Going to replace these bolts ...

[yam240sx]

Does anyone have any idea the best replacement bolt size , or type for these bunk board brackets .... my guess is class 5 zinc? maybe 1/2 inch ... with locking nut ? They basically hold all the weight of boat

thanks

 

[dgfreeze]

I'd recommend stainless, especially if you're in saltwater. It looks like your trailer is galvanized, so I'm making an assumption there... As for the size of the bolt, what size wrench fits the hex heads? If it's a 1/2" wrench, it's a 5/16" bolt. If it's a 9/16" wrench, it's a 3/8" bolt... It could possibly be metric also, but I doubt it... Just judging by the picture, I doubt it's actually a 1/2" bolt, but it's hard to tell for sure. If I had to guess, I'd go with 3/8" bolts, about 1 1/4" long.

 

[yam240sx]

it seems it is 7/16 x 1 inch ... my local hardware store has stainless in stock .. but says even at 5 + years the old ones should not have rusted as in the picture ... which makes me wonder ? grade 8 ??? maybe ... the original in picture is grade 8 strength

 

[dgfreeze]

So you’re likely using a 5/8” and/or 11/16” wrench? Usually with 7/16” bolts, the bolt heads are 5/8”, and the nuts are 11/16”, but not always.

Here again, salt water? If not saltwater, I’d agree, but if it’s going into saltwater, I’m not surprised. Either way, go stainless. I’m strictly fresh water, and I used only stainless for my bunks.

 

[anmut]

Stainless - it's worth the peace of mind for the few extra dollars.

 

[yam240sx]

I have confirmed they are 3/8.. And that makes me more want to go with grade 8 ... id rather have peace of mind knowing the strength will hold my boat rather than rust ... i am assuming i will only get a few years out of them and have to replace again ... if they were 7/16 or 1/2 id go stainless ..but the 3/8 makes me iffy

 

[dgfreeze]

Get a drill bit, and drill them out to 7/16", and use stainless. Piece of cake, if you're worried about it.

 

[mrcleanr6]

That 3/8 is plenty. Thats prob a grade 2 from the factory. You really dont need a grade 8 bolt. I wouldnt hesitate to put a 3/8 stainless bolt in there. Keep in mind what your putting that bolt in to. That grade 2 - 3/8 bolt is stronger than that little angle bracket that is held to the bunk with just wood screws. Remember something is only as strong as the weakest link.

 

[yam240sx]

That 3/8 is plenty. Thats prob a grade 2 from the factory. You really dont need a grade 8 bolt. I wouldnt hesitate to put a 3/8 stainless bolt in there. Keep in mind what your putting that bolt in to. That grade 2 - 3/8 bolt is stronger than that little angle bracket that is held to the bunk with just wood screws. Remember something is only as strong as the weakest link.

here is another caption .. the hanger l bracket is resting on the frame on an angle held flush with a bolt ..there is no way a 3/8 bolt is stronger that the bracket ... maybe im wrong .. your probably right the 3/8 stainless will work fine .BUT! why did they rust for if they were stainless to begin with ? . i went with the grade 8 ... i wash my trailer down after every launch ... so il probably keep eye on them

 

[dgfreeze]

Who said the old ones are stainless? Are they magnetic? With the exception of a few outliers, stainless bolts will not be magnetic.

 

[drewkaree]

here is another caption .. the hanger l bracket is resting on the frame on an angle held flush with a bolt ..there is no way a 3/8 bolt is stronger that the bracket ... maybe im wrong .. your probably right the 3/8 stainless will work fine .BUT! why did they rust for if they were stainless to begin with ? . i went with the grade 8 ... i wash my trailer down after every launch ... so il probably keep eye on them

That bracket will bend or the eyes will be rounded out before that bolt gives way.

 

[tdonoughue]

Stainless is only stainless as long as it is exposed to oxygen to allow it to replenish its oxidation layer. So when your trailer is out of the water, the stainless works fine. While it is underwater, it will have its oxidation layer and then ultimately the metal slowly eaten away. Same happens anywhere water can get trapped (like between the plates there).

Details: Not So Stainless Steel

 

[AuburnVFR]

Look at the markings on the bolt head to tell grade

 

[mrcleanr6]

I can tell ypu right now that no trailer mfg is putting stainless bolts on their trailers. That bolt rusted because it was a low grade bolt with a crap galvanize coating on it.

 

[yam240sx]

I have decided to go with these : grade 8 with goldish color coating im guessing will offer some corrosion protection for a little while ... I agree Mrcleanr6 the factory were probably cheap bolts ... but at least il have peace of mind hauling to trips this summer with the fam and not have to worry about boat flyIing off trailer on highway .

 

[yam240sx]

Look at the markings on the bolt head to tell grade

way too corroded to see any markings .. they have faded if any

 

[Cambo]

If we are on the subject of trailer bolts how is your pivot bolt that connects the two leaf springs . It has a grease zerk but even with replacing them I can not force grease in . One rotates if I put a 28 mm socket on the head the other is frozen.

 

[dgfreeze]

You replaced just the zerk? Those "wet bolts" rarely get greased, and the hole gets plugged with rust and dried grease after awhile, even on regular trailers. I'm sure boat trailers are even more prone to it. As for the bolt rotating, vs not rotating, these bolts have a serrated shoulder just under the head that is supposed to be forced into the hanger bracket on the trailer. Also, the nut is a lock nut. This means once things have been tightened, the bolt is locked to the hanger bracket, and the nut is locked to the bolt. I'll send a pic of what I'm trying to describe, but you should be able to replace the suspension components without too much trouble. Worst part is removing the old stuff, we usually use the "blue wrench"...lol

 

[dgfreeze]

Here you can see the serrated shoulder, and where the nuts have been crimped to make them lock nuts. For the record, it wouldn’t really concern me if one spins, and the other doesn’t, but they’re designed that way so the bolt stays still, and as the suspension works, the hanger bracket that is welded to the trailer doesn’t get worn out, but the rest of the system does instead...aka, all the replaceable items.

 

[Cambo]

You replaced just the zerk? Those "wet bolts" rarely get greased, and the hole gets plugged with rust and dried grease after awhile, even on regular trailers. I'm sure boat trailers are even more prone to it. . Worst part is removing the old stuff, we usually use the "blue wrench"...lol

I thought the zerk was rusted so I swapped it out these trailers don't have that type of bolt with a zerk and Im almost positive they don't have the serrated shoulder either . Someone posted a picture of the bolt with wear marks from being frozen so the pivot point changes and eats into the bolt

For the Bunk bolts they are carrying a fairly heavy load about 500lbs each maybe more in the back compared to the front @yam240sx were did you get the bolts and nuts?