Drilling a Mejzlik prop

[plaster93]

I just got a new mejzlik prop that was drilled by the previous owner and never used.The holes look like the guy used a cordless drill, some are alittle wider on one side than the other, not much but just sloppy.When I put the prop on,the bolts drop in just fine but theres about an 1/16- a lite 1/8 of play in the prop on the shaft and bolts just a couple turns in.
My question is....is it OK,just leave well enough alone or should I fill the bad holes with epoxy and redrill.I just hate to shear some prop bolts, you know what I mean. Any props that I've had before I did on a press,front and back and the bolts drop in perfect,no slop.

Thanks Steve

[Temptation]

A lot of guys drill their prop holes one size to large, and there is absoutley nothing wrong with that. I drill mine 13/64" for my DA 150 on a drill press with a DA drill guide. That works good for me. One thing that can happen when drilling a carbon prop, is that the bit can walk as it goes through the prop, due to the nature of the carbon. This doesn't happen with wood props. This is the reason a lot of guys will overdrill their props. An overdrilled prop is just fine. When installing it, you just need to make sure that you turn the prop so that it is backed up to the bolts before final tightening. If your prop bolts can be installed by hand all the way without binding I think you will be o.k. as long as you back the prop up against the bolts like I mentioned before. You also want to make sure you back the prop in the direction it is going to go when the engine is running. Sounds like you will be o.k. This is one reason I don't like to buy props that have been drilled. Just remember that it is common for the bit to walk when drilling carbon props. The key to drilling carbon props is to use a good sharp bit, with the proper drill guide on a drill press, and take it slow while backing the bit out every little bit to make sure the hole is clear of any shavings. Drilling carbon fiber can dull a bit rather quickly. I use a Drill Doctor to sharpen my bits, and always use a freshly sharpened bit for every prop. It's a small price to pay to aid in preventing prop bolt shearing. One more thing that I would like to add, that you may already know. I like to thread all of the bolts into the hub with the prop washer installed. Then measure the space between the hub and the prop washer. Make sure this distance is smaller than the thickness of the prop. This will prevent a bolt from bottoming out before it is tight, making you think it is tight. This is pretty common, and I think is the single most common reason for prop bolt shearing. Shorten them with a cutoff wheel in your Dremel if necessary. Don't forget about the spinner backplate thickness if you are running one. Also if you usually run a spinner, then one day do not, you could run into the proble of the bolts being to long. Always double check prop bolt length. Also when tightening the bolts do it in a star pattern until all of the bolts are tight. Make sure to check the bolts tightness after each flight for the first 10 flights on a carbon prop. In fact I install my spinner backplate, but not the spinner for those flights just for that reason. Wood props you need to check them for about 20 flights because they will compress more.

Hope this helps,

Mike Darr

[plaster93]

Thanks for the good info Mike!

[Temptation]

My pleasure. I haven't ever had a prop shear the bolts yet, and I hope I never do. This is why I take great care when drilling my props. I would hate to see it happen to someone else, especially if I could have helped prevent it. Sounds like you are good to go. Now go turn that prop and burn some fuel.

Mike Darr