1990 Johnson 90 hp throttle arm question and starboard cylinder head too warm

oldboat1

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Head gaskets are pretty hardy, and should survive installation and test running without much risk. If mine, I would consider using some lapping compound to clean up the discolored areas in the bores, then resurface the heads and install the new gaskets. I would use the existing bolts in that fresh water motor. Torque to specs, and test run in a tank deep enough to cover the pump by six inches or so. After idling a bit, check temps -- if in the 140-150F range or below, I would conclude the t.stats were doing their job. Retorque after a couple of heating and cooling cycles.

Measure the bores, as mentioned, and post the findings. Beyond possibly replacing t.stats, though, and correcting that small leak at the exhaust cover, I think at this point you might have a good runner.

All IMO, of course.
 

havoc_squad

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Just to clarify, I am just replacing head bolts that have too much corrosion on them and re using the rest since they should not be TTY bolts.

One concern while I wait for circumstances to get the accessible part of the clyinders measured, is very small debris captured by the piston rings.

I seen a video of a scored cylinder possibly due to debris caught by the rings when a customer changed head gasket.

Other than wiping good to pull the debris outside the cylinder when debris falls on the cylinder wall before the pistons move and ensuring mating surfaces are cleaned before re installing the head, is anything else just being obsessive/compulsive?

I do know if debris does get lodged in the rings, the only way to fix is the powerhead comes apart.
 
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havoc_squad

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Information update.

From where I live, there is not a single place recommended nearby that I can drop it off to get cylinders mic'd. Anything suggested that is good/recommended is probably a 2 hour drive or more on a business day.

Everyone I speak to says the engine machine shops nearby here are not worth requesting any of their services.

If its getting checked, the powerhead probably would have to be pulled, stripped down, and shipped.

From speaking with most of the service managers who are also master Merc/OMC techs looking the cylinder photos I had, they say to just clean up the surface rust, deal with the leaking gaskets, and if it has good even compression, run it.


Now, onto the other details:

I got the exhaust cover off without too much drama, but the actual exhaust manifold is a real bear. I can only get some leverage at the top left corner, but the manifold and gasket surface doesn't want to spread in releasing. I'm trying to avoid doing too much prying in one spot but I can't get any starting point anywhere else far enough to get it to pry off.

Any suggestions on getting the exhaust manifold off? Get a bunch of tiny flat screwdrivers and wedge it out?

Also, is there a way to tell the difference between powerhead bottom/base gasket leaking at the stern and the bottom of the exhaust manifold gasket leaking?

Regarding the thermostat, that infamous relief hole on the valve body was 100% clogged for a freshwater motor. If flushing isn't regularly done, that thermostat valve body will be the arch enemy of whoever owns a V4 crossflow.

I put the thermostats in my ultrasonic cleaner and warmed up the temp gradually. At 150 degrees F, the thermostat opened a small amount. At 160 to 165 degrees F, it appeared the thermostat was fully opened.

They don't look terrible and appear to be working, but I'd rather not have to deal with crossflow V4 thermostat fun again. Any reason to replace the poppet valve, grommet, or spring if nothing appears cracked, brittle, or too weak?
 

oldboat1

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The cylinder heads should come off with a little gentle prying -- might try a rubber mallet to loosen. Thermostats should be 143F (5005440 for oem, 18-3543 for Sierra). IMO, the advice you received makes sense ("From speaking with most of the service managers who are also master Merc/OMC techs looking the cylinder photos I had, they say to just clean up the surface rust, deal with the leaking gaskets, and if it has good even compression, run it.") I would add, use a thin blade and scrape out the water passages you can reach when the heads are off.
 

havoc_squad

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Oldboat----I think the cylinder heads are off !

Technically the heads are loosely bolted back on, but the exhaust plate/manifold is still on there really good.

There is a service proceedure for mis-reading a written description of a problem.

The steps are below:

Step 1, verify hot coffee is ready.
Step 2, consume 1 cup of it
Step 3, read problem description
Step 4, follow up
Step5, if your reply indicates lack of alertness and focus, repeat steps 1 through 4.
Otherwise if your reply is now correct, then proceed to step 6
Step 6, discreetly facepalm the moment.
 

havoc_squad

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Yay, victory over the exhaust manifold. No serious whacking required, but it did require me to buy one of those heavy duty prying scrapers that has a bend angle.

Now for the questions and possibly undesired answers I'll get.

I have two key questions:

1. Does there appear to be any damage/issue with the following area circled on the photo below, or is this just an aluminum casting imperfection?

2. I remember reading another forum topic that reported piston rings sticking when he had to take off an exhaust manifold for a 150 HP crossflow. The port sides on my outboard piston rings (#2, #4) are all perfect and wonderful, the starboard side piston rings (#1, #3) on the top ring and bottom ring are stuck. The piston sides look as normal and usual as expected and I don't see any visible carbon buildup around the piston ring groove.

Is this another situation of powerhead separation required to remove piston and clean the ring grooves? Or should I try doing a OMC engine power tune can procedure first, and then check it via the bypass cover to see if it is bad enough to require piston ring removal?
 

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havoc_squad

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Status update, obtained all parts for pulling powerhead except for cherry picker.

I can get a 2 ton one local with 1000 pound limit on the longest setting. More capacity than needed is always better for lifting.

Planning about a week from now to grab cherry picker and get to work.

I have a flywheel turning tool for the flywheel nut after powerhead is pulled off the motor.

Is there any tools and procedures recommended for the following situations:

1. Getting stubborn powerhead off midsection when all bolts and nuts for mounting are verified to be off and lower unit is off.

2. Driving out the wedge pins that hold the powerhead halves together.

3. Storage/care of crankshaft when removed from its seat on the block.

4. Best/most DIY method to mark cylinder number for piston.

If any dissaembly steps need to be emphasized other than bag & tag for this model, please post them.

Regarding re-assembly:

What is the standard procedure for top and bottom crankshaft seals and crankshaft O rings? Replace both if over 5-10 hours run time since last replacement? The obvious would be of course if a leak was found or if signs of wear were present.

The intent of my question was to determine how accurate the OEM manual is on which crankshaft seals must be replaced every time the powerhead comes apart.
 

racerone

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Dec 28, 2013
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I put one scribe line on #1 connecting rod cap.---2 on #2 rod cap and 3 lines on # 3 rod cap.-----That is the only marks I need to make on a V-4 like that.-----The 6 crankshaft sealing rings are cast iron.----The top and bottom crankshaft seals will last up to 2000 hrs. or more.----How many powerhead bolts / fasteners do you have off now.-----Is it 4 nuts, 2 short bolts , 6 long bolts and 2 short 1/4 bolts that hold the cowling ?
 

havoc_squad

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Have not started work yet on removal or loosening of bolts. Won't have time until next week as mentioned in recent status update.

I am guessing from memory that it is the 4 or 6 long bolts on port/starboard and two small nuts from double side threaded bolts screwed into the powerhead.

I don't have my manual nearby to see what is specified in OEM manual, is permatex aviation form a gasket fine for non-slick/non-oily corrosion protection on those powerhead mounting bolt threads?
 

havoc_squad

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Short status update, the powerhead is now off in my garage and sitting vertical on first a large sheed of cardboard with a regular (not treated) sheet of plywood on top of a disposed of wooden pallet specially made for products delivered at my work.

I was warned about and had already bought some nuts for the rear powerhead studs to back them out. Those came out easy.

However, when I attempted to do the front studs, they seem to refuse to move. I tried the double bolts method on both of them once and failed.

I didn't try it again because I wanted to get more info about those and not mess them up unless there's no other way/method to get them out.



Powerhead is wrapped with plastic to keep humidity, bugs, dust, dirt, etc. away since there is no engine cover.

Here are my questions:

1. The front threaded studs, do I need to worry about getting them out. If so, what techniques are used on more stubborn studs?

2. The rubber seal on the outside of the driveshaft coupler, is there any issue/danger to that seal failing while the powerhead is standing veritically?

3. When slowly and very gently lowering the powerhead, I did not recognize the shift arm was vertical and the motor was lowered down on all contact points, which some of that weight ended up on that shift arm.

Most of the weight did go towards/leaned towards the rear of the powerhead and nothing was brute forced or "dropped".

How durable are those shift arms from being bent/distorted and is there a way to tell if it is damaged? I didn't notice anything in it's movement or shape that indicated issues.

4. What is the best tool to use to drive out the taper pins? Looking at the service manual, the punches used don't look that the normal ones that I could go to NAPA, O'Reily, Autozone, etc. to drive them out.

I just don't remember seeing any punches that long and big of diameter.

If I got to buy online to get the right part, that's fine. Just don't want to buy a collection of punches I won't be using.


As for the saying, it never happened if there's no pics. Tommorow when things settle down I'll post a photo of a midsection with no engine and the powerhead on the pallet.

As for when I get to the disassembly, the next time I get time to focus on it. At least now it can be an "indoor" project.

That will be flywheel puller time and using a flywheel turning tool. I'd rather not bugger up my flywheel magnets with an impact gun.
 

havoc_squad

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Any answers to my numbered questions?

Regarding taper pins of the powerhead body, do they just get pushed in flush to free it up or all the way out?

I don't remember the manual saying this detail.

Going to start dissaembly this weekend and I'd like to resolve as much unknowns as I can.
 

havoc_squad

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Mar 5, 2011
Messages
694
Status update, powehead is now completely apart.

Other than small amounts of minor surface rust caused by air condensation on non critcal areas of the crankshaft and the piston oil rings sticking on certain pistons.

No obvious signs of scoring on the pistons.

No rust or serious wear was seen on surfaces where bearings are.

Cylinder measurements will be posted later, trying to decide which manufacturer and combo I should choose for bore mic based on best value for the performance.

Any suggestions, as I would like to avoid paying stupid ridiculous markup like Snap On charges for some of their brand name tools that are no better than premium models at Harbor Freight. (Example, Floor jacks)

Additionally other important stuff has diverted my focus right now so the mic numbers are probably 1.5 weeks out.

Crankshaft overview video: https://youtu.be/gC_4tcxQIDI

Cylinder overview video: https://youtu.be/vetBy_feme8

Piston #1 video: https://youtu.be/ltmnd8UZNPg

Piston #2 video: https://youtu.be/W0-3peKjo6M

Piston #3 video: https://youtu.be/4oTYQrWfYJc

Piston #4 video: https://youtu.be/fRoMxoHAN-o

Expert opinions welcomed.
 
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