Warning-Warning-Warning about Shock Length

[toomanytoys2]

I have never heard of this happening, but it did to me. I have a hammerhead twister 150 and I installed Blaster front shocks on the rear of the buggy. This did a MAJOR improvement in ride quality. The shocks have been on there for a couple of years. I don't just blast around fields, but I take it to the desert and put some serious miles on it. Last time out we decided to go for an ice cream run. Where we camped is called Searles Station. It is in CA off of 395. About 20 miles away is a tiny town called Randsburg, and they have an old fashion ice cream fountain, and you can drive your off road vehicles through town.

About half way there, the buggy seemed to ride like #@$%, and it was killing my back. I also thought that I was getting a whiff of fuel. Once we hit town I discovered a major problem. The engine's head had punched a hole in the fuel tank. The problem happens when you put longer shocks on a particular style of rear suspension. The first picture is the type I am describing, and the problem is with the silver link arm.

In a properly working suspension, when it hits a bump and compresses the link arm moves in the direction of the arrow in the second picture. However, when you install longer shocks, the link arm goes from a slanting forward position to a vertical position. Then if you unload the suspension (catch air) and the frame flexes, the link arm will go past center, and travel in the opposite direction like in the third picture. When this happens the engine will flip. So the cylinder and head will go from a horizontal position to a vertical position, and crash into the bottom of the fuel tank. In my case the head punched a hole in the bottom of the fuel tank.

I'm pretty sure I know when it happened. There was a pretty mean ditch that I had to cross, and the exit wasn't very pretty. Once we got to Randsburg and stopped, the fuel smell was over powering. So I got out of the buggy and looked and there was the engine's head hitting the fuel tank, with fuel running out. Luckily, one of the families with us had driven by truck, so I bummed a ride back to camp, picked up my trailer and brought the buggy back to camp.

I then drove into Ridgecrest and got a fuel tank repair kit from a FLAPS and was able to patch the tank. To get the suspension back into its correct position, I jacked the back of the buggy up and we kicked the suspension links until they returned to the original positions. I then used a rope to make a limiting strap to control how much the rear suspension would droop. Now I have to figure out how to make a more permanent limiting solution.

I have never heard of this happening, but I just wanted to put the word out there, so someone else doesn't get their ride ruined.

[ckau]

Some Hammerheads and also early Dazons used this type of 4 link rear suspension. It was dubbed the "Dog bone suspension". It's strong and gives smooth swing arm travel. The ride is more cushy too but like you found out, it's possible with longer travel shock for that dog bone link to over articulate.
Limiting straps are your best bet. There's some good info here
http://www.filthymotorsports.com/Lim...limitstrap.htm

[SYCARMS]

The problem with a longer shock is when the suspension rebounds the carb will hit the fuel tank.

[toomanytoys2]

Tom, I'm the one who talked with you a couple of days ago about a 250 cam, any luck?

[SYCARMS]

Been really busy here, haven't had a chance to call. I'll try to this week.