When bolting together a Street Stock engine, or even performing a rebuild, there's a lot t
At Circle Track, we're all about doing it yourself when it comes to working on your race car. You can save a buck, it's fun, and hopefully, when done right, doing your own work and knowing its done right can give you a leg up on the competition.
Lots of racers have the fabrication skills to make practically anything when it comes to the chassis, body, and suspension, but few are comfortable tearing into their race engines. It's true that some aspects of race engine building that require specialized tools are best left to the professionals. But there's a lot that you can do yourself, especially if you are running a Street Stock-level class that requires stock, or stock replacement, components.
Even if building your own Street Stock engine from a bare block-including all the machining processes-is beyond your capabilities, a rebuild probably isn't. With a rebuild, you already have your parts recipe, including the critical cam grind, so that isn't an issue. You may also need to take the block and heads to a machinist to be checked out. But putting everything back together isn't that big of a deal. You may also be upgrading a stock engine with rotating assembly package-crank, rods, pistons, bearings, and rings-from a speed shop like many of the advertisers in this magazine.
This is a brand-new rod, and the housing bore measured perfectly round right out of the bo
This topic came up recently in a bench racing session with brothers Ken and Kevin Troutman of KT Engine Development. As professional engine builders, they've seen it all. And to help you out, they've come up with a handful of useful tips that we think can be helpful when building-or rebuilding-your own race engine.
Obviously, this isn't everything you need to know to hang out a shingle and open your own engine-building business. In fact, this isn't even the basics. Instead, we've tried to offer some advice to help you avoid the pitfalls that most often trap beginning engine builders. Race engine building is all about minding the details, because more often than not it's the missed details that require expensive repairs. So here are a few details that can help you avoid the dreaded phrase, "I don't know what happened, the engine just died."
1. De-Stress Your Connecting Rods
Lots of racers who have never even built an engine know that one of the most important aspects of the process is getting the right clearance between the rod and main journals and the bearings. But a large component of that, when it comes to fitting the rod bearings, is making sure the housing bore on the big end of the rod is sized correctly.
Sometimes you will notice the wristpin inserts into the first of the piston's pin towers e
This can be a bit tricky, because most rod manufacturers will send you a set of rods that measure up correctly. For example, for a standard Chevy small-block, the rod journal on the crank is 2.100 inches. For that journal, the correct size of the rod's housing bore (this is the diameter of the big end of the rod without the bearing installed) is 2.225 inches. You may measure the housing bore diameter of a new set of rods, get the correct size and think they are ready to go into your engine-but there is a catch.
Honing the rods to size causes a lot of stress on the rod material. A lot of this stress can be relieved by unbolting the rod cap, removing it and then bolting it back up, but some connecting rod manufacturers do not do this step. So the very first step you should take after unboxing a new set of connecting rods is to unbolt and remove the caps and then reinstall them to the proper torque spec (or stretching the rod bolts to approximately 0.0055-inch).
This is a quick and easy test to see if your rod bearing may contact the crank fillet. Not
Now measure them again. If the rods haven't been stress relieved during the honing process from the factory, they will sometimes pull tighter along the parting lines when bolted back together. This means the diameter of the housing bore will be smaller by as much as 0.0005 along the line where the rod and the cap connect. It doesn't sound like much, but that will in turn squeeze the bearing just a little tighter along the parting line and increase your chances of getting a spun bearing.
If this is the case, you will need to have your engine machinist re-hone the rods. Most engine builders do this as a matter of course with every new set of rods, so it's always a good thing to at least check.
2. Size the Pins
Like checking the housing bore size on the connecting rods, this tip will likely require a little help from your friendly neighborhood machinist, but you can at least do the measurements yourself with a micrometer and dial bore gauge to check if any machining will be necessary.
There is no bearing between the wristpin and either the pin bore in the rod or the piston, so the bore in both the rod and piston must be a perfect fit. Piston and rod manufacturers often leave the pin bores a little tight because engine builders almost always want to ensure the tolerances are correct by honing them themselves.