Outboard Engine Mounting Bolts - How Tight?

C

Chester

New member
My research suggests the engine's anti-ventilation plate shouldn't be immersed while on plane. Ours are and I can raise the motors one notch without drilling new holes.
I doubt if that will be enough to raise the plate out of the water but we'll see if it helps.
My question is how tight do the engine mount bolts need to be torqued?
Don't wanna crush the core or have loose mounts.
Like Goldilocks porridge they need to be just right.
 
Chester":l3is5ttv said:
My research suggests the engine's anti-ventilation plate shouldn't be immersed while on plane. Ours are and I can raise the motors one notch without drilling new holes.
I doubt if that will be enough to raise the plate out of the water but we'll see if it helps.
Click to expand...

I have the same situation - likewise I am going to raise the engine one "hole." (Another Brat with my same engine/mounting height already did this and reported favorable results.)

Chester":l3is5ttv said:
My question is how tight do the engine mount bolts need to be torqued?
Click to expand...

Good question and I will be reading the replies with interest. Right now it looks like my engine was put on with galvanized fasteners; I got ahold of some "stock" coated Yamaha fasteners and will use those. I wonder if there is a torque specification for the fasteners themselves? I suppose many people just do it until it seems "right," but I'd like to know more.

Chester":l3is5ttv said:
Don't wanna crush the core or have loose mounts.
Click to expand...

I hear you there. What I am going to do is remove the core in the way of the fasteners and replace with thickened epoxy. That way there will not be crushable (and/or "soakable") core there. Not that this means they shouldn't be torqued correctly, but at least I won't be tightening them against balsa (or other coring).
 
The 90 ETEC service manual that I just got says to torque to 40 ft lbs. On other google search threads, it also says to use a backing plate. That seems like a good idea as does the undercutting and epoxy fill if you have totally removed the engine. I would hope that the original installer did that but I'd bet not.

Oh, and anti-seize stuff seems like a good idea if you ever intend to do it again.

Charlie
 
Captains Cat":39dxd3ic said:
On other google search threads, it also says to use a backing plate.
Click to expand...

That is a good idea, and I intend to add that (on the inside of the splashwell) when I remount the Yamaha (main engine). There are a few companies who sell them ready-made (TH Marine and Bob's Machine, for example).

When I re-installed my secondary engine on a Mini Jacker, I found that there weren't any "pre-made" plates for that mounting spacing (because it ends up being the Mini Jacker that one wants to "back," and it's not the same spacing as the engine clamps themselves), so I made a couple of oversized "fender washers" of fiberglass board, gelcoated them, and used those underneath the metal fender washers. One side benefit is that I was easily able to make one a bit of a "waxing gibbous" where the GRP washer came close to the curve of the splashwell. The extra backing is probably not necessary on the Mini Jacker, but I like having it anyway.
 
BrentB":2z8lcv1d said:
torque varies with bolt size

google yamaha rigging manual


For M12 bolt, it is 38 lb ft
M10 it is 27
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Thanks for the info. I was able to find a 2012 Yamaha rigging manual for download (and did download it), but no luck on the 2002. At any rate, I doubt the torque that a specific year fastener can take would change, so I'll measure mine and go from there.
 
I didn't see it mentioned, but I have always used NYLOCK nuts on the bolts. That keeps them from vibrating loose lock washers not withstanding. If you don't use NYLOCKS, I would double nut the bolts for the same reason.

As far as motor height is concerned, I haven't seen any C-Dory yet where the motor wasn't too low when it was rigged by the dealer. I admit I haven't seen that many (6), but that's a pretty bad track record for "professionals" rigging engines.

Tom
 
tpbrady":3nen4wou said:
I didn't see it mentioned, but I have always used NYLOCK nuts on the bolts. That keeps them from vibrating loose lock washers not withstanding. If you don't use NYLOCKS, I would double nut the bolts for the same reason.

As far as motor height is concerned, I haven't seen any C-Dory yet where the motor wasn't too low when it was rigged by the dealer. I admit I haven't seen that many (6), but that's a pretty bad track record for "professionals" rigging engines.

Tom
Click to expand...

Or locktite!
 
Chester":28sysbz6 said:
SNIP.... how tight do the engine mount bolts need to be torqued?
Don't wanna crush the core or have loose mounts.
Like Goldilocks porridge they need to be just right.
Click to expand...

Understandably, wanting your engine(s) to stay on your transom is a valid concern directly related to torquing the mounting bolts. Checking your owner's manual is a good place to start looking for "ft lbs" of torque. Of course, you'll need a torque wrench to read the recommended ft lbs of torque by exerting the appropriate pressure on the wrench.

In some situations, a torque wrench is not always handy or available. In these situations here in the boonies, I use my own "grunt torque" matrix which hasn't let me down yet. It goes something like this when knowing the required ft lbs:

5 - 25 ft lbs: 1 grunt
25 - 60 ft lbs: 2 grunts
60 - 95 ft lbs: 3 grunts
over 95 ft lbs: all the grunts you can muster, then check your pants

Using this, I've never lost an engine and rarely need to change clothes.

Aye.
 
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