Broken Engine Mounts

[Cedaw]

My 2011 X55 keep breaking the front starboard motor mount bushings. I have the Cadillac supercharged 6.2L LSA motor, and the mechanic shop manager(Tige dealer) told me that it was because of the torque of the engine. It also results in the prop shaft seal to go out and I’ve replaced it three times now. I’m thinking of having the new local MasterCraft dealer replace the prop shaft and replace both front motor mounts, he replaced the prop shaft seal last summer and it lasted less than 50hrs.
Anyone else have this issue? Any suggestions?


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[mikeg205]

Wow..... maybe less pitch on the prop... easier on throttle? following

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[jpwhit]

Has the alignment been checked?

[Olaff]

Cadillac "turbo" motor? is this a turbo charged V-8? The reviews from 2011 spec an Ilmor MV8 6.2L with 430hp and 446 ftlbs of torque. Also, this is a V-drive, no?
Albeit a big and heavy boat with a lot of power, all that should be over-engineered to keep from breaking motor mounts.
Starboard-front... may by overtorqueing. To you drop the throttle to the firewall from dead stop frequently?

[Cedaw]

Broken Engine Mounts

Has the alignment been checked?

Yes last summer when the local dealer replaced the prop shaft seal, and less than 50 hrs use since.


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[Cedaw]

Cadillac "turbo" motor? is this a turbo charged V-8? The reviews from 2011 spec an Ilmor MV8 6.2L with 430hp and 446 ftlbs of torque. Also, this is a V-drive, no?
Albeit a big and heavy boat with a lot of power, all that should be over-engineered to keep from breaking motor mounts.
Starboard-front... may by overtorqueing. To you drop the throttle to the firewall from dead stop frequently?

Isn’t google wonderful? Everyone is an expert now with a few clicks. No I don’t hammer the **** out of my boat, it cost 150k new and it needs to last me. I’m surprised there hasn’t been anyone else have this problem, there is a reason they sell replacement bushings, and now have a new part number.


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[Olaff]

Isn’t google wonderful? Everyone is an expert now with a few clicks. No I don’t hammer the **** out of my boat,
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A little sensitive? Just asking to confirm, no accusations there brother.
So is it a Turbo charged V-8 or not? Google expert. Hmph.

[Cedaw]

A little sensitive? Just asking to confirm, no accusations there brother.
So is it a Turbo charged V-8 or not? Google expert. Hmph.

It’s a Turbo 6.2L V-8. It only had 454 hrs and is ten years old. Some bushings were replaced in 2016 along with prop shaft seals by the Tiga dealership ( no MastCraft dealer here then) no specific info on which bushings were replaced. Went back this week to get shop records and they claim they haven’t seen this issue since or before. Shop Forman said they have problems with the lag screws rounding out mounts and stringers though, and I should check those and bushings and alignment every 100 hrs or yearly. With the change in the bushings part number makes me wonder if it’s been up graded. Still no one has had this issue? Puzzling.


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[TolCarMan]

You have the Indmar 6.2 supercharged LSA (same motor that was in the CTS-V of that era). I think it runs 540 hp/540 lb tq. Tons of power even by todays standards. I'm sure a reason why we haven't heard of these issues before is because MC only put the LSA in a handful of boats, and yours happens to be one of them... needless to day it has its pros and cons lol. I've heard stories of this engine blowing through transmissions in Malibus and have come to realize those older parts (such as your motor mounts and prop shaft) are not quite up to the task of handling the power of the LSA.

Wish I could help more. Following.

[88 PS190]

Benefit of a boat is you can always drive it softer. So if its breaking mounts.... Maybe don't drive it like that?

A lot of boats have the torque to literally tear up their underwater gear and they rely on the ship's captain to restrict themselves and transfer power properly.

If this was a tug boat and it kept breaking cables the owner of the ship line would fire the operator. Same thing this is a boat with more power than it needs and it is on the operator to manage that power appropriately.

[Olaff]

You have the Indmar 6.2 supercharged LSA (same motor that was in the CTS-V of that era). I think it runs 540 hp/540 lb tq. Tons of power even by todays standards. I'm sure a reason why we haven't heard of these issues before is because MC only put the LSA in a handful of boats, and yours happens to be one of them... needless to day it has its pros and cons lol. I've heard stories of this engine blowing through transmissions in Malibus and have come to realize those older parts (such as your motor mounts and prop shaft) are not quite up to the task of handling the power of the LSA.

Wish I could help more. Following.

THERE WE GO! Not “turbo”, but supercharged. So that allows us to reach a more rational conclusion. Wasn’t aware of any turbo-charged V-8’s in modern gas tow boats. And the normally aspirated V-8 shouldn’t have been ripping motor mounts apart. But add 25% more Horsepower and torque (especially torque, which a turbo wouldn’t affect as significantly) and oualla, we have our answer. Heavy boat, powerful engine; you found the weak link in the system.

[Olaff]

Benefit of a boat is you can always drive it softer. So if its breaking mounts.... Maybe don't drive it like that?

A lot of boats have the torque to literally tear up their underwater gear and they rely on the ship's captain to restrict themselves and transfer power properly.

If this was a tug boat and it kept breaking cables the owner of the ship line would fire the operator. Same thing this is a boat with more power than it needs and it is on the operator to manage that power appropriately.

X2. Also Cedaw, I see in your profile that you are the owner of a 1997 Commodore with twin “mercs” (assuming that is 2 Mercruiser 350ci Sterndrives). I bet with a couple of beers and a few bikinis a Captain may be encouraged to firewall those throttles from a standstill and not experience too much stress on the drivetrains.

When I was a crewmember on the KC-130’s we had a Pilot who transitioned over from Harriers. He earned the call sign “O.T.”; shortened from Captain Overtorque. His turbo-fan jet throttle habits didn’t bode well in a turbo-prop. He learned his lesson when the C.O. made him (on a blazing North Carolina Summer day) assist with hanging the 3rd engine he twisted. On the first two he said “I advanced the throttles normally.” The Flight Engineers got wise to his antics and caught him on the 3rd one.

[1redTA]

I worked in a machine shop while re powering and replacing the running gear on a few tug boats and supply boats, the shafts were sized for the engine/clutches being run and a Detroit 12149 isn’t exactly an engine that revs really fast swinging a huge prop and shaft.

I’m glad to see a new bushing has been designed for your combo. It will be interesting to see if this fixies the problem

[Cedaw]

X2. Also Cedaw, I see in your profile that you are the owner of a 1997 Commodore with twin “mercs” (assuming that is 2 Mercruiser 350ci Sterndrives). I bet with a couple of beers and a few bikinis a Captain may be encouraged to firewall those throttles from a standstill and not experience too much stress on the drivetrains.

When I was a crewmember on the KC-130’s we had a Pilot who transitioned over from Harriers. He earned the call sign “O.T.”; shortened from Captain Overtorque. His turbo-fan jet throttle habits didn’t bode well in a turbo-prop. He learned his lesson when the C.O. made him (on a blazing North Carolina Summer day) assist with hanging the 3rd engine he twisted. On the first two he said “I advanced the throttles normally.” The Flight Engineers got wise to his antics and caught him on the 3rd one.

Not sure of your point, and no the Regal will barely plane out, even after I upsized the trim tabs. High quality floating trailer is all it is. The 30-40 ft Regals run circles around it. Last trip to Lake Powell we never exceeded 1500 RPM, just putted around. Oh and you can skip the prop talk, wasn’t born last night. Now my old 94 21’ 215 Glastron 215SSV with carb 454 and bravo 1 that hauled ***, and never bla bla bla bla bla bla bla. FOCUS, please anyone have experienced motor mount bushing failures?


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[Olaff]

What? Prop talk? Wasn’t born last night?
“the Regal will barely plane out”, “Glaston... bravo 1” - that is the point. The conclusion is that your throttle habits with stern drives that don’t have either the torque and hp or the weight in front of an individual screw like your 540hp Supercharged Mastercraft that you ballast out and then drop the throttle is twisting your engine loose.
Maybe a lack of experience or understanding of physics, force, inertia, leverage, torque, and materials prevents you from getting it. But I would bet if you opened the engine hatch and watched in the back while someone else firewalled your throttle from dead in the water and spun your engine from 800 to 4,000 rpm in an instant, you would understand.