Checkmate Motor mount upgrade
 

I have an '89 Checkmate Convincor. It originally had a 454 Mag. I am currently building a 502 EFI with M-1 Procharger for it. Do you think it is necessary to upgrade the front motor mount from the standard top of stringer design to the offshore cradle design on angle brackets thru bolted to the stringers? All input would be greatly appreciated. Thanx,

Dave

Sounds like you know what you need to do to make it right. And use backing plates too, not just washers.

The principle purpose for the "offshore" mounts is not to hold up the engine, but to brace the stringers. The torque from the motor is taken at the mounts on the outdrive on a Bravo and most other outdrives..Some are different, such as #6's. There you do need better mounts. I have done blower installs on both types of mounts with a Bravo with no noticeable difference. If you go faster and need the stringer bracing, go to the plate mounts.

hey dave..
you are correct..checkmates have a history of hauling out their own lag-bolted motor mounts...while the motor is out...a beefy set-up is a snap...be sure to fill all holes to form a solid foundation,and to keep out water....just my .02....chris

I don't follow your post here. The mount at the transom is not solid. There is a fiber washer, spring washer and the bolt with a shoulder to keep from tightening this mount dead tight. If there is any torque from the motor, it would twist some at the point just from all this controled clearance. This would be possible, if it were not for the solid mount at the front motor mounts. Lag bolts screwed into stringers tend to pull the threads from the stringer under torque. Thru bolted with backing plates using an offshore mount would have to rip the stringer from the hull in order for any movement. Or at least have to split the stringers at all the bolt hole locations. So the way I see it is that the front mounts are what prevent any twisting of the motor, hence, offshore thru bolted mounts. Do I understand this correctly? Just my thinking.

I just posted a question just like this in the General Discussion section.
I have the original set up from the factory in my 25 Sunsation, which is, through bolted L-brackets on the inside of the stringers for the front mounts. I am repowering this spring and since upgrading from the standard Merc Coupler to an HP, I wanted to look at any other weak areas (I know the drive should be my major concern).
I would think that a one peice cradle would do a better job of distributing any stress from the drive through the crank to the mounts/stringer.
If I am alright with front mounts on a L-bracket that is fine, but I just saw another boat with a stringer that had a crack just in front of the through-bolted front mount and it made me think.

Seamate,

Did you buy Eric AKA Checkmate F-1's Checkmate?

Aggressor 25,
No, I didn't buy F-1's Checkmate. I 've this boat for about 3 years and it came from the Hudson river in New York.

Dave

i agree with 1500 the fiberwasher and alows for little if any movement and the front mounts are usualy rubber isolated anyway

I didn't think that the front of the engine put a great deal of torque through to the stringers. I also thought that the torque was absorbed in the rear transom mounts. I can't see any way that the a couple of lag bolts could hold down all that torque to a piece of wood. In my opinion, the front mount just keeps the motor aligned with the drive. I feel it is under more load when you launch over a wave and come crashing back down. Don't get me wrong, I know that offshore mounts are a much better system. I just don't feel that the front mounts have to hold that much torque.

SeaMate;
The problem with installing offshore mounts in your year ( or my) Checkmate is getting to the back of the stringers for through bolting the mounts. You would have to drill an access hole in the wood that covers the outward side of the stringers.