HPI ignition

[RustyRD]

I ran across a video from Allen Millyard installing a new rotor on a crank and he used lapping compound to seat the two. I was unaware of this approach, however it makes sense. I am sure some of you might be aware of this method.  I had the opportunity to weigh stock rotor and HPI rotor thought I would share the info. The total weight savings is greater due to the stock stator not being used.

[1976RD400C]

Huge weight difference. I've had mine for many years. I never lapped it to the crankshaft but use a hardened thick washer on the mount bolt and have not had a problem. I use a timing light and precisely set the timing, install some iridium spark plugs don't even think about the ignition system for the next 12 months.

[RustyRD]

cool, great to hear about the reliability. I have a vape unit on a 75 rd350 , I did not lap the rotor on it either and have not had an issue with it slipping. I guess it could be an added measure in some situations.

[m in sc]

you technically shouldn't lap them by hand, but people do so i'm not going to argue that point because it isn't going to change anyone's mind, and it does work but real easy to get a slight bit off and reduce contact if you don't have a very steady hand.

 I've run an HPI on my lightweight for 5? years now and have been running the vape cdis since 2007. the best way ive had them work was to heat the rotor up to 200-250 degrees and press it on so its a shrink fit. did that with the hpi as well.  and im still running the original 2007 rotor on the lc, and ive had it on and off the motor like 7-8 times, so heat that low will NOT weaken the magnets.

nice to see millyard using the hpi though.

some info on tapered shaft fitments:

https://www.sciencedirect.com/topics/engineering/shaft-taper

[RustyRD]

Thanks for the info, I used only light pressure and only enough time to make a slight change in surface appearance. I also heated the vape rotor when I installed it, been on the engine for 3 yrs now, and has not budged.  I think I read about heating it from your post. the link is great info. Thanks.

[teazer]

lapping the two parts is common practice.  Mark is right that if the rotor is not square to the shaft, it might be possible to make things worse, but in practice that's not a problem.

The reason to lap them together is to ensure that both tapers are exactly the same and to identify and remove any high spots caused by say loose key hammering the slot. I like to start with fie valve grinding paste and end with metal polish. With a small amount of oil on the tapers, the two parts should "ring' together and be hard to remove - even without the but on the shaft. The keyway is only there to make it easy to time.  It is not designed to hold the rotor in place.

[LMS]

So HPI uses a keyway, vape does not unless you go with HVCcycles keyway? What is HPI set at, timing wise as hvc is set at what, 1.8-2.0?

[rodneya]

So HPI uses a keyway, vape does not unless you go with HVCcycles keyway? What is HPI set at, timing wise as hvc is set at what, 1.8-2.0?

HPI does not have a keyway and is set at TDC. It does not run static timing like the stock vape, it has a timing curve.

[m in sc]

^ yup.

one other thing i do when putting one on is seat it lightly with a rubber mallet. Not like a caveman, but a light 'tap' it should bite enough to be able to rotate the motor over w no bolt of plugs in by rotating the rotor. 

[LMS]

OH nvm, I was looking at old rotor.

[rodneya]

Hpi has an adjustable stator plate so that you can easily make small adjustments without removing the rotor.

[RustyRD]

Removing the mass from the crank should provide longer life to the bearings, that is if your not revving it to the moon