Chassis Evolution

[Ji Gantor]

Hi vmx42,
I am so glad you are enjoying my topic about "Chassis Evolution".
Your reply to my topic has very little to do with chassis evolution.
I was going to post aluminium in bike frames to day but 1 step forward 3 steps back I have spent all my time defending what level of tensile strength is mild steel and now Titanium is not brittle because they use it in aircraft engines.
They use a lot of glass in car manufacturing too but it is brittle under impact load and is not suited as a bumper or an engine valve because when there is an impact load it will shatter. I don't know much about aircraft engines but there would be several tones of titanium bolts per engine alone. Titanium used in the right situation is the right product as it is strong and light.

May be you should do a materials property course so you understand that brittleness is only a problem under impact load and long term fatigue. Apart from valves in an engine are there any other components that receive impact load, metal hitting metal?

As I said titanium has been used for all sorts of parts in handguns. The parts that receive impact load have not been successful but other components like sear springs have.


Ji

[vmx42]

Whoa slow down Ji,
Nobody says you have to DEFEND anything. Foolishly I thought that this was a simple discussion and not just a series holy 'pronoucements from on high'.

I don't remember seeing a rule on this site stating that we have to supply a detailed resume stating our qualifications to make comments on various subjects in a post - if it exists then I must have missed yours.

As for my crime that my reply doesn't have anything to do with chassis evolution, then you should go back and reread your posts, they don't address chassis evolution, as such, but discuss the progression of various material improvements involved in motocross frames over the last 30 years.

My comments were made in good faith and only to attempt to add to the discussion not to add to your DEFENCE time.
You really need to lighten up.
VMX42

P.S. and JohnnyO, yeah I saw the GP results. It was a good start for the CCM boys. It will be interesting to see how they progress over the course of the season. It is always good to see an underdog make good.

[GMC]

If you feel the need to defend yourself Ji its because you have generalized all mild steel as being 430 MPA..
The 26.9mm and 21.3mm diameters are odd sizes & would be useless when trying to fit into tube bending formers which are all still based on imperial sizes such as 7/8” – 1” – 1 1/8” etc.
I think you will find that the common mild steels such as ERW tube would have a much lower tensile strength.

Cro-Mo rusts a bit slower than mild steel but not significantly to be able to tell what type of material your looking at.

Your right Ji, my swingarm is of thinner wall compared to stock but the long gusset down the top is more to support the extra stresses of having the shock mounts forward mounted. When mounting the shocks at the rear in the normal 74 CZ position then the long gusset is unnecessary & therefore not used.
Frame design has come a long way with perimeter frames etc. Also with single shock bikes the frame needs it’s strength at the shock mount & the sub-frame is only needed to support the seat & rear guard, unlike a twin shock that has the shock mounts at the rear of the sub-frame.

I don’t know that I would consider Cro-Mo as a brittle material, maybe compared to mild steel but that is far outweighed by the extra strength.
The fact that a frame has cracked doesn’t really mean anything due to the diverse conditions that any one frame can be subjected to.

Drakies original CMS frame which was made in the 70’s form heat treated 4130 has survived well to this day. I did some repairs to it maybe 15 years ago & that was only some cracks in the headstem gussets which weren’t braced all that well & the exhaust mount which hangs out in the breeze a bit on the CZ’s.
I believe it is a credit to the original builders.

I think we may be generalizing Titanium a bit too.
None of the elements are of much use to us in their pure form ( except maybe gold & silver) & Ti. is no exception. There are many different grades of Ti. alloys. Beryllium is one that comes to mind that is mixed in with Ti.

I have found modern Ti. exhaust systems to be a bit on the brittle side, especially the “Y” piece in the twin muffler CRF 250 as I have had to weld up a few of these, some of which weren’t very old.
The grade of Ti. & the manufacturing process would not be the same in a after market exhaust system & a jet engine.

[Ji Gantor]

When did Australia become the centre of the universe for making motocross bike chassis's or materials?
The largest producers of bike frames is Japan, followed by European countries.
Why are some members trying to relate vintage motocross frame making techniques and materials to what we have here.
Please enlighten me, When did Australia make a CZ, Maico..... frame for their respected companies?

It has been established that the Rickman frames are in fact made from Reynold 531 which is a metal that is very difficult to obtain here, ergo their metals are different from what we get. The tensile strength of mild steel in America is 450mpa so may be we can say that the tensile strength of different metals in Europe and Japan are similar after all they are true manufacturing countries.

Japan and Europe are metric and have been since the VMX bikes were made. The tubes they use are metric sizes. Apart from the good old USA that did not make Maico's, Cz's.... are one of the last countries that use the imperial system. Stahlwille tools in Germany no longer make imperial tools as they believe the world is now metric. During the week I received some tool catalogues with pipe benders for sale and they do sell the dies for imperial, but they also sell dies that are for metric tubes. If Australian's were making high volume frames I would think the company involved would have a die made to measure the tubes they commonly used.

Geoff you say "From my experience all Cro-Mo becomes brittle next to the welds (the heat affected zone) no matter what it's welded with. I always heat treat my frames to "normalise" the Cro-Mo" and then you say "I don’t know that I would consider Cro-Mo as a brittle material" I am now confused, which is it?

I will have to do some more research to discover that CZ and MAICO lied about using CrMo in their frames or used a very watered down material as stated. If they did use a watered down CrMo then this too supports the premise that different countries have different metal standards from our own.

Ji

[Phil]

Ji, As much as we all enjoy reading your posts, you could learn to be no so defensive and to lighten up a bit. You don't have to jump in, arms swinging every time someone disagrees with your opinion. This is a discussion forum, not the 'Gospel According to Ji Gantor'. Open up and accept differing and further opinion and you'll find the seed you've grown with your posts will grow into information oak trees!

[LWC82PE]

thanks VMX42 for clarifying the CCM frame construction. i knew it was something like that but i couldnt quite remember.

[GMC]

Sorry to see you get so toey Ji, you opened the discussuion, added a disclaimer & I am just adding my 2c worth as I know it.
Despite some rumours in other threads I don't consider myself the "God of frames"
Not sure about your first rant, I can only imagine that you have confused GMC with CMS?
CMS was an American Co. that produced after market frames in the early 70's.
I make replica's of these frames.


they also made them for Bultaco's


So in effect I make in Aust. a replica of a US frame made for a Czech bike, I make them from Imperial size Cro-Mo imported from the US of which I then send to the UK & back to the US

I have no doubt that some mild steel is rated at 450 Mpa, my point was is mild steel comes in so many shapes & sizes for so many various purposes & that it won't all meet that standard.
Water pipe for instance I doubt would be made to that standard yet it is still considered mild steel. (The Chinese seem to think it's good enough for frames )
Bright round & flat bar probably meets that standard
I don't have any specs to quote, and are going off my gut feeling that ERW tubes which are reasonably common and size wise would be suitable for frame repairs are a bit weaker.

Cro-Mo is a strong & tough material, it becomes brittle in the heat affected zone which is next to the weld. This brittleness can be removed by heat treating to "normalise" the Cro-Mo. It's common state is normalised.
It may be considered more brittle than mild steel but I believe it is misleading to claim that a Cro-mo frame would be brittle. Because it flexes less ( which makes them better handling frames) it is less likely to fatigue.

Chrome-Moly is the name of the material, it is basically normal steel with the addition of Chromium & Molybdenum. With certain amounts of each added it gains optimum strength & is defined by a number, being 4130.
Not sure if Cro-Mo is available in other grades but with different amounts added it would still be Cro-Mo just not 4130.
Standards are similar worldwide allthough most countries have different standard code names.

It's not the first time I have stated that I doubt that Maico's & others used 4130 in their frames & it's previously brought up some interesting debates.
At the end of the day it is just my opinion, gained from working with 4130 (80 frames now) & repairing many different frames.

[LWC82PE]

heres somethingi would like to know. I read all the old bike tests and sales brochures for example on the old suzuki RM/PE's and they have offten said 'chromoly frame's' but ive always thought this not to be true and theres no way a PE400 frame is chromoly

what japanese frames were chromoly?

[pancho]

very interesting discussion ,it doesn't matter if people get a bit excited it can and should lead to more and better info. i can't add much except to recite Phil irvings comment from way-back when he did say among other things that the only reliable way to join reynolds 531 tubing was to bronze weld [commonly &incorrectly called brazing], the material while heating only to a dull red so as to not heat the material above the critical temp. point.  i think the other point about titanium being brittle is interesting&agree that it must depend on different alloying content for differing applications, i think you would not want brittle valves on an engine that is likely to suffer severe valve bounce in the heat of the moment. a question will a magnet stick to chrome moly?

[Ji Gantor]

Hi Wally Cox,
Yes, a magnet will be attracted to CrMo.
Great add about the reynolds 531.

Ji

[Ji Gantor]

This is an extract from the FIM rule book.
As I said Titanium can not be used much on modern motocross bikes but I don't think this applies to VMX bikes.

25.01
The use of titanium in the construction of the frame, the front forks, the
handlebars, the swinging arms, the swinging arm spindles and the wheel
spindles is forbidden.
The use of light alloys for wheel spindles is also forbidden (except for Trial
motorcycles).
The use of titanium alloy nuts and bolts is allowed.
Titanium test to be performed at trackside:
25.01.1 Magnetic test (titanium is not magnetic).
25.01.2 3% nitric acid test (Titanium does not react. If metal is steel, the
drop will leave a black spot).
25.01.3 Specific mass of titanium alloys 4,5-5, of steel 7,5-8,7 can be
ascertained by weighing the part and measuring its volume in a calibrated glass
vessel filled by water (intake valve, rocker, connecting rod, etc.)

Ji

[Ji Gantor]

This is another extract from the FIM rule book.
Again I can not see in MA rules where this applies to VMX bikes.
I guess we can lighten our bikes to what ever we want to achive the power to weight ratio we think we require.

01.19 MOTORCYCLE WEIGHTS
Weights of motorcycles without fuel
19.01
The minimum weights are:
for the 85 cc class 85 cc - 2T 65 kg
150 cc - 4T 73 kg
for the 125 cc class 88 kg
for the 250 cc class 98 kg
for the 500 cc class 102 kg
A 1% tolerance in the weight of the machine after the race is accepted.

Ji

[JohnnyO]

It would be interesting to see how light you could get a vintage bike. No one has really bothered about weight too much before. I guess it gets expensive to make a lighter frame or take weight out of a heavy engine.

[mx250]

It would be interesting to see how light you could get a vintage bike. No one has really bothered about weight too much before. I guess it gets expensive to make a lighter frame or take weight out of a heavy engine.

What do you reckon would be cheaper, lose weight (titanium et al) or gain Uber (useable) horsepower or quality handling (within the VMX reg restrictions). Which would be most beneficial (lap/race times) .

[Ji Gantor]

I think that weight reduction is more beneficial in regard to dollars spent per seconds off lap times, our bikes already have more power than most of us can use. Suspension certainly helps track time, over jumps and braking bumps before corners.

I have taken my stock CZ400 1973 that has a manufacture weight of 105kilos down to 98kilos with just bolt on modern material parts. I think I can remove another 3 to 4 kilos without drilling stuff.
The more reduction in unsprung weight the faster and better handling the bike will be.

Ji