Check your motor mount bolts..Today

[motocross269]

Well it is getting close to halfway throught the season so I decided to check my motor mount bolts...They were all at least a half a turn loose....I also tightened my TM mounting screws, they were loose as well...

[MadWags]

Talk about having a screw loose!

[motocross269]

Talk about having a screw loose!

Just a little loose...Must have been to many sudden stops,,,

[bassinman#1]

My 2005 TR-186 Triton has been tight since day 1.

[Firefighter Jeff]

Well it is getting close to halfway throught the season so I decided to check my motor mount bolts...They were all at least a half a turn loose....I also tightened my TM mounting screws, they were loose as well...

Thanks for the reminder. 

[SethV]

The motor mount bolts used by most OEM's are really a problem.  Many use brass fine thread nuts - they use brass to avoid galling, but there is a serious strength issue.  The fine thread SS with brass nuts was fine in the days of 150 hp motors, but with the heavy 250 DI motors and big jackplates, you are set up for failure.

I did some clamp load testing with the OEM fastners.  The nuts fail before the bolt - a major sin in fastener design.  You can not detect a failure until it is too late with this setup.

I put all new fastners on my boat, coarse thread all stainless with heavy hex nuts.  Ultimate strength tested over 50% higher than the stock configuration.  Of course, I still check the torque a couple times a month.

Seth

[motocross269]

Seth...Where did you get the SS bolts and nuts???

Do you just change them one at a time and re-silicone them in(jackplate to transom)?

Thanks
Brian

[djkimmel]

Loose motor mount nuts and bolts not good... Check them every time you get off the water. Particularly if you've run a ways or been in rough water. Over the years, I've seen many failures occur simply because the owner didn't regularly check the bolts and nuts. The alternatives to a habit of checking are very expensive and can be very bad.

My bolts on my Yamaha VMax HPDI 225 are longer coarse thread stainless steel on with double nuts also to make sure they stay tight. D & R Sports Center put them on for me a while back after my last outboards motor mount failed and I was fortunate to get the turn the key reliable Yamaha.

[SethV]

Seth...Where did you get the SS bolts and nuts???

Do you just change them one at a time and re-silicone them in(jackplate to transom)?

Thanks
Brian

I got them from Grainger - F593c spec.  They also have the heavy hex nuts.  I am in talks with ARP to produce a bolt kit for outboards that would be a high grade stainless, stronger than Grade 8 cold steel.  Won't be cheap....but neither are outboards.

You can change 1 at a time and not need a engine hoist.  Also, be sure to use a thread lube, something that will not generate too low of a k value, but prevent galling.  Swagelok's Blue Goop gave me a K experimentally derived of about .18 - .2.  With the lube, I went to 70 ft lbs, and this give about 2x the clamp load of fine thread brass at 85 ft lbs.

Seth

[DDBethke]

Thanks Moto... Always a good reminder! Mine were getting loose....

Duane

[LipRip]

If you use a locknut and blue locktite when you initially torque the nuts you shouldn't need to check them very often. Blue locktite is the berries!

[SethV]

If you use a locknut and blue locktite when you initially torque the nuts you shouldn't need to check them very often. Blue locktite is the berries!

Do not use loctite!  Nylock nuts are the way to go as they give a predictable prevailing torque.  Loctite will give you a false "ok" when you check the torque as you have no idea what the prevailing torque value is.

[zooker]

long trailering will also cause them to loosen..loc tight is ok on a lawn mower. never on an outboard for ANY reason...

zooker 

[LipRip]

If you use a locknut and blue locktite when you initially torque the nuts you shouldn't need to check them very often. Blue locktite is the berries!

Do not use loctite!  Nylock nuts are the way to go as they give a predictable prevailing torque.  Loctite will give you a false "ok" when you check the torque as you have no idea what the prevailing torque value is.

I understand what ur sayin SethV. I agree that using blue loctite will not allow you to get a 100% accurate torque reading when checking the torque, but, it will however keep them from backing off once you put the initial torque on them. Nylon lock nuts are good, but you will have to check the torque often.

Zooker, i bet you NASA uses loctite! Not just for lawn mowers anymore!

I'm an ASE Master Certified Medium/Heavy truck tech, Most trucks come from the factory with loctite on fasteners instead of locknuts because its more effective.I don't know if its bad to use loctite on your outboard motor mounts, but i don't see how it would hurt. Guess I need to ask a marine tech!

[SethV]

 

I understand what ur sayin SethV. I agree that using blue loctite will not allow you to get a 100% accurate torque reading when checking the torque, but, it will however keep them from backing off once you put the initial torque on them.

Nut may not turn, but that is not the only way you can lose torque on a clamp joint.  Even the best fiberglass will compress over time and stainless bolts stretch each and every time you load them.  In the load ranges that we are operating, the F593c spec SS bolts are not purely elastic.  Granted, it is a small amount, but these heavy motors and 1/2" bolts just don't get you a lot of safety factor.  I would love to see the industry go to 3/4" bolts.

Preload is the key here.  If you loose preload, then you get the motor mount in motion relative to the transom or jackplate.  This is when bolts bend/break and motor mounts also do not like to be flexed and they tend to break.  I have seen several broken motor mounts that I belive are a direct result of lost clamp load.  Typically the top bolts carry the most load due to the moment action of the engine.  Also, don't overtighten them to try and achieve more preload.  That will increase your preload for sure, but as the motor dynamically loads the bolts, you may enter into the plastic region of the bolt.  Then you will see a loss of clamp load for sure.

This is not really similar to the typical automotive joint that is way over designed.  Just trying to caution people here as this really is an industry wide problem with these bolts.  Loctite may be ok for some applications, but not this one.

Seth

[Bender]

Seth, I don't know much about stainless fastners, do they allow for any of the stretch like Grade 3? You said they are stronger then 8s, which do not stretch so I was wondering.

[SethV]

Seth, I don't know much about stainless fastners, do they allow for any of the stretch like Grade 3? You said they are stronger then 8s, which do not stretch so I was wondering.

Typical stainless fastners are about 50 - 80 ksi tensile.  This is a bit less than a grade 3 cold steel.  They are very "strechy", and although the elastic offset is close to the 2% similar to cold steel, they do have some plastic tendencies through all load ranges - but you MUST stay out of the purely elastic range.

When i mentioned the Grade 8's, that is a project i am working on with ARP - high grade stainless that is stronger than Grade 8 cold steel.  Exotic stuff, not cheap, not off the shelf.  Think funny car head bolts.  (building & designing 8,000 hp drag motors was a former job....)

Seth

[Durand Dan]

As an Engineering Manager in my last position for an OEM we discovered a product that greatly reduced effects on threaded applications due to vibration. Check out this website. I use some of the products, however I don't run a large motor as some of you do.

http://www.vibra-tite.com/light_cure_adhesives.jsp

[zooker]

When i mentioned the Grade 8's, that is a project i am working on with ARP - high grade stainless that is stronger than Grade 8 cold steel.  Exotic stuff, not cheap, not off the shelf.  Think funny car head bolts.  (building & designing 8,000 hp drag motors was a former job....)

Seth

yeah but over torque an#8 using lock tight and...






nuff said

zooker