winter project - customizing '81 Seca w monolever & doulever

Bodywork and monolever rear were done last year, working on the front end this year. Plan to build a wood and plastic model to get the dims for my jig right, then a test version in hand milled aluminum and DOM steel, then maybe a final version in Chro-Mo steel and CNC milled aluminum. Just got my joints form QA1, and ordered some carbon fiber to play with for the linkages from the bars to the steered upright.

 

Good sir, are you aware that your Seca tank has become a fender? Very nice. Looking forward to some more shots of this.

 

Yah, the tank was rusted out. Seller gave me a Virago tank, figured out how to bolt that on and ... things got a bit out of hand. Grinders and ebay purchases were involved.

 

Re: winter project - customizing '81 Seca w monolever & doul

cool project, can't wait to see the conclusion.

CN

 

Very cool indeed. I'll be watching this closely. I read an article on a race bike with a Hossack front suspension and it was amazing. But for some reason the idea has never really taken off (except for the BMW version).
The theoretical benefits are substantial.
Keep us posted!

 

Re: winter project - customizing '81 Seca w monolever & doul

Quixote - I suspect maybe the bike you read about was John Britten's V1000? Motorcycle Magazine did a KILLER spread on it in the mid '90s, which was right around the time I bought my first mid-sized bike. Amazing machine (and builder) for sure.

If it wasn't the Britten, do you think you could scrape up a reference / link to the article? That's the only racing build I've ever seen press on, would love to find more. I know Hossack (and Fior?) raced the design, but I've only seen passing references and occasional single photos.

 

Re: winter project - customizing '81 Seca w monolever & doul

I remember the John Britten bike (fantastic design and performance) but the article that first got my attention was even earlier - mid to late eighties. I think it was in Cycle Canada but could have been some other mag. It had a Ducati-like trellis frame and scant bodywork and was being raced by some privateer - wish I could remember who.
Just did some googling and couldn't find the article but did find a picture that looks familiar. It may have been this bike.
That site mentions that Alan Cathcart raced it - that sounds familiar too, he's a freelance journalist/racer who writes articles for Cycle Canada and other motorcycle mags. Good chance he wrote the article.
I'll do some more searching and see if I can come up with the article.

 

Will that be a straight line bike ?

 

Other bikes with similar front suspension (Hossack's builds, BMW k1300, Britten v1000, Brough Superior SS100) all turn just fine. The COG might be a bit higher than average because I raised the seat and am putting the battery under than tank. I'm not planning on racing or doing gymkhana, so if that's what you mean by "straight line bike', maybe. I like some stability vs side winds, is one reason I prefer larger, heavier bikes. That, and I'm over 6 foot / 200 lbs myself.

Planed trail is 4" (adjustable) with a 15 degree head angle- unusual, but not unheard of / untried, and reputed to work well, should feel pretty much like a normal motorcycle. Wheel base will be a bit shorter than stock, mostly to bring more weight on the front wheel to take advantage of the better suspension and anti-dive. Steering lock will be (intentionally) limited by the upright frame contacting the lower control arm (with a rubber bumper), but should still be a healthy 30+ degrees to each side. The lower control arm end pivot will be an automotive ball joint, the upper a heavy duty wide angle rod joint; both offer much more mobility in all directions than the linkages will allow (got the parts sitting on my desk).

 

No matter how many times I look at your posts and that link, I can't seem to fully grasp the front suspension. Can't wait for your progress to shed light on the subject for me.

Once again, nice work thus far.

 

Corrupt_Reverend - its pretty simple in principle. If you've ever pulled the front wheel off a car that has upper and lower A arms, or looked at the front end of an ATV, you've seen all the same parts. In fact, the guy who invented it based it on his experience with racing car suspensions. He just took all the parts and turned them 90 degrees, effectively bolting a motorcycle fork in place of the wheel.

The two lines going forward from the frame are the A arms, and can rotate up / down around the purple dots. The red dots at the front ends of those arms are ball joints, which allows the 'fork' that holds the wheels to both move up and down, and rotate for steering. The rest of the stuff is just to connect the shock unit (in my case from a gsxr, mounted to the lower control arm as it would to a swing arm) and give the handlebars a way to push the 'fork' back and forth without resisting its up / down motion.

Here's a picture of a different version of the same system; I picked it because it is free of any of the non-structural components (shock, steering linkages). The only difference in this image is that instead of using ball joints, the designer actually mounted a steering head on pivots at the end of the A arms. That's a purely cosmetic difference, but does make the system easier to conceptualize.

 

Oooohh, now I get it!

Can't wait to see it all finished up. Thanks for the explanation.

 

Moving forward a bit. Got all my rod ends, and some carbon fiber tubing so I can make high-zoot tie rods for the steering linkages. Also picked up a nice CNC red ano throttle, and ordered some Royal Enfield style reverse levers (possible to use because I got the cable actuated front master, only used on the '81 seca that I know of).

 

Tony Foale sells a program that makes it easy to analyze expected behavior of linkage front ends of various styles, finally picked it up and plugged my design into it. After a bit of tweaking, I found numbers that worked for me in terms of performance (strong anti-dive, minimal major rake and trail variation) and construction (linkage pivot locations etc reasonable for my fabrication).

Finished building the welding jig for the upright yesterday, and made a rough model to check my part dimensions and to use as a kinematic model (checking range of motion doesn't result in parts hitting each other). Even this crappy model (held together with hot melt glue) is pretty stiff!



The two legs on the model are different because I wasn't yet sure how I'd be attaching the axle clamp.

 

what's the plan to hold the heim joints in the cf tubes?

 

The interior of the cf tube is just a hair over half inch (its 15mmx13mm tube). I'll buy half inch aluminum rod, cut it to 1 inch sections, and drill & tap 5/16" holes in the centers (on a lathe), then epoxy those in the ends of the tubes and thread them heims in like any other double ended rod. I need to buy a left handed tap, but the rest is easy-peasy.

By my math, the remaining cross section once I tap the half inch rod is a bit more than the cross section of the 5/16" heim thread, so should be equally strong (same goes for he tube, but its a better material). Epoxy should be up to the job of holding the rod in the tube, there will be ~1.5 in^2 of contact.

Only reason I picked cf for this was looks, and because buying an appropriate metal tube wouldn't have been much cheaper (prices for small tubing are silly). Also gives me practice with a new material, and a feel for what it can maybe do (really amazing stuff, but very expensive for larger parts).

 

http://www.carbonfibertubeshop.com/
good info here
on a lathe you want to use a hss cut-off tool sharpened after each cut. the gray on the id is fiberglass it has mold reliese on it, you have to sand it and clean it really good.
put some glue groves in the aluminum or some knurling to hold the glue.
it would ruin your day if one of those fails

 

Yup, good info- was basically going by what they say on http://www.carbonfibertubeshop.com/cut%20&%20bond.html

Is the lathe cutting tool for the carbon? Was just gonna chop that with an ultra fine tooth blade and then sand. I've done CF handlebars that way before.

Good idea on the glue grooves, I'll be sure to run those in before I chop up the rod (no easy way to do it after). Knurling would be nice, don't think I have access to a tool for that.

Yeah, it would suck if one of those came loose. I'll be testing a 500lb tension on the rods before I use em. Also looking at a design that basically runs two redundant linkage systems tensionally opposed to eliminate slop, but also offering redundancy.

 

Re: winter project - customizing '81 Seca w monolever & doul

You mentioned that you were looking for articles on race bikes using Hossack front suspension - have you seen the Amarok electric race bike?

Here's a link to a short article:Amarok
And the company's web site

They don't talk too much about the suspension, and when they do it's mainly about the weight savings rather than the handling. They did race at Pike's Peak this year though so that should answer the question about whether this front suspension is only for a 'straight line bike'.

I have a much longer article in a print magazine about the development of the bike - PM me with your email address if you want it, and I'll scan it and email it to you.

 

it cuts with a lathe and cut-off tool but you'll have to sharpen it after each cut the sharper the better, it's some abrasive stuff.
if i were going to use a chop saw, i'd look into a abrasive blade, maybe one for cement. it might not splinter as much. is a diamond tile saw blade big bucks?

 

When I said "shop with a fine tooth blade" I was talking about using an exacto style saw, which has something like 60 teeth per inch. Requires sanding after to clean up fray, but has worked when I wanted to trim carbon handlebars.

Diamond tile saws can be had for under $100, but usually come with rough (~80 grit) blades, so you gotta get a finer one (or sand, but the higher speed causes more fray I think). Carbonfibertubeshop says a carbide hack saw blade or works well (if a bit slow and laborious), is clean (low dust) and accurate (can use a miter box), and they are cheap, so that's the route I'll go.

 

Did a full scale kinematic layout to figure out if all the parts would fit where needed and the wheel wouldn't run into anything during compression. Its a pretty radical geometry - less than 18 degrees of rake, with a negative 25mm offset to get the trail at 100mm. Steep rake and minimal / neg offset seems a pretty popular option with custom builds using suspension style though. Its a bit ungainly looking, but the model just shows the lengths between pivots, NOT the shape of any of the parts, which could change the look a lot.

Model helped gel the design a fair bit. Locations for mounting the pivots look great, but there's not enough room to put the shock where I had planned (tire might hit it), so I gotta figure out something else. Already have an option in mind that might look (and work) better- running it back between the downtubes, above the engine! I think it will fit, though I'd likely have to chop out the oil cooler mount / bracing (will be adding plenty of other bracing).

Since the shock isn't under the head tube, I can potentially push the front wheel back an inch or two (shortening wheelbase and shifting weight forward. Need to build in some blocking to stand in for the exhaust pipes, to test that notion.

Uncompressed (full extension):


Compressed (full bump):

 

any progress on this bike? I'm no engineer but I am curious to see what it could become

 

Re: winter project - customizing '81 Seca w monolever & doul

No new fabrication in the past few months. I've been building up the jigs and parts for the steered upright and 'front swing arm' supports, and have purchased all the pivots, tube ends, etc. I only get to do 6-10 hours a week of workshop time, and recently have been working on other projects. Hope to get back to putting more time on the bike build once those wrap up.

 

Re: winter project - customizing '81 Seca w monolever & doul

Been 4 months or so since I posted, but the project is still going.

Got the main Hossack components mostly done - they still need the rear ends cut to length and rod ends mounted back there, and some additional decorative & functional machnining.

So, I bolted it all up and put it in the stand to get an idea of what it will look like rolling. Pretty damn happy with what I got.

 

Work continues. Got the pivot points mounted, but will end up building new control arms. Mocked up the arms in wood to finalize measurements, check stance, and ensure full range of motion without parts hitting. I based my design on work by Hossack, but the end result very closely matches system patented by Claude Fior - http://www.google.com/patents/US4388978 - which, interestingly enough, saw execution on a Yamaha XS1100 (converted to shaft chain drive)


Shock will be compressed by pull-link mounted to lower arm, making it easy to adjust ride height and leverage ratio. Would probably sit with gas cylinder to rear, to avoid wheel hitting it and make space for fender. Obviously heat could be an issue; a good reason to use pipe wrap.



Has a full 45 degrees lock on each side, maybe a bit more. Will mount plastic bumpers on the parts that hit.



At about 3" bump. Arms need slight deign revision to allow 6" travel.

 

I think you mean that the XS1100 was converted to chain drive. They came with a shaft from the factory.
Very happy to see you progress on this project.

 

Finally got it rolling on two wheels. Am pleasantly suprised with the 'stance'. Is very lumpy though, gonna tweak the flow a bit by angling the tops of the side plates and otherwise sharpening some of the blunt bits up front. Still intentionally breaks every rule about graceful lines, but the fact it's crazy low (bars will only come up maybe 1 inch from head tube) may help it work.

 

You know what will make it work aesthetically? A dustbin fairing


What really matters though is that it rides the way that you want. Asthetics are overrated. Can't see the bike from the saddle.

 

I agree 100%, have been thinking that for some time. Although I'd like to somehow make it transparent, to keep the brainfuck factor high. I've looked into vacuum formed lexan, its do-able but hard. A rod frame with clear plastic stretched over it might be easier.

Also good for highway performance & milage. Would need a tail to avoid wind problems, but its already halfway there.

 

A bit more work done - made a new top arm setup that is much shorter, bringing the wheelbase down to (I think) a bit under stock. This is about the tightest setup I can mange given my range of adjustability, was checking to see shock clearance. Looks OK.


Different angle view, after I trimmed the side plates down to final height and added some radius to the corners to reduce wind noise. You can see where I accidentally hit my VIN sticker with a wire brush. Can anybody supply the first half of a 1981 SECA 750 vin for my paperwork?

 

Had it all apart for a while so I could redesign the arms to be much shorter and without any threaded parts getting flexed, and do some cutting to lighten parts like the fork bridge. Got the lower shock mount done, bolted it back up, and started fitting the shock link turn buckles.

 

Its on its own two wheels and able to bounce up and down on the shocks now. Album of pics is http://imgur.com/a/3Vu0s

 

I got the shock mounted, did some load tests, etc. Now working on the steering links.

Here's a video of the shock in action.


Here's a video of the brake load test.

 

Looking good. It's nice to see that you are doing a thorough job of testing.

I need a shop that size

I recognize the lift cart that you use in the second vid. I changed many a plastic shredder with one just like it. They are fun to use with an overhanging load that is just barely weighted to the rear, and is only 20 pounds short of the cart's maximum load rating.

 

Yep, is a nice space. Is about 4,000 sq feet, there's the metalwork area shown (with two millematics, an ancient miller tig, and a gas rig, as well as a couple forges and a foundry capable of melting steel), a machine tools area, electronics lab, woodshop w/ cnc and conventional tools, 40 watt laser cutter, project storage room, general arts area, and lounge.Its a community workshop with 200+ members (of whom maybe 40 come in on the regular, and maybe 20 I know by name). There's occasional frustration from sharing workspace (misplaced / broken tools, messes left on work surfaces, having to pack things away rather than leaving projects set up) but the fact that I had turn-key access to a constantly improving variety of tools, plus a lot of room to work in, makes it a much better option for me than trying to set up my own shop.

That lift cart came in handy, but probably under-rated for the purpose. It was not happy with 300 lbs on it, the locking pawl got bent (is why I was casting about for vice grips).

Testing is really critical on such a weird build, and I'd suggest it for ANY structural mod made by an amatuer (or pro for that matter). I still need to test the rear shock setup, for example, even though its quite simple. I have no certainty how good my welds are, so I ran a big safety margin on top of the highest (static) load I figured could be imposed. I could still have issues with fatigue failure, but with an 80% safety margin over max possible load, they shouldn't happen for a decent time. I was actually getting close to what I thought might be the static limit for one particular "Jesus nut", where all the brake load (with the fork providing leverage) is translated to a pull-out force on 6061 aluminum 5/8 fine threaded part. I conservatively estimated the theoretical pull-out at ~10,000 lbs for 1 inch of thread, and the rig ran it up to 3,375 lbs. Probably not the safest possible design, but the fine threading allows me to adjust trail in 2mm increments. Had that part failed, I'd have had a big noise, but it would have been fairly easy to re-fabricate in steel.

 

This is the patent for the oldest of the machines I used to work on (it has a seriously old-school control system). Ironically it happens to have the lightest of the shredders. IIRC they were around 230 pounds, and the big shredders in the vacuum-silo machines were pushing 400 pounds.
http://www.google.com/patents/US4784251

 

Wrapped up 2016 by getting the engine back in. Exhaust even fits with the shock in place, no need to build a new set of pipes.

 

Looking good. You're about three years ahead of me. I'm just now getting to see if the engine on my Virago will fire. I still need to make an intake manifold. Once that's done I might start a thread. Lots of math to do yet though.

 

Been working ion a custom airbox. Same volume (or close) as the stock box, and the stock snorkle fits in a plate that goes between the air filter and the airbox. Also mounted up the oil cooler. The "puck" that goes under the oil filter and plumbs the oil lines fit right on, although it was a pain in the ass with the (aftermarket) pipes in the way.