Engine Mount Torque

marob

Well-known member
Joined
Dec 19, 2020
Messages
79
Fluid Motion Model
C-28
Vessel Name
Viking Rose
I was cleaning in the engine compartment when I noticed one of the engine mount nuts was finger tight. Just need to know how much to tighten and is this common. Our boat is a 2021 and bought new.
 
If you are talking about the large nuts that hold the engine and alignment in place. (4) of them. I would first check your engine alignment to confirm it is correct. Many times when a top mount nut is loose this is because that mount has a (soft foot). If it has a soft foot, when you tighten down it pulls the engine down and changes the alignment. Chances are if the mount nuts are loose the alignment needs some tuning. Once the alignment is checkered and confirmed to be with-in spec lock down each nut. I'm sure there is a torque spec but it is usually hard to get a torque wrench on the nuts because of clearance. I use a properly sized wrench and get each nut GOODEN TIGHT! After the nuts are fully tighten, confirm alignment did not change. While you are doing this check the lag bolts that hold the motor mounts to the stringer. There is wood placed in the stringer for anchoring the engine using the lag bolts. The lags also can become loose.
 
BB marine":1qhvbvp8 said:
If you are talking about the large nuts that hold the engine and alignment in place. (4) of them. I would first check your engine alignment to confirm it is correct. Many times when a top mount nut is loose this is because that mount has a (soft foot). If it has a soft foot, when you tighten down it pulls the engine down and changes the alignment. Chances are if the mount nuts are loose the alignment needs some tuning. Once the alignment is checkered and confirmed to be with-in spec lock down each nut. I'm sure there is a torque spec but it is usually hard to get a torque wrench on the nuts because of clearance. I use a properly sized wrench and get each nut GOODEN TIGHT! After the nuts are fully tighten, confirm alignment did not change. While you are doing this check the lag bolts that hold the motor mounts to the stringer. There is wood placed in the stringer for anchoring the engine using the lag bolts. The lags also can become loose.


Do you have any info regarding the lag bolts going into the stringers I have on lag bolt that will not tighten just spins loose I wasn’t sure if fluid motion runs just would of added a metal plate that is threaded for the lag bolts to go into?
 
Not sure about your C-28, however on my RT25SC I was told there is an aluminum plate in the stringer that the lag bolts screws into. This was discovered when my boat was being re-powered with a different engine than originally installed by the factory. Maybe all you need to do is install a larger lag bolt. I would contact the factory and get advice from them. Be sure to check engine/shaft alignment.
 
The Cutwaters have wood glassed to the grid stringer for the Lag bolt to grab. Old school build that proved to be inferior over the years. I know of many Ranger and Cutwater owners that have experienced the same issue lag bolts stripping out. I know of a few that the wood was not placed properly when the stringer /grid was molded and the lag was only catching fiberglass.

I had one lag strip out in my C26. I removed the mount and drilled a 1/2" hole where the lag was stripped. I then epoxied a 1/2" dowel rod (oak) into the hole. Once the dowel rod was set and epoxy hardened. I drilled a 5/16" hole in the center of the rod. This gives the lag something to grab.

The aluminum plate is what the factory should use. This would be tapped with a machine thread and a standard machine bolt used. This is the preferred way and an industry standard for most backing plates on boats. The wood backing plates went out years ago. If it is aluminum and a lag bolt is used that is not a good way to fasten an engine to a stringer. That is not even old school that is shade tree at best. I think the factory may have given some incorrect information or their method is a bit crude. Why would they not tap the aluminum plate using a machine screw? This would be a forever/never fail fastener??
 
Brian,

Using a lag bolt on the original engine was what I was told by the folks doing my re-powering. The re-power folks did what you suggested by drilling and taping into the stringer plate to attach blocks that support a shorter and narrower engine. Those aluminum blocks were then drilled and tapped to accept the engine mounts.

If it is an aluminum plate, my suggestion to use a bigger lag bolt is inappropriate. Drill out and tap for a machine bolt.

Dick
 
BB marine":5th2aj2f said:
The Cutwaters have wood glassed to the grid stringer for the Lag bolt to grab. Old school build that proved to be inferior over the years. I know of many Ranger and Cutwater owners that have experienced the same issue lag bolts stripping out. I know of a few that the wood was not placed properly when the stringer /grid was molded and the lag was only catching fiberglass.

I had one lag strip out in my C26. I removed the mount and drilled a 1/2" hole where the lag was stripped. I then epoxied a 1/2" dowel rod (oak) into the hole. Once the dowel rod was set and epoxy hardened. I drilled a 5/16" hole in the center of the rod. This gives the lag something to grab.

The aluminum plate is what the factory should use. This would be tapped with a machine thread and a standard machine bolt used. This is the preferred way and an industry standard for most backing plates on boats. The wood backing plates went out years ago. If it is aluminum and a lag bolt is used that is not a good way to fasten an engine to a stringer. That is not even old school that is shade tree at best. I think the factory may have given some incorrect information or their method is a bit crude. Why would they not tap the aluminum plate using a machine screw? This would be a forever/never fail fastener??


Ok good to know rather disappointing to know it’s only wood securing the d4, during my survey they noticed the bolt had backed out and my surveyor said he would have tightened it up but didn’t have a wrench I think it then go tossed on the back burner and forgotten in leu of some other issues that needed attention. I was in a different state during all this other wise I would have found this out.
 
TristenT":dgusnzc9 said:
Ok good to know rather disappointing to know it’s only wood securing the d4, during my survey they noticed the bolt had backed out and my surveyor said he would have tightened it up but didn’t have a wrench I think it then go tossed on the back burner and forgotten in leu of some other issues that needed attention. I was in a different state during all this other wise I would have found this out.


Wood used to lag a engine down to works. It was done for years by many quality boat builders. The issue with using the wood became a problem because many boat builders did not fully encapsulate the wood in resins, to protect the wood from moisture. Moisture is always present below the water line. Even the manufactures that had high standards in manufacturing and build processes would have failures to the wood in the stringers because improper sealing of the holes that were drilled into the wood. This seemed to be the biggest issue with wood used for reinforcement in fiberglass boats. Anytime a hole is drilled into the fiberglass there is wood backing it needs to be well sealed. If it is not, water penetrates and the wood rots. During the 60's, 70's, 80's and up to the mid 90's using wood as backing material in the transom and decks was common. Most engine beds were structurally made with wood and the encapsulated in fiberglass. The problem with this method was the wood in many cases was poorly encapsulated in resins. The other problem was when equipment (engines), deck fittings, ladders, the list is long are mounted and improper sealing occurred. There was structural failure (Rot). The other cause of failures in structural wood is improper drilling . Holes to large for the fastener used. Holes not drilled straight causing a failures at the anchor point and the fastener strips out after a short period of time. I worked in the marine industry during 80' 90's and early 2000's and made many repairs. including complete transom replacements, wood stringer replacements, deck replacements. All because wood was used and not sealed and fastened to correctly.


In the mid 90's the manufactures learned that the boating industry was getting a bad reputation. Quality boat builders were loosing customers because the manufactures products were known for wood below the water line, above the water line, resulting in rot. The new marketing was NO WOOD BELOW THE WATER LINE. or we do not use wood in our stringers, transoms, or backing plates. This was a big selling point for the manufactures and a good thing for the consumer.

Wood is strong and makes a good structural frame. It just needs to be done correctly and kept dry. I have a 2002 Mainship Pilot that has all wood stringers. The wood stringers used in the engine room are well sealed and the boat has a good drain system design. When I purchased the boat I did moisture readings every where I could on the boat. I did find a few places in the decks that moisture readings were above 20%. The cause was loose fasteners and poor sealing. I did make repairs to these areas. The stringers were showing 12% which is pretty good for a 20 yearly boat. I did do a core sample and it proved to be dry wood. If it is done correctly and sealed correctly the wood works but does not meet todays standards in boat building. The engine bed in the Mainship has 1/2" aluminum backing plates and aluminum mounting tables. A good way to mount an engine. This was Mainship standard 20 years ago.


Today there are not many boat manufactures that use wood for structural. Wood is generally used for cosmetic or trim work. There are marine products made that are as strong as wood if not stronger but not suspect to rot that causes loss of structural integrity. Aluminum backing plates are used today along with many well known compositions materials that have proven to be lighter, stronger and increase the integrity of the boat.The quality boat builder has adopted the practice of using these products along with new technology in the fiberglass lay up processes. The old school hand laid, sprayed and rolled process is gone. This is not to say it doesn't work. It does and has been done for years. But the results have shone to have integrity issues as the boat ages. Learning from experience is better than saying, this is the way it has always been done.

My point of this is wood works. It will hold your engine in place. Make sure the lag maintains a tight hold. If it doesn't make a repair that is structurally as strong if not stronger then it was. Make sure that every thing that is fastened to the boat is sealed. Sealed well! My findings while owning my C26 Cutwater was during manufacturing sealing fasteners and fittings was not a top priority in the manufacturing process. I found many areas of that water was leaking into the boat. All the storage compartments have wood flooring that is gel coat sealed on the top side but unsealed on the bottom side. There are rangers and Cutwaters ten year or less that have a significant amount of rot in theses areas. I have seen it and talked to owners that had to make repairs. This should have been either resin sealed or better yet a composite material used. That cost money, Cutwaters and Ranger Tugs cost money. Fluid Motion builds a very nice boat. I could never figure out why they skimp on build processes. The consumer loves their product and they are paying a lot of money for it. A few extra $1000.00 even $ 10,000.00 per boat using better methods in the build process will easily be accepted by the consumer that wants a Fluid Motion product. My opinion.

A 2023 Regal 28' Express has the same amenities as a C288 retail manufacture price is 100,000.00 less than the Cutwater. The boat has half the horsepower compare to the C288. The Regal weighs 2500 lbs less, cruises on plane @ 24mph with a 9 GPH burn getting 2.5 mpg. The Cutwater C288 at 1000 rpm burns 2.6 gph making 5.8mph and getting its best fuel economy of 2.2 mpg. The optimum cruise speed is 30 mph getting 1.4 mpg. My point, I'm not saying the Regal is a better boat ( they use up to date build processes ). I'm saying the customer that is purchasing a Cutwater is willing to spend more money for a comparable boat because they feel that the Fluid motion product is better quality. Better than proven production line boats. The Ranger and Cutwater consumer will spend more money to power it too. So why doesn't Fluid motion build to the highest standards using the newest quality build products and technics ? Yes it will cost more money. But their boats are already expensive and customers are standing in line to purchase a boat!!!

Tour the factories of some of the major players in the marine industry. Apples to Apples, manufactures that are producing 28' boats that cost over 300K or 25' boats over 200K. Compare their build processes. You will be amazed at the technology used in the build of the boats today.
 
TristenT":2efjims9 said:
Do you have any info regarding the lag bolts going into the stringers I have on lag bolt that will not tighten just spins loose I wasn’t sure if fluid motion runs just would of added a metal plate that is threaded for the lag bolts to go into?

I have a 2021 C-30S and also found the forward most lag bolt, port side forward engine mount (not the alignment bolts) was free-spinning as you describe.

I wound up having a local boat yard conduct a fiberglass fill and repair and then tapped that for the new bolt stud.
 
JDubya":2hkhqawl said:
TristenT":2hkhqawl said:
Do you have any info regarding the lag bolts going into the stringers I have on lag bolt that will not tighten just spins loose I wasn’t sure if fluid motion runs just would of added a metal plate that is threaded for the lag bolts to go into?

I have a 2021 C-30S and also found the forward most lag bolt, port side forward engine mount (not the alignment bolts) was free-spinning as you describe.

I wound up having a local boat yard conduct a fiberglass fill and repair and then tapped that for the new bolt stud.



Gotcha kinda one of those thing you don’t want to deal with but isn’t really that hard to fix I’ll probably get after it in a few weeks here and do a similar repair
 
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