Engine Building Fundamentals: Preparing Threaded Holes
Preparing Threaded Holes
- While we're preparing the engine block, it's also a good practise to clean out all of the threaded holes in the block.
This is most important for the critical threaded holes for the likes of the head bolts or studs and main bearing cap fasteners; however, it's a good practise to clean all of the other threaded holes while you're at it.
This process ensures that any corrosion or debris is removed from the threads in the block, and can also be used to repair any damage to the threads.
All this adds up to reducing the potential friction between the threads and the block, and the threaded fastener you're going to instal.
This is essential to prevent damage to the fasteners, as well as ensuring you achieve consistent clamping force.
When we're dealing with the less critical threaded holes that we're likely to find on the engine block---perhaps those used to secure the sump to the sump rails, or perhaps even for items such as the engine mounts or external brackets---it's still valuable to clean these threads to ensure that your bolts are going to instal easily, and that you're not going to risk damaging the thread, damaging a bolt, or, worse still, having a fastener snap off in the block.
The process of preparing the threaded holes simply involves running a tap through the holes.
There are specific thread chasing taps available on the market that are designed for this specific purpose.
However, I've always used a general tap to do the job.
If you're cleaning out blind holes, then you're best to use what's known as a bottoming tap, or plug tap, which has less of a lead-in and will clean the threads all the way to the bottom of the hole.
Once the threaded hole has been cleaned out with a tap, it's important to remove any remaining debris with compressed air and a product such as brake clean.