View Full Version : Engine mounts/sliders

03-25-2007, 08:14 PM
I am in desperate need of information on the construction of an 83 mastercraft that I am rebuilding. I am getting to the end of the project and have hit a big dilemmas with putting the engine back in the boat. The engine sliders, that mount to the side of the bilge area, where very rusted due to some wood planks that the previous owner put over the top and we had to take them out and paint them to prevent any further corrosion.

Part of our project was to fix some separating floors so we cut out the floors, replaced the foam between the fiberglass stringers and reglassed the floor. However we only cut out a portion of the floor about 3 inches from where the sliders mounted. Now that we have replaced the carpet and are ready to put the engine sliders back in we are having a hard time getting the 4 inch lag screws to set. Every time we try to tighten they strip and do not get tight at all. This is on the port side of the boat, and do not know if it has something to do with the torque from the engine.

With few options the only thing that we could think to do was fill the holes with fiberglass cloth and epoxy, drill and try to tighten the lags. This resulted in the exact same thing. We desperately need to understand what those lags attach to and how we can reinforce in order to get those lags to hold tight. Any information would be very much appreciated.

here is a link to a sire where we have posted pictures on our project.




03-25-2007, 10:50 PM
I'm guessing that in an '83, the stringers are a piece of wood (2x6, maybe), covered with fiberglass. After many years, the wood tends to rot, which is why newer Mastercrafts make the stringers out of (I believe) solid fiberglass.

I think you're in for a fun time of cutting off the top of the fiberglass caps on the stringers, removing the rotten wood, replacing it, and reglassing the stringers.. Perhaps this is why the previous owner had put wood over the top of the engine mounts - he knew the stringers had rotted, and was trying to reinforce things.

I had a friend who did this to his old S&S; not as big a job as it sounds, at least if you have a cut-off wheel and a willingness to eat fiberglass for a few hours.


03-26-2007, 08:22 AM
Yeah, the stringers are definately rotted. They switched to fiberglass stringers sometime during '83 is the consensus on here I believe. Obviously they switched sometime after your boat was built. It's a shame that you've already re-carpeted.

03-26-2007, 12:10 PM
We've already pulled up the floors and replaced them because they were sperating from the Stringers. The stringers are without a doubt fiberglass. What I am trying to figure out is what these lags are screwing into. For instance in the attached picture I can't quite make out all the words, but this is the same architecure used on our 83.

I believe The wood over the top oif the sliders was actually to raise the engine cover about 4 inches to account for a perfect pass they had installed.

Bruce Carr
03-26-2007, 12:35 PM
Your late '83 will not have any wood in the hull. From the drawing, there should be an alumunum or steel angle under the deck which the bolts thread into. Do the bolts that you removed have very course threads like a large wood screw or are they finer threads like for a nut?

If they were originally drilled and tapped for machine threads (finer threads) then you will need to either move the bolt holes over an inch or so, drill undersize to the appropriate diameter and then tap threads into the metal angle underneath the floor or alternatively, you could drill and tap the existing holes for the next size larger bolt.

If the bolts are actually the course threaded "lag" bolts, the holes in the underlying angle are probably stripped out. Using the next size larger diameter lag bolts will probably work.

Using a flash light, can you see any metallic fitting (angle) on the back side of the fiberglass decking?

03-26-2007, 12:53 PM
I would have tought they would have been metal threads. It's really bizzare. That was half the reason we orginally pulled the floors, we figured since they were lag bolts (course threads) than we must have wood stringers. We didn't cut the floor over these mounts though, we were about 4 inches from them. Didn't feel that we needed to pull that part of the floor up at that time.

I can not see anything metalic in the holes, we simply can not determine what type of material is in there, but I do not believe it is metal. With a flashlight I was able to see that the consistency of the material is a lot like plastic, which I am assuming is why our attempt with filling with epoxy and re drill 1/8th holes for the lags didn't work. I don't think the epoxy every realy binded to anything.

I think that our next attempt is going to move to a bigger lag bolt, only problem is that the next size up from a 3/8ths is a 1/2, can't find a 7/16th anywhere. If that doesn't work I think that we are going to try lag shields, and then if that doesn't work maybe drill brand new holes in the sliders... Really don't want to have to go with options 3.

Bruce Carr
03-26-2007, 01:06 PM
Try this:

Move forward or aft of one of the holes an inch or two and drill another hole about 1/8 to 1/4 in. diameter. Pay close attention to what chips come out of the hole. If there is metal underneath (like there is supposed to be) it will be apparant.


03-26-2007, 01:19 PM
I agree, if they are lag bolts, you'd assume they were lagged into wood - OR - someone who didn't know what they were doing drilled the original bolt holes out and replaced what WERE bolts with lags only to find out they had screwed up...

Maybe do a test hole an inch or so away from what's there and see what you drill into...hopefully metal, if you get wood then it's tear into and replace the stringers time...

03-26-2007, 01:20 PM
Thanks for the feedback. That's a good idea to get a feel for what is under there. I don't see how it could be metal if they are using lag bolts. Does that make any sense using lag bolts to screw into metal?

I also sent a message the MC technical Services, hopefully get soemthing back from them on this. Anyone ever have any expierence with MC Technical Services?

03-26-2007, 01:22 PM
Pray for metal filings....

Bruce Carr
03-26-2007, 01:58 PM
If the backup fittings are aluminum and not particularly thick, lag screws would work. You will not find wood under the floor anywhere with your particular hull configuration. MC went to the all fiberglass design mid year '83. The early '83 had a plywood deck and wooden stringers. You definitely have the fiberglass model.

03-26-2007, 02:04 PM
I would drill and tap for new BOLTS if you find ALU.