787 Counterbalance shaft oil & seal question

Doug Overkill

Active Member
Working on my 1997 Seadoo Challenger 1800 with twin 787's. Some may have seen my other recent post about 2-stroke oil leaking past the crankshaft seal and hydro-locking the Mag cylinder on the port motor. After a bunch of overthinking it, I decided to tear apart a good working motor to solve that problem. I hoped things would look good and adding Yamabond4 to the crank seals would solve the issue. If only things went as smoothly as that...

First thing I noticed is that the counterbalance shaft is supposed to have a top fill plug and a bottom drain plug for adding the 1oz of SAE30 to the gear. My cases have the top fill port but the spot that is supposed to be a drain plug has no hole in it. Picture from manual shows where it should be. the pic from my case doesn't have this drain hole. WTF? The Starboard 787 motor does have this drain plug...
1698780227839.png 1698780716094.png

The next thing I noticed is the Mag side counterweight area has a lot (couple ounces) of what looks like 2-stroke oil in it. As best as i can tell this area should not have any oil/lubricant in it. The seals SHOULD keep the oil out of this area. Am I missing something or is there supposed to be oil here? I'm wondering now if the issue with 2-stroke getting into the MAG crank journal is actually coming from the rotary valve via this counterweight journal??? Anyone have any thoughts? It certainly looks like the seals on the counterbalance are bad and should be replaced.

Typically the drain on the 787 cases is on the end and not the bottom. If it was on the bottom you couldn't drain it in without pulling the engine.
the early 787's didn't have a drain or a fill so you could have mismatched cases which is bad too.

Shown here in red...

As far as the oil, it isn't a sealed cavity and the oil is replaced with 2-stroke oil as the engine is run, it is only needed as first start-up of a new engine. the rear crankcase is open to the balancer cavity through the rear crank bearings so the oil is always exchanged.

You should not have any oil in the area that you noted "Oil ?", that is a dry chamber and the two balancer shaft seals actually keep oil OUT of that area.

If your cylinders are filling with oil, it is from the inner crank seals that separate the cylinders from the rotary chamber and not the balancer shaft.787.jpg
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Thanks for your thoughts on this. I hope I don’t have mismatched cases. My starboard motor has the drain hole on the bottom as shown in the manual (bolt order pic above). This port motor has the fill hole and no drain in either of these 2 possible casting areas.


Obviously every company that puts a gasket kit together may do things differently. I bought a kit online and am trying to determine if the seals for the counterbalance shaft are in it. I hope it arrives today but does anyone know if the ‘full 787 gasket kit’ usually come with those?

Looks like these worn seals is clearly why I had oil in the dry end of the counterbalance shaft.

I’m not going to redo the crank at this time. My plan/hope is to yamabond the inner crank seals to the case and hope that stops or slows the oil. As per the other thread, if that doesn’t work I’ll add a valve to reduce the head pressure from the tank.
On the inner crank seals I feel more comfortable using Loctite 518 or equivalent. These sealants are anerobic so they won't harden until air is removed. I use Motoseal for the cases and I surely don't like how quickly that stuff sets up but I imagine it remains pliable enough to squish properly. I do go very quickly once I put that goop on the parting surfaces. So again, I use Motoseal for the partings and 518 on the outside diameter of the inner seals.
My wife's jet ski (787) I installed the crank with no sealant on the inner seals and her ski has had a oil leak since the beginning. I talked to a very knowledgeable builder that said he also found out the hard way of not using sealant on the inners. Some people get away with not using sealant but I've rarely been lucky... I gotta be "on my game" Ha ha. Good Luck !!
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might need to start my own thread, but this one kind of applies to me.

I lost 1 o-ring that goes on the crank. PTO end. It was orange. Does anyone know the size I need?

Looking for another o-ring that goes on round counter balance seal that is held in place with a ring. Does anyone know the size I need?
Goto the Seadoo site and Identify the part number. You can order from them are go to Ebay. Seadoo shipping charges add a lot to the cost.

As etemplet suggestedm, find the part# online and check ebay with it. I like seadoopartshouse.com for easily searched fiche of these parts. I believe the PTO end crankshaft o-ring you asked about is #420430782. When I bought the full engine gasket kit, I had intended to measure all of these orings and make some notes as to actual sizes. It always drives me nuts to pay $6 plus s&h for 1 o-ring when a 25 pack is $8 IF you know what size you need. In the end i got busy and just wanted the motor together and didn't measure them. I do not see any o-rings on the counterbalance shaft, just 3 seals.
thanks Doug. I meant the o-ring on the round cover on end of counterbalance. I found the part numbers and like you....wished I had just measured them and not over pay for just one.

In a pinch when you wanna get done.... clean the o-ring and groove and put some 518 loctite on there or even some Ultra-gray RTV and it will seal just fine (I put a thin coat of Ultra-Gray even when they are new) As ya'll mention some of this stuff doesn't come in a full kit... which it should., especially the bottom water cover gasket on the RFI and DI. I buy 5 at a time. I hate running out of parts. :D My supplier takes care of me pretty good on pricing and helps me with part identification and availability. I bet I got more Seadoo 2-stroke parts that anybody in Louisiana and most of Mississippi. :)