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Rebedding to hold new motor mounts

Al Emondi

Member II
I was wondering if anyone has had to rebed the stringer where the motor mounts attach to? My mounts are old and worn, I have removed the engine from the boat for some fix’in and in the process I noticed that the mounts were held in place with lag bolts. Also, on the starboard side, some oils/diesel has worked its way down into the wood in the stringer compromising its strength. Also, a few of the lags had broken off in the stringer. So… now I have the lags drilled out, and I am wanting to rebed all the holes with epoxy. However, will epoxy hold with a vibrating engine? I was thinking of drilling and taping the epoxy to provide a threaded seat rather then lagging it. Anyone have any experience rebedding the holes of the mounts?
 

ted_reshetiloff

Contributing Partner
Sounds like a pretty good idea. Another solution would be to use threaded inderts. These have wood screw threads on the outside to screw into your stinger then they accept maching screw/bolts internally. These should hold pretty well under vibration. Another method would be to reuse the lags screws but intstall them with some sealand like the dreaded 5200.
 

chaco

Member III
Get the WestSystems Repair Manual. You will find how to do this repair to last
for another 20 years. You will mix epoxy with High Density Filler to get the
strength you need to hold the new lag studs. Use stainless steel studs and
nylocks to hold your engine down. My stringer system was completely shot.
Replaced the mount system with epoxy/fiberglass stringers molded over foam.
The new stringers worked great with no wood to rot in the future :D

Good Luck :egrin: :egrin:
 

jreddington

Member III
My yard should be remounting the engine this week. I had an issue where I tighted the engine mount to stringer lag bolts and they just spun. When going counter clockwise they would not back out.

I though there might me a glassed in bolt down in the stringer which had come loose and was now spinning. No, just lag bolts.

However, these bolts have a smooth unthreaded shoulder. Yard thinks that the threaded part of the lag bolts had mostly passed through the solid part of the stringer and were hanging out in the hollow area.

When remounting they will used lag bolts with a shorter shoulder to make sure the threads bite into the stringer. They will also use 5200 sealant to hold it tight and prevent the mounting lags to vibrate loose. Important note is that because of the sealant I should not periodically try and retorque the bolts since this will break the sealant.
 

P Abele

Member II
This job is on my list as well but unfortunately pulling the engine was not in the cards for this year so it will have to wait until next. We use threaded inserts in epoxy castings at work which would seem to be great for this application. They are knurled on the exterior and have standard threads inside so are very solid once cast in place. The ones we use are brass which I wouldn't use but suspect a fastener supplier could find them in stainless.
As for cementing them down, I wouldn't recomend doing that since they may need to be removed someday and 5200 would make that nearly impossible. Good luck and I will be interested to hear how this job goes so I may learn from your experiences!
 
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