Some advice required?

>>Why, you may ask, do you want to do a conversion

That's the one question that this form cares nothing about. Why? Because you want to!!!!!!

>>The biggest problem may be the change of wheels i.e. what hubs to use in the build of 21" & 18" wheels.

Can you reuse the existing hubs and relace them to the appropriate size rims?

I'd start by researching all the relevant parts in the microfiche and around the net. Figure out what's the same and what's different. Things like the fork tubes and painted parts are hard because they'll have different part numbers for different colors of the same part. Stuff like bearings and axles will have the same number if they're the same type. That'll tell you what you need to change or adapt.

In addition to the obvious parts, check the rear subframe/fender/whatever in the back to make sure there's room for the new rear wheel.


For the painted parts you might find someone who has the bike(s) you're trying to match and let them drink your beer while you measure parts on their bike.

The companies that sell aftermarket suspension for the X bikes might be able to help too. A lot of people don't like the XC suspension, so going straight to aftermarket might be the way to go. It's probably cheaper than new OEM prices anyway.

Thanks for the feedback gentlemen

Got in touch with the Oracle, the Moto Pornographer: Colebatch. He pointed mr in the direction of the suspension, and all things 'X', uber guru Baz at Hypermoto in Cloggyland. I think all shall be well...

Thanks again.

Disappointed I didn't find this thread until now but better late than never. Thanks for offering guidance to those of us who can't leave well enough alone.

I bought a TTR250 last spring to get back into trail riding & at this point am quite happy with its air-cooled, low-maintenance simplicity. Though it's a bit dated & a bit heavy it's certainly enough for me to get into trouble.

Anyway, I am thinking I would like to upgrade the suspension since it is tired & because the TTR was not sold here in great numbers, options are limited. The front end seems fairly straight forward (pun partially intended) & there is a Racetech re-valve available as well as some documented fork swaps out there. Seems the '06+ YZ forks are the most sought after. I am thinking the USD forks might be a little lighter but don't know.

For the rear, there is also a Racetech re-valve available but other than that, not much out there. I am wondering about fitting a WR/YZ shock to the back & this is where my question comes in.

The suspensions seem very similar to me, shocks seem to be about the same length, orientation, etc. BUT the linkages between the frame, shock & swingarm are backwards from each other, ie; the TTR has the double-link connected to the swingarm & the 3-hole boomerang shaped link connected to the frame. The WR/YZ is the opposite with the double-link connected to the frame.

I am not sure how this affects spring rates, damping, etc. & if it is fool-hardy to try an “as-is”swap or if the TTR should be modded to use the WR/YZ linkage. Not sure of the differences in swingarm length but the TTR has around a 3" shorter wheelbase (55.3) than the WR/YZ (58.1)

OR I could always leave it alone but that wouldn't be much fun.


Thanks again, TD


pics of each:


TTR




YZ

>>The front end seems fairly straight forward (pun partially intended) & there is a Racetech re-valve available as well as some documented fork swaps out there.

The Racetech stuff is works well but if you do a fork swap you get all the benefits of the more modern design: better stiffness, usually more rigid axle connection, and a well designed fully adjustable damping system. That's what I would do in your place.

>>I am wondering about fitting a WR/YZ shock to the back & this is where my question comes in. The suspensions seem very similar to me, shocks seem to be about the same length, orientation, etc. BUT the linkages between the frame, shock & swingarm are backwards from each other..

You'd be surprised at how similar the actual wheel rates are for link systems that look completely different. The main constraint for a rear suspension is packaging (fitting it in the available space) so there end up being a lot of ways of achieving the same thing.

The first major battle of finding a shock to fit seem to have already been won.

The second item to consider is the overall travel of the shock and wheel. If both measurements for both bikes are similar (+/- 1/4" on the shock, +/-1/2" on the wheel) then you are pretty close so bolt it on and see how the ride is.

If the wheel/shock travel are not that similar than you will most likely have to respring it to get the static and laden sag set properly. You can see how to set sag at http://racetech.com/page/id/30#2

Once you get it sprung properly then you may have moved the damping needs beyond the range of the 'clickers'. Only a test ride will tell you this. To get the damping adjustment back in the middle of the adjustment range someone will have to go in and change the shims and maybe piston. This is not a big deal and any suspension tuner will have the tools and parts to do it.

In general dampers are very stupid devices. They only respond to the speed of the movement of the shock (or fork) shaft. They have no idea if they are connected to a cantilever, linkage or whatever style suspension. The result of this is that if the wheel and damper travels and approx weight of the bike are about the same then the damper will be close enough to try out.

Good luck, let us know how it works out.

Thanks for the insights. I will probably gather some parts & give it a try though I'm running out of winter down-time. Want to have the bike ready to go as soon as I can get back out in the woods.

I did check the travel, not as close as I would have hoped, 11.0" vs 12.4" & looks as thought the bottom shock mount varies some on the YZ/WR which may require a different 3-hole link.

Anyway, thanks again.

Best, TD

I'm adding a rekluse core EXP (centrifugal) auto clutch to a cr500. (The company does not [officially] support this application)

Making it fit is the easy part. Making it function may take a bit more thought. What I'm attempting to calculate is the clamping force at various RPM to see how effective additional weight would be (really the only variable easily changed).

what i'm working with


measurements from the exp "ring":

Total wedge weight 159g
wedge spacing diameter (centers) min 124mm, max 131mm
ramp angle 18.5 deg
spring force ? (not yet measured)

engine parameters
primary reduction 2.52:1
idle RPM 1500 rpm


I believe the correct equation to be:

F_c = m v²/r
= m (n 2 ? r / 60)²/r
= 0.01097 m r n²

where
n = revolution per minute - rpm


​

Or in this case

.01097*m*r*(n*n)
m = .0159kg
r = .062m
rpm = 595

.01097*.0159*.062*(595*595) = 38.3N

which when the 18.5 degree ramp angle is included (3:1) the clamping force would be 114.9N

Can anyone tell me if the basic calculation is correct?

You're correct with the calculation.

As you point out mass is the only variable and since mass is included only once then it is a linear relationship. Double the mass, double the force.

One thing to do to get a ballpark mass adjustment figure is to look at the primary reduction ration of the donor part bike and the primary for your bike and see what the difference in gearing is. Even at a 1500rpm engine idle speed the clutch shaft is spinning at a different rpm so the v²term will be different. You already have the force for your bike, now calculate the force for the bike the part is originally intended for and see how big the difference is and how much mass you need to change to get them to be equal.

Even after doing this the easiest thing to get a real world answer will be to throw it on the bike and test it as-is. If it works you're done. If its too weak you won't be able to go at low throttle. If its too strong you won't get the slippage at low speeds. Either way no damage is done and if it needs tweaking its behavior should confirm your calculations for more or less mass.

Thank you.

The wedges are universal across the exp product line, with only the diameter of the ring changing across models.

The two bikes this specific setup is used on both have higher ratios
Cr250 is 3:1
Crf450 is 2.739:1

I was initially wondering how the plain exp held up on the ktm990 until I realized the primary is in the 1.9:1 range.

As for the exp on the 500:

Dear Chris and Fellows,
Please correct at will ,"still" intake air is a function of volume/required intake . Could sufficient "still" air be supplied by a smaller air box with positive pressure ?
My starting point sv650 carbed ,has seemingly a very small exhaust cam , -2mm lift ,-24 deg less than intake. Intake cams are routinely installed with nice power increase ,and no obvious torque holes. Is it reasonable to assume that EGR effect is behind exhaust cam strategy ? Raw # like 8.1mm /271deg intake 6.1/247deg exhaust.
I am looking to move power curve down +/- 2000 rpm , peak tq 4500 rpm ,and hp 6500 rpm ish. I intend to advance intake and exhaust cams 6 to 9 degrees and replace 39mm cv mikunis with 35mm flat/oval/round slides .
Should I expect to need accel pumper carbs for sharp off idle response ?

I have in mind 650 thumper lunge with v twin balance .

I have to go rewind my propeller beanie.
Regards,Ed

>>Could sufficient "still" air be supplied by a smaller air box with positive pressure ?

Positive pressure like a turbo, yes! There is not much pressure to be had by even a very efficient airbox system so going down on its volume is hard to compensate for. That said, will it make a lot of difference? Are you racing? If not, then not much.

>>My starting point sv650 carbed ,has seemingly a very small exhaust cam , -2mm lift ,-24 deg less than intake

Exhaust cams are usually smaller then intakes, just like the valves. The intake has to suck air from the atmosphere which is hard to do and you can only pull 14.7psi of vacuum so if your intake is not efficient your cylinder does not fill fully which has a horrible effect on power. Exhaust gas can be pushed out by the piston so can have a lot more than the intake's 14.7psi max pressure differential to drive its flow. You can lose some power by having a compromised exhaust cam profile but if it is in the interest of making the intake work better then in the end you have a more powerful engine. This pdf has a lot of technical information but there is a section discussing each phase of the cam profile and how short changing one can help another. If you can find an online PDF copy of 'Empiricism and Simulation in the Design of the High Performance Four-Stroke-Engine' by Blair he goes a lot more into the design tradeoffs of intake and exhaust cam profile design.

>>I am looking to move power curve down +/- 2000 rpm

That's a lot! Why?

>>I have in mind 650 thumper lunge with v twin balance

Gearing can't accomplish this? A lot of times a 650 single is geared for a much lower top speed than a 650 twin would be and that is what accounts for the seemingly better acceleration. Same reason Harleys are great stoplight machines compared to a GSXR1000. The Harley will top out at 120, the GSXR at 180. Changing the gearing so they both top out at 120 (or 180) and the GSXR would win.

Changing from a CV to a non-CV carb would greatly increase your lungability. The CV carb only opens as fast as vacuum allows. There are mods to be don to CV carbs to increase their throttle response and usually involve increasing the vacuum port hole size.

I'd start by playing with the carbs and cams and gearing before you buy stuff and see how much of an improvement you can make.

/\
Igonore this troll.

And welcome back , Chris !

Found info about porting slide vacuum holes. But nothing about cutting slide springs...

I never messed with the slide holes on my carbs. I removed 10mm from each slide spring and the throttle response was crazy.I never realized how much lag was in them until that mod.I got the mod idea from PeteGS over on Do The Ton forum.

Thank You for sharing expirience.
Had any problem with mid-range mixture goes richer/leaner after shortening springs?

I experienced no side effects,just faster throttle response because the slides rise faster.

1 st I have heard of this also .

Hi,

I didn't notice this thread before I posted here:

http://advrider.com/forums/showthread.php?t=1050059

Asking about the affects of tilting a motor forward or backward in a frame when doing an engine swap or custom build.

If anyone could post here or there I haven't gotten a solid answer.

Thank you!

Hi Frey,,,,it all depends on whether the motor is wet sump or dry sump and how the oil pick-up is orientated. I am not an engineer but I am quite certain that this could be a limiting factor. If you have a wet sump motor and the motor is tilted either forward or back to the point that the pick-up for the oil pump becomes oncovered either going uphill or down, then the motor will become oil starved and loose pressure,,, don't think that I need to say what will most likely happen next.
All the best,
THUMPER>>>>>>>>>>>>>>>.