Bolt grade question

[Quick-man]

I am replacing a couple of bolts that sheared off. This attaches the powerhead to the mid section. They are 3.5 inchs long. The reason why they sheared off was because the other bolts were loose and the torque of the engine finally won.

The question I have is that the bolts are grade 8 can I use grade 5 instead? I've got grade 5's and grade 8's are 23.00 each! yikes!! I figure that I could use 4 grade 8, and 2 grade 5.

Here is a link of what bolt grades mean and their specs.

http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

 

[Pony]

Re: Bolt grade question

If it were me I would look at a schematic of he engine, grap some part numbers, and get some bolts from a jonnyrude dealer. That way the metal, the grade, the length, and the threading will be up to spec. I did this when I broke a blot off in my lower unit. The bolts themselves werent very expensive either. JMHO, thats just the way I am. Others can chime in with some more expirience.

 

[fire831]

Re: Bolt grade question

Probably best to put back what they had in it. They do things for reasons at the factory. JMHO.

 

[reelfishin]

Re: Bolt grade question

I'd say your best bet it to stay with the OEM original bolts, unless for some reason they aren't available.

I find it hard to believe that any decent quality steel bolt would shear if it was properly torqued. I wouldn't think that it would require Gr8 bolts. The harder bolt can often actually shear faster since they are more brittle. If it were me, and fastory hardware was not available, I would look to maybe find some stainless steel bolts in the proper size, but corrosion is a big concern here since I run mostly in saltwater.

 

[Quick-man]

Re: Bolt grade question

Thanks everyone, I also tend to stick with what was supplied. I just can't believe they are 23.00 for each bolt. I do have grade 5's of the same length and thread.

I did read an article about grade 8 vs grade 5 and they said what imported_reelfishin said, that they shear faster and are brittle. The article went on to say that they now use grade 5 to bolt on their mast to the steep and those bolts never shear, they bend a little but don't break.

Stainless would be great if I can find them.

 

[F_R]

Re: Bolt grade question

Stainless steel can be more of a pain to get out after they have been in salt water than the steel ones. Believe me, I know. 24 years repairing salt water motors.

The bean counters at the factory wouldn't let them use grade 8 unless there was a good reason. Believe me, I know that too. I am retired from my most recent profession, purchasing manager for a national marine manufacturer. Every penny counts.

 

[Quick-man]

Re: Bolt grade question

Stainless steel can be more of a pain to get out after they have been in salt water than the steel ones. Believe me, I know. 24 years repairing salt water motors.

The bean counters at the factory wouldn't let them use grade 8 unless there was a good reason. Believe me, I know that too. I am retired from my most recent profession, purchasing manager for a national marine manufacturer. Every penny counts.

So you used Grade 5 to attach the powerhead to the midsection? Grade 8 is so expensive, and I never realized that stainless would be more difficult to get out. Maybe stick with Steel Grade 5 and see what happens. I do have 4 Grade 8 that I can use. Just the two that were broken will need to be replaced. I will use those in the center of each side so that the high strength Grade 8's are used at the ends. Imagine if I was to replace all 6 at 23.00 a pop. Almost cheaper to get a new engine

 

[BoatBuoy]

Re: Bolt grade question

They're only $19.07 at ishopmarine.com. Boating is expensive.

 

[jeeperman]

Re: Bolt grade question

I don't know where your sourcing your bolts but grade 8's should only be about twice the price of grade 5.
Example: grade 5, 1/2" x 3.5"lg hex head = 56 cents.
Same bolt in grade 8 $1.01

And stainless fasteners such as bolts are not rated because they are weaker than grade 5.

 

[Quick-man]

Re: Bolt grade question

I don't know where your sourcing your bolts but grade 8's should only be about twice the price of grade 5.
Example: grade 5, 1/2" x 3.5"lg hex head = 56 cents.
Same bolt in grade 8 $1.01

And stainless fasteners such as bolts are not rated because they are weaker than grade 5.

jeeperman, do you have a source? I used the part number of the bolt and researched online to get those prices.

 

[CATransplant]

Re: Bolt grade question

If the lengths match, you can get grade 8 bolts at any GOOD hardware store. You said these were 3.5" long. That's a standard length. I'll bet that every one of those bolts is a standard length. That's how manufacturers like OMC worked. If they could design to standard hardware, they did.

 

[F_R]

Re: Bolt grade question

5/16-18 x 3-1/2 inch zinc plated grade 8 bolts, $12.12 per pack of 25. Part number 90257A597. McMaster Carr. I smell a crook.

 

[Willyclay]

Re: Bolt grade question

Found Grade 8 bolts for my flywheel puller at Bumper to Bumper Auto Parts. The 5/16-24X2.5inch were only $0.32 each!

 

[CATransplant]

Re: Bolt grade question

5/16-18 x 3-1/2 inch zinc plated grade 8 bolts, $12.12 per pack of 25. Part number 90257A597. McMaster Carr. I smell a crook.

Maybe. Maybe not. If the bolts have some special machining on the heads so they aren't standard, then he'll need the actual parts. If not, then the hardware store bolts will work just fine.

It's not unusual on cars and other machinery for the bold heads to be machined to have a bearing surface. I have no idea if that's the case here.

 

[Quick-man]

Re: Bolt grade question

There is a lock washer (3.32 each) that also goes with these bolts. The head looks and feels normal nothing special there. Looks like a trip to Sears is in order.

 

[BoatBuoy]

Re: Bolt grade question

McMaster-Carr is a good place to buy. I bought something from them last Monday and had delivery by 10:00AM on Tuesday. mcmaster.com

 

[Chris1956]

Re: Bolt grade question

Quick, The powerhead mounting bolts were not stainless? If not SS, then you should replace them with the same grade bolts. AS Jeeperman said, stainless are not as strong as grade-8 bolts.

When I needed to find grade 8 bolts for my Merc motor mounts, 7/16 X 6" fine thread, grade 8 was specified. Merc wanted $12 ea, the web (with shipping) wanted $10 ea. I finally bought them at a local "Bolt Bin" store for less than $2 ea. I could have gotten them at a local HW store, but they did not have a 6" length.

 

[Quick-man]

Re: Bolt grade question

WOW I just went to mcmaster and they want less than a buck, that's right, $1 dollar for each bolt, so what you have to buy 10, the reduced cost pays for itself even with shipping. Thanks BoatBuoy for letting me know about mcmaster. Now I know where I will be shopping for any bolts that I need. Oh and those washers at 3.39 I can get 100 for $11.00

 

[jeeperman]

Re: Bolt grade question

jeeperman, do you have a source? I used the part number of the bolt and researched online to get those prices.

My source was as already mentioned.......McMaster-Carr.
Standard shipping will usually get you what you order the next day via regular UPS.

But since you were trying to find the bolts via "part number of the bolt" that tells me you were looking for the bolts per the engine parts book.

Now you need to compare the entire bolt from what you need versus what is a standard hardware bolt.

Like previously stated, the OEM bolt might appear to be a standard bolt but the head could be different. It might also have more or less threaded portion or have some special surface treatment or the area between the threads and the head might be of a reduced diameter, etc. Also the threads themselves could be of special fit quality much better than a standard bolt. But those points would not stop me from using standard hardware store fasteners if they were the right grade and looked close in comparison.

SS bolts are less in strength than not only grade 8 but also less then grade 5.

 

[Quick-man]

Re: Bolt grade question

I just went to Home Depot expecting to find, well nothing. To my surprise I found the bolts, 5/16 x 3.5 (18 thread). They had them in grade 8 and even had grade 8 lock washers as well. Here is the kicker $0.77 each...(yeah I got all 6) and a 4 pack of locks were only $.063, so I splurged and picked up two packs. That is a far cry from $3.37 for each lock x 6!

Now I am thinking that something can't be right, those were the bolts that were in there but I am not sure if these are correct or did someone just pick a bolt that fit and that is why they were loose. The web doesn't tell me the spec of the bolt to attach the powerhead, only the part number. Look at this link and bolt number 16 and waher number 17.

http://www.crowleymarine.com/brp_parts/diagrams/27750.cfm