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Author Topic: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT  (Read 28009 times)

Offline teazer

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Wheelbase will alter with head angle and swingarm angle as you know.  I wouldn't worry too much if it ends up at 54-56 inches. 

I hear you about some sag when you sit on it, but the starting point is so far away from useable though.  Might I suggest that you take a good look at say a stock SV650 for comparison and maybe say a MotoGP bike which lives at the edge of total instability.  The shock mounts will have to be changed or find a shorter shock assembly.

Here's a link to someone looking at the same issues.  http://pinkpossum.com/GT750/phattrakka/part4a.htm

edit:  I went back a page or two and see where you took a wrong turn that is causing the current issues.  That shock is designed and valved and sprung to work with a linkage and the linkage would in turn have allowed a better swingarm angle.  If the stock SV linkage mount is still on the lower side of the swingarm, you can probably pick up a linkage arm cheaply and then month the lower end of the link to the lower rear frame rail.  I suspect that will bring things back into alignment.

It will also allow the frame to rotate backwards to an angle that is a lot closer for the steering head. 
« Last Edit: Jan 09, 2017, 01:20:41 by teazer »

Offline EL Sammo

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Totally awesome! Love the top end graft.

Offline BillyGoat4130

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Wheelbase will alter with head angle and swingarm angle as you know.  I wouldn't worry too much if it ends up at 54-56 inches. 

I hear you about some sag when you sit on it, but the starting point is so far away from useable though.  Might I suggest that you take a good look at say a stock SV650 for comparison and maybe say a MotoGP bike which lives at the edge of total instability.  The shock mounts will have to be changed or find a shorter shock assembly.

Here's a link to someone looking at the same issues.  http://pinkpossum.com/GT750/phattrakka/part4a.htm

edit:  I went back a page or two and see where you took a wrong turn that is causing the current issues.  That shock is designed and valved and sprung to work with a linkage and the linkage would in turn have allowed a better swingarm angle.  If the stock SV linkage mount is still on the lower side of the swingarm, you can probably pick up a linkage arm cheaply and then month the lower end of the link to the lower rear frame rail.  I suspect that will bring things back into alignment.

It will also allow the frame to rotate backwards to an angle that is a lot closer for the steering head.
I will revisit the rear again at everyone's behest.  The Sv linkage set up is not feasible for several reasons -  like it's offset to the left where my carb and air filter need to ride (directly in line with the shock), the distance from the bottom of the frame where the linkage mount is to the center pivot is about 2 inches lower on the Sv to allow for the sump of the 4 stroke motor. So I'd need to build a new lower frame section closer so a mount is not hanging out in the wind. The upper shock mount is also too high then and you wind up with a negative angle on the arm under compression in order for the shock to reach it.

I won't say it's impossible because I cut up a snow mobile engine and made it fit the 250r,  but I question the feasibility of going through all of that for what it may accomplish.

Will keep it in mind and explore options.

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Offline irk miller

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I may be reading this all wrong, but by all descriptions it appears that's not the right shock.  Why not utilize a non-linkage shock (90s Ducati SS, maybe) instead?  You'd have more work to do to adapt the swinger, but the way they're setup you'd find even more room for carbs and air. 

Offline BillyGoat4130

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I may be reading this all wrong, but by all descriptions it appears that's not the right shock.  Why not utilize a non-linkage shock (90s Ducati SS, maybe) instead?  You'd have more work to do to adapt the swinger, but the way they're setup you'd find even more room for carbs and air.

The problem with most other shocks I have looked at is the attached reservoir, that gives me some of the same clearance problems. I have found a few shocks shorter than the SV, but most have that problem. The Bandit 1200 pre 2000 according to a shock chart is shorter and does not have the reservoir.

I could probably make use of one of those with a stock 250R engine, but the intent is to put the Hybrid in here eventually, and it is a really, really cozy fit with the OEM parts so I just have to be very conscious of what I build this bike with to account for that.
The question isn't who is going to let me, it's who is going to stop me.
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Offline teazer

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How about a different intake set up to move the carb enough to get the shock where it wants to go? Or dump that swingarm and grab an older GSXR600 arm with centrally mounted shock - say a 2001 on.  It has teh same sort of linkage as that SV arm, but mounted dead center.

Offline BillyGoat4130

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Can't move the intake and carb any further over to the right or center because than the bell will rub on the side of the engine cases housing the kicker gears and shaft :) The intake is a custom billet aluminum machined one, and while you could change it slightly, it wouldn't overcome the problem without getting kind of radical and making the thing do a 90 and stick straight out the side of the bike.

That may be an option though...

The picture is during mock up of the hybrid engine several years ago but gives you an idea of the confinement issues I face between everything. PS I did away with that coolant elbow and went elsewhere as that clearly was not going to work, haha.
The question isn't who is going to let me, it's who is going to stop me.
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Offline Eleganten

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That engine is absolutely batshit crazy! Love it!


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Offline BillyGoat4130

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Just some mockup progress.

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The question isn't who is going to let me, it's who is going to stop me.
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Offline BillyGoat4130

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The question isn't who is going to let me, it's who is going to stop me.
You can't reason with the unreasonable.
Too dumb to quit.

Insta: https://www.instagram.com/hondaatc/

Photography: http://wgolightly.smugmug.com

Real Job: http://landsofnorthflorida.com