HPI stator repair
Situation: Your HPI (Horse Powered Ignition) mini-rotor coils are scratched or otherwise non-functional. You've tested for resistance and continuity and there is none or you've confirmed that a loss of performance/power is due to a faulty coil and are unable to get a replacement under warranty.
This guide will teach you how to install a new set of pickups re-using the old stator plate. This saves money and cuts down on waste. Plus you get to pick the color of your plate!
Note: Depending on your budget and exchange rates, it is probably going to be much easier to just purchase an entirely new stator directly from the HPI website. The only way to purchase pickups separately is from emailing the company or from a friend who has extra.
But, again, you'll spend more money buying the complete stator. If you really want to be cheap you can try to rewind the defective coil itself. This is not recommended. For more info you can consult Graham's blog which also contains links to the relevant forum discussions. With practice and luck you might be able to restore it and even upgrade the output.
Also there is no warranty on these types of parts so be sure to inspect them for any flaws or damage immediately upon receipt. The shipping process itself is very fast (even from Belgium) using UPS and taking only 3-4 business days to the U.S. provided you sent the money with the required parts request and contact info.
First you'll want to inspect your stator for any damage or sign it's become loose, has been rubbed by the magneto, or was damaged by you using a clutch puller to access it. The photo below shows a damaged ignition coil.
If you can't visually determine if the coil is damaged (or just want to be sure) then you can test for continuity with a multi-meter. Below is the reading from a healthy HPI ignition coil tested for resistance between the blue and white wire. It says 5 ohms.
Once you have identified a defective or damaged coil then remove the allen bolts securing it to your stator plate and flip it over. Notice the glued spots.
Gently pry off the existing wires taking note of where they are connected to. It is recommended to photograph this portion in case you get distracted or forget where they go.
Carefully remove your new pickups from the packaging and set it down side by side to compare. Most of the ignitions all use the same assembly but you want to be 100% sure before you proceed. Note where the wires are going to be reconnected.
Next you'll want to slowly remove any soldered wires from the old pickups and give lots of thought to how you'll reuse them. The grounds themselves are bolted to the stator plate so shouldn't need to be removed but you'll want to leave enough room so they can still reach the bolts. Luckily they usually provide some extra length of wire.
Then you'll simply solder the wires onto the new leads by copying how they were hooked up before like below. Pay special attention to the grounds and insert a bolt to make sure they still reach. Next you will then begin applying a thin layer of your adhesive of choice. I used a clear Loctite Stik' N Seal for this tutorial so you can see how the wires are attached.
Make sure it's a durable adhesive with some slight give as you want it to absorb vibration and not crack.
Then it's simply a matter of waiting for it to dry in a warm environment and applying several layers until the wires have been secured to the pickups. You do not want them to be able to jiggle or pull on the connections at all. Remember the adhesive is also there to insulate the connections from interference! Don't overdo it. Leave room so reassembly is possible (too much and the pickups won't lie flat)
After you are satisfied of this then carefully reassemble your stator with the grounds being bolted back as they were and any excess cable being cramped under the top of the plate. You want it to lay flat so there is no rubbing of the wires against the magneto. This is very important.