Merc.Clamp Brkt.bolt size to Jackplate?????

[johnt]

I think this is more of a technical issue than a setup question so I am posting here. I am installing my new Merc. motor on a new jackplate. My question concerns the bolt's that attach the motor to the jackplate or transom for that matter. My 150 was attached with 1/2" bolts to the previous jackplate and 1/2" bolts to the transom. I have installed my new jackplate to the transom and both were drilled for 1/2" bolts so that is what I used. Getting ready to install the motor and I find out the clamp bracket is drilled for 9/16" bolts. New jackplate is drilled for 1/2" bolts. I checked both motor's and both are drilled for 9/16" bolts. Seems like guy's are using 1/2" bolts to attach the motor the the jackplate, however, this provides for alot of slop, in my oppinion. I did not want to start drilling on a $600 jackplate until I posted this. It seems to me that the bolts should match the hole size in the clamp bracket even if this means drilling out the holes in the jackplate. Would really like some help on this..
thanks

[Rickracer]

9/16" is a "clearance" hole, meaning that the bolt won't bind going in. Transoms are not all drilled exactly, since most are done "in the field" and not in any kind of a jig like the jackplate or the motor's clamp bracket. Therefore, a little "wiggle room" can definitely be a good thing. :cool:

[Raceman]

You sure about that Rick??????? I've been workin' on one of the STV's today, changin' the jakplate around and I'd be VERY surprised to think a 9/16 bolt would fit in the clamp brackets. Y'all can correct me if Im wrong, but I think if a bigger bolt fits it should be used. Seems like undersized encourages movement which allows thngs to work loose. Again, y'all correct me if I'm wrong 'cause I'm just speculatin'.

[Rickracer]

However, I just went out and measured the slots and holes in my '80 OMC 235 clamp bracket, and they are 9/16" too. I also measured my Merc single ram mid, and they about 17/32". They both came with 1/2" bolts. I really don't see anything wrong with drilling the jackplate and using 9/16" bolts, other than availability of the bolts. I just hope the transom is drilled pretty accurately, or the holes will have to be wallowed out or redrilled to get the bolts though them. :cool:

[johnt]

thank you rickracer and raceman for your reply's..I noticed the 9/16" bolts were "snug" going into the clamp bracket but with the heavy coat of paint Merc puts on that paint is also in the holes I just took that into account. Since motor is going to be bolted to the jackplate as much as a foot away from the transom I think I will drill out the jackplate holes for 9/16" bolts. I don't doubt that 1/2" bolts are the norm and that they will probably hold but if the motor comes loose at the speed some of these things run I don't think I would want to be in the boat. 9/16" stn stl bolts were easy enough to find but the 9/16" stn stl nuts with nylocks were abit EXPENSIVE..Side bar here.. using stn stl bolting I always chase the threads with cutting oil and always use anti-sieze on the thrd's to keep the threads from gallling..stn stl is really bad about that.
thanks again