[SEL] Question re tapered gib keys

[Jerry Evans]

Hi to the knowledge base (that's all you guys out there in engineland) :-)

         A few questions re tapered "Gib Keys" but first I'll explain the 
problem - this may be a bit long winded!

         The flywheel on my little Ronnie N keeps coming loose. (To be 
fair, Arnie did warn me that, if I called him Reggie I should expect 
trouble :-)).
<http://www.oldengine.org/members/evans/reggie/index.htm>

         After restoration (and a few "rallies") he developed a knock 
(which sounded just like a bearing knock) and I discovered that the 
flywheel was loose. Closer inspection revealed a crack in the flywheel hub 
starting in one corner of the keyway and going to the outer edge of the 
hub. (A common problem with them, I believe, related to incorrect removal 
of the flywheel).
         I had the hub machined (just a tad) to fit a reinforcing steel 
ring around the outside of it and had the whole lot professionally welded. 
This welding was done with a mandrel (sp) a few thou smaller than the 
crankshaft inserted and clamped up with the bolt to prevent distortion.

          The welders did a great job and it worked fine for 3 rallies but 
then the knock (and loose flywheel) started again although the crack has 
not reappeared - the repair has held.
         The flywheel is cast with a teardrop shaped slot (opposite the 
keyway) into the web of the flywheel and going "all the way through" to the 
crankshaft.
         Fitting entails sliding the flywheel onto the crankshaft, lining 
up the keyway on flywheel and crankshaft, fitting a straight key, and then 
tightening a large bolt which theoretically clamps the flywheel to the 
shaft - the key just there to locate it and prevent the flywheel slipping 
around the crankshaft.
         Removal entails loosening the large bolt and inserting a wedge 
into the teardrop shaped slot (from the back) and knocking it in just 
enough to loosen it (the flywheel) from the crankshaft. This is where the 
damage "happens" if done incorrectly ie. wedge hammered in too far causes 
the crack on the opposite side of the hub (in the corner of the keyway 
which is a "weak spot").

         The repair has held (as mentioned earlier) but now I'm wondering 
if a tapered gib key is not the answer. (I wonder why the manufacturers 
never used that system in the first place as it seems infinitely better 
than what they did but it was 1936 and the design was even earlier so maybe 
that will explain why they went that way).

         O.K. that covers the explanation of the problem - now my questions?

         a) What do you guys think of the idea of a tapered key to replace 
the straight key - I would knock it in very slightly first - then tighten 
the clamping bolt as tight as possible - - then give the tapered key a 
whack to seat it - after a few "runs" of the engine maybe another whack? 
(ie. after a good few hours of running).

         b) How do I measure to be able to give the key manufacturer the 
correct dimensions? I know that most standard tapers are 1:100 (and I'd 
probably go for this unless otherwise advised). The question is hard for me 
to describe but what I'm trying to establish is, is there a point along the 
key where the taper must start to grip (eg 1/3 or 1/2 way along). Is there 
a tried and tested formula for this? I do not want the key to go in too far 
so that I cannot "Grip" the head to remove it later and it must also not 
stick out too far and interfere with a crankhandle adapter I have on there 
to enable me to use the same crank as my Wolseley engines. ( I put an 
adapter on each of my engines so that I only have to take 1 crankhandle to 
any rally.)
         3) Is it  acceptable to use shimstock under a tapered key if I get 
the measurement wrong and the key goes in too far?

         Thanks in advance for any suggestions.

Keep the revs up (or down)
Jerry Evans
Near Johannesburg in Sunny South Africa.
Etched Brass Engine Plates made to order:
<www.oldengine.org/members/evans/plates/index.htm>