SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: spectralen on December 07, 2010, 10:52:11 AM
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I'm getting ready to put on a Harmin Marine engine mount and the size of these 5/16 timing cover bolts seem very twinkie. :o I measured a depth of between 5/8 and 11/16 of threads and about 3 1/2 overall length under the head of the bolt. So I'm looking at getting some 4 inch length stainless socket cap and cutting each one down to get max threads with a washer and lock washer.
What seems messed up is the holes through the motor plate and the timing cover have what I consider a lot of play. :o It almost looks like it could call for a special shouldered bolt to take out the extra movement.
Just wondering what everyone else has been using on their BBF front mounts? ???
What about studs with a beefier thread at the cover? ??? Do they make them?
And what would be a good torque spec on the motor plate?
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Seen alot of bbf's hang off of them tiny bolts....bolts are pretty strong...i would say get some black oxide grade 10 or even grade 8 and let it rip...
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What about stainless?
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Stainless is nice but lacks tensile strength...i believe stainless is between 2 & 5 grade....
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Not to contrdict you Nordie, but I used the stainless, and they been there 5 years now ;)
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No its cool...thats what this site is for...i use stainless on my chevy...but those are 3/8 and like an inch n a quarter...front bolts are 7/16....i know on the bbf being that the bolts i used were 3 1/2" long...i went overkill i suppose
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Not overkill imo, I was just thinking rust, is why I went stainless. Was my first jet build, and every freaking bolt or plug was rusty on the thing when I got it. Wasn't thinking strength then, but was a little aprehensive when I put it together with those chickenshit little long bolts tho :sly:
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Hell half of those bolts, as rusted away they were when I pulled them, I am surprised they even came out in one piece :screwy:
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What about something like these? :-\
Anyone use anything like this shouldered bolt?
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I am aware of blown alcohol engines generating north of 1500 hp while being mounted at the front of the engine by those 5/16-18 bolts, so I don't think a 700 hp jet boat engine is of concern.
A 5/16-18 stainless bolt has less than half the tensile strength of a 5/16-18 black oxided bolt but even if the SS bolt's tensile is rated at, say, 75 000 pounds I'd think that's plenty...it's shear strength that matters in this application. In the typical jet boat application I'd probably go with the stainless because of the marine environment.
If you're still uneasy you can alwYs re-tap up to 3/8", but in most lake boat builds it's not necessary.
LO
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I ended up buying the stainless at 4 inches in length, threaded them in all the way, with the mount on, measured the slack between the head and the front of the plate, and cut each one down so that with a washer and lock washer I will be grabbing maximum threadage. Sort of custom like. ;)
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I ended up buying the stainless at 4 inches in length, threaded them in all the way, with the mount on, measured the slack between the head and the front of the plate, and cut each one down so that with a washer and lock washer I will be grabbing maximum threadage. Sort of custom like. ;)
X2 Just how I did mine :thumbup: