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1990 175 VRO 90deg V6 O/heated badly, new to outboard engines lots of questions!

A

Avanti

New member
So I am new to outboards but am very experienced in heavy equipment repair, so I figure much of it will be the same but on a smaller scale. So it really over heated today and stalled out on us, engine had a new impeller fitted, it had the oil level alarm going off prior to the failure but still has oil, the port head lower 2 cylinders were extremely hot, melted the coils and a couple of wires that touched that head, prior to this it ran extremely well.

I go it home and figured to pull the port head - cylinders look good, the lower two head chambers were extremely clean - water in the combustion chambers maybe???

the head bolts were loose when i removed them, it had a new port head gasket prior to purchasing it, do the heads need to be retensioned???

Could that have caused the failure??

there is a sensor at the top of the port head light brown single wire - was not connected, similar two wire one on starboard head - are they temp sensors???

there is also a magnet failure in the flywheel, I am yet to pull that off to see if there is any stator damage and replace the damaged parts,

Do the heads suffer with cracking or going soft?

Can I just replace the gaskets after cleaning the surfaces?

Will the thermostat require replacing or can they be tested?

What tension are the head bolts?

Any further advice would be appreciated.

Lastly does Yamaha share engine components with this engine or copy the engine design as I have seen a 200hp yamaha for sale, 90 degree v6 with what looks like identical heads and air intake.

http://i.ebayimg.com/00/s/MTIwMFgxNjAw/z/ia4AAOSw-W5Uw1hb/$_57.JPG
 
Check out the center area of this picture. You see the water deflector is distorted and is blocking the water flow.
The deflector is meant to keep water from going between the cylinders, and it should be positioned to allow water to go around the cylinders.
That water deflector is badly deformed, swollen, and out of place.
You likely have the same issue that caused the overheat. While you have the head off, check your deflectors out, and I would even go as far as to say repplace them, even if they look good.

20150115_212223.jpg


Get a factory service manual (OMC only).

The head bolts must be re-torqued after the engine comes up to temp. The torque will be in the neighborhood of 22-24 ft-lbs, but this is from memory, so get the figure from the books or another poster. Torque starting in the center, two passes, evenly as you would an auto engine.
Heads should not be cracked, etc, but might be warped. Use machinists straight edge, 0.003 is the max gap.
No sealant on the head gasket.
The disconnected wires are indeed the temp sensors.
Thermos can be tested in a pot of water...bring up to temp on stove and look for them to open. 142 is the temp when they open.

There are no parts that are the same from Yamaha to OMC.
 
Avanti said:
it really over heated today and stalled out on us, engine had a new impeller fitted, it had the oil level alarm going off prior to the failure but still has oil, the port head lower 2 cylinders were extremely hot, melted the coils and a couple of wires that touched that head.

the head bolts were loose when i removed them, it had a new port head gasket prior to purchasing it, do the heads need to be retensioned?? [The sealing surfaces of the block and the cylinder heads will require cleaning and a thorough inspection to make sure the surfaces are perfect. New head gaskets will be required.]

Could that have caused the failure?? [Lower unit picked up a plastic bag, cutting off the water flow... Water pump failed for some reason... powerhead water deflectors are swolen, stuck thermostats.]

there is a sensor at the top of the port head light brown single wire - was not connected, similar two wire one on starboard head - are they temp sensors??? [That's exactly what they are (tan wires - overheat sensors). With those disconnected, it would be impossible for the overheat warning to sound from the warning horn. The only knowledge you would receive of a overheated engine in such a case would be when the engine screeches and seizes to a grinding halt! The other wire of the two wire sensor pertains to the "fast start" feature of the engine... being disconnected causes that feature to be non functional.]

there is also a magnet failure in the flywheel, I am yet to pull that off to see if there is any stator damage and replace the damaged parts,[Evinrude/Johnson dealerships can provide you with a kit... replacement magnets and epoxy.]

Can I just replace the gaskets after cleaning the surfaces? [No, being overheated to that degree necessitates more than that simple gasket replacement.]

Will the thermostat require replacing or can they be tested? [Yes, absolutely (replacement!). Don't bother testing them though, just replace them and the other various parts you see in that thermostat area.]

What tension are the head bolts? [That would be 18 to 20 foot pounds, tightened in the following sequence where each number is a head bolt.]

13..14
9....10
5.....6
1.....2
4.....3
8.....7
12..11 [Starting at left center, then continuing on in an ever widing circle.]

Any further advice would be appreciated. [Strongly suggest you check with a trusted knowledgeable Evinrude/Johnson technician on various matters that may be foriegn to you... and also purchase a specific service manual for that engine... NOT a manual that covers a half dozen models that would confuse the majority of boaters.]

Lastly does Yamaha share engine components with this engine or copy the engine design as I have seen a 200hp yamaha for sale, 90 degree v6 with what looks like identical heads and air intake. [No, Yamaha copied their engine design from OMC which resulted in OMC suing Yamaha (OMC won). Although the parts look near identical, they are not enterchangable. Avoid the temptation to purchase that Yamaha.]

NOTE: Check and tighten all bolts, screws, nuts, associated with that powerhead. Being overheated to that extent would cause everyone of them to loosen.
Click to expand...

Frankly, it sounds like someone saw you coming as the saying goes and took full advantage of your ignorance of the outboard design... no offense intended.


 
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daselbee said:
Check out the center area of this picture. You see the water deflector is distorted and is blocking the water flow.
The deflector is meant to keep water from going between the cylinders, and it should be positioned to allow water to go around the cylinders.
That water deflector is badly deformed, swollen, and out of place.
You likely have the same issue that caused the overheat. While you have the head off, check your deflectors out, and I would even go as far as to say repplace them, even if they look good.

20150115_212223.jpg


Get a factory service manual (OMC only).

The head bolts must be re-torqued after the engine comes up to temp. The torque will be in the neighborhood of 22-24 ft-lbs, but this is from memory, so get the figure from the books or another poster. Torque starting in the center, two passes, evenly as you would an auto engine.
Heads should not be cracked, etc, but might be warped. Use machinists straight edge, 0.003 is the max gap.
No sealant on the head gasket.
The disconnected wires are indeed the temp sensors.
Thermos can be tested in a pot of water...bring up to temp on stove and look for them to open. 142 is the temp when they open.

There are no parts that are the same from Yamaha to OMC.
Click to expand...


So if the deflectors are out of place where should they be and what should they look like? Mine look just like those in the pic, thank you.
 
joereeves said:
Frankly, it sounds like someone saw you coming as the saying goes and took full advantage of your ignorance of the outboard design... no offense intended.
Click to expand...


Thanks for the response and the honesty, I purchased the boat at a price which was well below the value of the hull and the trailer, most people have estimated the boat's value at 100% - 150% more than what I paid, the previous owner told me about the history of that engine and was very honest about the use and how long it had been in service for etc, I wasn't aware of the poor design and I'm guessing that he didn't either because this is the first time I have heard of this even though I have spoken to a couple of Boat workshops. I'm still happy with my purchase and may at a later date update the engine.
 
That should be a big bore 175 with humpback exhaust. Check the cylinders really good as the sleeve are extremely thin and bad about turning and coming loose from aluminum casting or cracking in exhaust ports when overheated...
 
Avanti said:
Thanks for the response and the honesty, I purchased the boat at a price which was well below the value of the hull and the trailer, the previous owner told me about the history of that engine and was very honest about the use and how long it had been in service for etc, I wasn't aware of the poor design I'm still happy with my purchase.
Click to expand...

Your later explanation of the purchase puts a totally different light on the matter... apparently a honest seller and an advised buyer. Glad to hear that. However, the design is a good one... it becomes a bad one when the safety features are bypassed. Wish you luck on your future decision.
 
Thankyou to all that gave their advice, it's back together and running well, no further signs of overheating, no damage to the bores etc, replaced 3 magnets and the stator, removed both heads and found all of the deflectors were swollen blocking the coolant flow, replaced them all, replaced both thermostats, both had their centers removed so didn't work, replaced head gaskets, replaced 3 coils, I just need to check timing advance etc.

One issue I did encounter was the availability of gaskets, I know there is a capacity difference between the 150 and the 175 and everywhere I looked was not listing the head gaskets as available for the 175, I believe the gaskets I purchased are ones for the 150 as they are a slightly smaller bore, the protruding crown of the piston actually hits the gaskets and once clamped in place and turned over the pistons worked their way through the edge of the gasket, shaping it into place, it hasn't affected it's performance.

I still need to sort out the tacho, which won't be difficult, apart from syncronizing the carbs, base timing, timing advance and checking it gets full throttle, are there any other adjustments that can be made for tuning / performance?
 
Except they list the same head gasket for the 150 as the 175, there is only one available and they won't ship the parts on this site to me.
 
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