Unfortunately, a lot of recreational vehicles use aluminium for their cases. Doing a bolt up tight in an aluminium case can very easily result in stripping of the threads in the case. In these situations you have to resort to using a thread repair kit to recover the cases, or you just have to bite the bullet and buy new cases. There are multiple ways to repair a thread. Heli-coil, recoil, staked inserts,etc. I prefer the inserts made by Time-Sert. They far exceed a heli-coil in every aspect. Lets take a look at how it actually works.
Determine the size of the kit you need:
For experts in sizing bolts, you can skip over this part. I've included it because I think it's important to show to newbies how you do this sort of stuff.
In this case, I'm doing a motorcycle sump plug. I know that it is a metric bolt, and grabbing the trusty vernier calipers says it has a diameter of almost 12 mm (so it is an M12 bolt) and each thread is separated by ~ 1.5 mm, so it is an M12x1.5 mm bolt.
Measuring the diameter of the bolt. Nearly 12 mm means this is an M12 bolt.
Measuring the thread pitch. The image below shows where you measure on the threads - it's from one point to the corresponding point one thread up. This measurement is how far the bolt will insert for one rotation, if you'd prefer to measure it that way.
Here's how you measure the thread pitch. In this case, I'm measuring from the bottom of one thread to the bottom of another.
Pretty simple. But, like I said, I wanted some photos to show people how you measure these kinds of things.
Find an appropriate insert kit
There are a number of insert kits available. Common ones are Helicoils and Recoils, which are very similar, and the Time-Sert kits.
I am using a Time-Sert kit in this case, as:
It is a solid insert so it has less chance of leaking oil
It has a tapered top so it has less chance of being wound into the crankcase after installation
It features an installation method that grips the entire way around the insert, making it more difficult for the insert to come out whenever the sump plug bolt is removed
The insert is installed using the entire body of the insert, not a tang, so there's no chance of the tang snapping off halfway through, buggering the install, or bouncing into the crankcase necessitating splitting the cases to remove the little bugger.
A major downside to the Time-Sert kits, however, is that they tend to be expensive. Most local bolt shops should have all of the types, and you can also order them over the internet, for example, you could get a Tme-Sert kit here. Speak to a bolt place or someone with lots of knowledge on this (more than I have, for example!) before you decide which kit to go with.
No matter the kit you buy, you can chose to buy them either as a kit for a single size or in a multitude of sizes. The kits with many inserts are good economy if you think you'll be repairing a lot of different bolts. Me, I tend to aim to get only the sizes I need. For this project, most of the insert kits only have inserts up to M10 anyway so you need to be separate kits for the big sizes. More often than not big bolts, unfortunately, seem to be the ones I see stripped.
Contents of a kit
Contents of a single Time-Sert kit (I bought additional and longer inserts though)
Inserts. On the left are the 9.2 mm drain plug inserts that came with my kit, and on the right the 15 mm inserts I purchased separately.
I bought a kit which came with 9.2 mm inserts (it is intended to be a drain-pain installation, so they are quite short). Just in case I needed deeper ones, I also grabbed some 15mm inserts. Inserts are cheap once you have the installation tools.
Drill bit from the Time-Sert kit
You use the drill to remove all of the old threads in the hole. You also want nice clean sides to the hole to make it easier to tap in the threads for the insert.
Countersink bit from the Time-Sert kit.
This is contained in the Time-Sert kits and not the other types of insert kits. The tapered top to the Time-Sert means you require a countersink portion at the top of the hole to make it work.
The Time-Sert insertion tool.
To Be Continued...
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