Topic: adventure bike front end on our bikes

[Shtonecb500]

Hello,

I'm looking to install 2015 KTM 1190 Adventure-R front forks on my 74' 750. Has anyone modded our bikes with a taller, off road front end on the forum yet?

I have an extended box swing arm that provides the stock and a 2" further back axle position, it also has two lower shock mount positions... What issues do I need to be concerned with running a longer than usual rear shock, I already run a 14" set of rear twin shocks....what about angle of the swing arm, how long before that becomes an issue?

Ill post pictures of some triumphs and harleys that are running similar forks  and brake system so you have an idea of what Im looking fork - the triumph swing arm looks like its at a crazy angle but im guessing its been engineered to be at that angle....I wouldn't be able to run my swing arm at that angle, would I?

picture of my swing arm provided and pictures of the bikes influencing my decision to go this route.


Ill have a LOVELY 8.6" of travel at the front wheel some other fork options offer as much as 300mm of front wheel travel. My buddy is using a set of KTM with 300 on his R80 build and will be modding springs to about 230mm when finished.
Right now the pair of forks will cost $450 and the pair of calipers will be $230 and will be running dual disc brembo...Im going to see if I can buy the front wheel off the guy but I really want to use the black rims already on the bike.

I have a Cosman quick change rear hub on another 750 and I would take it off donate it to this bike to gain triple disc brakes.

I havent dug much into options for a custom triple tree, probably going to be around 1k - cognito will be obvious quick easy choice.

Custom low profile seat will be mandatory in combo with rear shocks that provide some good sag.

[Shtonecb500]

Silence usually means no one is attempting the said mods so Ill just continue details in my build thread. With that being said, the only SOHC I found documented modded for off roading was a cb400-4

some build details and pictures.
https://www.advrider.com/f/threads/1973-cb750-adventure-bike.1013252/

"I converted a CB400/4 into an XR460/4

It rides well and is very stable in the dirt.

I fitted XL250R forks, custom spindle. extended the swingarm 100mm and installed some Husky Ohlins on the rear I found on Fleabay.

The 400/4 engine (now has a Yoshi 460 kit) has 6 speed gearbox and 10,000rpm red line however it is light"


He extended his swing arm by almost 4 inches

[C317414]

The power characteristics of an inline-4 are probably not that great for riding in the dirt.

[ekpent]

I bought all the take-offs once from a guy who incorporated Kawasaki moto x stuff with a 750 engine and frame and he was building a hill climber. The engine was a 72 but the gas tank was a wrinkle tank and the pipes were HM300 in great shape. I was really happy with those and the other parts I got from him. The project eventually stalled I heard and I tracked him down but he had already sold the rebuilt engine.

[Tim2005]

There's a build thread about that XR460/4 which would be well worth you reading 


http://forums.sohc4.net/index.php/topic,57271.0.html

[Shtonecb500]

There's a build thread about that XR460/4 which would be well worth you reading 


http://forums.sohc4.net/index.php/topic,57271.0.html

thanks for that, couldn't find it.

[seanbarney41]

Why do you want so much suspension travel?  Do you really intend to ride it offroad?  I would be surprised if you don't start seeing bad problems with longer than 14" shocks...first one will be chain clearance, next one will be anti-squat geometry gonna turn around on ya and fold up!...plus you will need longer rears to get your trail numbers lower than the stratosphere, yeah, or custom triples with like 6" offset (exageration cuz I don't know the real numbers)  Just saying, changes in these directions are gonna cause 2 more problems that will need drastic measures to fix and then these drastic measures each cause 2 more problems....etc.

[Shtonecb500]

Why do you want so much suspension travel?  Do you really intend to ride it offroad?  I would be surprised if you don't start seeing bad problems with longer than 14" shocks...first one will be chain clearance, next one will be anti-squat geometry gonna turn around on ya and fold up!...plus you will need longer rears to get your trail numbers lower than the stratosphere, yeah, or custom triples with like 6" offset (exageration cuz I don't know the real numbers)  Just saying, changes in these directions are gonna cause 2 more problems that will need drastic measures to fix and then these drastic measures each cause 2 more problems....etc.

I was waiting for you to chime in, no i have zero intentions of off roading this thing. Our bikes have like 5"-6" of travel and we get like 3"-4" of that in the real world, the new forks stating 10 inches of travel are prolly only going to give me 6-8 inches of real world travel. About the rear shocks, I'm only attempting this because I have the extended swing arm already, I was looking at Ohlins shocks, specifically the vintage motocross replacements, you can see some here
https://www.propilotsuspension.com/index.php/vintage-mx/

I was wondering if its even possible to run this type of shock on our bikes? What do you mean fold up? The custom shocks on those triumph scramblers are long as #$%*, why cant I attempt something similar?

I know the the geometry might be a #$%* but the numbers of the bikes are actually very similar to one another out of the factories, which should help me out a little...I was going to use rear shock extensions to mock up the rear once the front end is on to achieve the desired steering head angle...then order custom shocks....also planned on talking on the phone with shock experts too.

just to be clear, im not off roading this thing, im just looking to NOT feel as much of the road imperfections as possible....this is still going to be a road touring bike...just much higher sitting.

edit: they are 220mm/8.6" of travel, plus i can drop forks maybe half inch, could also mod springs reduce travel and have shop do the rebuild.

[Alan F.]

You might want to begin simply and cheaply by adding spacers beneath your fork dampers to increase front fork travel, add an inch then slip the forks up an inch in the triples. Maybe drill another compression hole on the damper stem and drill the rebound hole one size larger, then experiment with fork oil grades and fill levels.

Otherwise I'm subscribed, making your bike ride the way you want it to in the places you ride is a good exercise. Plenty have made their bikes perform better at speed on smooth roads, but this is a different goal entirely.

[seanbarney41]

The thing with rear geometry...the ideal is for the swingarm pivot to be exactly centered on the output shaft.  In this configuration, acceleration (and really, deceleration forces too) forces have the least affect on suspension load...,the amount of squat.  For obvious reasons, sturdy set ups with this configuration have traditionally been extremely expensive and difficult, basically to the point of impossibility.  Take a look at where the swingarm pivot is in relation to the chain and sprockets.  Now look at a modern dirtbike, or probably even your pictured Triumph.  I don't have the digital drawing skills or vocabulary to describe what can happen...but there is a lot going on back there that you need to understand before making such drastic modifications.  I am not saying what you want can't work, it just may be practically impossible to realize an end product that does anything better than what you started with. 

[seanbarney41]

Maybe, instead of doing one or two devastatingly drastic mods, try several subtle tweeks that are more easily reversible if they lead to related problems.  How about a gl1000 swap?  Gains of up to 2 inches more travel but the adjustability is there to go back to the exact geometry of a stock cb750 if it is not working out.  Then try revalving with lighter fork oil to make sure you are using all the travel available.  That will lead you to making sure you have the correct spring weight and pre load, next slow down the rebound with some emulators.  Go to war against stiction next...so many things you can do to set up your front end to do what you want without buying a single part...just several examples.  Run taller tires and slightly lower tire pressure.  There are lots more.  Few even bother to set things up right after removing the front wheel, which can really screw up your forks when you get it wrong.

[andy750]

If you are looking to reduce road imperfections as much as possible might I suggest getting a decent set of rear shocks and work on your front suspension as well. MikeR did this with his CB750F2 and when I rode his bike (I have a K2 and K4) it was like riding on air -even on crappy roads (and we have lots here in Boston/MA). Thats the reason I bought the Hyperpro shocks off Mike when he sold them. Made a huge difference. I have straight front springs in the my K2 (firm) with rear hyperpro shocks (I had to change the spring for my weight) whereas the K4 has progressive front springs and Hagon rear shocks. I wouldnt say I have Mikes level of comfort on his F2 (longer swingarm) but its def better than it was. Id suggest re-valve front suspension and get a decent set of rear shocks. Trying to add in an ADV suspension is even more variable in my opinion.

Good luck and looking forward to how you make out.
cheers
Andy

[andy750]

Maybe, instead of doing one or two devastatingly drastic mods, try several subtle tweeks that are more easily reversible if they lead to related problems.  How about a gl1000 swap?  Gains of up to 2 inches more travel but the adjustability is there to go back to the exact geometry of a stock cb750 if it is not working out.  Then try revalving with lighter fork oil to make sure you are using all the travel available.  That will lead you to making sure you have the correct spring weight and pre load, next slow down the rebound with some emulators.  Go to war against stiction next...so many things you can do to set up your front end to do what you want without buying a single part...just several examples.  Run taller tires and slightly lower tire pressure.  There are lots more.  Few even bother to set things up right after removing the front wheel, which can really screw up your forks when you get it wrong.

Good advice Sean