Twisted Z Bar

[DD16]

I purchased a Zink C4 last summer. I've asked a lot of questions and gotten a lot of great feedback. After disassembly I have been gradually replacing or renewing parts and slowly reassembling. I'm an experienced racer but new to FV as I have been retired and whizzy bits cars are too expensive. Very intimidating as everything I've learned over decades doesn't transfer except prep is still number 1. I was trial re-assembling my Z Bar. I discovered that It is badly twisted. When lying flat on the floor one end is 2 inches higher than the other. I didn't think a Vee saw the type of forces to twist a solid steel bar of 11/16 dia.With everything that has to be adjusted on a twin spring car to get it set up I'm not sure I can reach the goals with such a twist. Has anyone seen such a twist before? Is there sufficient length available on the bar to reach a balanced set up. The Zink Z bar is designed with a bend in the bar about halfway between the mounting on the car and the end of the bar so I don't have the same length to adjust the links as say a Lynx. I appreciate your feedback.

[S Lathrop]

Put the bar on the car with the bends going upward. Then you bend the bar down to fasten the links. The amount of loading to fasten the links is important.

What has happened to the bar you have is that it has yielded over time. But the spring rate has not changed. Over time the bar will likely yield to something like you have now.

You might consider going to a 3/4 or 7/8 inch bar and a bit less preload. It might work better.

The bars were 304 stainless steel.

[john f]

Put the bar on the car with the bends going upward. Then you bend the bar down to fasten the links. The amount of loading to fasten the links is important.

What has happened to the bar you have is that it has yielded over time. But the spring rate has not changed. Over time the bar will likely yield to something like you have now.

You might consider going to a 3/4 or 7/8 inch bar and a bit less preload. It might work better.

The bars were 304 stainless steel.

Why would you use 304 for a Z bar??? Low yield strength. Just wondering.

john f

[crypt0zink]

My Z-bar also has a twist in it and Fred Clark told me “The bars get the bend after you run them for a while, it’s OK to press the bend out, does not seem to hurt anything”

[DD16]

Thanks Steve. The best answer I could hope for. I don't have to buy a new bar! Locals suggest an inch and a half pre-load from just loose links. Sound about right to start with? Then chase the tail with droop and preload. Thanks everyone! What a fantastic resource - ApexSpeed rocks.

[Ed Womer]

You can always make a new one and I have made a few in the past for guys and use cold rolled steel and bend it with my Hossfield bender.

Ed Womer

[S Lathrop]

The last version of the Z bar for the C4 was a tube that mounted where the current Z bar mounts and there was a bar inside that tube, maybe as much as 1" in diameter. There were bushings inside the tube for the bar to pivot in. There were arms welded to the ends of the bar that angled down ward so that when every thing was loaded, the arms were perpendicular to the actuating links. There may have been some made with heavy wall tubing to reduce weight and get the desired spring rates.

[R. Pare]

Why would you use 304 for a Z bar??? Low yield strength. Just wondering.

john f

Simple - the loads were not expected to be higher than that when they were first designed and made.

[john f]

Simple - the loads were not expected to be higher than that when they were first designed and made.

I mainly was getting at the low yield strength and high cost of stainless vs using a pc of stress proof or pre-hard. Unless it was left over from something else and was used to cut cost. Just curious.

john f

[S Lathrop]

I mainly was getting at the low yield strength and high cost of stainless vs using a pc of stress proof or pre-hard. Unless it was left over from something else and was used to cut cost. Just curious.

john f

That is the material that Ed Zink chose. At that time is was just a student in his class room. And he had more than a couple SCCA national championships before I was in the room

[john f]

Fair enough. If it ain't broke, don't fix it.

john f