1995 Johnson 175's

[268_Grady]

Recently purchased a boat w/twin 1995 Johnson 175's
\Model #'s: J175EXEOM and J175NXEOM.
Any things I should look out for?

See Compression below

Port

Cyl	Comp	Cyl	Comp
2	95	1	95
4	95	3	88
6	85	5	80

Stb

Cyl	Comp	Cyl	Comp
2	100	1	115
4	100	3	105
6	90	5	96

[Joe Reeves]

Normally, it's been my experience that on the late model engines of my time (retired in 1991) in the new V$/V6/V8 class, the compression would be 90 psi on the starboard bank and 95 psi on the port bank due to the engine design... Never did get a straight answer from any rep.

Now, your engines..............

Port engine = 15 psi difference between the highest & lowest cylinder. Cylinders 3 & 5 could be failing due to related fouled carburetors running lean (piston scoring), or possibly a head gasket (if so equipped) could be failing between cylinders... OR... if no gasket but rather sealing "O" Rings... unlikely two O Rings would fail in the same manner... BUT... if overheated at some time, loose bolts would allow leakage. At any rate, you want to keep your eye on those two cylinders. If it were me, I'd remove the cylinder head for an inspection of #3 & #5.

Starboard engine: Compression seems high on a few cylinders (same compression gauge?). The psi numbers just don't come across as normal as compared to engines of the past (in my case). However, there is a 25 psi difference between the highest and lowest cylinder here... and that's not good at all. Perhaps the readings are wrong? On this one, again if it were me, I'd be removing both cylinder heads for an inspection. Fouled carburetors causing a lean running engine are always subject if so equipped.

Check the ignition/spark with all spark plugs removed so as to obtain the highest cranking speed. The spark should jump a air gap of 7/16" with a strong blue lightning like flame... a real SNAP! Does it?

No tester? See the following:
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(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

This can obviously be modified to a 6 or 8 cylinder setup tester.
********************

[268_Grady]

These tests were conducted on land at the marina the boat was in when I inspected it.
The engines were not properly warmed up (not cold) and the throttles were not at WOT.
I just wanted to get a general sense of the health......I saw the low cylinders and the large difference in numbers.
I was of the opinion the engines were usable and probably need a carb rebuild (X12!), change the T-Stats, filters, impellers, lower gear lube, etc, and be run a bit; then check the compression again.
If need be would it be worth replacing the power heads w/ reman'd ones? Any recommendations of suppliers?
What about fuel consumption? How will the fuel usage of these OB's compare to a SBC Mercruiser 350 Mag?

[268_Grady]

Brought the boat home today........new to this for, looking for guidance.
Shouls I start a new thread as my questions come up or continue w/ this one?
TIA!

[Joe Reeves]

For the time being, continue with this thread. I retired in 1991 so your 1995 may be a little foreign to me in its design. The engines normally do not change much thru a few years but there always comes a day when the engineers come up with more sophisticated components that I may not comprehend... but I'll do what I can. Should I encounter something I'm not familiar with, I'll turn you over to "Boat.net" of this site and hopefully someone who hasn't retired yet.

[268_Grady]

Thanks Joe,
I ran both engines when I got home. Noticed (2) things:
1) single beep every 30-40 seconds low oil?
2) gas leak, need to locate source: can I run the engine w/o the air box?

[Joe Reeves]

Beep constant & steady = Overheating or Fuel Restriction.
Beep every other second = No oil at oil pump.
Beep every 30/40 seconds = Low oil level (Normally down to 1/4 tank)

On a crossflow engine, the carburetor face plate removed makes no difference in the engine's performance.

On a loop charged engine, the heavier face plate has a thick rubberized gasket within it that in effect causes a air flow restriction that if the face plate with that gasket is removed... all of the carburetors run slightly lean. In my time at the bench (1960-1991) this resulted in a condition that also affected the crankcase pressure that operated the fuel pump. The end result was that the engine acted as if it was running out of fuel, slowed down and died.

However, this condition may have been corrected, but if not, running without the face plate for test purposes isn't going to hurt anything... to run that way for a month may be another story. I just wanted you to be aware of the "slow down & dying out" possible condition and the cause.

[268_Grady]

Got it thanks. I think these engines are loopers? They ste 60* blocks.
will reply with results when available.

[Joe Reeves]

Got it thanks. I think these engines are loopers? They ste 60* blocks.
will reply with results when available.

Easy way to tell..... Crossflow has 3 aluminum carburetors.... loopers have 6 plastic ones.

[268_Grady]

Definitely loopers then....6 carbs each!
Let me also say I ordered a Factory Service Manual.

1) Added oil to both oil tanks.......still got the Low Oil Warning beep. I'm assuming the sensor is in the tank. how can I T/S?


2) Found the top port carb leaking pretty badly......heard about these bowls warping.
Thinking I may as well rebuild all (12) since I don't really know the history. Your thoughts?
Do you think it would be a good idea to remove and disassemble the "VRO" pump for inspection while I'm at it?

3) Please see the following video of the water exiting the engine, specifically where my finger is pointing........is this normal?
https://youtu.be/5uMRfiAJWcE

[Joe Reeves]

Smart move... Purchasing service manual, especially a factory manual covering one specific engine.

Testing the oil tank electronics... easiest way is to have the oil level lower than the 1/4 level... beep should occur every 20 or 40 seconds, depending if it's a early design tank or later model... AND... then add oil to at least 1/2 tank whereas no beep should occur..

The water leakage area you point to is a metal to metal surface and that leakage is normal after a lower unit repair or water pump replacement. It normally fills in with marine debris fairly quick... and the only time it seems to leak is when it's out of the water. If it bothers you,... you can drop the unit 1/4" or so without hurting anything and install l he following sealer (real sticky stuff). Comes in a tube, easy to apply.

OMC Adhesive is now Bombardier 3M Product #847 and may be listed as Scotchgrip 847, part number 776964

[268_Grady]

Thanks Joe...think I will continue w/ my numbering system for my questions if that makes sense...

1) Oil tanks are close to 3/4 full, gauges are operational.

Any other hints on T/S here?

2) What are your thoughts on the leaky carb issue as stated above? Should I rebuild all 12 (Twins)? VRP Pump maintenance?

3) Good to know water leakage at those spots is OK, water pressure gauges seem to be operational.

Going to add another question:

4) Both engines appear not to be charging, One reads (@ the battery) ~ 12.0V either at idle or 1500RPM's; the other increases to maybe 12.2V at 1500RPM's (Note: separate batteries for engines). Possible bad rectifiers? Can they get damaged by charging w/ external charger?

Thanks again.........Tony

[268_Grady]

Thanks Joe...think I will continue w/ my numbering system for my questions if that makes sense...

1) Oil tanks are close to 3/4 full, gauges are operational.
Any other hints on T/S here?

2) What are your thoughts on the leaky carb issue as stated above? Should I rebuild all 12 (Twins)? VRP Pump maintenance?

3) Good to know water leakage at those spots is OK, water pressure gauges seem to be operational.

Going to add another question:

4) Both engines appear not to be charging, One reads (@ the battery) ~ 12.0V either at idle or 1500RPM's; the other increases to maybe 12.2V at 1500RPM's (Note: separate batteries for engines). Possible bad rectifiers? Can they get damaged by charging w/ external charger?

Thanks again.........Tony

[Joe Reeves]

1 - The wires leading from the oil tank have always looked like lamp-cord. I'd suggest looking for that lamp-cord at the powerhead... one will be connected to a TAN sensor wire, the other will simply lead to a powerhead ground. Disconnect either wire (the easiest) while the oil tank warning is beeping every 40 seconds. If the beeping stops, then obviously the tank electronics is flawed. A flaw that one can live with as long as one keeps track of the oil level.

2 - The leaky carbs of course need reworking.... the rest? There's that old saying "If it ain't broke, don't fix it!" If the engines are firing on all six cylinders each at all rpms, I'd wait but that's me... you'll need to make that judgement call to clean/rebuild all 12.

To determine if all are firing at idle, simply have the engine running and do a "Drop Test"... when pulling a spark wire off (6), you should get the same rpm drop on each cylinder. At full throttle while underway, cylinder firing would be judged by general performance, the desired rpm, that sort of thing.

3 - Yeah, that metal to metal leakage area (top of gearcase)... that's a question I hear many times a month. Normal & hurts nothing.

4 - OMC came out with a method of testing those things that was (IMHO) so complex and confusing that I devised my own test since any flaw in that regulator/rectifier assembly interfered with a tachometers operation..... as below:

Charging batteries will not cause harm to the regulator/rectifier assemblies UNLESS the charger is hooked up backwards. However, although it's not necessary, it's best to turn the battery switches to OFF if they exist.

********************
(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

However.... those water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

NOTE: For the later models that DO NOT incorporate a wiring terminal strip, splicing into the "Yellow Wire" mentioned will be necessary.

Normally the Gray wire leading from the tachometer is attached at the terminal strip to another Gray wire which leads from the water cooled voltage regulator/rectifier...... remove the gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.
********************

In reading back thru your notes, it appears that both tachometers are functional... that may be because (possibly) the tachometers were acting up and the above test was made by the previous owner who left the gray tachometer wire attached directly to the stator wire as listed in red above.

If the gray tachometer sensor wire is already spliced into the yellow stator lead, the previous owner would be to blame as he would have left them connected in that manner to have the tachometers functional... and to avoid replacing the two regulator/rectifier assemblies.

Hopefully my typing is okay here... I get migraines (w/o the pain) in the form of a technicolor lightning storm in my head that practically blinds me... got a beaut about 3 minutes into this. ... one hellava lightning storm!

[268_Grady]

First, let me say thank you for taking the time to write these answers..........greatly appreciated!

1) Understood, will look into further when time allows. Is the sensor in the oil tank just a open or closed connection or more of a potentiometer effect like a fuel tank sensor?

2) Will confirm cylinder drop test. Will advise when results are available.

4) I failed to mention that the stb tach was not working. I may have a tach from a I/O engine.......will that work for T/S? I will try that when I find the tach. Hope it's not the rectifier......not a cheap part! What do you think of my voltage readings? Port engine increased to ~12.2V at 1500 RPM.....is that corr

Thank you again! Hope your migraine has subsided.......I sometimes get ocular migraines.....causes tunnel vision!