the existing weld back and running it right to the existing 1/4" bottom plate. Is there a higher risk of burn thru than when we cut the stock filter assembly off? I'm thinking the 1/4" wall tubing tied into the bottom plate would be as strong as I can hope for. I'm sure it will be more work but I want to make sure I build this strong enough to beat on it. Or am I missing something?

--DC--
 

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....I think tying everything together would definitely be the strongest set up. I looked through my scrap pile and I have a section of 3" i.d. 3.250 o.d. (1/8 walls) The i.d. actually measures 3.06. You could probably tighten it up with a little heat. Don't know the specs but it is round tubing (not pipe). If you think you may could use it, pm me with your email address and I will shoot a photo to you.
 

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Nice project.
I'm just finishing up my '72 oif. tr6
I had to weld on the oil tube in a couple of spots (seat bracket & coil bracket) and did fine with my arc welder on a medium/low setting. I just kept the heat mostly on the bracket so I didn't burn thru the tube.
I did my motor mounts in a bolt on style similar to stock, the attachment point was a lug welded to the new bottom frame tube Kinda tough to see in pic so I added the white arrow.
Guess it's too late now, but if you wanted to mount the motor like you are, why didn't you just use the swingarm tube that was there?
Rick.
 

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R.E. I can't remember how the rear mounts are on a OIF frame. So your rear mounts do not attach to the backbone? I don't see anything at all wrong with your setup, just couldn't remember how they were stock. The design boomstick has drawn out kind of replicates the pre OIF rear mount, and with a 3' o.d. tubing I think it should be plenty strong.

GW
 

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rear mounts on a OIF bolt to the bottom of the frame cradle where it transitions to the diagonal shock mount tubes,,,,,cutting these eliminates the rear mounts.......i was forewarned about welding to the oiltank tube so i made hardtail mounts that went to the swingarm tube, left the diag. tubes there [and rear motor mounts] and just faired the diagonal tubes into the top hardtail tubes...looked pretty good.....ltr on, i cut the hardtail loose from the oiltank tube up top and opened the tube up for a early yamaha monoshok, letting it pivot on the swingarm mount where the bottom was originally attatched.....cut the diagonal tubes loose from the hardtail and made a solo saddle rear mount bracket....monshok hardtail.....reason i`m straying so far afield of this threads intent? THAT OILTANK TUBE IS REEEEAAALLLYY THIN! less than an 1/8th thick. 16g? be carefull and bracket the `ell out of it!
 

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Discussion Starter · #17 ·
Nice project.
I'm just finishing up my '72 oif. tr6
I had to weld on the oil tube in a couple of spots (seat bracket & coil bracket) and did fine with my arc welder on a medium/low setting. I just kept the heat mostly on the bracket so I didn't burn thru the tube.
I did my motor mounts in a bolt on style similar to stock, the attachment point was a lug welded to the new bottom frame tube Kinda tough to see in pic so I added the white arrow.
Guess it's too late now, but if you wanted to mount the motor like you are, why didn't you just use the swingarm tube that was there?
Rick.
The embarrassing truth is that I believed the shop that welded my frame that i wouldn't need the rear motor mounts (He did admit that he had zero experience with OIF frames). After reading more I disagree and have decided I do, but the swing arm tube was already gone. I hadn't given much thought to mounting them as you have.

At this point I just want to make sure they are sufficient and strong and the pre OIF style mounting seemed to make the most sense. At least until I realized that the tube wall is very thin. That's when I started this post to figure out how to best move forward.

Nothing is too late, everything in the above pics is either bolted on or held in place with welding magnets. I think that plating the tube with some 1/8" tube and heavy brackets will work but its all theoretical. I appreciate the input as OIF frames are all new to me (and my local shop apparently).
 

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I think the way you're going at it is fine.
The oil tube is plenty strong, the factory attached the swing arm to it. it did also attach to the outer frame rails too, but it included pegs, motor mounts, swing arm, brake lever...
Will your motor mounts hold pegs & stuff too?
You could also put in gussets on the bottom if you think it's necessary.

If you're putting your battery low, will the mount interfere?
 

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Discussion Starter · #19 ·
The motor mounts will not have pegs etc. Everything will be moved to (GASP) forward controls. I should have plenty of room for batt still, but will wait to finish motor mounts before I figure out final placement. Im hoping bu plating the back of the tube and running it right to the bottom plate that i can transfer the stress away from the oil tank. If not ill start cutting gussets :)
 

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I have no problem with forwards, They're comfortable & I have them on my soft tail, I just wanted my feet under me for my first rigid in case I need to use my legs as shock absorbers. :)
 
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