Top Mount Bolts Snapping

[Banana Shark Dave]

Mercury 300xs

A few days before the CTC I broke my top mount bolts and they were replaced with two more of the high tensile bolts with the Allen key heads at £10 each. Suppose to be the strongest there is.

Well they have snapped again. Does anyone know of a solution to this????

They already go into a solid mount.

Many Thanks

Dave

 

[Captain Chaos]

Usually that means you've tested the product to distruction. So probably the answer is to go a little easier on them!

 

[Banana Shark Dave]

Broken bits

Captain Chaos Sir, this is suppose to be racing engine, it's an offshore leg ect..

In fairness with the exclusion of a silly 5 minutes I have been driving thinking of my wallet rather than how I'd like to :/

All these companys that make them go faster would be better spending there time trying to get them to stay together!!!!

 

[nickskip]

Mounts

Dave I can make you a set out of nitronic 50 stainless steel,it's double the strength of 316 or you can have them the same as merc original hi tensile,
Pm me if interested,nick.

 

[RossM]

Stainless steel is like cheese compared to a 12.9 HT bolt

 

[racefan]

I'd normally recommend a trip to your local ARP dealer, but I don't think they do 1/2" in that length.

Seems odd that you've broken the new ones so soon. Sounds like an installation problem to me, You sure there isn't something out of kilter thats causing the breakage?

 

[Frenchbruno]

2 possible references and size availables, depend the serial number of your engine.
On one generation they are UNC and on the other they are Metric
for the metric type the steel grade is 8.8
for the UNC grade 5 is ok
Don't go to higher grade on these bolts as the shear effect on these bolts is important due to the weight of the powerhead when impacting waves? and they broke.
Here a link where you can choose a lot of bolt from your caterpillar dealer.
http://www.hpetersen.com.py/repuestos/pdf/hardwre.pdf
Don't forget to choose the nut is the same steel quality of the bolt steel too, and same for the washer choose the same steel grade quality.
don't forget to use the torque recomandation by mercury too:
NOTE: A – Torque nut to 120 lb. in. (13.5 Nm) and then back off 1/4 turn.
Hope that helps.

 

[RossM]

2 possible references and size availables, depend the serial number of your engine.
On one generation they are UNC and on the other they are Metric
for the metric type the steel grade is 8.8
for the UNC grade 5 is ok
Don't go to higher grade on these bolts as the shear effect on these bolts is important due to the weight of the powerhead when impacting waves? and they broke.
Here a link where you can choose a lot of bolt from your caterpillar dealer.
http://www.hpetersen.com.py/repuestos/pdf/hardwre.pdf
Don't forget to choose the nut is the same steel quality of the bolt steel too, and same for the washer choose the same steel grade quality.
don't forget to use the torque recomandation by mercury too:
NOTE: A – Torque nut to 120 lb. in. (13.5 Nm) and then back off 1/4 turn.
Hope that helps.

Dave, your bolts are 1/2" unc.

Frenchbruno why are you recommending grade 8.8 and grade 5 when 12.9 is stronger in sheer as well as tensile strength, its also what Mercrury fit as standard!

 

[Frenchbruno]

METRIC or UNC

Dave, your bolts are 1/2" unc.

Frenchbruno why are you recommending grade 8.8 and grade 5 when 12.9 is stronger in sheer as well as tensile strength, its also what Mercrury fit as standard!

Not exactly ROSSM!
I've a merc racing engine too, 250 XS mod 2004 and the upper mount bolt are stamped grade 8.8, and it's original bolt form MERC racing factory, after 10 years of use they are still at the same location.
For the use of like 12.9 I've seen several times they don't like shear effect and hi vibration installations.
On some German engine too , after discussion with engineer from the builder following warranty problem on massive broken bolts, they proposed when the bolt is made in a hi grade if you need more ''elesticity'', install a longer bolt and a spacer on it( this proposal works at perfection). For this application it's not possible.
So after another discussion with 2 another mecanical engineers againfor Dave's problem, they agree to reduce the grade to grade 8.8 than using grade 12.9 which apparently breaks on Dave's 300XS.

on serail 1E052058 and up the screw rep 21 is sold in 2 references
8M0000517 which is M12x190
108M0000517 wich is M12x175
I don't have the serial number of daves engine so Metric is a possibility
on serial 1E001867 thru 1E052057
Serial 1E051205 & Up the screw reference is
8M0000517 which is M12x190

on serial 1E051204 and below the bolt reference is: 108495811
diam 1/2-13 lenght 7.75 inches

That's why I wrote the bolt is possibly a metric size, but Dave with his serial number will be able now to find out the good reference for his engine.
Over torque is also a possibility of the broken bolt on Dave engine.
Hope this explanation is good enough now....

 

[RossM]

Yawn, okay run the fudge bolts then.
I'm sure 'elastic bolts', solid mounts and a 200 kg slide hammer will last for ever running hard offshore

sorry using merc's stock part was a bad example, as they are clearly cost cutting, my engine came with 12.9 bolts, however the part number is now a gr8.8 hex head....

Merc have since moved to the cheaper and even weaker M12 bolt.

Grade 12.9 has higher tensile strength and higher sheer strength, use which ever one you want.

p.s if your worried about vibration why are the rod bolts in your engine ultra high tensile, pretty sure there's more vibration there.

[/COLOR]
Not exactly ROSSM!
I've a merc racing engine too, 250 XS mod 2004 and the upper mount bolt are stamped grade 8.8, and it's original bolt form MERC racing factory, after 10 years of use they are still at the same location.
For the use of like 12.9 I've seen several times they don't like shear effect and hi vibration installations.
On some German engine too , after discussion with engineer from the builder following warranty problem on massive broken bolts, they proposed when the bolt is made in a hi grade if you need more ''elesticity'', install a longer bolt and a spacer on it( this proposal works at perfection). For this application it's not possible.
So after another discussion with 2 another mecanical engineers againfor Dave's problem, they agree to reduce the grade to grade 8.8 than using grade 12.9 which apparently breaks on Dave's 300XS.

on serail 1E052058 and up the screw rep 21 is sold in 2 references
8M0000517 which is M12x190
108M0000517 wich is M12x175
I don't have the serial number of daves engine so Metric is a possibility
on serial 1E001867 thru 1E052057
Serial 1E051205 & Up the screw reference is
8M0000517 which is M12x190

on serial 1E051204 and below the bolt reference is: 108495811
diam 1/2-13 lenght 7.75 inches

That's why I wrote the bolt is possibly a metric size, but Dave with his serial number will be able now to find out the good reference for his engine.
Over torque is also a possibility of the broken bolt on Dave engine.
Hope this explanation is good enough now....

 

[kitten]

Sounds to me like something is hammering. Do you have bungee on the leg?

 

[Frenchbruno]

p.s if your worried about vibration why are the rod bolts in your engine ultra high tensile, pretty sure there's more vibration there.

No, I've no vibration on my engine connecting rods, If it is your case it should be a problem soon... for you.
The steel quality for rod bolts is not the same than 12.9 grade as you for sure already know.
My engine is from merc racing and use 8.8 without problem,if you don't like grade 8.8 recommended by the engine manufacturer it's up to you.But after 10 yeras of use I think this perid is not also a bad experience.
If you use 12.9 and have no problem whith them it's perfect too.But Dave wrote he used Hi strenght bolt Allen head without success, unlucky,may be a defective bolt? So he need advices to improve this.
Mercury employ many engineers to test products and if you don't trust them what I can do ! For sure some parts can be improved and even Merc sometimes makes strange design, like SM geargase seals support under the water pump.
I've seen many broken hi strenght bolts when installing on system with hi vibrations (and not on small 300hp outboard). And seen also a few bolt with defect in metal, may be the case of the broken Dave's bolt.
There are also many discussions on Hi strenght bolt more brittle than lower grade, I 'm not telling you the 12.9 is weaker than a 8.8 not at all, I hope you understand what I'm trying to explain.
This thread is to help Dave to find a solution, as Kitten suggest , does Dave have bungee in the engine leg...Better to check if there is a ''play'' in the swivell and on the lower mounts.

 

[Paul E]

12.9 or 8.8, they shouldn't be bending and snapping after a few weeks use...

There must be an underlying issue - torqued too much or not enough, something else loose causing big shock loadings, could be many things

 

[Marinautic]

Merc have since moved to the cheaper and even weaker M12 bolt.



.

That's not strictly true.

The 1/2" socket head bolt is used in the H/D swivel bracket, the M12 hex head metric is used in the Std swivel bracket.

Either type doesn't break that often, so you need to find what's causing the problem.

 

[Frenchbruno]

May be comparing your broken bolts with the pictures on this renowned bolt maker you can have a path:
http://arp-bolts.com/p/technical.php#p7TPMc1_3
Hope you still have the old bolts for comparison.

 

[Renegade]

Is yours on a genuine 300xs offhore mid?

 

[racefan]

Captain Chaos Sir, this is suppose to be racing engine, it's an offshore leg ect..

In fairness with the exclusion of a silly 5 minutes I have been driving thinking of my wallet rather than how I'd like to :/

All these companys that make them go faster would be better spending there time trying to get them to stay together!!!!

Maybe it's a harmonics issue, caused by an inbalanced flywheel