Seadoo XPL 951 Piston Scoring on rebuilt engine

[Bacardi]

I built my last engine all with oem parts, and prox piston, cylinder to wall 0.12/0.13mm (0.005) and i can hear a bit of piston slap, 0.007" is a lot of clearence

 

[WaterJet]

I see what you’re saying, don’t want it to be too loose. I dropped the parts to the machinist just before and went for a .006” clearance. Thanks again for the input it has helped a lot.

Jake

 

[WaterJet]

Trying to work out the cause for the scoring. I just tested the oil pump with a drill, worked fine, oil was dripping out. Tested oil injection fittings in intake manifolds, can blow through them although very restrictive.

You can see red 2 stroke oil in the lines, that’s what it was like on the ski when I was using it too!

Yet the inside of the engine was very dry... any ideas about how oil could not be getting in?

 

[Bacardi]

The nipples are a one way valve, oil only flow on one direction, change that oil lines, they are old.
The inside engine is normally, a bit dry, seadoo's have very low oil consuption compared to a yamaha, that's why you should only use API TC low ash oil, first tank don't forget to add oil to gas

 

[mikidymac]

Running lean is typically a carb issue not an injection oil issue. Air leaks and carbs are the most common culprits.

 

[WaterJet]

I noticed they are 1 way valves. I’ve decided to delete the oil pump anyway, I got an SBT oil block off kit for it.

Do I need to pull off the magneto cover to pull out the plastic drive mechanism for the pump? I couldn’t seem to pull it out from where the pump came off but didn’t want to use too much force.

 

[GGuillot]

Trying to work out the cause for the scoring.

I'm surprised nobody pointed it out, but it looks like a RAVE clearance issue the way it scored up the pistons.

 

[WaterJet]

An update...

Got it all back together and have put a tank of fuel through it today successfully! Towards the end I did a few WOT runs and was pushing just about 7000rpm, it was about 6900rpm before. I went with .006” piston clearance which was noticeably less sloppy than before and a 0.5mm ring end gap. Here’s a few photos of the new parts going in.

I also converted to premix even though the oil pump was most likely fully functioning. I bet the scoring was already on the engine when I bought it even though the engine was “freshly rebuilt still needs to be run in”. I figured I’d rather go premix just to be sure.

Thanks again everyone for the help!

 

[WaterJet]

Guys, It’s happened again!!! Wide open throttle pushing over 7000rpm and it seized up. I think the damage is being caused by a lean mixture at WOT. The PTO piston seized. Running .006” clearance with 1mm over SBT pistons. Here’s what the seized piston looks like. Definitely looks like the piston was running too tight but the clearance feels plenty wobbling the piston in the cylinder by hand.

Does running 1mm over bore require a re jet?

The bloke I got it off replaced the carbs, and deleted the accelerator pump, so I’m sure it’s a lean condition. His specs were:

“Disconnect accelerator pump
Low screw. 1 1/2 turns out
Pilot jet: 85 (72.5 stock)
Main jet: 162.5 (stock)
High screw: 0 (closed off)
Needle & seat: 2.3 (2.0 stock. I have drilled the stock one to 2.3)
Spring: silver
Pop off: 20-22psi”

Would turning the high speed screw 1/4 turn out be enough adjustment to make it the right mixture (it was pushing over 7000rpm so can’t be too far off?), or should I get a bigger main jet?

I’m going to rebuild it again, and sort the carbs properly this time!

Any advice is greatly appreciated.

Cheers

 

[GGuillot]

What was the break in procedure? What premix are you running? Was the piston clearance machined to what was recommended? On the HS needles, I have carbed 787's skis and on both engines I don't run them shut. Not saying that's your cause, I don't know, you have a 951 carbed. I have both carbs set anywhere from 1/8 to 1/4 out, but never zero. It runs cooler when pegging WOT, which I don't like to like to do for long or very often. Actually each ski, I ran the HS needles at 1/2 out on both carbs for about the first 20 hrs of rebuilding, before tweaking them in some.

But I don't know about your carbs set up, doesn't seem it should be leaning out...

 

[Mraw]

Stock 951 carbs have high speed needles all the way in.

 

[WaterJet]

Well, I may have found the cause... cleaned these when I first got the ski 2 months ago as well as replaced fuel lines. I should’ve put an inline fuel filter before carbs because look at the state of these filters, this has got to have been the cause of the lean condition at wot...

You live and you learn I guess, I’m going to check the filters on my other ski’s now, they have an inline filter before the carbs so hopefully they are fine!!

 

[GGuillot]

Stock 951 carbs have high speed needles all the way in.

Nothing says they 'need' to be all the way in. Same thing on the 787 carb before 1997, it was recommended to run them shut, at zero, then starting that yr model there was a recommended change to run the PTO 1/2 out. Why? because Seadoo found the PTO cylinder could fail at WOT and it ran hotter, the recommended change was to compensate for this.

Not saying running the 951 carb with the HS needles all the way in could have caused his PTO cylinder to seize at WOT, but I still wouldn't run it at zero and peg WOT for long. Cracking it open to 1/4 could make all the difference to prevent it from happening again. On each carb, I start 1/2 out on the HS and go in 1/8 at a time until I see no further gain, then I stop, then back off 1/8.

 

[GGuillot]

I should’ve put an inline fuel filter before carbs because look at the state of these filters,

You don't want to do that, it'll be a sure way to a lean condition, adding a fuel filter can cause a restriction.

 

[mikidymac]

Who did the machine work and setup clearance?

Btw my 01’ XP is all stock and runs the closed HS screws as per spec and runs WOT as long as I want with no issues.

Do not add an inline filter other than the OEM strainer.

 

[WaterJet]

I think I’ll run the high speed screws 1/4 turn out to be safe. The accelerator pump was deleted. So I’ve bought some used carbs off a stock 951 ski so it’s all how it would be from the factory. But I’m certain the lean condition is from those filters being clogged, even the one in the water separator was gummy! The guy I got it off cleaned the tank, so maybe there is some gum left behind from the cleaning process, not sure what it could be considering I replaced the fuel lines, I’ll definitely have to keep a watch on the filters!

I’m glad you mentioned not to run fuel filters! On my 787 97XP and ‘93XP with the 657 I’m running an inline fuel filter before the carb, should I remove them? Or is it only the 951 because it is sucking more fuel? They are automotive size...

@mikidymac , I had a shop called HM gem engines do the machining work.

 

[mikidymac]

None of the seadoo 2-strokes should run any additional fuel filters. Just the clean OEM style ones.

 

[WaterJet]

Ok good to know... while checking the carb filters in my 97XP I noticed one of my accel pump nozzles is clogged.

On the 787 engine what size pilot jets do I need to install to remove the accelerator pump?

 

[WaterJet]

Hi guys, rebuilt again, rebuilt carbs and have put 1.5 tanks of fuel through it.

I just did a WOT burst and plug chop with new plugs, and the plugs are white!! Then it occurred to me that I have not got the stock air intake, it has these R&D filters on it... I feel like an idiod, now I just need to get a stock intake and should be sweet. I was considering turning out the high speed screws to tune it for these R&D filters but it probably needs bigger jets to get it right.

Should’ve mentioned it had these air filters at the start of the thread

 

[Mraw]

I would definitely go back to the stock intake, super easy to eat water on those R&D

 

[WaterJet]

I’m going to try find a stock one! I’ve got the exhaust off now, looking into the PTO cylinder there is a black seizing mark, only one mark from what I can tell and it doesn’t look anywhere near as serious as the last marks. The engine didn’t seize and I only did a few (<10sec) wot runs, the last 2 being plug chops. I’m probably just going to keep running it as is with the mark there once I get the stock intake. Then in 100 hours or so I’ll do another top end and replace the cylinders while doing it, at the moment it’s 1mm over bored.

I’m surprised how sensitive it is to running lean that’s just 1.5 tanks, a lot of low rpm for break in running really well and it’s already got a black mark on the cylinder.

 

[mikidymac]

Yes, you will be really lea running stock jetting with an AM filter especially on top end.