Some advice required?

Well, here it goes.....

The purpose of this thread is to give design/engineering advice to those in need of it for bike modification projects. As you can see on my 'Lots of Assembly Required' thread I'm a degreed engineer with a decent amount of experience with motorcycle design and a lot of experience being a garage hack!

I'm opening this thread to provide advice to those who are adventurous enough to start hacking on their own bike but need some technical assistance from time to time. It is not a general all questions answered thread but more for construction techniques, material recommendations, design philosophy. Questions like 'what is the best tire to use?', 'how do I install heated grips?, 'What is the correct tire inflation pressure?' are not suitable for this thread and I likely wouldn't be able to provide a better answer than the vendor you buy the parts from. Questions like 'What material should I use for a custom subframe?', 'Why is a long swingarm good?', and such are and hopefully I will be able to help your project move along a bit faster.

Now for the disclaimer: This is the internet and regardless of the advice I give you modifying your vehicle is a potentially dangerous hobby that can lead to serious injury or death. Any modifications you undertake are done at your own risk.

Tweaking season is now open.


Chris
http://moto2-usa.blogspot.com/
Lots of Assembly Required

This is just a quick endorsement of Chris - he's the man!

I've been a teammate and friend for over 15 years now and the help, advice and insight that he's offered has been absolutely invaluable. I encouraged Chris to start this thread since it's basically what he's been doing for me since I've known him. What end mill is best for aluminum? What speed should I turn with a carbide insert if my part is 3" in diameter? If I put a smaller front wheel on my bike do I lose or gain trail? These are all good questions for him.

Chris is not just a CAD jockey but a true, grease under the nails mechanic and ace fabricator. He knows more about building and fabrication than anyone I know and he's even worked on stuff for NASA. He can weld, machine (manual and CNC) and knows everything about what makes a motorcycle handle.

I'm lucky as he's been my teacher as I've learned to weld, mill, design and fabricate my own projects. I hope you hit him up with all manner of technical questions and I look forward to watching this thread. Consider him your resident "Prof. Motorcycle".

Gregor

I have a question! I have a 1985 RZ350 that has gone through a bit of transformation. The idea was to put modern suspension and tires/rims on the street legal RZ350 2-stroke. I fitted R1 USD forks, R6 rear shock, R6 radiator, FZ600 swing arm and an SV650 rear rim/GS500 cush drive.

Replacing the old parts with modern aluminum and composites, was a 25 lbs reduction in weight. But the main reason for doing this, was being able to run modern street tires and modern suspension bits on a mid 80's street legal two stroke.

To the question: I have to make some spacers for the rear rim, but not sure how to center the rim relative to the frame. Should the rear rim be centered relative to the steering stem, subframe, swing arm, or by weight distribution? Theoretically, I think there should be even weight on either side of the bike when the bike is standing straight up and down but I'm curious how others do this.

I don't have any recent pictures of it, but here are a couple shots from early in the build. (BTW, I have a spacer on it now, that's a bit off center. Even so, this bike is a BLAST to ride, soooo light!)

What is the airspeed velocity of an unladen swallow?

http://style.org/unladenswallow/

Never built a frame in my life, so feel free to shoot me down in flames.

The wheels and steering stem need to be inline. If not the bike is going to handle badly.
Weight central is ideal, but the rider can correct for that (even if he does walk a bit lopsided after long rides) - wheels and steering out of line, nothing you can do about it while on the bike.

Cheers
Pete

Cool bike and good question. Curious what Chris has to say. I know my BMW and a lot of older boxers actually didn't have the wheels in line due to the driveshaft.

word. I'll be tempted to ask a zillion things, but I'll do my best to make sure only the really tricky problems (or the really, really stupid ones) show up here.

african or european?


Chris
http://moto2-usa.blogspot.com/
Chip in and help!

Cool bike, its hard to beat the water cooled 2 strokes for light weight and performance. I did something similar in my early days on a 1980 kz1000. It was still a big heavy pig but handled a lot better!

I just used the following alignment technique on an old Dunstall Norton frame that was twisted and the resulting bike handles excellently and tracks straight.

I like to use the steering head as the first point of reference. Since this is where the turning process is initiated it is crucial that everything is properly oriented with respect to the steering axis. The first step is to ensure your swingarm pivot axis is perpendicular to the steering axis. I do this by bolting the swingarm pivot in place and fixturing the frame on a flat surface and shimming it until the swingarm pivot is as close to vertical as you can manage. You then bolt a set of tapered cones and a ground shaft (same things used on some manual wheel balancers) into the steering head bearing cups and use a scribe or height gauge to see if the ground shaft is parallel to the flat surface the frame is on. If it is great, if not get out a long bar and start carefully bending the frame until it is.

Getting a good bending technique is essential to making small changes and not see-sawing around the point you actually want. What you want to do is feel for the yield of the material and be able to sneak up on it without going too far. The procedure is to slowly apply force and feel for a change in resistance which is the yield point. Any bending before the yield point is elastic bending and the structure will return to its original shape when the force is removed. This type of bending feels like pushing against a spring. Bending after the yield point is what produces permanent changes. To sense the yield point you need to apply force slowly and the yield point is when you feel the structure seem to relax a little bit without you having reduced the force. I recommend practice with scrap tubing. It is a subtle change but once you feel it you'll know it.

Back to alignment. Once the swingarm pivot is square to the steering axis you can start bolting parts into the chassis. I install the forks and front wheel without spacers. If you are using modern stuff the steering stem likely has a thru hole which is very convenient. I have a ground shaft with a pointed end and turn up plastic bushings for a tight fit that allow me to use this center hole as an alignment reference. Slide the bushings and shaft in and adjust the wheel until the pointer is pointing at the middle of the tire. Then measure the side gaps and make spacers as needed. Always double check after the final spacers are installed and the front axle is properly tightened. Now you know the front tire and its contact patch is centered on the steering axis and the swingarm pivot is square to it. Check brake caliper to disc clearance as this may have changed and you don't want the rotors rubbing on the calipers.

Now check the swingarm to see if the rear axle is parallel to the swingarm pivot axis. I assemble the axle without the wheel and pivot race/shaft into the swingarm and shim it on a flat surface so that the swingarm pivot is parallel to the table surface. Check to see if the rear axle is parallel to the table. If not bend one or both arms until it is. Don't worry about the chain adjuster direction, that can be done next.

Now assemble the swingarm into the frame and the rear wheel into the swingarm with no spacers. The goal is to line the rear wheel up with the front wheel. There are various techniques to do this: string, straight edges, laser alignment, etc. Sometimes it is nice to do this with no tires installed so you can work directly from the tire bead mounting surfaces. Once the rear wheel is in line with the front: measure, make spacers, install, then do a final check. Don't forget to double check the chain run and make sure both sprockets are aligned. For what its worth any misalignment only means worn chains and lost horsepower........

For adjusting chain tension it is nice to have a fixture or good ruler to measure from axle center to swingarm pivot center on each side to make sure the rear wheel is pointing towards the steering axis.

None of this mentioned weight imbalances. I don't think many bikes are off balance enough to have to compensate in wheel alignment. A slight shift of rider position, usually subconsciously, is enough to compensate for even the worst imbalances.

You would be surprised on how big a misalignment can be tolerated with no serious side effects at street pace. This is how BMW got away with having the wheels out of line on a production bike. The rear was offset but still pointing straight ahead so the affect was not to have unwanted rear wheel 'steering' inputs. I must say that I think this is sloppy engineering of the worst kind and am surprised it came from the Germans.

Even though you can get away with reasonably large misalignments you _will_ notice a difference switching to a properly aligned motorcycle.

Hope it helped.


Chris
http://moto2-usa.blogspot.com/
Chip in and help!

I have a 1987 Vmax (yay, the crowd roars......a bit).
It's a lot like the bike world equivalent of a 426 Max Wedge Superstocker. Turns are approached with a certain amount of trepidation, but in an excited way, a bit like "Heehee, which way will she go this time?" Braking is best done after the old girl has stopped.......eventually. Get the big old girl in a straight line and pull the pin though, and it bucks and bellows and wobbles its way down the chute with little control and a huge grin! Question time:
I know the usual practise for these things is a fork brace, frame brace, and swingarm bracing to reduce the fun.
1. Fork brace - will filling the standard die-cast Ally mudguard piece with hard-setting resin work as well as a 1/2" thick billet piece? The resin is really light.....
2. Frame brace - Would using hi-strength/lo-elastomer Polyurethane engine mount bushings strengthen the frame without having to resort to big chunks of railway track across my bloody lovely V4? Bushes are light......
3. Swingarm brace - This I need, now. Without Vboost, 90rwhp, cool. With Vboost, 110rwhp, not cool, very wallowy and a gentle shimmy all the way to 1/2 track on the 1/4. With my 4-1, 120rwhp, very uncool, the wallowing makes the tyre buzz up. I plan on 160-200rwhp, you see my dilemma. I was going to get a 1" CM tube, bend to follow the swingarm profile, then stitch weld to it. I thought it would have more strength than the usual triangulated affairs, along with less weight (no joining tubes to the arm). Would this work, or is the triangulated monstrosity the way to go for reducing wheel axle deflection (up and down)?

Thanks Chris, have a lovely day!

THANK YOU!

I've never printed out an advrider post before now....

We found the real engineer!

Story:
About five years ago, we get a new manager and he's holding his first staff meeting. It's his first time as a manager and he's nervous. He goes though a bunch of stuff, then tells us a little about his background.

Finally, he says, "Does anybody have anything they want to ask me?" Nothing.

"Really, I don't mind the tough questions, I'm an open book."

So I ask, "What is the airspeed velocity of an unladen swallow?"

He looks at me incredulously and says, "What the hell does that have to do with anything?"

One of the other engineers says, "He failed the test!" and about five of us started laughing. He took it in good spirit. I guess he was a Trekkie.

Best alignment description I've heard!

>>We found the real engineer!

Just don't ask me what my favorite color is, I always screw that one up. Classic movie making if there ever was such a thing....


Chris
http://moto2-usa.blogspot.com/
Chip in and help!

>>floor sweeper?

Let me get out my sweeping compound.......


Chris
http://moto2-usa.blogspot.com/
Chip in and help!

The Vmax is definitely a beastly bike. The early years suffered from Japanitis in that it had a frame that was woefully inadequate to the engine. With a hacksaw and welder this can be fixed!

1. Fork brace - will filling the standard die-cast Ally mudguard piece with hard-setting resin work as well as a 1/2" thick billet piece? The resin is really light.....

The resin will work but likely not as well as a billet piece. For a piece of a given size the heavier material will usually be the stronger part. Resin may seem strong but it is not when compared to metal and you also have possible bonding/separation issues. Making or purchasing a fork brace would be the strongest solution. Whichever route you go you need to ensure that the fork brace does not pinch the forks at all. That would lead to binding in the forks and very poor suspension performance.

2. Frame brace - Would using hi-strength/lo-elastomer Polyurethane engine mount bushings strengthen the frame without having to resort to big chunks of railway track across my bloody lovely V4? Bushes are light......

Same as above. The stiffer bushings will deflect less but installing solid metal bushings would be even better. Vibrations may be an issue with solid mounting the engine but it can't hurt too much for a quick test. Even if the vibrations are low enough to accept from a rider's perspective the increased vibration will likely cause more long term cracking of various frame and bracketry. Not too bad for a racer as frames are always being checked and repaired but not so nice for a street bike that is not constantly being disassembled. Adding frame braces will definitely stiffen things up but there is still some danger that the stiffer frame can cause long term fatigue cracking. The bracing does not need to be too large. This article on Tony Foale's website shows a real world example of stiffening a mid-80s tube frame with lots of details. He does highlight one of the dangers of DIY frame stiffening:

Frame stiffening as discussed will in most cases significantly reduce the stress levels in frame members as well as stiffening the whole structure, but there are occasions where the stiffening of one part of the frame may lead to increased risk of failure in another unstiffened area.

So be careful. I was helping a vintage racer friend get his bike to go faster and as the frame started cracking I'd weld in a brace. Then the next week he's come back with the next weakest area showing a crack. I'd repeat until he was finally able to spring for a true roadrace frame which has not given him any trouble. At that point the original frmae had additions all over the place!

3. Swingarm brace

Triangulation is the most efficient way to stiffen a structure. Doubling up with a tube and stitching them together as you say will work but making a triangular brace will work even better. You can triangulate below the swingarm if you need to, it doesn't need to be above it. However, if you don't like how a triangular brace looks a stitched second tube will work and may work well enough for your needs. More than doubling the engine output will make some modifications necessary!

One thing to check is your swingarm pivot bearings. Any slop in this area will definitely introduce a low frequency oscillation to the bike when it is on the gas.

Also, maybe install a quality steering damper.

Let us know how the mods go.


Chris
http://moto2-usa.blogspot.com/
Chip in and help!

Thanks Chris.
Nice to have my own thoughts confirmed, even if I'd prefer the easy way suggested!

Chris!!!

I have a question.


This may seem out of place here, but I was directed to you and this thread from a distant place on the internet, (thumpertalk) that you are the knowledgeable guy willing to give advice. so here it is.


Cooling systems. What's the deal with running dual rads parallel vs series?


If you'd like to read my whole build thread, it's right here: I'm an amateur, first real bike build, lots of experience working on stock bikes.

http://www.thumpertalk.com/forum/showthread.php?t=969189&page=12

Short version is this: 1996 KTM 300 2t engine in a 2004 kx250f motocrosser. It's going to be an full time woods bike, no motocross. I do pretty long rides, usually 50-80miles a day. I ride in all weather conditions from blazing hot to snow. alot of the riding is fast, but in stock form with the ktm300 I overheated a couple times because I do ride some stuff that's just brutal challenging and good material for overheating. So....I need to cooling system to be above par.

The stock KTM radiators are a little bigger than the kxf radiators, but the kxf ones I'll be using are the heavy duty alum fluidyne copies so they're thicker. The OE ktm setup is plumbed in parallel, the kxf stuff is plumbed in parallel also, albeit in a little different fashion. In either case I will probably end up having to reweld all or most of the cooland line ports on the rads, so that's not the issue, BUT in order to run them in parallel I'll have to do another frame mod, and maybe run a cooland line behind the engine. It can be done, but it's alot easier to set them up in series. Also, I was planning on running a single 12v computer fan to improve my low speed cooling, and running rads in series lends itself very well to this because I can put the fan at the hottest spot and have the greatest efficiency. BUT, what's the deal with parallel vs series. I'm getting all kinds of conflicting advice on thumpertalk and doing research, but it seems to me that the main issues are increasing fluid flow velocity with series, which could in turn raise the pressure in the rads, in turn lowering the pressure in the head. It's my understanding that would be bad.


I'm pretty much in the dark here though, so should I run the rads in series and see what happens, or spend another week doing frame mods to run them in parallel.


If I do run them in parallel, where should I put the fan? Will i need to then run 2 fans to get any benefit?




thanks so much for any advice anyone can give,

Thanks,

Joe

Ah, I remember the thumpertalk days. There may still be some pics of my original bikes floating around that site.

I think a parallel radiator arrangement would work best for 2 reasons: mainly flow resistance and secondarily heat transfer.

Flow resistance relates to how much power the water pump consumes to push the water through the rads. Series and parallel flow resistance is treated the same as basic electricity flow, series resistance adds, parallel resistance adds in reciprocal. If you had 2 radiators that each had a flow resistance of '2', in series the total flow resistance would be '4' (2+2) and the parallel flow resistance would be '1' (1/2 + 1/2), or 1/4 of the series version while having the same radiator area, a pretty good decrease in flow losses. In this way the mfgrs are making the engine see the 2 rads in parallel as the same as one wide radiator like most street bikes have. Dirt bike mfgrs seem to have an allergy to designing the bike with one wide rad (maybe because of the large front suspension travel they need) so this how they have enough radiator area for cooling without having excessive flow resistance.

The heat transfer issues is a related to efficient use of radiator area. When we talk about heat transfer we have to think about what is going on. Heat and temperature are not the same thing. Heat is energy and can accomplish work. Temperature is just a gauge of how much the moleclues in a material are vibrating. Heat (energy) can only be transferred across a temperature difference. This makes sense as you can't transfer energy in the form of heat between two bodies of the same temperature. There is no driving force, similar to two bodies of water at the same altitude, water won't flow from one to another on its own. If you move one body of water down (or cool down one body) then water (heat) will flow from one to another until a new equilibrium is reached. The bigger the difference in height or temperature the greater the flow. What this is getting to is a description of how a radiator transfers heat from the coolant to the atmosphere.

If we imagine ourselves floating in the coolant stream as we enter the top of the radiator we can see that we are very hot, just coming from the engine. We can assume the outside atmosphere does not vary in temperature from the top to the bottom of the rad, a good assumption. As a result, at the top of the radiator there is a big tempature difference between the water and the atmosphere and therefore a lot of heat flow from the water to the air. As the water moves to the bottom of the radiator it cools. This cooling results in less heat being transferred from the water as it travels down the rad. You can imagine that if you had a really long radiator that the water would be at the same temp as the air well before it reaches the end of the rad. Any radiator after that point is a waste of space and flow resistance.

So the combination of a wide and short radiator (or 2 skinny radiators in parallel) allows for both low flow resistance and an efficient heat transfer profile.

KTM has a good fan kit that I use in some race applications. A computer 12V fan may not have enough oomph to make a noticeable difference. I think the most efficient place for it is where the coolant is the hottest which would be at the rad inlet but you need to be sure the fan is blowing on a part of the core that is always full of water.

All this is not to say that a series arrangement will not work it is just saying that a parallel arrangement will work better.


Chris
http://moto2-usa.blogspot.com/
Chip in and help!

First up, great idea for a thread. Love this thread and your other build thread.

I am not an engineer or anything, just a mechanic who works at a fab shop and who loves researching different designs.

Re the cooling system.
I remember reading somewhere on the web (can't find it right now) about a guy who did some testing on his cooling system (Subaru SVX IIRC) because he couldn't get straight answers from anybody why his car kept overheating. He set up clear rad hoses so he could see the coolant flow, he had pressure gauges set up at various points in the system as well as temp gauges everywhere, etc. Anyway his conclusions were that the flow restrictions in his cooling system (rad hose size) were creating pressure drops (think carby venturi) and it was these pressure drops that were reducing the boiling point of the coolant even though he had upgraded rad caps, etc.

What you said Chris about the radiators being in parallel rather than series corresponds to these theories. I agree with everything you said there and I just thought I'd add this as it may help somebody doing a cooling system upgrade if they have problems with overheating still, even with bigger radiators, etc. They may have to look at other areas like rad hose size, elbows, tee pieces, coolant passage size instead.