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Author Topic:   Eng mount bolts corroded/jammed in '66 16'

Gene in NC posted 06-02-2003 10:48 PM ET (US)
Original aluminum engine mount bolts for 100 Johnson are corroded/jammed in transom. Lower bolts have exposed heads but uppers recessed in eng mount. First lower nut off OK, but second wrung off as did heads of lower bolts and upper bolts. Good lower bolt would not budge to 4 lb hammer. Obvious that driving with drift pin will prob cause mushrooming.
Classic solution to drill out. Chem engineer recommends muriatic acid (75% hydrochloric + 25% I forget) followed by household amonia to neutralize.
Acid will attack corrosion and the alum. Will test alum for reaction before trying. Some alum alloy plenty hard. These bolts took lotsa torque before breking.
Experience/recommendations?
DanT posted 06-03-2003 08:20 AM ET (US)
Gene, I faced the same problem when I removed the original 100hp Evinrude from my 1966 Eastport. After I snapped the first lower aluminum bolt I realized they weren't going to be easily removed. I would recommend you remove the motor from the transom independently of the brackets. This will give you more room to work. The motor is attached to the brackets by two bolts which are located on the side of the left and right brackets near the top. With the motor removed you will be left with the two brackets attached to the transom. I shielded the transom and applied heat from a hand held propane torch to soften the sealant they used on these bolts. I was able to drive the bolts out by protecting the exposed end with a block of wood and hitting it with a hammer. The one bolt that I broke was removed by hitting the end with a similar size steel bolt after applying the heat. I think the the real key to getting them out is softening the sealant to allow some movement of the bolts.
Gene in NC posted 06-03-2003 07:35 PM ET (US)
Thanks, Dan T. Suspect this corrosion may be the same as that at the connection of steering cable sheath at the engine. Ed Sherman, in his excellent book on outboards, recommends heat and keeping the fitting hot while unscrewing. I can vouch for his method and the rehardening of the corrosion if allowed to cool. Heating a steel bolt will sometimes break the rust in the therads but it must be cooled before removing.
The reverse to remove corroded alum is counter intuitive but it works. I will report back. Will need to drive lower bolts to splash well and upper to rear.
Sal DiMercurio posted 06-04-2003 01:15 AM ET (US)
You better be super carefull when using heat, as you can scorch the booat real easy.
I prefer cutting the head off the bolt & driving out with another bolt of the same size, ....hit it hard enough & it will break loose.
Have someone grab the other side of the bolt with vise grips & pull as you whack the headless side, it works.
No need to pull the engine off the bracket
Sal
Duckin Whalers posted 06-05-2003 12:40 PM ET (US)
I had the same problem when I took my merc. off of my 13'. I used a grinder to take the head off then drove the bolt through with small punch. One of the bolt heads broke when I tried removing it, that was the easiest one. I got replacement stainless steel from a local fastener store.

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Author	Topic: Eng mount bolts corroded/jammed in '66 16'
Gene in NC	posted 06-02-2003 10:48 PM ET (US) Original aluminum engine mount bolts for 100 Johnson are corroded/jammed in transom. Lower bolts have exposed heads but uppers recessed in eng mount. First lower nut off OK, but second wrung off as did heads of lower bolts and upper bolts. Good lower bolt would not budge to 4 lb hammer. Obvious that driving with drift pin will prob cause mushrooming. Classic solution to drill out. Chem engineer recommends muriatic acid (75% hydrochloric + 25% I forget) followed by household amonia to neutralize. Acid will attack corrosion and the alum. Will test alum for reaction before trying. Some alum alloy plenty hard. These bolts took lotsa torque before breking. Experience/recommendations?
DanT	posted 06-03-2003 08:20 AM ET (US) Gene, I faced the same problem when I removed the original 100hp Evinrude from my 1966 Eastport. After I snapped the first lower aluminum bolt I realized they weren't going to be easily removed. I would recommend you remove the motor from the transom independently of the brackets. This will give you more room to work. The motor is attached to the brackets by two bolts which are located on the side of the left and right brackets near the top. With the motor removed you will be left with the two brackets attached to the transom. I shielded the transom and applied heat from a hand held propane torch to soften the sealant they used on these bolts. I was able to drive the bolts out by protecting the exposed end with a block of wood and hitting it with a hammer. The one bolt that I broke was removed by hitting the end with a similar size steel bolt after applying the heat. I think the the real key to getting them out is softening the sealant to allow some movement of the bolts.
Gene in NC	posted 06-03-2003 07:35 PM ET (US) Thanks, Dan T. Suspect this corrosion may be the same as that at the connection of steering cable sheath at the engine. Ed Sherman, in his excellent book on outboards, recommends heat and keeping the fitting hot while unscrewing. I can vouch for his method and the rehardening of the corrosion if allowed to cool. Heating a steel bolt will sometimes break the rust in the therads but it must be cooled before removing. The reverse to remove corroded alum is counter intuitive but it works. I will report back. Will need to drive lower bolts to splash well and upper to rear.
Sal DiMercurio	posted 06-04-2003 01:15 AM ET (US) You better be super carefull when using heat, as you can scorch the booat real easy. I prefer cutting the head off the bolt & driving out with another bolt of the same size, ....hit it hard enough & it will break loose. Have someone grab the other side of the bolt with vise grips & pull as you whack the headless side, it works. No need to pull the engine off the bracket Sal
Duckin Whalers	posted 06-05-2003 12:40 PM ET (US) I had the same problem when I took my merc. off of my 13'. I used a grinder to take the head off then drove the bolt through with small punch. One of the bolt heads broke when I tried removing it, that was the easiest one. I got replacement stainless steel from a local fastener store.