There is an apparent problem with the way crate rocker arms are being checked and the way some rockers are being manufactured that are in conflict. We conducted a study at the request of a racer who experienced the problem first hand. The results are very interesting. There is a serious problem associated with crate motor rocker arm ratios. If you run a crate motor or you are a tech official who checks crate motors, you need to read this and understand this problem. Honest racers are being DQ’d for having “legal” rocker arms installed on their crate motors. And for some reason, this is associated with the GM crate motors and not so much other crate motors so say the tech officials. We’re not so sure it doesn’t affect both.
This might be thought of as a procedural rather than a cheating problem. As we talk you through the origin and progression of this situation, keep in mind that we found that no one, racer or manufacturer, had or has any intention of cheating the system.
This year, certain racers who run at Nashville Fairgrounds were being disqualified for having non-compliant crate motor rocker arms. The rockers were being checked on a rocker checker manufactured by a company in St. Petersburg, FL. This checker, we’ll call the Precision checker, is currently being used throughout the Southeast at tracks like New Smyrna, Five Flags, Nashville Fairgrounds, etc.
That rocker checker is built to the same specifications as a true engine and raises the push rod 0.100”. The “valve” end of the checker then moves a fake valve using a weak spring to hold everything in place. If the “valve” cap moves 0.150” then the rocker is a 1.5 ratio (0.100 x 1.5 = 0.150”).
I double checked the dimensions of the checker myself and found it to be a very accurate duplication of how the parts in a real crate motor work based on push rod angle versus valve stem angle and rocker height. But there is a problem associated with using this checker that I will explain in a minute.
There is another rocker checker made by General Motors for checking 1.5 and 1.6 ratio rocker arms made for those motors. With that device, we’ll call the GM checker, you lay the rocker onto the fixture and the pivot shaft moves along a stud. The push rod end cup fits onto a stationary push rod shaped shaft and both must fit together perfectly. On the valve stem side, the rocker roller fits into a fixed shaft with a cup shaped end. Again, the roller must fit perfectly into the cup in order for the rocker to be deemed legal.
Here is the problem. Some rocker arms fit the GM checker, but do not calculate as a legal ratio on the Precision checker. I obtained one of the Precision checkers and an area engine builder had one of the GM checkers. So I went to work checking multiple rocker arms including the actual one that was the reason for the DQ’d in Nashville.
What I found was that the aluminum rocker that was the reason for the DQ is stamped as a 1.6 ratio rocker. This rocker checked on the Precision checker at a 1.7+ ratio, but still fit the GM checker. Moreover, when I checked this same rocker on an actual motor using precise methodology, it evidently flexed because it checked a legal 1.6 ratio.
Upon further research, I discovered that some years ago, the highest level engine builders working in Cup realized that the aluminum rockers were flexing enough to cause a loss of HP. They converted to steel rockers and the problem went away.
Some manufacturers of the rockers that are intended to be run on the crate motors also realized this problem. They designed a rocker that fit the GM template but operated at a higher ratio when not under valve spring loading, hence the DQ using the Precision checker.
That same DQ rocker was reduced to the legal rocker ratio when loaded by the stronger valve spring. It is actually legal on the engine, but not on the Precision checker that cannot load the rocker the same way a stiff valve spring does.
So, if you run one of these rockers, you are technically legal, but illegal if they are checked on the Precision checker. The only thing you can do is run a specified rocker and at New Smyrna the rules recommend the Crane Cams rocker. We checked a Crane rocker and it check legal on both checkers. Does that mean it checks out at the stamped ratio on the engine, maybe, maybe not. We only “engine” checked the rocker that was deemed illegal at Nashville.
In our opinion, it doesn’t seem fair to DQ a team when technically they are not cheating if their rocker checks to the correct legal ratio on the motor. The problem comes in the enforcement of the rules. It is very difficult to check the rockers on the motor. I had a difficult time with the engine mounted to a stand inside an air conditioned building.
The lead tech officials I spoke with told me they were not going to change the way they tech rocker arms. So, as a racer, you can either run an aluminum rocker that checks OK, but might give up a little valve lift on the motor, or run steel rockers like the Cup guys do. It’s as simple as that. But now at least you know the situation and can act accordingly.
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