insuring against stuck bolts? torquing head bolts with marine grease?

[bill van steenwyk]

To Flabum1017:

Your comment regards "the casting threads will shear long before the yield strength of the bolt is achieved" is very correct, WITH THE TYPE FASTENERS AND CASTINGS generally used in outboard motors. I was NOT suggesting otherwise, in fact I think if you will consider your comment further, the use of any type lubricant when NOT called for by the manufacturer could make that problem worse, not better, as the lubricant would tend to reduce the friction between the threads of the bolt and casting and cause the torque applied to apply MORE tension force to either the threads of the bolt and the threads in the casting, leading to the type damage you describe. If you use lube it REDUCES the amount of torque required to tension the bolt to the desired yield percentage, it does not increase the torque required to reach that percentage. That is why any bolt chart you look at will have LOWER torque figures to tension the bolt to the desired percentage of yield when lubricant is used.

Another problem in this type application with dissimilar materials, especially in marine use around salt or brackish water is the "galvanic corrosion" problem, which probably causes as many of these type problems as anything. Perhaps a non-lubricating sealant used just where the threads of the bolt enter the casting and placed in the proper location on the bolt before assembling would help to achieve some type seal so as to keep water out of the threads after assembly.

To pcrussell50:

Regards your comments "it would be hard to believe that torquing to yield would be right". If you are referring to something I said in my earlier post that led you to believe I was suggesting fasteners were to be torqued to their yield point as common procedure, you got the wrong impression. NOWHERE did I say it is correct to torque a fastener to yield. Most fasteners are recommended to be torqued to between 50-70% of their yield, depending on the fastener material and the type material they are in, their size, and other factors so as to provide the proper amount of "clamping" force to keep the assembly together while operating and also provide a safety factor so the fastener was not stressed beyond it's yield point in the case of some type of overpressure of the assembled equipment.

I am certainly not an expert on threaded fasteners on outboard motors used in a marine environment, but there are certain common factors that influence the correct assembly of bolted together machines. The correct method of assembly of bolted flanges regards what you are trying to achieve by using torque was the thrust of my comment, nothing more. Surely after this length of time of outboard motors being on the market, the manufacturers have procedures they recommend. If it were me, those are the ones I would follow. The dissimilar material situation by itself is enough to cause problems of the type described earlier with out using incorrect assembly procedures (i.e. lube where not recommended) that can further complicate the matter.

[pcrussell50]

To pcrussell50: NOWHERE did I say it is correct to torque a fastener to yield.

Not saying you said that, friend. I'm the one who said it. some automotive engine bolts are "torque to yield". they are designed to be that way. and of course, they are definitely a one-time-use-only affair.

-peter

[Jay Smith]

I use the Lubriplate assembly grease on the clean male bolt threads and a shot of light oil on the bolt flange as well as the washer...

Works for me, never had a stock head bolt snap when installing OR removing from one of MY former assembly jobs..

Jay

[flabum1017]

#1 step i recomend is chasing the threads of the block and the stud with taps and die's. Then blow the threads of the block out to make sure you get all the loose material out. Then use anything to keep the lube. Better yet buy a head stud kit from Brendan power and throw all your worries in the water. I havent made the investment but if this is a real problem for you then its wise to do. He's a member on the boards and has a website too, if ya need his # pm ill grab it for ya.

I pulled the threads outta my block on 2 studs last summer and i credit it to no cleaning all threads.

Jay

I prefer using a thread chaser over a tap for cleaning out aluminum bolt holes. Taps tend to cut into the threads especially if the threads are heavily corroded or dirty.

Pulling the threads out of that block may have been due to cleaning those threads with a tap and weakening them from the shaving they received from the tap.

[bill van steenwyk]

The term "torque to yield" was used earlier in this thread, and can be misleading when used in describing bolts used in certain applications. You might think that by being called by this term the bolt is tensioned to the yield point when tensioned. This is incorrect, for no other reason than if you tension a bolt to it's yield point, it will no longer provide the clamping force required for the application for which it is designed, the simple reason being you have destroyed the ability of the fastener to "rebound" when excess load is applied, and consequently continue to do the job for which it is designed. The more correct term for this type bolt would be a "torque to THRESHOLD of yield". Also as mentioned in an earlier post, they are designed to be used only one time. Much helpful information on these type bolts, and other bolting information in general on head bolting applications can be found at enginebuildermag.com/.../threaded_fas...

This is very good information and could be very helpful to anyone interested in the problems this thread addresses.

[thornl01]

Went to OMC training in Atlanta in late 70's & we were taught to use Permatex avation sealer ( brown gooey stuff in can w/ brush in lid.)

I have used this on all bolt threads since then & never had a sticking / gauling problem. The sealer drys just enough to stay put, but remains gooey enough to remove. ( always use it on prop shafts) Have had boats stay in salt for 1 yr + & prop comes off w/ ease.

[mn808gade]

mmmm peanut butter goooooood

[pcrussell50]

This is all fine and dandy in steel or Iron castings, but the bolts on an outboard screw into an aluminum casting. The casting threads will shear long before the yeild strength of the bolt is acheived.



I'm with ActionDave.... gasket sealing compund.... good stuff

This is what is fascinating to me...

On the one hand, you want to achieve a certain preload on the bolt to get it into the right internal stress for proper preload. On the other hand, if you do what a lot of hot rodders do, and use high strenght bolts, the proper torque to achieve proper preload might as Ron is saying, damage or tear out the threads in the light metal outboard engine block.

It almost makes we wonder if those nutty expensive stock OMC head bolts are special, low strength bolts so you can torque them lightly and they will still reach the internal stress to be properly preloaded?

On one of my crossflows, I replaced the pitted stock head bolts with a set of ARP "bin bolts", forW, not their " real" head bolts), for way less than half the cost of the OMC's. They still may be too strong though. I torqued them to the minimum specified by ARP, but I still worry that it's too hard on the block threads.

-Peter

[panther150]

some motor assembly lubes such as ARP ,give you the torque spec with their lube. basicle anti sieze. dropped my head torque on my pontiac from 120 lbs to 90 as I remember.http://www.tillagetools.com/uploaded...rqueCharts.pdf here is a chart.

[powerabout]

torque to yield means torque to plastic or elastic?
plastic is my guess then you have to buy a new bolt
Like to see ultrasonic stretch gauge save all that hard to use mic etc

[pcrussell50]

Power, bill gave a good description a few posts ago, (back in 2010). The highlight is that you don't actually pull the bolt all the way until it goes plastic and yields. But you do pull it right up to just before that point.

The main takeaway is that TTY bolts are still one time use only, even if they are not actually pulled until they go plastic.

-Peter

[olboatman]

[QUOTE=flabum1017;1977121]This is all fine and dandy in steel or Iron castings, but the bolts on an outboard screw into an aluminum casting. The casting threads will shear long before the yeild strength of the bolt is acheived.
This is a good reason to replace bolts in areas that are going thru constant reassembly with studs, washers and nuts when possible. Also helps lining up parts during reassembly. Gary