One Step Forward, One Step Back

If you recall, work stopped on the 383 due to push rod length issues. Because of different valve stem lengths we had to use non stock length push rods. We had ordered them over a year ago, but never really got around to checking how well they worked.  The basis for all this is they fact that we were using roller tip rocker arms. An oft overlooked part of engine building is checking where the roller tip contacts the valve stem over the duration of the cam’s lift. When using standard stamped rocker arms this is really a non-issue. The large radius of the contact pad is very forgiving of push rod length issue. However roller tip rockers have a very narrow contact patch. While this reduce horsepower robbing friction, it also puts enormous pressure on a very small area of the valve stem. If this contact patch does not fall on the correct part of the valve stem it can lead to mushrooming (deforming) of the valve stem tip. This picture from Comp Cams illustrates the proper location of the contact patch at various points of a cam’s lift.

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You check the location of the contact point by puting dye on the tip of the valve, setting the cam at mid-lift, and rotating the roller to leave a wear mark. After a little trial and error with an adjustable length pushrod  you can find the proper pushrod length. Here is a picture of ours:

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The smaller mark is our second try with the stock rods. As you can see it is nearly at the center of the valve stem, which is exactly where we want it to be during mid-lift. So we FINALLY have the pushrods sorted out.

While installing the valve springs we noticed the latest issue. The inner valve spring interferes with the valve stem seal. Some higher spring rate springs, like ours, use dual or even triple valve springs. Some how this was not measured correctly back when all this was ordered a few years ago. Initially we planned on moving to teflon seals which have  smaller outside diameters. However the cheaper option looks like getting new springs and selling the old ones.

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No clearance

We also swapped out the rocker arm studs, the old ones were too long and didn’t work with our posi-locks.

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New shorter studs on the top

Once the new springs come in we will be able to wrap up the valve train. The only new things to be installed at that point are the intake, valve covers, and fluid damper. All the other components will be swapped over from the existing engine. I’m really hoping this is the last of the unseen issues, however based on the fact that this engine has been doing everything in its power to resist being built, there most likely will be.

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