Broke something...its not pretty...

[westcoaST]

I pulled mine, got it penetrant inspected at work. No problems. I did the same thing with the roll resistor bolts, but I did buy at least two sets of them. No problems with the upper mount bolts. Small Crack in the roll resistor bolt.

 

[mercdank]

Someone with knowledge of the motor and transmission mount locations should post a little guide with the specific torque values for each. I'd incorporate this initio my pre/post track inspections.

 

[Sourskittle]

I broke that bolt in Dec 15 or so, and it ended up costing me about $300 total.

When I used to break bolts in my srt4 ( also uses a stock neon mount in the same place ), the only solution I ever found was to drill the bulk head out and put a bigger grade8 bolt in its place. I broke a 12.9 hardness bolt before that. The harder bolt actually broke easier because the shock. The grade8 bolt flexed a little before snapping. The bigger bolt fixed it for good.

We could always run a stud down into the mount and double nut the top, its not going to pop two bolts worth of threads off at once...

My friend had this happen to him on the street as well. He ended up having to replace the entire mount because it destroyed it. Luckly, he works at a dealer.

 

[westcoaST]

The numbers on metric bolts do not correspond to hardness, but to ultimate tensile strength and yield strength. You can purchase a higher strength bolt that has more % elongation, you just have to pick the right bolt. On a previous post, I went over what the metric classes of bolts mean. Get some A286 or PH stainless metric marine or aerospace bolts. You will not need to bore out your mating mount holes, and the bolt will yield without snapping.

 

[Sourskittle]

The numbers on metric bolts do not correspond to hardness, but to ultimate tensile strength and yield strength. You can purchase a higher strength bolt that has more % elongation, you just have to pick the right bolt. On a previous post, I went over what the metric classes of bolts mean. Get some A286 or PH stainless metric marine or aerospace bolts. You will not need to bore out your mating mount holes, and the bolt will yield without snapping.

Lol. Your obviously light years ahead of me on this one, lol. Just tell us what to buy and where to buy it from, lol.
PS: I took those shaving samples you asked for and also have a solid sample as well, I just need to mail them still.

 

[Wimp Lo]

I'll agree that the strength and ductility are not always inversely proportional but generally they track that way.

The amateur racers I know use grade 5 out of cost, convenience and generally being strong enough. Going exotic is very expensive in a race car and I would rather have an inexpensive street car.

Any way in engineering there is the idea of a design factor, a part should be designed so that the expected load is below the yield limit at the number of expected cycles in its service life.

Obviously the design factor was low and changing the load by a Cobb tune pushed that below 1.0 so it broke. With the life time I saw, I'm estimating that the strength was about 80% of a 1.0 factor part and I like the sound of a 1.4 factor a lot better than 1.0 so I need a bolt with a fatigue limit about 75% higher than a 12mm 10.9 bolt or close to that. A super alloy isn't going to do that without being as brittle as glass. I can gain a little with super alloys but I suspect an improvement of more than 10% or so is unlikely. The UNF thread form gives me a few more but fastener diameter is the only practical way to get the other 60% and solve the problem for good.

I have a DHM Quick Spool turbo kit coming so the problem is only going to become more critical for me...

 

[koozy]

IIRC, this issue occurred with the OE Rear Motor Mount. Has this happened to anyone with an aftermarket RMM?

 

[Wimp Lo]

The motor mounts do two things, absorb vibration and resist drive shaft torque. I'm pretty sure vibration isn't the problem.

The lower mount that the aftermarket has improved resists a front to back motion, the side mount resists the vertical component.

My car never had the banging sounds that the RMM upgrades are supposed to cure which is why I never did an upgrade.

Any way, I'm not sure if that means my RMM was stiffer than most or my engine compartment has more wiggle room.

In preparation for my DHM kit, I'm going to install a Powerflex RMM large bushing which seems to be the softest upgrade available (because I want to avoid false knock) and I intend to address the side mount fastener. Hopefully the third mount won't become the weak link.

 

[koozy]

well... I installed the Cobb RMM early, false knock is null and I haven't experienced a broken mount bolt even with clutch dumps so just wondering if a stiffer RMM may be a preventative measure for a broken bolt.

 

[dyn085]

well... I installed the Cobb RMM early, false knock is null and I haven't experienced a broken mount bolt even with clutch dumps so just wondering if a stiffer RMM may be a preventative measure for a broken bolt.

I don't think anyone has broken an RMM bolt and I don't think anyone has experienced legitimate false-knock either. If anything a stiffer RMM should make the stud more likely to fail due to the additional torque having to be distributed there instead of absorbed/distributed by the RMM.

 

[koozy]

I don't think anyone has broken an RMM bolt and I don't think anyone has experienced legitimate false-knock either. If anything a stiffer RMM should make the stud more likely to fail due to the additional torque having to be distributed there instead of absorbed/distributed by the RMM.

yeah, I don't think I've read of anyone that has broken a RMM bolt. I haven't really taken a look at the mounts to see what's what because I haven't needed to, but was just thinking that a stiffer RMM prevents movement not just back and forth, but overall which may prevent stress on the trans mount bolt. Looking back at a few responses to this thread I see that the question whether an aftermarket RMM may help has been answered before. We need more data from others with or without an aftermarket RMM who have snapped a bolt.

http://www.fiestastforum.com/forum/...g-its-not-pretty?p=79196&viewfull=1#post79196

 

[dyn085]

yeah, I don't think I've read of anyone that has broken a RMM bolt. I haven't really taken a look at the mounts to see what's what because I haven't needed to, but was just thinking that a stiffer RMM prevents movement not just back and forth, but overall which may prevent stress on the trans mount bolt. Looking back at a few responses to this thread I see that the question whether an aftermarket RMM may help has been answered before. We need more data from others with or without an aftermarket RMM who have snapped a bolt.

http://www.fiestastforum.com/forum/...g-its-not-pretty?p=79196&viewfull=1#post79196

That is not a good example of whether the RMM helped considering the fact that he had already replaced the stud. Now you have an added variable and it very well could have not broken again even without the RMM change. An assumption, but a reasonably logical one.

Torque is created and transmitted in the direction of the engine, perpendicular to the vehicle. While the front motor mounts are essentially there just to hold the engine in, a certain amount of torque will and does get transmitted through them. It's not uncommon in many communities to upgrade one mount just to cause a separate to fail. Considering the fact that the upper mounts are the same as the na model, it's not a huge stretch to assume that there will be more.

I definitely agreed that more people will have to break mounts for us to establish a trend.

 

[westcoaST]

I took my FiST to the dealer in September, last year to get the trans pulled in order to fix a squeak in the clutch bearing. They did not properly torque down the RMM bolt that attaches to the trans housing after they put everything back together, and it broke about a week later. They promised to get me a replacement bolt but that never happened, so I needed to pull a piece of the RMM bolt out of the trans housing, and had to look for a RMM replacement bolt. I used a left hand drill to remove the RMM bolt that remained in the transmission housing.

I ordered a replacement bolt from bolt depot, made out of 17-4PH stainless steel. I then got it penetrant inspected, then installed it and torqued it down with my torque wrench. Torque values can be obtained from the boltdepot website or other sources, including the Helms manual.

This fastener is much stronger than the OEM bolt.

 

[Wimp Lo]

False knock has been data logged very legitimately and seen many times anecdotally. It is real, the causes are a bit hard to track down but having a super stiff RMM doesn't help.

My theory is that the low gear torque is placing an upward thrust on the engine and the hydraulic mount is not stiff enough to slow that vertical leap to 0 before the mount tops out and the motor mount bolt gets shock loaded. My proposed solution is to make the bolt big enough to survive that shock loading for the life of the car.

A stiffer RMM should reduce the movement of the engine, possibly slowing the vertical leap and certainly increasing the loading on the RMM bolts.

I don't think anyone has actually blown out the hydraulic mount, just the bolt so fingers crossed, I hope a bigger bolt and upgraded RMM will be enough to hold it together.

 

[koozy]

why not try out a replacement bolt made of 17-4PH stainless steel that is stronger than the OE like westcoastST did before trying a larger bolt, which would require some modding? seems like a simpler solution and if it breaks you still have the option to bore out to a larger bolt.

 

[dyn085]

False knock has been data logged very legitimately and seen many times anecdotally. It is real, the causes are a bit hard to track down but having a super stiff RMM doesn't help.

I should have been either less-vague or stated what I said in an easier manner to understand. Yes, false-knock can and does exist, but it's generally due to poor maintenance practices and has yet to be positively identified from a specific RMM (or any other specific aftermarket part, actually). A year ago there were lots of claims of RMM false-knock so I created a thread on how to diagnose it and the claims disappeared. The brand of RMM will have no impact on negative corrections as long as it's installed properly.

 

[Wimp Lo]

why not try out a replacement bolt made of 17-4PH stainless steel that is stronger than the OE like westcoastST did before trying a larger bolt, which would require some modding? seems like a simpler solution and if it breaks you still have the option to bore out to a larger bolt.

As I said, that is not going to give me the 75% increase in strength I am looking for but my plan is to swap in a replacement motor mount and replace my CV joint boot just in case it's torn. I will try to avoid temptation in low gears for a while, extract the broken bolt from my old mount, determine the size of a replacement (and share), then look to see if there is enough meat for the big upgrade. If the big bolt upgrade looks possible, I will drill and tap my old mount and swap it back in when I install my DHM kit.

If I break the new bolt before I get to the big bolt upgrade, I will replace the broken bolt with an upgraded bolt and hope that it holds. If my old mount with a big bolt seems to be too soft, I will do the big bolt mod on my new mount, swap and then look for a stiffer hydraulic motor mount with a good fastener that I could weld in to the Fiesta mounting brackets or else gut the old mount and fill it with urethane casting resin.

Bottom line I want a solution not a band-aid.

 

[twolf]

Shocking that this bolt survived it seems! haha

 

[dyn085]

It shouldn't be, crash forces are generally linear as opposed to radial.

 

[frankiefiesta]

As I said, that is not going to give me the 75% increase in strength I am looking for but my plan is to swap in a replacement motor mount and replace my CV joint boot just in case it's torn. I will try to avoid temptation in low gears for a while, extract the broken bolt from my old mount, determine the size of a replacement (and share), then look to see if there is enough meat for the big upgrade. If the big bolt upgrade looks possible, I will drill and tap my old mount and swap it back in when I install my DHM kit.

If I break the new bolt before I get to the big bolt upgrade, I will replace the broken bolt with an upgraded bolt and hope that it holds. If my old mount with a big bolt seems to be too soft, I will do the big bolt mod on my new mount, swap and then look for a stiffer hydraulic motor mount with a good fastener that I could weld in to the Fiesta mounting brackets or else gut the old mount and fill it with urethane casting resin.

Bottom line I want a solution not a band-aid.

I've been trying to find stiff hydraulic motor mounts for months can't find a damn thing.

I did come across some guy (on an old porsche forum post) who gutted and filled their hydraulic mount on some type of Porsche with success. I have my old busted mount sitting I plan on trying to fill it in the spring. If it works then it'll be a solution of some sort