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Main Bearings and Heat Welcome back. This week I'd like to talk about main bearings and heat. Heat is one of the major factors for the survival of our bikes. We here at X-Man Products have seen time and time again, heat related problems such as the rear cylinder head gasket leaking. What we are seeing is that when the bike is operated in an over-heating condition, such as running without an oil cooler or stop-and-go traffic, there is an extreme over- expansion of the metals, like in the cylinder and the head. When this metal expands and contracts outside of its normal range, something has give. As an example, let's say the head bolts are grade 8 and about 10-inches long. The expansion rate of the bolts and the expansion rate of the head are different, and when things get hot, something has to give. The gaskets have what's called a "footprint," and this footprint is made once the head bolts are torqued to their 50 lbs. and the gasket is smashed into a particular pattern. Now if the motor expands outside of the range that the gaskets were engineered to operate in, they will either start leaking or stop working. More often than not, we see the head bolts pulling out of the engine case itself. This is interesting because the engine cases are sand-cast and are not soft. Most of the time it is the rear cylinder at the front or rear left corner where the bolts pull out. A leak can develop between the bottom of the valve cover and the head (due to the fact that the right gasket was not used for the amount of heat the engine generates). After a while, the paper of the gasket shrinks and the bolts will come loose; most of the gaskets on our bikes can't handle the heat generated for long periods of time. I am working with James Gaskets to replace all of our factory gaskets with new gaskets of superior material. The main bearings are also experiencing problems with heat and short-shifting (or lugging) the engine. When the engine over-heats, the aluminum cases grow and lose their grip on the interference fit of the bearing. This allows the bearing to rotate in and out of the oil supply. X-Man Products has a procedure that allows us to pin the bearing that stops this from happening; contact us if this is happening in your engine. Lugging the engine will cause bearing damage on mainly the left side of the bearing. We have seen several cases where the the left bearing side is actually beaten flat. Lugging, for those who don't know, is where the engine is running at a lower RPM than it should be, and a pounding action is occurring which literally beats the main bearing flat. So in a nutshell, we need to get our engines to run as cool as possible. We are shooting for 220° F. maximum. With the use of a good oil cooler and our ECM software, we should be able to make it happen. One thing we will be testing in the future is how much heat the powder coating of the engine contributes to holding the heat in. Next week: Tell Us What You Want - xman-tech@superxowners.com |
