Very high compression 787 motor

[Logantw2543]

Hello, I recently purchased a 1999 seadoo challenger 1800 with 787 engines in them. I’m having a few issues with them that I can’t figure out.
1- on one of the motors the compression readings are around 210 on each cylinder. And I’m not sure why that is. I’m no mechanic but that doesn’t seem right lol. The other engine is reading right around 150. Why would the compression be that high on one of the motors? What do I need to look for or do? I’ve cranked the engine without the spark plugs and had some liquid come out but eventually stopped.

2- the engine with really high compression will not crank with the plugs in. Like at all. You can hear it try but it won’t crank it. The starter isn’t bad because I actually switched the starter from the other engine and tried cranking it but it won’t. So why won’t it crank? I’m guessing the high compression but I’m not too sure.

3- the purge lines that lead up to the fuel pump and not sucking any gas out. I can feel air coming out a little when I crank by hand. Would this be just a bad fuel pump?

Sorry I’m all over the place. Just really getting aggravated with these motors lol. But any advice will help. Thanks!

 

[AKnarrowback]

The motor with the high compression, is there more evidence of oil in the cylinders? With the plugs out, and cranking the starter, is there an oil mist coming out the plug holes. Are the plugs covered with oil when you first remove them? Hold a clean paper towel over the plug holes and crank the motor and see what gets sprayed onto the towel.

Check these things against the motor with lower compression and get back to us.

 

[Logantw2543]

The motor with the high compression, is there more evidence of oil in the cylinders? With the plugs out, and cranking the starter, is there an oil mist coming out the plug holes. Are the plugs covered with oil when you first remove them? Hold a clean paper towel over the plug holes and crank the motor and see what gets sprayed onto the towel.

Check these things against the motor with lower compression and get back to us.

When cranking the starter with the plugs out when i first did it there was a bit of oil coming out. But ever since then its been basically just air. I'll get little sprinkles of oil every once in a while. And when i first removed the spark plugs I can't 100% remember but I want to say oil was on them when removing. I've done the last part you recommended already and like I said its a little little little bit of oil.

For the motor with lower compression I've already done the same process as the other. Pulled plugs, crank, papertowel, etc. One cylinder had a little amount of oil you could see on the piston. but the other was bone dry.

 

[AKnarrowback]

Crank the high compression motor with your thumb over the plug hole. Try to work out as much oil as you can until you can get the motor to crank with the plugs in.

It sounds like you have a failed seal inside. Pretty common.

See if you can get the higher comp motor started and see if it puts out a HUGE amount of smoke.

 

[Logantw2543]

Crank the high compression motor with your thumb over the plug hole. Try to work out as much oil as you can until you can get the motor to crank with the plugs in.

It sounds like you have a failed seal inside. Pretty common.

See if you can get the higher comp motor started and see if it puts out a HUGE amount of smoke.

If I put my thumb over one hole it does not want to crank. And what seal? and easy or hard fix? I also thought a bad seal would make low compression not high?

 

[mikidymac]

Either a bad starter or high resistance in the wires. Even full of oil it should crank over no problem with your thumb over the holes. The only thing that would cause that high of compression is fuel or oil in the engine trying to be compressed.

 

[Logantw2543]

Either a bad starter or high resistance in the wires. Even full of oil it should crank over no problem with your thumb over the holes. The only thing that would cause that high of compression is fuel or oil in the engine trying to be compressed.

well if thats the case the compression should eventually go down shouldnt it? and both of my starters are bad even if they start the other motor?

 

[mikidymac]

I would suspect the cables or connections.
As long as you can get it to fire and burn the oil out the compression will come down until it fills up again.

 

[AKnarrowback]

Yes the oil can cause higher comp numbers, but as said, even with excess oil the motor should still turn over. My 97 gtx looked like a whale blowhole with oil flying all over when I cranked it, but it still cranked over snd started with plugs in.

 

[AKnarrowback]

If I put my thumb over one hole it does not want to crank. And what seal? and easy or hard fix? I also thought a bad seal would make low compression not high?

There are seals in the motor that serve different functions in different areas. The seal(s) around the rotary valve shaft area can leak oil into the case from the chamber where the rv shaft and crank shaft gears are, they sit in an oil bath tied straight into the oil injection tank. They have nothing to do with the combustion chamber pressures, except temporarily raising compression when the excess oil is drawn up into the chamber. The numbers wil drop again after the oil is burned off in the first few minutes of running.

 

[Logantw2543]

There are seals in the motor that serve different functions in different areas. The seal(s) around the rotary valve shaft area can leak oil into the case from the chamber where the rv shaft and crank shaft gears are, they sit in an oil bath tied straight into the oil injection tank. They have nothing to do with the combustion chamber pressures, except temporarily raising compression when the excess oil is drawn up into the chamber. The numbers wil drop again after the oil is burned off in the first few minutes of running.

Would I be able to take the carbs off and tip it on its side to see if any comes out? I guess I need a new starter that’s got more power to turn it. Idk

 

[AKnarrowback]

No, tipping won't help.

Make sure the battery is fully charged throught this process. Never jump or boost the battery while it is connected to the machine. I always disconnect the positive cable before charging the battery in the machine.

Do not crank too much at any one time. Don't overheat the starter.

Always rebuild your OEM starter before you EVER put an aftermarket starter in. Aftermarket starters are junk, plain and simple.

 

[mikidymac]

I have had a few that would not crank over until almost all the oil was out and even then once you got a good cough and the oil would come up on top of the piston it wouldn't crank over again. Very frustrating and time consuming. But with your thumb over the hole it should just blow your thumb off if the starter, battery and cables are good.

 

[Logantw2543]

I have had a few that would not crank over until almost all the oil was out and even then once you got a good cough and the oil would come up on top of the piston it wouldn't crank over again. Very frustrating and time consuming. But with your thumb over the hole it should just blow your thumb off if the starter, battery and cables are good.

Sorry for all the questions. But have both plugs out correct? And put my thumb over one hole? And for how long should I do this and how many times? I got the engines out of the boat btw.

And why would my pulse line not be working with the fuel pump to get fuel to the carbs? It’s not getting any fuel at all

 

[mikidymac]

You will do this until no more oil comes out and the engine will start with a little fuel down the carbs.

Oil can get into the carb's fuel pump from the pulse line and stop it from working.

 

[Logantw2543]

You will do this until no more oil comes out and the engine will start with a little fuel down the carbs.

Oil can get into the carb's fuel pump from the pulse line and stop it from working.

That makes sense because it’s the engine with lower compression had a little bit of oil coming from the pulse line. That all should clear up though hopefully. Thanks for the help btw. Furthest I’ve gotten so far.

 

[mikidymac]

No, if you got oil in the pulse line you need to take the fuel pump block apart and check for oil and damaged seals and clear diaphragm sheet.

 

[Logantw2543]

No, if you got oil in the pulse line you need to take the fuel pump block apart and check for oil and damaged seals and clear diaphragm sheet.

hey, been trying all day to get oil to come out of the plug holes and nothing. got a good charge on the battery and everything. any ideals?

 

[Logantw2543]

After plenty of cranks it finally started coming out. When should I stop? When there isn’t anymore coming out? Or when it cranks over easy?

 

[jts32]

That doesn't look good. You should be seeing just straight injection oil coming out. That looks like oil/water mix. You can keep trying to clear it and see if it will eventually start. Keep cranking until you get nothing on the rag, throw the plugs in and see if you can get the motor to cough or fire for a couple seconds, pull the plugs and repeat until it will stay running. It will smoke like crazy and puke chocolate milk out the exhaust. If there is water in the crankcase, that motor is on borrowed time. I'd personally pull it and do a teardown

 

[Logantw2543]

That doesn't look good. You should be seeing just straight injection oil coming out. That looks like oil/water mix. You can keep trying to clear it and see if it will eventually start. Keep cranking until you get nothing on the rag, throw the plugs in and see if you can get the motor to cough or fire for a couple seconds, pull the plugs and repeat until it will stay running. It will smoke like crazy and puke chocolate milk out the exhaust. If there is water in the crankcase, that motor is on borrowed time. I'd personally pull it and do a teardown

The motor is already pulled. And do a teardown on what? The top end or the whole engine?

 

[Mraw]

Whole engine, as said it looks like water oil mix

 

[gazzaskirepair]

I am doing the same on a 787 RFI
Engine runs for 3 secs and shuts down tons of smoke
Found loads of oil around the rotary valve
Going forward a full tear down

 

[Logantw2543]

I am doing the same on a 787 RFI
Engine runs for 3 secs and shuts down tons of smoke
Found loads of oil around the rotary valve
Going forward a full tear down

Really wish I knew more about these. But my engine won’t turn over at all with plugs in. But how would I start a full tear down? Is there a video or anything on it?

 

[mikidymac]

It won’t crank for a couple reasons.
1. Oil flooded. You are going to have to get the oil out by cranking and getting it running.
2. Bad battery.
3. Bad starter, do not buy an aftermarket one.
4. Bad cables and/or connections.