90 hp johnson Vibrating at low idle

[bwilson2626]

O.K., so, thanks to the guys on this site that have helped me out, I have the Ol' Johnnie purrin like a mad kitten! Once again, thank you so much for the advice!!

And of course, now its something else.. Took it out today for a spin & although the motor was smooth & runnin great, it now has a Hard vibration at lower rpm's while in foreward gear. Smoothes out at higher speed. Was near some shallow enough water to get out & take a look, figuring it might be the prop. Prop looked perfect, so I spun the prop, in neutral, and noticed a slight wobble. almost like the prop shaft is bent. About a 1/8" movement from side to side, about 1/16" from center.

If the shaft is bent, how hard is it to change it? Or might there be a different culprit? Bearings? I will be taking off the lower unit tomorrow to start the hunt, but if anyone has any insight on what to maybe look for, I would much appreciate some guidance..

 

[jakedaawg]

Shafts can easily be straightened with vee blocks or rollers, an indicator, and a press. Many home gamers dont have this but a decent job shop should be able to do it affordably. That's if it's the shaft. If you notice it with the prop on it may just need a new hub, any prop shop can rehub.

however, a vibration at idle only is more likely a low speed miss due to plugs or improperly tuned carbs.

 

[bwilson2626]

I could see the shaft itself out of center as it spins. Is 1/8" enough to cause vibration?

There is very little vibration while in neutral, it only shows up when in gear.

 

[racerone]

The shaft is bent.----Big money item.-----But it the shaft is bent the gears also took a hit and need to be checked.-----Model # is ??

 

[bwilson2626]

J90TSLECM

I am searching around for a used inexpensive lower, without any luck yet. Jakedaawg mentioned having the shaft straightened at a work shop.. machine shop?

I guess buying a used one on ebay is too dicey?

 

[jakedaawg]

Once you teardown the lower unit any decent machine shop should be able to straighten it.

I straighten 3 or 4 a season, never had a problem. They will need to check to make sure it's not cracked. It's stupid simple.

They tend to bend between the prop splines and the bearing. The manual lists the tolerances for straightening. I can look the spec up on Tuesday but I am away from manuals for the holiday. Honestly though, I get em back to within a thou or a thou and a couple tenths and have never had an issue. Done this many times as we have a lot of rocks and a lot of novice boaters with money in the area.

You need a special tool or two to tear it down but you can improvise. Keep track of the shims so they go back in the right place and order.

 

[bwilson2626]

Thanks bud, I have the manual for any specs needed, what spooks me is the bearings under the dog gear. Never dove that deep into a motor before. I dont mind improvising on things I am familiar with, but not so much here...

I wonder if my local boat shop would install that for me, knowing I would be doing the rest of the work. I have a couple of machine shops around here, will be talking to them next week..
thanks for your help Jakedaawg. Much appreciated

 

[bwilson2626]

Racerone, you were right. Big money item was exactly what it was. Or probably will be in the future. But for now, its running smooth as it ever has.. Now I'm sure that some of you may not like this, but ...


after reading the post about a "prop straightening device", I decided to investigate, Did alot of you-tubing & blog searching & decided to give it a try. After all, it was broke & not being able to afford $1200 to get it fixed at my local shop, I figured what the heck..

Took alot of tinkering to get the recipe right, but finally succeeded in getting the spin to guage @ .0005. (Started @ .115ish) The literature I read shows .003 is in tolerance. Now dont get me wrong, I understand that I may have just spelled disaster for the gears & who knows what else, but it was a gamble I was to the point of taking. Did a positive pressure test on lower gearcase & held 10psi for 5mins, w no loss. Have ran it for about 3 hrs on the water, drained the gearcase oil & looked perfect.

I know what I did isnt recommended by anyone who knows what theyre doing, but I just wanted to update the guys who have helped me out.

Once again, MUCH THANKS to you guys!!!

 

[jakedaawg]

It'll be fine, good for you.

 

[Bosunsmate]

Racerone, you were right. Big money item was exactly what it was. Or probably will be in the future. But for now, its running smooth as it ever has.. Now I'm sure that some of you may not like this, but ...


after reading the post about a "prop straightening device", I decided to investigate, Did alot of you-tubing & blog searching & decided to give it a try. After all, it was broke & not being able to afford $1200 to get it fixed at my local shop, I figured what the heck..

Took alot of tinkering to get the recipe right, but finally succeeded in getting the spin to guage @ .0005. (Started @ .115ish) The literature I read shows .003 is in tolerance. Now dont get me wrong, I understand that I may have just spelled disaster for the gears & who knows what else, but it was a gamble I was to the point of taking. Did a positive pressure test on lower gearcase & held 10psi for 5mins, w no loss. Have ran it for about 3 hrs on the water, drained the gearcase oil & looked perfect.

I know what I did isnt recommended by anyone who knows what theyre doing, but I just wanted to update the guys who have helped me out.

Once again, MUCH THANKS to you guys!!!

Can you explain how you did it? Almost everything i do is a chance to save money

 

[bwilson2626]

Ended up w a 3 ton floor jack elevated to be horizontal with the shaft. Thats with the motor still on boat & l/u still in place. With the prop nut on the shaft, hand tight as far as it would spin, I put a 3" long piece of 2" square tubing over the nut & shaft (for thread protection & pressure distribution ). The axle of the jack rested on the tubing about 1" behind the nut. I used a 2×6 to cushion between the lifting part of the jack and the above part of the motor housing. Apologies for not knowing correct termonology. The axle of the jack had to be blocked from rolling foreward, when pressure was applied. Made zero progress untill i did that. Once I was able to stop the jack from moving, I applied pressure & let it sit for about 20 mins. That gave me my first progress, about .040". I continued with that procedure, varrying times, and finally got it where I wanted.
As I said, book tollerance is .003, but i am anal. I figured if i can get it to .003, why not try to improve ...

fyi.. I used a 3 ton jack because the 1 ton & the 1.5 ton I used to start didnt have enuff power to make the changes. I never did max out the 3 ton. Just applied pressure till i started getn worried & stopped.

Sorry to be so long winded, but it was a 2 day process, & Im hoping to save others some time.

 

[racerone]

That may have been hard on bearings.--------Time will tell.