2002 GTX RFI (Rebuilt 15 hrs ago) no start

[TxAg15]

Recently rebuilt my 02 GTX RFI and everything went together beautifully. Started right up with no issues and made sure to follow break in procedures. After break in it ran like a champ. Even went about 5 mph faster on plane compared to pre-rebuild. Only observed thing even slightly out of perfection was that if it was at operating temperature and you killed the engine, then you had to run the starter for 5+ seconds and it wouldn't start, then it would start right up the second time you ran the starter. But I've heard this is normal for 2 strokes to be harder to start while warm.

Last weekend my buddy was riding it and the engine cut on him and he couldn't get it to restart. I swapped the plugs on the water since it was the same plugs used at break in but still no start. Can't even get it to start on the trailer. Thinking it was a fuel issue I swapped the fuel pump and pressure regulator. No improvement. Sometimes it will sputter when you run the starter but that's it. Almost sounds like it could be knocking. Had the fuel injectors rebuilt by fuelinjectorman.com 15 hrs ago so I am hoping that's not the issue. I did turn it over with the injectors to observe spray pattern and it looks like it starts strong, but then gets weak on both injectors. Could this be the issue? Or is the mpem metering the total amount of fuel prior to start to avoid flooding the engine?

Starting to think it could be electrical. But battery is fully charged and and I've never seen a 12v low or experienced any rectifier related symptoms.

Any ideas what could fail so suddenly? What to check?

 

[GGuillot]

Thinking it was a fuel issue I swapped the fuel pump and pressure regulator.

It's just a guessing game swapping parts in, which can lead to not knowing if the part itself you're swapping in is good or not to begin with. You need a more detailed diagnostics ck to narrow it down. What is the fuel pressure output with either part you swapped? Is it the same with each one? what is fuel pressure spec needed? what's the voltage going to the fuel pump? Does it stay constant when starting? Does fuel pressure remain steady during starting? Are the injectors pulsing? getting voltage?

I don't think there's a silver bullet, but only the troubleshooting process of elimination works, what's good, not good, etc.

 

[POPPS]

Recently rebuilt my 02 GTX RFI and everything went together beautifully. Started right up with no issues and made sure to follow break in procedures. After break in it ran like a champ. Even went about 5 mph faster on plane compared to pre-rebuild. Only observed thing even slightly out of perfection was that if it was at operating temperature and you killed the engine, then you had to run the starter for 5+ seconds and it wouldn't start, then it would start right up the second time you ran the starter. But I've heard this is normal for 2 strokes to be harder to start while warm.

Last weekend my buddy was riding it and the engine cut on him and he couldn't get it to restart. I swapped the plugs on the water since it was the same plugs used at break in but still no start. Can't even get it to start on the trailer. Thinking it was a fuel issue I swapped the fuel pump and pressure regulator. No improvement. Sometimes it will sputter when you run the starter but that's it. Almost sounds like it could be knocking. Had the fuel injectors rebuilt by fuelinjectorman.com 15 hrs ago so I am hoping that's not the issue. I did turn it over with the injectors to observe spray pattern and it looks like it starts strong, but then gets weak on both injectors. Could this be the issue? Or is the mpem metering the total amount of fuel prior to start to avoid flooding the engine?

Starting to think it could be electrical. But battery is fully charged and and I've never seen a 12v low or experienced any rectifier related symptoms.

No, it is not normal for a 2 stroke to not want to start after it has run...I good 2 stroke will start within 1 second, DI's, RF'is,,,and a properly running car'd motor will start before the fly wheel makes a full rotation...usually it will start on a dime,,,1/2second,,,if all is correct,
Sure sounds like fuel delivery.

Any ideas what could fail so suddenly? What to check?

 

[TxAg15]

Thanks for the help guys. Forgot to mention that I did check fuel pressure and it jumped up to 60 psi like it should. Fortunately, I figured out what the issue was, but unfortunately something a bit more serious than I was hoping. Read somewhere that a guy was having some issues with his rotary valve so I pulled the intake only to find that my rotary valve was spinning freely without the crank moving. Immediately knew that I had somehow shredded the brass RV gear. And I just pulled the engine and split the case and confirmed that. Thankfully the gear on the crank looks fine and the seals contained all of the brass shavings so it won't be terrible. But only reason I can think this would happen is the RV somehow binding. Any clue what would cause that? Or any other reason you've seen the brass RV gear fail? It was ground to a pulp in the case. And I replaced it when I rebuilt the engine

 

[GGuillot]

Any clue what would cause that?

Either bent RV shaft, or worn RV shaft bearings.

 

[etemplet]

You may have had undue resistance on the rotary gear bearings or something. Make sure you check the clearance on the rotary valve housing but that would be strange to have too little clearance there. Are you sure you are getting sufficient oil to the chamber?? How are you planning on repair the gear,rebuild the shaft, bearings gear, seal etc. ??? Or just replace it as a unit.

 

[TxAg15]

Already split the cases and swapped out the RV gear and reinstalled the RV shaft. The bearings feel smooth and solid with no play. And the seals are clean. I don't have a dial gauge to check the RV shaft but it looks straight to the naked eye. I know shop manual calls for a max run out of .003 in which is impossible to see but it's the same shaft I pulled out before so I would have had to bend it during the rebuild. Plenty of oil poured out of the chamber when removing the engine and its never gotten low on oil but obviously there's no pump supplying positive pressure so I guess hard to say 100% for sure it didn't just get dry.

I know most of the time people have issues with too much clearance for the rotary valve due to wear, not too little. But I did experience some binding in the RV during the rebuild. No clue how that happened, all torqued to spec with a new O ring. But my RV had a small lip in it and I saw others didn't so I flattened it out and it wasn't an issue anymore. Hence my thought of thermal expansion causing binding.

What would be symptoms of too much RV clearance? Running roughly?

Hoping all this info might help someone else who has had similar issues

 

[GGuillot]

If you just swapped the brass gear hard to say if you'll prevent it from happening again. It's difficult to tell if the shaft bearings are bad or the shaft is bent or not. On both of my 787 builds (carbed) I swapped the shaft bearing out for new ones, I figured after 20+ yrs and hundreds of hours spinning it was time. Cost? about $7 on each ski.

Recheck the assembly of the shaft and if you have it all the way seated. I've heard from a couple builders the shaft can't have any run out, not even .001 or it'll trash the brass gear..

 

[etemplet]

Agree.... too much clearance is what the test is for. I don't know what causes the brass gear teeth to strip. Other than a bearing failure or something getting caught in the rotary valve... runing out of oil etc....