Motor locked up when lower unit is installed

[JCurry2885]

Motor is a 78 Evinrude 115. Lower unit was cracked so I sourced another one. Motor cranks and runs fine with the lower unit removed, but once I install my new "used" lower unit the motor is locked and will not spin. I already made sure that the unit is not in gear, as I can spin the prop shaft freely. Also the lower unit driveshaft rotates free when it is not installed onto the motor. I had no issues installing the lower unit onto the motor, I just rotated the engine a little to line the splines up and it slid right into place, I did not have to force anything. Shift shaft length is adjusted correctly. Only thing im finding different is my driveshaft length on the new lower unit is about an 1/8 inch or so longer than my old one, but I didn't figure that was an issues since the unit installed so easy, and I did not have to force anything.

Any ideas??

Thanks!

 

[racerone]

The replacement unit came off what motor ?-----Post picture of the splines of the 2 shafts.

 

[JCurry2885]

the replacement is off of a newer motor I believe, not sure of exact year. Ill will take some pictures when I get off work today.

 

[racerone]

Yes because a 1977 is a totally different unit.----They are " not all the same " as you have now found out.-----May be as simple as cutting an 1/8" of the shaft.

 

[JCurry2885]

what would cause it to bind up and not allow the engine to spin over? I figured if the splines were wrong or the driveshaft was too long, that the lower unit would not have mated up easy.

 

[JCurry2885]

I installed a new water pump assembly on the lower unit prior to installing if that makes any difference

 

[Joe Reeves]

The length of the driveshaft is critical... that 1/8" difference had the driveshaft jammed against the crankshaft and the pinion gear of the lower unit jammed against both directional gears. No way in hell will that allow the engine to crank over.

 

[Tim Frank]

Do you mean the actual driveshaft turns freely or the L/U propshaft?

Loosen/separate the lower unit by 1/8" to verify that it is the extra length that is causing the interference.

 

[F_R]

My guess is that the longer drive shaft is bottoming out in the female splined crankshaft. That is pushing the driveshaft downward, which is mashing the gear teeth together, locking it up.

Easy enough to prove, simply back off all the gearcase attaching screws and let the gearcase drop down 1/8" inch. If motor will turn freely, well there ya go...

 

[racerone]

?????----Well---- it could be that the last 0.010" of up movement you jam the crankshaft lower bearing !----Something you will not notice with a wrench.-----So back each bolt off 1/4 turn at a time to see when it loosens up..

 

[Joe Reeves]

Well C'mon JC.... Did'ya have a machine shop cut off a 1/8" or so from those driveshaft splines.... stick some washers between the gearcase and the long exhaust housing, what?.... You've had all day ya'know!

 

[boobie]

Ya, lets hear from you ????

 

[RaisedByWolves]

How about just using longer bolts?

The longer bolts will bind up in the threaded holes and not snug up the lower so much.

Who knows, could be a new go fast secret?

 

[flyingscott]

How about just using longer bolts?

The longer bolts will bind up in the threaded holes and not snug up the lower so much.

Who knows, could be a new go fast secret?

I hope that is a joke. If not quite possibly one of the worst ideas ever!

 

[racerone]

You have to wonder where JCurry went.----At first 4 posts in an hour.----Now nothing.----I am done trying to help.

 

[RaisedByWolves]

I hope that is a joke. If not quite possibly one of the worst ideas ever!

I was of the opinion there were jokes being tossed about?

 

[Joe Reeves]

You have to wonder where JCurry went.----At first 4 posts in an hour.----Now nothing.----I am done trying to help.

Perhaps the law finally figured out that it was JC that masterminded the "Brinks Job!"

Seriously, he's probably in the process of tearing that LU down to find a driveshaft that'll switch over... or another lower unit, and has nothing to add yet.

My mention of having a machine shop cut the driveshaft... I wonder if that would suffice or would the C/S splines run into the un-splined portion of the driveshaft which would result in the same lockup condition? I sold all of my similar driveshafts and can't quite picture that area. However that area if cut down just the depth of the O Ring slot shouldn't weaken the shaft... or would it?

 

[RaisedByWolves]

I would think that any good shop who would cut the shaft down would re chamfer the end.

If for no other reason than to knock the burrs off of the splines.

If the job came to me I would both re chamfer and deburr and chamfer the individual splines to a factory like condition..

 

[Joe Reeves]

I would think that any good shop who would cut the shaft down would re chamfer the end. If for no other reason than to knock the burrs off of the splines. If the job came to me I would both re chamfer and deburr and chamfer the individual splines to a factory like condition..

I assumed that any reliable machine shop would do just that (as quoted above). My wonderment of post #17 pertained to the lower portion of the splines where the shaft returned to its solid state.

 

[boobie]

Sure would be nice if the op posted something back. O' well.