Heavily rusted engine mount-what caused? with pictures

[jim dozier]

I recently acquired a 97-115hp Evinrude60 degree V4. The engine appears to be in good shape with good compression. I am doing some routine maintenance (water pump, etc.)on it prior to rigging it on my boat and replacing the existing engine. When I removed the lower cowling to do some minor ding repair I noticed a rust stain on the lower leg that led me to notice the engine mount that the steering arm is bolted to is badly rusted. The steering arm itself is in pristine condition. It is attached by 2 large bolts to a steel forging that is attached beneath the powerhead. The steel mount is covered in rubber and the rubber has split from the expanding rust. I'll try to post a picture if I can bring home a digital camera. When I chipped away the loose rust and scale I could see that the damage was significant on the port side and probably not significant on the starboard side. As this is how the boat is steered I am leaning towards replacement. This requires removal of the powerehead on an otherwise decent engine <br /><br />The real reason for this long winded posting is WHY did this mount rust so bad. Nothing else on the engine is corroded. Has this been a problem on other similar engines or is this indicative of some other problem such as a leaking powerhead gasket? I guess I'll find out when I pull the powerhead but if anyone has some input on this I like to know in advance. I am currently waiting on the OMC service manual I ordered.

 

[alcan]

Re: Heavily rusted engine mount-what caused? with pictures

Hi jimd<br />It is hard to say exactly how bad your problem is with out seeing it. Most all outboards tend to develope rust in this area. Most of the time this rust is just supperfacial. It looks worse that it really is. This area is exposed to water splashing about and is for the most part out of site. Most folks do not wash and rinse this area vary well or often. The steering arm is one of the few pieces that is made of steel type metal. Most folks will greese the swivel pin (shaft) and greese it well and often. This tends to build up excess greese in the area. This greese tends to trap moisture which promotes galvonic corrosion. In your case this part was coated with rubber,plastic,paint,etc. Moisture got under the coating and was trapped. I do not recall ever having to replace this mount part do to corrosion. I don't think I'd worry about it unless it was 50% gone. Galvonic corrosion will attack certian parts and not bother others. This rust on your motor is no indication as to the condition of the rest of the unit. There are many ways to limit galvonic corrosion. It would be impossible for me to say exactly what will work for your conditions (all are a little different). Some easy hints might be to clean excess greese,wash and flush more often, disconnect batteries when moored (trailerd/stored). You may need to develope or up-grade a bonding system.

 

[llfish]

Re: Heavily rusted engine mount-what caused? with pictures

Could also be a lower grade of metal. Out side of engineering spec. for that part.

 

[jim dozier]

Re: Heavily rusted engine mount-what caused? with pictures

I hope to have a picture tommorow. This particular part is a large forging that extends like a threaded tube towards the steering arm. The threaded tube is about 1" in diameter with a large long bolt from the steering arm threaded into it about 1.5". There is one on each side going to the steering arm (2 bolts). The steering arm itself is not corroded at all. Neither is anything else. Just this stupid hard to get to mount. Alas the port mount appears to have lost more than 50%. The diameter is rusted down to slightly more than the bolt diameter which I am assuming by the head to be a 1/2" bolt. My guess is that when I try to remove port side bolt from the steering arm the sucker is going to collapse and break off the mount. I am worried that there may be a leak beneath the powerhead that has contributed to the localized rusting. The starboard side shows signs of rust beneath the rubber cover but not nearly as bad. If they were both like the starboard side I would just leave it alone. If they were both like the port side I believe the steering arm would have broken off already.Hhheeelllpp.

 

[jim dozier]

Re: Heavily rusted engine mount-what caused? with pictures

Here is a picture of the port side that is the more rusted mount. I have removed quite a bit of the loose rust scale that was clinging to the rubber.<br />

<br /><br />The second picture is the starboard side which is less rusted<br />

 

[R.Johnson]

Re: Heavily rusted engine mount-what caused? with pictures

It makes we wonder if this is a case of a bad ground between the main engine case, and the mounting bracket, note the ground strap in the last picture. I have never dealt with salt water engines, so this is just a quess. It reminds me of some sort of electrolysis action.

 

[alcan]

Re: Heavily rusted engine mount-what caused? with pictures

Hi jimd<br /><br /> Sorry, from these pictures, I still do not see any damage worth the trouble to replace. I think I might just clean this up a bit so it will drain moisture and paint it. I do not think there is any way to get this rust stopped. I can,t say for sure, but I,ll bet that the motor will wear out long before that mount breaks. Have you priced that part? The good news is, if you decide to replace this, you will have an exellent idea as to the condition and intimate knowlage of your outboard (not a bad deal).

 

[walleyehed]

Re: Heavily rusted engine mount-what caused? with pictures

I'm gaining experience "slowly" on salt-water engines, and I see this on about every one that has a few years of age on it. After about 10yrs, this is common sight on freshwater engines at times. There may be something speeding the process, but this area in paticular seems to be a common starting point...why?? I can't answer that. My '97 115 was the same way when I bought it with a stuck piston. I tore it clear down and actually removed all of the loose corrosion I could, and it really didn't look so bad after it was cleaned up and repainted. The bonding straps help, but I don't believe they are large enough to carry a true bond of metals.

 

[umblecumbuz]

Re: Heavily rusted engine mount-what caused? with pictures

Hi Jimd,<br /><br />I'm making a guess or two here. <br /><br />This does look like galvanic action, coupled with neglect. Salt water is often corrosive by its very nature, so anything hidden under rubber, for instance, gets overlooked. Add in a few hot days and you have a little humid cauldron in there - especially as you also have dissimilar metals in contact with the rusty part - I see stainless bolts, for instance. If the previous owner had neglected his zincs, your casting would be doing the job instead - ie. it would become the 'sacrificial' component. <br /><br />It may even be probable that the motor ran a stainless prop. If the prop had been aluminum and the anodes had been neglected, the prop would probably have corroded first - a kind of early warning.<br /><br />Sometimes grease will act as an isolator, and then galvanic action is limited to those metals within the grease in direct contact with each other.<br /><br />Two lessons here of course - use the right anodes for your water conditions (they can vary from zinc, through magnesium, through aluminum, or any mixture of those, plus other trace metals) and keep them in good shape, and second - never cover or isolate any metal component so that it cannot be easily seen, or so that it could form its own unseen and unprotected galvanic circuit. <br /><br />I know this doesn't help fix your rust, but it might alert a few others new to the forum.<br /><br />Ciao

 

[Solittle]

Re: Heavily rusted engine mount-what caused? with pictures

You have more going on than normal salt water rust. I have been running outboards in salt water for over 30 years and I have never seen one like yours.

 

[jim dozier]

Re: Heavily rusted engine mount-what caused? with pictures

SoLittle, that what has me wondering. There doesn't appear to be corrosion going on elsewhere. The engine block, bolts, lower unit, and ancilliary equipment aren't rusted, just these stupid mounts. I am wondering if there is a leak underneath the powerhead spewing salt water on the mount constantly. When I get it running I plan to look carefully for leaks there.

 

[Tinkerer]

Re: Heavily rusted engine mount-what caused? with pictures

Maybe you're looking in the wrong place for the source of the problem.<br /><br />I've never had a motor made after about the mid 70's. The ten or so motors I've had have all run in salt water for three to five decades. None of them have anything remotely like this.<br /><br />I'm wondering if this is another case of modern production using inferior materials to save money.

 

[umblecumbuz]

Re: Heavily rusted engine mount-what caused? with pictures

So you've got three differing experiences here. <br /><br />I've come down on the side of localised galvanic corrosion, but as Walleyhead said:

I see this on about every one that has a few years of age on it

and as Solittle says:

I have been running outboards in salt water for over 30 years and I have never seen one like yours.

I can't buy the 'it's got corroded because it's splashed with salt water' suggestion. Boats running in salt water are splashed and more all the time, and corrosion like yours is not a normal result.<br /><br />This galvanic corrosion throws up mysteries still. It's not yet an exact science, and there's a lot more to learn. Having thought about your problem further, I can't find anything that would make me alter my opinion. I have seen localised severe corrosion like this before, and it was halted by cleanliness, bonding and careful anode sizing and placement. Yours fits my own limited experience, operating in one of the warmest, saltiest seas on earth.<br /><br />Be very interested to find out what you discover if you strip it down.<br /><br />Ciao

 

[phatmanmike]

Re: Heavily rusted engine mount-what caused? with pictures

jim, these guys are dead on. being from florida also, on the gulf, i have motors from the 60's and 70's and newer too, but NONE look like this, and they are salt water exclusive.<br /><br />

I'm wondering if this is another case of modern production using inferior materials to save money

sounds like a combonation of these two quotes to me <br />

The bonding straps help, but I don't believe they are large enough to carry a true bond of metals. <br />

have you read the new FAQ, there is a peice about corrosion and what metals cause what.<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000031

 

[jim dozier]

Re: Heavily rusted engine mount-what caused? with pictures

I am familiar with the galvanic corrosion process. From what I know I would expect the aluminum parts to be the first to go and not the steel as aluminum is less noble than steel. However, the stainless steel cable ground strap visible in the photo was not connected at the end when I got it so I suppose anything is possible. I guess its just a decision I'll have to make whether to watch it and wait or fix it.

 

[Dhadley]

Re: Heavily rusted engine mount-what caused? with pictures

Thats pretty standard looking for a 60 degree motor in a saltwater environment. My 1993 150 6V6 looks just like that -- my bolts may be a tad better but its basically the same. The upper mounts in a 60 degree are a little easier to see than on a crossflow or 90 degree looper. Just keep an eye on it. Just check the bolts to make sure they're tight.

 

[umblecumbuz]

Re: Heavily rusted engine mount-what caused? with pictures

Hi Jimd,<br /><br />You may just have solved your own problem. You say

the stainless steel cable ground strap visible in the photo was not connected at the end when I got it

If that was a long-standing situation, and the grease/paint/rubber covered or isolated the casting, which would also allow it to remain damp underneath, you have a classic self-contained corrosion circuit. Stainless bolts will accelerate corrosion in 'weaker' metals, especially around their area of contact.<br /><br />I've plugged this mantra for yonks. We tend to think 'I'm OK - I've got stainless this or that - I'm free from corrosion problems.' Not so - if stainless does not have its own anodes, it can hasten corrosion on any weaker metals in contact or proximity. If you've got a below-par casting there, withot a bonding strap, isolated in company with stainless, and long-term salty wet, you've got an ideal meal for the galvanobug.<br /><br />Ciao

 

[Solittle]

Re: Heavily rusted engine mount-what caused? with pictures

galvanobug - - Neat!!!!