ElectroAir MTH Internal Oil Seal Failure
 

Hi Folks,

I have 2 ElectroAir EIs on my plane. A few years ago, at about the 250hour mark, my right MTH developed an internal oil leak. The bearing/seal around the shaft was allowing oil to pass from the engine into the housing and fill the area with the trigger wheel and magnetic sensor. Wanting to get the plane back up and running quickly, I opted to have them cross ship me a new MTH (returning mine as a core) instead of having mine sent in for rebuild. Now a few years later and with 480hours on it, the other (left) side MTH has developed the same problem.

This time I could be OK without the plane for a couple of weeks, so I call them up and inquire about getting mine rebuilt. Instead I'm told there is no way to replace the bearing/seal, and that I will have to simply purchase a new MTH. This seems ridiculous for a simple seal failure.

My sensor is functioning fine electronically, and I don't see any evidence of wear metal in the housing, so no reason to suspect it needs anything other than a new seal on the shaft. Has anyone attempted to replace the bearing/seal themselves, and have a source and PN for it?

-John

Sorry no answers, just more questions
 

What time frame did you purchase your electronic ignition system in? Does your MTH have the original small pick up sensor? Or the later larger-diameter one?

Charlie

Hi Charlie,

Both are of 2011 vintage, which is the newer XDI based system and utilizing the larger magnetic pickup.

-John

The MTH comes apart pretty easy but you have to press out the shaft and bearing. The most important part to check for wear is the bearing. A worn bearing would make the seal fail. The bearing and seal should be off the shelf parts. I've been using ElectroAir's for 20 + years. I've only seen one old MTH fail, the bearing wore out, spun and damaged the case.

I know the MTH housing has changed a little in the last 20 years (at least a larger hole for the pickup sensor), but any idea if the shaft to housing assembly is the same?

I suspected it might be a press fit. Does the trigger wheel need to come off the shaft first? Is the seal integral with the bearing? Which direction does one press the shaft and bearing out? I don't have the MTH out of the engine at the moment, so apologies if this all becomes evident once it's out.

-John

The newer housings are smaller than the old old ones. I'm sure yours are the latest ones (black). Remove the cap and the gear is exposed. There's a hex head bolt holding it on with lock tight. Remove the bold and the gear comes off. Remove the sensor before you do any work on the MTH. You might be able to remove the seal without removing the shaft but bearing inspection is a must. It's sealed ball bearings. It's been so long since I've opened one up I can't remember if there's a separate seal or the sealed bearing is the oil seal. I have some at MTH's my hangar, I can look tomorrow.