How tight is tight?

jkidd

jkidd

Active member
I'm raising my main motor up one hole. I knew when I took the motor off that the holes might or might not be done right they were not. Before I took the motor I put a torque wrench on just to see how tight the bolts were. They were sitting at about 20 ft. lbs. So my question would be how tight do you think these bolts should be? Do you think 20 ft. lbs. is enough or should it be more?
 
Jody, does the owner/operation manual for the engine have any details on torque?

Are you raising the engine to get a better alignment for a Permatrim plate? I've thought about doing that, too. I think my engine is just a tad bit high.
 
55 foot lbs is the commonly specced torque for the transom mount bolts. However, I would watch the transom very carefully to be sure that it is not being crushed in an older or foam cored boat.
 
The bolts are 12mm nothing in the shop manual or the owners manual about how much torque. 55 ft. Lbs. sounds like a good number. I don't want to crush the core. When I routed out the core it looked like balsa. 20 lbs seemed kind of light so I guess I'll just kind of ease up on them and see if I can get 30 or 40.
 
Wandering Sagebrush":2e1jy3x9 said:
Jody, does the owner/operation manual for the engine have any details on torque?

Are you raising the engine to get a better alignment for a Permatrim plate? I've thought about doing that, too. I think my engine is just a tad bit high.
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My boat kind of plows the water and sprays water everywhere. There was a thread earlier that was talking about where the cavitation should run in the water. Montana Kev raised his up one hole and had some good results so I thought I would give it a try. At least the holes for the motor now have been filled with epoxy and I don't have to worry about water getting in there. I just have a lot more places to check for that.
 
jkidd":1lg1phlh said:
I routed out the core it looked like balsa. 20 lbs seemed kind of light so I guess I'll just kind of ease up on them and see if I can get 30 or 40.
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It sounds like you have over-drilled and then refilled the holes with thickened epoxy (before re-drilling for the fasteners)? If you've done that then I would think you would have sturdy annuli and not have to worry about crushing the core when tightening the fasteners (to me that's one of the benefits of the overdrill/fill/re-drill routine).
 
First, I think all later model C-Dorys have a structural foam insert in the transom. The C-25's do and it's there to provide rigidity and strength, so I wouldn't worry about over-tightening as long as you're in spec.

So, what's spec?

Honda manual (for 150) provides a general spec for 12 mm: 54 N-m, or as we say in the USA: 40 ft-lbs

From the internet:

M12 x 1.75, Grade 8.8, Dry, clean: 65 f-lbs Lubed: 49 f-lbs

Looks like 40 ft-lbs is a minimum, and at least 55 ft-lb is rational.

Like Bob said, watch the stern surface.

What surprises me is that Honda doesn't provide mounting instructions for their big outboards. The service manual doesn't even touch it. Maybe someone like Matt Gurnsey could tell where they get the info needed to mount a Honda engine?

Boris
 
Sunbeam":3grum0r3 said:
jkidd":3grum0r3 said:
I routed out the core it looked like balsa. 20 lbs seemed kind of light so I guess I'll just kind of ease up on them and see if I can get 30 or 40.
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It sounds like you have over-drilled and then refilled the holes with thickened epoxy (before re-drilling for the fasteners)? If you've done that then I would think you would have sturdy annuli and not have to worry about crushing the core when tightening the fasteners (to me that's one of the benefits of the overdrill/fill/re-drill routine).
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Yes I did do that butt there are times that I have stripped the threads or broke the bolt off so I'll use a torque wrench to tighten them up. Hopefully I won't mess up.
 
I was sort of curious about that too...

So when you guys go to repower, I assume you are undercutting the hole filling with epoxy and redrilling?

I've been reading so much on wet cores that I am concerned that whoever mounted the outboard(s) in the first place didn't do it right. Has this been a major source of the water intrusion into the transom or is it coming in from above?
 
My motor has on the boat for five years and there wasn't any sign of water intrusion. Glad for that. I do need to check all the holes in the transom. If you get lucky the shop did it for you. My guess would be if the motor holes weren't done nothing else was.
 
jkidd":1q8f5kix said:
My motor has on the boat for five years and there wasn't any sign of water intrusion. Glad for that. I do need to check all the holes in the transom. If you get lucky the shop did it for you. My guess would be if the motor holes weren't done nothing else was.
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Should have said: My motor has been on the boat for five years
 
journey on":8nt7enbu said:
First, I think all later model C-Dorys have a structural foam insert in the transom. The C-25's do and it's there to provide rigidity and strength, so I wouldn't worry about over-tightening as long as you're in spec

Boris
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My 2003 C Dory 25 had plywood in the transom core, not wood. The 2006 C Dory 22 has a foam core--so apparently in the 2004/2005 era is where the transition was made to foam.
 
thataway":485re1fb said:
journey on":485re1fb said:
First, I think all later model C-Dorys have a structural foam insert in the transom. The C-25's do and it's there to provide rigidity and strength, so I wouldn't worry about over-tightening as long as you're in spec

Boris
Click to expand...

My 2003 C Dory 25 had plywood in the transom core, not wood. The 2006 C Dory 22 has a foam core--so apparently in the 2004/2005 era is where the transition was made to foam.
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Bob is it possible that there are 2 layers. When I look in a hole it looks like balsa and then a layer of something else?
 
Yup. Just looked at my 2012 Honda Marine Outboard Rigging Guide. All 12mm engine mounting bolts- 40-225 HP engines- 40 ft/lbs of torque. They come pretty long from the factory- don't be tempted to use an air tool to run the nuts down...you'll probably gall the metal and ruin the bolts and/or nuts. No mention of lubing the threads. We install them dry. But be sure to seal the holes with sealant. And don't forget the jamb nuts...Aloha, Steve.
 
Jody,
Is that in the transom, or the hull?

I would not see any reason for two different materials in the transom--if you are going to use plywood, than I would suspect that it will be two thickness of 3/4"---

On the other hand, with multiple owners of the company in the last few years, there is no telling what was done....One of my criticisms of my 25 was that the plywood was not extended far enough in the transom--and was just between the two sides of the splash well--as though they had "engineered" the boat to allow the thrust to be taken by the splash well walls.....But then no real glass in the splash well walls....(2003 boat). All of that was changed by our rebuild, where we put biaxial glass layers with epoxy down to strengthen both the transom and splash well.

There are characteristics of end grain balsa which make it a very good material for the bottom of semi flat bottom boats. There are other materials better for decks and hulls sides (if you want to core them). There are many ways to build a very good boat, and no one way is all that better than the others.
 
Bob,
It was in the transom. I'll know better when I take the splash well tube out to see what happened there. Bigger easier to see. I got the motor back on today I could get to 50 ft. Lbs pretty easy a little bit of a compromise between 40 and 55 ft. Lbs. motor sitting one inch higher now. Will see how it runs at Yellowstone the end of July.
 
I don't think there is a specific torque specification for your application, in fact I know there is not. Each an every transom on every boat is constructed differently and can withstand different amounts of compression. It's really a judgment call as to how much you tighten the motor mount bolts. Use large stainless washers like 2", 2 or three to distribute the pressure. I would use new locking aircraft nuts, don't re-use the old ones. Use quick set 5200 sealant and let it cure for at least 72 hours. The 5200 should be applied on the shaft of the bolt, then push back and forth a few times, you want it to be gushing out of everywhere; wipe off the excess with a rag socked in acetone. When you start to tighten look for compression on the transom, stop tightening at that point. It's OK to have some compression, but if you go too far you'll crack the gel coat.
 
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