Big Twin Flywheel Connecting?

[Robert Ellis]

Hi, I've been working on a few 'big twin' motors lately (mid 60s 33, 40 hp) doing the usual ignition stuff but the problem I'm having is ... as often as not, when I re-assemble everything I have good spark, engine fires right up but then the 'key' between the drive shaft and flywheel shears. Can someone tell what I'm doing wrong. Is there a torque setting for the big nut on the end of the drive shaft - perhaps I'm not tightening it enough?

 

[racerone]

It must be assembled clean and dry.---Torque to 100 FT-LBS--------If there is damage on the crank and taper in the flywheel, you would use valve grinding compound to lap them for a proper fit.

 

[HighTrim]

As mentioned, SOME of the Big Twins require 105 ft/lbs. Taper must also be clean and dry. Also, use OEM key, not hardware store.

 

[Robert Ellis]

Thanks for the reply. Clean and dry ... oops... what I've been doing is putting a dab of grease on the key so it sticks in the drive shaft recess, putting a little oil on the flywheel face and then carefully aligning the channel in the flywheel with the key as i slide the flywheel down onto the drive shaft. Maybe that grease and oil has been the problem? I've been cranking the nuts down pretty good but I don't have a torque wrench so I can't be sure I got 100 ft/lbs on them. Is it somewhat common for this key to shear or is it peculiar to me?

 

[racerone]

No it is not common for it to shear.----The key is only there to align the flywheel for proper ignition timing. --The flywheel is driven by the locking tapers.----If tapers do not match properly and are not clean and dry not torqued to 100 FT-LBS then it will not work as designed !

 

[Robert Ellis]

ok. ... thanks .... I'm not sure how keep the key in the drive shaft without grease but I'll stop putting oil on the tapers (duh)! I'll also invest in a torque bar - I wonder if most 1/2" drives ones go up to 100 - are the ones that click when you reach the right torque the best to get?

 

[racerone]

Only use a factory key !------Couple of punchmarks on the sides will hold the key as well as needs to be.

 

[HighTrim]

Factory key requires no grease. Sometimes hard to get out actually.

 

[Tim Frank]

Verify how the key should actually be aligned.
Sometimes they align with C/S centreline, sometimes with the taper face.

I have both configurations.

 

[Robert Ellis]

I start by using the key that was in the motor - of course after I shear it I have to replace it and I am using factory keys (my local marina charges $6 a key lol - he warns me his stock is getting low thanks to me ha ha - of course he also wants to sell me a new evinrude 40 for $7200). Interesting about what you say High Trim about them sometimes being stuck in the drive shaft - the only ones I've experienced have been all too happy to come out (except the sheared ones) - I presume from all the penetrating oil applied prior to popping the flywheel. I'll try the 'punch idea rather than a dab of grease - never would have thought of that in a million years!

Tim, I'm sorry but I have no idea what you mean ... c/s centreline??? taper face?

I appreciate the help.

 

[nwcove]

first pic the key is aligned with the taper, second pic the key is aligned with the crankshaft ( center line)

 

[Tim Frank]

The keyway is cut with a Woodruff key cutter.
Depending on the reference angle used in the machining setup you need to orient the key so that the "chord" line segment of the key is parallel to either the centre line of the crankshaft,(c/s) ~ OR ~ parallel to the face of the taper on the c/s end. At least according to the manual.

I honestly have no idea whether that difference is significant or not..... maybe some one of the gurus can weigh-in, but when I am not sure, I always just follow the OEM instructions.

 

[Robert Ellis]

ahhh ... I see now what you mean ... thanks for the pics, interesting but I have no idea which way mine are supposed to be. I'm not even sure what way I put them back in to be honest ... I was just kinda glad to get them staying in ... I believe I tried to have it so that the amount the key stood out from the shaft was even so that would be more like pic 1 (aligned with the taper). I wasn't fanatical about it though. My main concern was not to knock it out when I lowered the flywheel on it.

 

[Robert Ellis]

Ok, I did the ignition rebuild thing on a 33 hp evinrude last night. Punched the flywheel key, aligned it with the taper, fitted the flywheel and taper clean and dry, torqued the nut to 105 ft/lbs. Tank tested it today for about 15 mins while I fiddled with the carb needle adjustments etc and then ran her in the lake for a good half hour at various speeds. NO KEY SHEARING!!!!!!
Thanks so much for all the help!

 

[HighTrim]

Great! One of the situations where you dont want any grease or oil

 

[Robert Ellis]

Just a quick update note for anyone reading this prior to assembling their flywheel. I’ve recently been informed that the correct key alignment for both the 33 and 40 hp of this vintage is ‘parallel to the crankshaft centreline’ (the opposite of what I did of course lol). Further, If there is a mark on the key (punch mark?), the key should be fitted such that the mark is down (I just randomly stuck the key in, who knows what side was down).
It’s hard to know how important these two points are – I don’t think I’ll pop the flywheels off of the motors I’ve done just to inspect and correct the up/down and alignment issue but certainly the ones I do from now on will be done in accordance to the above.