787 RFI low power

[mattrourke]

Be interesting to see if once you get piston out if you can see more blow by on piston with lower compression. Blow by is dark colouring under piston rings. Or scuffing on bottom of piston from ring being worn and piston rocking. How many hours will you put on 3d in a year. If less than 30 hours a quick
Fix might work but if put 100 hours a year on might need more work.

I will take a look. I will try and do a leak down test before I fully rip it apart. I'm guessing the leak down test involves pressurizing the cylinder and seeing how fast it leaks down... This is a new one to me but see it refered to a lot.

I will probably put 30-50 hours at most per year on it. I'm in Canada and so only really get to hit the water june-august. It's sad but that's why we have sleds as well.

 

[mikidymac]

No, leak down is when you block off the intake and exhaust ports and put 8 psi of air pressure in the pulse nipple. You want it to hold exactly 8 psi for at a minimum of 10 minutes.

This is checking for air leaks in the gaskets and seals, 2-strokes won't run correctly with air leaks.

 

[mattrourke]

I will put the head back on today and do a squish test and do some searching for how to block off the exhaust and intake etc. for the leak down test. Here are some more pictures I took that show the thatching a bit better and I took a picture of the bottom side of the head. I couldn't feel any obvious defects in the cylinders but I know that we won't really know until the pistons and cylinders are pulled but I will try these other tests before I go down that road.

 

[mikidymac]

The cylinders are not showing signs of major damage but the shadowing and lines are a good indication of normal wear and higher hours.
The only way to be sure would be to measure the piston diameter and the cylinder bore diameter with a bore gauge to see what the clearance is.

The patterns on the head and pistons are also different enough to indicate that one fuel injector isn't flowing the same as the other.

 

[mattrourke]

The cylinders are not showing signs of major damage but the shadowing and lines are a good indication of normal wear and higher hours.
The only way to be sure would be to measure the piston diameter and the cylinder bore diameter with a bore gauge to see what the clearance is.

The patterns on the head and pistons are also different enough to indicate that one fuel injector isn't flowing the same as the other.

I really appreciate your input here, as well as everyone else. I know you and Pedec have suggested a few things to check now and I want to make sure I'm doing this in the right order. Here is what I have planned for my next tests, in order.

Put the head back on and torque everything to spec.

1. Squish test
2. Remove whatever needed and do a leak down test.
3. Remove head and cylinders and check bore and bottom of the pistons for obvious wear
4. Measure bore, piston, ring gap etc.

In the mean time I will order new injectors as it's worth eliminating that weak point as well.

 

[mikidymac]

Yes, but I would send your injectors out to the guy @etemplet uses instead of ordering new ones. Most aftermarket ones are less than great.

 

[mattrourke]

Yes, but I would send your injectors out to the guy @etemplet uses instead of ordering new ones. Most aftermarket ones are less than great.

Ok. I will take a look at that. Thank you.

 

[Pedec]

Cylinder doesn’t look terrible to me. Once you cylinder off see if there is any play in connecting rod up and down there should be none.

 

[Poormanracing]

Well thank you for staying calm and rational. Was not a hole. I posted pictures of what I found. The little bit of water in the one cylinder spilled in from the cover, it was not already in the cylinder. I think I was just hopeful to find the problem once and for all. All I could find was this small crack in the top cover... Would that cause any issues?View attachment 55585View attachment 55586View attachment 55587View attachment 55588View attachment 55589View attachment 55590

Sorry been busy as heck.im not sure if I said in this post but a compression gauge is a useless tool and no one at our shop owns one.the only way to tell is with a leak tester.any way glad you found problem.i have some rfi parts.new sea Doo remained cyl and a new combustion dome.not sure if it's a 800 rfi or carb I will look at pn I got some injectors and other misc stuff all new old stock let me know if you need something.and for the guys that still use a compression gauge throw them away and get a leak down tester

 

[mattrourke]

I'm not sure we have found the problem yet. Hoping to do a leak down test tomorrow. I think I have everything I need to block it off and get it pressurized. We will see what that tells us and go from there. I'm fine with doing or having a top end done or even dropping a whole new engine in, just don't want to do it and find it was something else all along.

 

[Pedec]

Take a couple pic of how you setup your leak down test. I might be doing one also if ECU doesn't work. The coil did not fix it. I took throttle bodies off and sucked out all the oil in crank just to see if motor was full of oil. I only got 10ml out and with new plugs still ran the same.

 

[mattrourke]

So I think I set up my leak down test ok and I can hear air moving. Doesn't seem to be escaping around any gaskets or hoses or tubes, it just sounds like air moving somewhere in the lower half of the engine and it won't build pressure. I blocked off the intake and the exhaust manifold and plugged a vent line on the exhaust and pinched off the tubes that come from the rave valves (not sure eif needed but they seemed to be getting air into them). And I connected a bike pump with a gauge to the spark plug hole. I'm not sure what to do next.

 

[Pedec]

Can not help you never done a leak down test.

 

[mattrourke]

Well, since I have all of this pulled apart and still can't find a cause of low power and my compression is already a little low at 135, and now maybe blowing by a crank seal, I think I'm going to continue pulling the engine and have it rebuilt. I found a place close to me with everything he needs to do the rebuild and I should have it back in 2-3 weeks. In the mean time, I can give it a good cleaning and checkup of everything else. I will also pull the pump and check everything in there so that I can be sure that this thing is in tip top shape. Might even be able to get a couple weeks of riding in at the end of the summer.

 

[Pedec]

Man I was hoping you could have pin pointed the problem just so we can all have I idea what to look for. Since yours does have lower compression I can see why. Your problems are different than mine and does point to a mechanical issue. Have you tried to suck out any extra oil out of your bottom end just to see how much is in there. Mine only had 10ml. I just used a hose and needle to suck it out through PTO intake.

 

[mikidymac]

If you have oil in the crankcase it will spray out when cranking with the sparkplugs out and bridge the gaps of the sparkplugs causing them not to fire.

 

[mattrourke]

Also noticed maybe a weak spot on this exhaust manifold gasket Nd a crack in the pipe. Probably a good thing this thing is getting stripped down.

 

[mikidymac]

WoW! Time for a new pipe.

 

[mattrourke]

WoW! Time for a new pipe.

Do you think it's safe to have that welded? I'm guessing the only problem I would see from the cracked pipe is getting water in the hull.

Also noticed the PTO exhaust port is very oily compared to the mag side.

 

[mikidymac]

If it's cracked on the inside too it will be a big problem.

 

[mattrourke]

If it's cracked on the inside too it will be a big problem.

Yeah, I tried to run a scope camera down there and couldn't see anything, but it's pretty full of carbon. Can't find any of these pipes for sale online. I'm in Canada so that doesn't help.

 

[mattrourke]

I think I will try to pressure test the exhaust pipe and see if it leaks into the water jacket.

 

[Pedec]

I can ask a guy I am in contact with stripping a 3d if he has exhaust pipe for sale. He lives in the states 05 3d not sure if pipe is the same with exhaust being different.

 

[mattrourke]

I can ask a guy I am in contact with stripping a 3d if he has exhaust pipe for sale. He lives in the states 05 3d not sure if pipe is the same with exhaust being different.

I will check to see if it is the same. Thanks!

 

[ihammond]

Thank you for that link. I found 2 of each in town and will change the filters as I swap them over. Also found a replacement pump in town which I may purchase as well. I don't mind having a few spare parts on the shelf. I don't live in a very big city so finding parts locally is pretty lucky!

I think I saw that a rivet gun is needed as well to reassemble after drilling out rivets to get at the internal filter so I will pick one of those up too.

I will report back.

@mattrourke Any chance you can share the part numbers for the items you found locally for the fuel strainers and fuel pump. All of the numbers I can find on these forums are old and do not seem to be valid anymore. Thanks.