720 Crankcase Seal Procedure

[Michael Hunt]

One of my Speedster's engines seized a little while ago due to a big end failure of one of the rods. Bless SeaDoo for making a twin engine boat otherwise it would have been a really long paddle back.

I removed the engine from the boat and stripped it down to the case. I knew I needed a new crank as one rod was seized (original engines, LOTS of hours, got my money's worth). Loosened 12 of the 14 case bolts (the 2 bolts snapped below the head, rear-most bolts of course) and worked on them a bit to try and separate the halves.

Spent a little time on the 2 bolts until I found out I could buy a 720 case for $80. Now my newer crank would have a new home.

Cleaned the new case and noticed that there was sealant even in the case grooves for the RV seals, all bearings, end seals even the rear metal shim. I have the SeaDoo manual and it only mentions smearing sealant (515) just on the case rails and buttoning up the bottom.

I can see smearing a little sealant around the end seals to the case, but not everything. So what's the proper or smart way to seal the case halves together?

Thanks for any help.

 

[Waterluvr]

I seal everything in a similar fashion to what you're seeing using Threebond 1211 just for the sake of it taking less time to remove from some of my regulars that tear motor's up in ski's having a little extra fun than the average rider and it works famously for me.

If you want a little extra insurance use Threebond 1104 instead, same stuff used in rebranded packaging for Hondabond etc. but you'll hate me if you ever have to take it apart.

Both will get you a seal that pressure tests after assembly, really can't go wrong with 1104 used sparingly if your not hard on the boat engines hopefully you won't ever have to get back in it again.

 

[Michael Hunt]

So, you coat the outside of the bearings with sealer as they fit into the case? And the internal RV seal grooves plus the spacer ring grooves (actually all the grooves)?

Glad I asked.

 

[Waterluvr]

So, you coat the outside of the bearings with sealer as they fit into the case? And the internal RV seal grooves plus the spacer ring grooves (actually all the grooves)?

Glad I asked.

Sure do, easy does it though you only need a tiny bit those tolerances are pretty tight already I wet a q-tip with acetone and clean some of the seal away from those areas before assembly so it can't run out of the seam all that is a little extra insurance on those close tolerance parts.