Jason builds a plane

the central piece of any engine.... the crank

5/8/2016

0 Comments

 
I haven't posted anything to the blog because I've really not made any progress in the past couple of weeks, other than research stuff.  Summertime is difficult....  hot and muggy and plenty of other family plans and activities to occupy my time.

Had a few minutes today though, so I thought I'd get out the core crankshaft I have safely stored in inventory and have a better look at it.  One of the first items I'll be sending away for prep work, but it needs to be measured to see if it still meets factory specs.

This is the crank I inherited from the inventory I purchased in February.  The previous owner had already completed some of the work to make it airworthy and it's in great shape:
Picture

The recommended prep work includes magnaflux testing for internal damage, straitening if required, heat treating for improved strength (ion nitriding) and grinding the piston rod journals to improve the fillet radiuses.  Larger journal radii help prevent stress riser cranks from forming, which has led to broken crankshafts in the past.  The process is quite common in certified aircraft engine cranks, so it's worth doing here.

One of the other processes that normally gets completed is to drill and tapping the centre of the end of the crank for a propeller hub safety shaft.  Because the previous owner was working from the official plans, he had already completed this process with his machinist:
Picture

I opened my Corvair shop manual, and found the engine spec reference page.  It contains all the measurements for the major engine components:
Picture

Using my digital caliper, I tried to measure as best I could the crankshaft main journals and connecting rod journals to see how close they are to factory.  I really should be using a micrometer for this, but my calipers should at least let me know it's in the ballpark.

The manual says the connecting rod journals (they call them crankpin journals) calls for a diameter from 1.7999 inches to 1.800 inches.  To make it easier to measure, I set and friction-lock my caliper to 1.7990 before placing it on the journal.  This is slightly undersize, but as close to 1.7999 I can get.  This way if the caliper slides over the journal without resistance, I know that it is below tolerance and no good for grinding. Anything larger than that leaves that much more room for the machining (good):
Picture
Preset the caliper....

With my lovely assistant Brenda taking an action shot with the camera, I carefully measure each of the bearings:
Picture
Picture
Picture

It's real hard to get a good picture, but the caliper won't span the largest diameter of the journal, so we can deduce that they and the main journals (using the same measuring technique) are clearly above the minimum spec and can be used for conversion.  I know it isn't a perfect measurement and my caliper may not be as accurate as a micrometer, but I think I'm in the ballpark at least.

I'm going to see if I can borrow a good micrometer from someone, or maybe buy one for myself to confirm this.  Once I'm sure, off to Florida the crank will go for prep.

Next Wednesday I'm having my first shop lesson with Ron, another Zenair builder.  He's rebuilding a Zenair 701 and has offered to let me help.  What a great opportunity to learn and prep for my build.

​More to come.....
0 Comments



Leave a Reply.

    New here? Try starting at:

    blog #1

    Author

    Husband, father and 911 dispatcher.  Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be.  First time aircraft builder. Looking to fly my own airplane.

    Categories

    All
    Airframe
    Airport
    Avionics
    Decisions
    Engine
    Interior
    Keep Looking
    Mentor
    Milestone
    Mission
    Motivation
    Paperwork
    Philosophy
    Priorities
    Scrounging
    Tools
    Ultralights
    Welcome Aboard
    Workshop

    Archives

    February 2021
    January 2021
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    September 2019
    August 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    June 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    February 2017
    January 2017
    December 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015

    RSS Feed

    build log

    Item Hours
    Engine 31
    Tail 151
    Wings 356
    Fuselage 0.5
    Interior 0
    Controls 4.5
    Avionics 5.5
    Other 64
Powered by Create your own unique website with customizable templates.