Full Bore


Sea Doo Tech Tips

Always refer to the proper service manual when removing and reinstalling an engine or for most service work.

This page is only to help with the most commonly overlooked or missed issues. 

RAVE valve or power valves.

After boring the cylinders on a Sea Doo 787/800 947/951 or any other engine with a power valve, you must relieve the  exhaust power (RAVE) valve for clearance or you will snag your rings and destroy your new top end.  The old rule of standard bore and first over don't need the valves relieved doesn't always hold true. As things wear they tend to get closer and eventually they make contact even on std bore with high hours. 

power valve

Valve on the right has been trimmed.

This edge can be relieved with a hand file or dremel tool (die grinder with sand paper drum)

You are only removing enough for clearance between the valve and the piston rings.

We do offer doing this for you on our top end kits.

Never reuse the old spark plugs from a failed engine in your fresh rebuild.  Small pieces of contaminates may be lodged in the plug and drop out after they heat up.

When disassembling the top end of Sea Doo (2 cycle) engine watch for the notorious cageless upper rod bearings the needles will fall out everywhere.  Take precautions and cover the crankcase when removing the pistons.  Full Bore top end rebuild kits come with caged needle bearings.

Removal of ignition flywheel

pulling fly wheel

When removing the flywheel be sure that you don't thread the puller bolts in too far, you can damage the ignition coils.  The holes for the puller go all the way through the flywheel and the stator coils are right behind them.

Pictured is a Sea Doo 720.  The 580 and 650 also remove in this manner. 

Note the Sea Doo 800 and 951 models use a different puller.

Sea Doo 580, 650 and 720 ignition timing.

sd timing mark

If you have your engine (Sea Doo 580,650 or 720) rebuilt by Full Bore you can simply align the line (nick) in the stator plate to the engine block.  This mark was made with your ignition, flywheel, crank, and engine cases at the factory when the engine timing was set.

This is another good reason to have Full Bore rebuild your seadoo engine instead of buying a remanufactured engine. We rebuild your crankshaft so the timing index stays the same.

Oil failure.

broken oil lin

The most common engine (besides water) failure on the mid 90's Sea Doo 580,650, and 720 is the small oil lines from the oil pump to the engine (rotary valve cover) break.  From the factory they were painted.  Over time they dry out and become brittle, then break.  Often times the oil pump is blamed: do yourself a favor and check the lines.

Note: Newer lines were also painted but they changed the thinner in the paint.

On a Sea Doo this little rubber bumper goes on the end of the drive shaft, one on each end.  Often you will find it stuck in the P.T.O. balancer after you remove the engine.   If you forget, it the drive shaft makes more noise (rattle) than normal.

rubber bumper

Don't use RTV silicone on any gaskets other than exhaust.  On exhaust use hi temp orange.  RTV will break down and dissolve when in contact with gasoline.  Read the tube!!!  Better yet, read the service manual and use the proper sealants.

Sea Doo cylinder alignment.

When rebuilding the top end of a Sea-D00 580,650,720 or 800 the cylinders need to be aligned properly.  After sliding the cylinders into place install the cylinder bolts finger tight.  Bolt on the exhaust manifold  this will properly align the cylinders then torque the cylinders.  Note be sure to put Loctite to the threads of the inner (cylinder) bolts on the rotary valve side of the engine.

When installing the rotary valve cover on a Sea Doo 720/717 be sure to use a thread locker such as Loctite on the bottom 2 bolts.  From the factory the holes are bored all the way through the cases.  The thread locker acts as a sealant to prevent air leaks.

Sea Doo 2 cycle engine Break-in

 non fuel injected

A break-in period is required before operating the engine at full throttle. Our recommendation is 1 operating hour for a fresh (Full Bore) engine or new top end. We can not speak for our competition this only applies to our engines and top end kits.

10 hour break in period is a thing of the past. Because our Premium HD and Platinum engines are kept to such tolerances and by design break in period is only 1 hour so you can get back to what you really want to do.

During this period, maximum throttle should not exceed 3/4, however, brief acceleration and speed variations contribute to a good break-in. Continued wide open throttle accelerations, prolonged cruising speeds and overloading the engine are detrimental during the break-in period.

To assure additional protection during the initial engine break-in oil (same oil as are using in injection tank) should be added in the fuel tank for the first full fuel tank filling only.

To add injection oil in the fuel tank, proceed as follows: 

Fill fuel tank with approximately 5 gallons of gasoline; then, add 2oz of injection oil for every gallon of gas.  Fill up fuel tank with gasoline. Do not overfill.  In simple terms if your tank holds 11 gallons of gas you would add 22oz of oil to the first tank.  This is in addition to the oil injection.

NOTE: It is important to proceed in this order to allow a proper mixing of the oil in the gasoline.

This is while also using the oil injection system as normal.

If you are running premix only on one of our engines we recommend 32:1 fuel oil ratio for break in and 40:1 after the initial engine break in. 

Read before installing.

When installing your top end rebuild kit always refer to a service manual for torque specs, and general how to specifics. No hammers required for assembly.

  Always wash cylinders before installation.

On WSM (and most 2 cycle engines) the arrow on top of the piston points to the exhaust port. The ring end gap never goes towards the exhaust, it will snag and break.

On power valved engines like the Rotax RAVE valved 787/800 or 947/951 you must verify clearance and trim the valve to avoid contact between the rings and valve. Failure to trim the valve will result in serious engine damage.

No thrust washers are used when installing WSM wrist pin bearings with WSM pistons.

When installing WSM rings if there is a polished edge, it is installed in the top ring groove.

On Sea Doo 947/951 the rings only go on one way, if they don't compress in the groove flip them over. Small letters near end gap face up.

When installing circlips be sure it is fully seated in the groove. Failure to do this may result in serious engine damage.

*Note resleeved cylinders often get discolored from heat involved in replacing the sleeve.

Now you can download Sea Doo service manuals for free online.  This page isn't ours but it is a free resource.

Download Free SeaDoo Service Manuals

A word about compression and compression testing a 2 stroke engine.

Every day I am asked what should I get for a compression reading.

Please read and we can go from there.

So many people are wrapped up in some magic number they should see when doing a compression test. It's almost to the point of pissing contests for the highest number.

Here is a question for you. Why doesn't sea doo publish a psi for compression test? First there are to many variables between testers let alone the condition of the starter, battery, and anything else that could alter the reading. So for example if they said your 717 should have 150psi compression what would happen? Joe Blow shows up with his harbor Freight compression tester, worn out starter and a tiered battery and gets a reading of 137 PSI. Now what? This joker will be screaming warranty when everything is fine. This would cost them millions. The point is there is to many variables and the first key is what is the difference between the cylinders.

So why won't engine builders not give you a magic number?

First because of the same variables for one and then when rebuilt there are other variables that come with different brand pistons. What brand pistons absolutely has an effect of what your reading will be. The actual deck height vs the piston dome at TDC is different from one brand to the next. Different style rings such as L rings vs keystone and the location of them will affect the reading.

Time for some controversy how to do a compression test.

If you ask 10 guys how to do the test you will get 9 different answers.

So other spark plug in or not? My way is all plugs out. Some well respected engine builders will disagree so I will explain why I do it this way. If the biggest thing you are looking for is the difference between cylinders then you want to keep the "control" the same. In other words if one side is good and the other is low it will effect the readings differently then the other side. So to not have the opposite side effect the reading we always remove all spark plugs. With that part out of the way lets get to the rest.

So spark plugs out and the caps grounded on the grounding straps. Gas turned off and throttle held wide open crank the engine. Here is the key ! Don't just blindly crank it forever to get the highest number you can. I limit the crank time to no more then 5 seconds. While doing this keep an eye out for what the reading is after the 3rd or 4th revolution verses the reading after the needle stops climbing or about 5 seconds. If the difference between the two readings is quite a bit your top end is probably tiered and on borrowed time. If it is only 5 10 PSI then it is probably pretty good providing it was a consistent solid number. More importantly what is the difference from one side to the other? most engine builders were taught the 10% rule including me. I don't live by that rule. If I see 6 or 7 PSI difference I tear it down and take a look. Guess what? every time I have seen 7 psi or more difference and tore down for inspection. There was definitely an a serous problem such as a stuck ring that oil was masking.

So focus on doing it right, what is the difference between the cylinders, what is the difference between the first few revolutions vs 5 seconds and using a good gauge.

This will help make a well informed decision on what is going on.

Contact us

Email us at info@fullboreonline.com

Phone 989-340-1321

9-5 Monday - Thursday

9-4 Friday Eastern time. 

Shipping address (shipping only)

Full Bore
486 S Ripley Blvd
PMB #228
Alpena, MI 49707