Building motor mounts for a 302

[erikgreen]

Hi all -

I just finished my new transom, and I'm moving on to building new motor mounts for my 302 ford block. The originals were integral with the old fiberglass deck, and would be impossible to replace (the stringers are coming out the rest of the way soon anyway).

Here's the issue: I need to make the mounts 38" by 7", and 5 1/4" tall on the inboard sides, sloping to 4" tall on the outboard sides. So, the bottom of the mount needs to get an inch and change shorter in the 7 inches of width to match the hull curve (deep V hull).

The only ideas I've had so far are to laminate ply on edge, using slightly narrower pieces progressively toward the outboard side, and keeping the top edge even. This gets the slope, but I'd be putting a vertical lag bolt into plywood edge-on.

Second idea: Laminate ply strips to the right size, then use a metal cutting bandsaw and a jig to cut the bottom of the stack to the right angle for the slope.

Tashasdaddy suggested maybe using some angle iron with the vertical ply idea to send bolts in from the side instead, but I doubt my ability to make that strong enough.

Other ideas gratefully accepted. I own only a trim router, I don't have a table saw. I do have a small set of machine shop tools, power hand tools, a drill press, and some air tools.

What's a good way to make a motor mount for this motor? It's 188 HP, and mounts using four large lag bolts through the adjustable motor mounts, plus the transom plate bolts.

Erik

PS: Here's a pic of the mounting location, I still have to remove half the old mounts:

 

[qaztwo]

Re: Building motor mounts for a 302

Is this on a searay, mine was like that. If so wasn't the first engine mounts layed ontop of a plywood frame then built up with fiberglass. You could even use foam for your structure it would be easier to form up and get the correct shape.

Some one else I sure will have some other ideas.

good luck.

 

[erikgreen]

Re: Building motor mounts for a 302

It's a 73 Sea Ray, good eye.

The original mounts were some small pieces of ply attached to the stringers, then heavily glassed to the deck and stringers and foam filled (with floatation foam).

I suppose what I could do is build out a level mounting surface first with foam, then laminate ply, then glass it in place to make up the rest of the height. I'd think that would be weak though, not having a solid base for the mounts?

Am I supposed to avoid making "hard spots" in the hull under the mounts? I'd think that would be impossible, given that most people want to mount the engine solidly connected to the transom and hull bottom.

Erik

 

[mkast]

Re: Building motor mounts for a 302

We had to do a 188 last year.
The stringers were shot also. After cutting and laying in the stringers(longeron), we built an eight inch by eight inch by eight inch block of marine grade plywood laminated with epoxy that was then through bolted to the outboard side of each stringer. The whole frame assembly was then glassed in.
The engine was installed with the aft bolts in the transom plate and the alignment bar installed. The Mercruiser stock motor mounts were bolted to the engine block, engine was lowered to the new wood blocks and marked for drilling. Upgraded to a four barrel 351 at the end of last year, have not noticed any problems so far.

 

[Bondo]

Re: Building motor mounts for a 302

I Donno,........ I think you guys are Seriously Over-building your Mounts........

My motor is Lag bolted to a couple of glued Plywood Blocks that are Just larger than the cast iron motor mount base,.......
The Blocks are just screwed to a piece of bent aluminum that is Pop-riveted to the hull......
'course,... I got a Tin boat......

If your using Epoxy,+ Glass,.......
You need enough plywood to hold the Epoxy,+ Glass in place long enough to Set......
Your Strength is in the Epoxy,+ Glass,......
You Only need a Block of Wood big enough to Sink the Lags into...........