Torque on thru hull bolts for Mini Jacker

Fairbanks Fisher

I am installing a Mini Jacker jack plate and am wondering if anyone knows what the 1/2 inch thru hull bolts should be torqued to. The torque charts for grade 2 galvanized bolts with 13 threads per inch is 39 foot pounds but I am unsure if that is too much torque for the transom.

Any info would be appreciated.

Roger

Captains Cat · Posted: Tue Jul 28, 2009 11:11 pm Post subject:

Who the heck knows! Shocked

Just snug that sucker down, use a lock washer and locktite and go for it.... As my late mother said, "that's good enough for who it's for." [nothing personal]

Oh, and if the transom has balsa core in it, be sure to overdrill the hole and "pot" it. If you don't know what that means, don't drill/mount it until you do.

Charlie Laughing

journey on · Posted: Tue Jul 28, 2009 11:24 pm Post subject:

I have 2 ea comments.

First, Grade 2 is a Chinese invention. Before they started making all our hardware, Grade 3 was the lowest.

Second, why are you using galvanized bolts, if this is going on your C-Dory? Stainless is not that more expensive, stronger and doesn't corrode as badly.

Third (freebe) I'm not of the drill 'er out and fill with epoxy school. Drill a normal clearance hole. If it's below the waterline, use copious amounts of 3M 5200 to seal the bored surface and where the washers seat. If it's above the waterline, use 3M 4200. That stuff is waterproof and bonds well. Remove excess, for neatness sake.

Boris

Fairbanks Fisher · Posted: Wed Jul 29, 2009 12:21 am Post subject:

Charlie,

I actually already bolted the plate on and did exactly what you suggested on the snugging. I just didn't want to leave the bolts under or over tightened. I did do the over drilling, ground out about 3/16 core and epoxied according to Bob Austin and West System's recommendations. Plenty of 4200 to bed as well.

Boris,

I agree, grade 2 kind of sucks but with 1/2 inch bolts I don't think they'll fail. As far as the galvanized, it looks to me like the main is bolted on with galvanized bolts as well - unless they are just a rough grade of stainless. Those bolts are from the factory. Maybe I mis-judged the material. I originally wanted stainless but was having trouble finding the lengths I needed for the through bolting.

I don't know if galvanized is a no no on these bolts but if so, I don't have any problem removing them and installing stainless. I'll just have to order the hardware if so.

Thanks for the feedback.

snal · Posted: Wed Jul 29, 2009 6:46 am Post subject:

Actually, stainless bolts are only slightly stronger than grade 2 bolts (stainless cannot be hardened like regular steel) and much weaker than hardened steel bolts.
I do use stainless, large washers, and lock nuts.
I've seen A LOT of engines and brackets mounted so tight that the gelcoat/glass cracked around the washers!...especially on the inside of the transom
Snug it up good...the lock nut will hold it there.

Fairbanks Fisher · Posted: Wed Jul 29, 2009 7:37 pm Post subject:

Okay. At the advice of Boris - and due to the guilt at putting lesser quality hardware on my C-Dory - I went somewhere besides the big box hardware stores and purchased stainless steel bolts, nuts, and washers to attach the Mini Jacker. Still don't know what they should be torqued to but I removed the galvanized during my lunch hour (4200 was still only partially cured) and put on the stainless hardware. At the least, I feel better about it. Cool

Now to tackle the problem of where to put the trim tab pump.... Neutral

journey on · Posted: Wed Jul 29, 2009 8:20 pm Post subject:

I'm so proud, I haven't made anyone feel guilty since the kids left home. Anyway, stainless is better, with less corrosion.

Actually, Grade 2 bolts are good for 940 lbs in working load. Nominally, for tensile strength, grade 2 is worth 74, 000 psi, with 302/316 stainless at 100,000 psi. Either is clearly good for the jack plate. My suggestion was based on operation in salt water.

Boris