New Used Johnson 90- Reassemble As-Is or Tear Down?

[RBuch1974]

Hello,

Bought a J90MLCNB (82' 90hp) with no electronics and planning to complete the motor by combining "stuff" from similar Evinrude. Beyond rebuilding/replacing the normal maintenance items like carbs, plugs and pumps, I am prepared to tear the powerhead down for machine shop inspection and replace bearings and rings if all else is well. But wait, should I?

The motor sat (barn kept) for an undetermined amount of time.

When I turn the flywheel w/o plugs, should it turn smooth or will it tend to "bump" on up stroke?

Any suggestions how I should approach testing in order to decide what to do?

Thanks in advance for any help. You folks here have helped me (first time boat owner) and have become an invaluable source of information for me.

 

[Bosunsmate]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

Squirt some oil in the cylinders and rotate it a few times,
Not sure what a bump is but you could rotate each cylinder to TDC and then press on the piston through the sparkplug hole with something firm but soft, you will often feel a little give but a lot indicates worn bearings.
You can undo the bypass covers on these very easily and inspect all rings for integrity. The gaskets for those are only a dollar or so each and worth doing since its currently stripped

 

[Bosunsmate]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

I just rebuilt one of these.
If that was mine and it had being sitting for a while. Id take off both the heads and clean out all the gallerys, replace the water deflectors and you can also check the cylinder walls while you have the heads off.
Id also change the two thermostats, make sure you put them back in the correct way.
And then do the routine impeller and gearbox oil.
If the exhaust bolts werent seized id take off the exhaust plates and clean in there too and replace the gaskets so the water/exhaust separation integrity is good back there. then put some antiseize on those bolts when you do it back up
They are good motors those

 

[rolmops]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

Delaware makes me think of salt. The bump might be caused by a rusty spot in the crank case. If you can do the tear down yourself,go for it. It really is not as complicated as it sounds

 

[V153]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

When you have the heads off check for any slop in the connecting rod/wrist pin bearings.

I'd be skeptical about buying a "good" motor with no electronics. When a motor goes sour, the electronics are usually the first thing to be pirated. I would scrutinize the block very closely.

 

[emdsapmgr]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

You should not feel compression with the plugs out. Put them in and you should feel definite compression phases when you turn the flywheel by hand-that's normal. Couple of suggestions: You can shine a pencil light into the spark plug holes-providing a look at the pistons tops and some of the cylinder walls. (look for any dents on the piston tops-that's a ring failure.) If you don't see any real problem, I'd do a compression check before any teardown. After you run a small amount of lube into the cyls-put a starter on it and do a compression check. A set of automotive jumper cables is all you need. Compression is everything on that engine. I'd be looking for about 100 lbs on all 4 cyls. If the compression is more than 10% off between cyls, then tear into it.

 

[RBuch1974]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

Did the oil (WD-40). Cool tip @ checking "slop" Thanks!

 

[RBuch1974]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

I was thinking replacing the thermos for sure too. Will checkout/clean exhaust.Thanks!

 

[RBuch1974]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

Delaware makes me think of salt. The bump might be caused by a rusty spot in the crank case. If you can do the tear down yourself,go for it. It really is not as complicated as it sounds

Little skeptical about the bump too. Spins smooth and didn't pick up any weird noise from top of piston using a stethoscope. Did a visual through plug hole and no damage to note but, I have to pull the powerhead anyhow. I have rebuilt several other kinds of motors (dirt bike/four wheeler, car) so I've already started reading up in the manual on breaking it down. Gotta get a in# torque wrench though. Thanks!

 

[RBuch1974]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

You should not feel compression with the plugs out. Put them in and you should feel definite compression phases when you turn the flywheel by hand-that's normal. Couple of suggestions: You can shine a pencil light into the spark plug holes-providing a look at the pistons tops and some of the cylinder walls. (look for any dents on the piston tops-that's a ring failure.) If you don't see any real problem, I'd do a compression check before any teardown. After you run a small amount of lube into the cyls-put a starter on it and do a compression check. A set of automotive jumper cables is all you need. Compression is everything on that engine. I'd be looking for about 100 lbs on all 4 cyls. If the compression is more than 10% off between cyls, then tear into it.

I like that idea. I will give it a spin with the starter. I've hit the cylinders with a thin "wicking" oil prior to rotating it at all. I'll try a little heavier oil for comp check. I would like to have some confidence in this motor when it's done (I have 7yr old twins who will be on the water with me sometimes) so, I'm thinking it's time to just clean off the exam table (work bench). Sounds like the Dr. is in. Thanks!

 

[RBuch1974]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

Thanks to all of you guys.

Had second thoughts while part shopping last night but, after reading all the suggestions I think I will just plan on checking some things out while/before breaking the motor down then have it gone over by machine shop. The Johnson motor was low priced but, I got burnt on a not so low priced out-of-state ebay motor last year (Georgia, I live in Delaware...I know, i know, sometimes I'm just a big dummy) that apparently had lots of saltwater use and really just want to know the mechanicals are solid before spending more time and money on this one. The other motor ran great in the water for @ 20min. doh! I've saved my pennies for a fair amount of motor work so, so be it. Really appreciate the input.

 

[emdsapmgr]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

Lubricating oil was mentioned as being good to make sure the engine rotates free-after a long period of storage in unknown conditions. Good idea. Adding additional oil just to before checking the compression is not necessary. It can skew the compression readings somewhat higher. Even if you do add additional oil, after cranking it 8-10 rpm's, the extra oil will dissipate by exiting the exhaust and compression readings will return to the true (normal) reading for that cylinder(s).

 

[RBuch1974]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

Hey guys,

Just an update...
Thanks again for all the advice. Tore powerhead down and what I believe I was feeling (the bump) was some corrosion on the cylinder wall. Nothing seemed too pitted or of any real concern. Everything else seemed nice and tight with no large amount of slop. A little bit of honing should fix. But, took the powerhead off and it goes to the machine shop tomorrow. Broke off about a dozen bolts tearing down. Only one head bolt broke below the surface (very hard bolt too, my center drill hardly cut a dimple in it), got the rest of the broken bolts out with no issue by scraping the base of the threads and I used Royal Purple penetrant. Repeated a few times as I was working on other stuff before trying to remove. The machine shop will handle the other, for $15. I am pleased to say, everything else looked pretty good (so far). Will hopefully start assembling soon!

 

[Bosunsmate]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

sounds good, replace the rings on all of them if you can afford it

 

[emdsapmgr]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

The engine may not have been winterized prior to storage... How do the crank journals look-clean an shiny?

 

[RBuch1974]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

Last post on this, just a final update to give everyone an idea where things ended up. Machine shop is punching out two of the cylinders (.30) and recommended all new pistons/rings. Rust pitting too deep in 1 cyl to hone clean and other slight groove. Bearings, rods and crank checked out OK.

So with 4 pistons/rings, machining, new rod bolts, honing, full gasket kit, removing 2 busted bolts (forgot @ 1 in previous post), cleaning and disassemble/reassemble short block brought me to 700 clams.

Stay tuned for more new threads. Thanks again!

 

[ib18]

Re: New Used Johnson 90- Reassemble As-Is or Tear Down?

you are very lucky. I am rebuilding a mercury 90 hp but block was ruined by the machine shop. So, $500 just to buy a new block, pistons. rings. etc.

I also picked up a Johnson 90hp 1982 as well, J90MLCNB. So, I just mounted the johnson to my boat and trying to connect the wire now.