Mark 25 key dimensions

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CaptChuck
Posts: 42
Joined: Thu Jun 22, 2017 11:28 pm
Location: Whidbey Island, Wa

Mark 25 key dimensions

Postby CaptChuck » Tue Oct 10, 2017 11:58 pm

A bit of a fix because my Mark 25 slipped into gear while I had it above idle (way above idle). Trashed the woodruf key. Can someone give me the dimensions of the key? Obviously I can measure the thickness. What I need is the height and depth. To buy a key online would be $6 + $7 shipping. To buy from the local ACE is $1 but I can't look it up with a merc part number.
1929 Evinrude Fastwin
1948 Mercury KE4
1953 Mercury Mark 15
1956 Mercury Mark 25 (2 of them)
1967 Evinrude 3702C (folder)
1975 Yamato 80

chuckw
Posts: 59
Joined: Mon Mar 09, 2015 7:23 pm

Re: Mark 25 key dimensions

Postby chuckw » Wed Oct 11, 2017 6:57 am

part number is 20907

CaptChuck
Posts: 42
Joined: Thu Jun 22, 2017 11:28 pm
Location: Whidbey Island, Wa

Re: Mark 25 key dimensions

Postby CaptChuck » Wed Oct 11, 2017 9:44 am

Thanks but I am looking for the dimensions. The part number works when ordering something on line but I am going into the parts bin at ACE Hardware. Height and depth if anyone has their flywheel off. Oh, yea, it's for a Phelon mag. I've got a Mark 20 but it has Scintilla so I don't know if it is the same or not.
1929 Evinrude Fastwin
1948 Mercury KE4
1953 Mercury Mark 15
1956 Mercury Mark 25 (2 of them)
1967 Evinrude 3702C (folder)
1975 Yamato 80

green thumbs
Posts: 213
Joined: Mon Jul 06, 2015 1:21 pm

Re: Mark 25 key dimensions

Postby green thumbs » Wed Oct 11, 2017 2:22 pm

Whittle key stock to fit with a file. Height will be total depth of key way in
flywheel and crankshaft or slightly less. Length and profile will be file to fit.
As long as key ways ok this should work. KEY only locates relative position of
flywheel to crankshaft. The lock up of taper between flywheel and crankshaft
is created by proper torque of flywheel nut. Taper should not have any lube
as the lockup is between dry surfaces.
If taper surfaces are scored or uneven, they can be "lapped" to mesh using
valve grinding compound...a process requiring patience. Remove all traces of
grinding compound when done. Old school technique.
Do not over torque (splits hub) or under torque (tears up key)
In addition to being part of magneto ignition, the flywheel absorbs, stores and releases energy so power of engine is smoother. This means flywheel is under forces that
lead and follow the crankshaft...if flywheel torque is insufficient the key takes
a beating and may fail or batter the key ways in both crankshaft and flywheel
Windy,but, important details.
Good Luck
Louis
A small vise to hold key while filing is very helpful.

CaptChuck
Posts: 42
Joined: Thu Jun 22, 2017 11:28 pm
Location: Whidbey Island, Wa

Re: Mark 25 key dimensions

Postby CaptChuck » Wed Oct 11, 2017 3:09 pm

Thanks Louis.

With your explanation I'll be able to get the dimensions right.
1929 Evinrude Fastwin
1948 Mercury KE4
1953 Mercury Mark 15
1956 Mercury Mark 25 (2 of them)
1967 Evinrude 3702C (folder)
1975 Yamato 80


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