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  1. #1
    Crash Test Dummy Smitty's Avatar
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    Detonation, Ignition, Lean condition?

    Ok..... the ski went BOOM last weekend; pulled the carbs, looked at the reeds, and found a couple of them on the rear cylinder distorted but intact. Pulled the heads, and found a hole in the piston. Pulled the piston today, and found small chunks gone and damage on the exhaust side.

    Issues we have found:
    The R&D stuffers that were installed didn't seat inside the cutouts in the R&D intake quite right. Might have caused a lean condition; the stuffers have been fitted now.

    I've got an older R&D CDI; more than one person has said they have had some problems with them. It's got a hell of a spark, it will even spark through the plug boot to ground if it's disconnected. I've never seen a spark travel through a boot before. The hole in the piston looks like something caused by a ignition problem, but it's off center enough that I'm not sure if it's it; plus, I've got the damage from the exhaust area.

    Bad gas? This happened as soon as I put in the water after I fueled up. I've got an ADA head, compression was 140 on all 3 prior to this. I filled up at an Exxon with 93 octane, but who's to say that it wasn't watered down? Mark Sheffield at Riva pronounced it bad gas with detonation before I even told him I had just filled up.

    A new piston and rings will be here today; I can barely feel any scratches in the cylinder (gotta love Nikasil). The stuffers have been matched to the intake, and I've got another set of reeds and cages to use (I'll upgrade to Nandos VF3's later this summer). I've got the stock CDI I can put back in. I'll be draining the gas and putting it in my car.

    So, what I'm asking, what was the cause of it all? I'd hate to toss the CDI if I don't have to, especial for when I'm offshore coming out of the water; I can really tell the difference from when I rode my GPR and it would land with the brake on.
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  2. #2
    Hydrotoys's Avatar
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    Smitty,
    Thowing this out there. Hope it helps.

    Water ingestion would be my guess. Don't rule out timing or crankshaft seal leak yet.

    You mentioned "bad gas." I had bad gas last night. It was rough around here. Seriously, if there were massive amounts of water in your gas (very, very, very possible if you use ethanol) then it 'MIGHT' provide enough to do that damage...but I'd go with water ingestion from an internal or external source...

    That hole in the top of the piston is a good indicator. Also you mentioned ADA head. Does your ADA o-rings have little rubber "stringlets" hanging off of them? ADA heads are notorious for internal water leaks and crappy machined bolts instead of rolled threads. I've SEEN THEM squirt externally into the carbs. I've SEEN THEM leak past the compression/water oring.

    Did the flame arrester have any evidence? The rear cylinder almost always gets water from the hull due to the coupler. Any evidence there?

    Consider the rear seal. Did it let go?

    The reed damage is from red-hot smegma melted aluminum-oxide bullets from the piston overheating the crank case.

    Can you pressure check the engine before putting it back on the water?

  3. #3
    Crash Test Dummy Smitty's Avatar
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    Water ingestion might be the culprit... a few weeks before we were out wave jumping and it started running bad, fouled out the plugs... we check the motor, found that the #1 plug wire had an open in it, wasn't making contact. Replaced the wire; also figured out that the rubber seal was missing from my front seat. That, combined with a missing coupler cover was slinging water around the engine compartment.

    We put a seal on the seat and rode the next weekend. It ran great, except that about 5 mins into the ride the motor just died, then wouldn't idle right. We farted around with it, and the RPMs came back after a few. Thought it might have been the fact that I had filled the tank to the brim and hadn't had a chance to build back pressure. The rest of the day it ran great, no loss of RPM or holeshot.

    The last time I rode it, I filled it to the rim again, and it did the same thing, lost power about 5 mins into the ride. This time, it never did get the power back, and kept backfiring when I tried to give it more than 1/2 throttle.

    Doubt it's the rear seal, the motor has less than 10 hours on it (and I'm replacing a pistson already.... GRRRRR). Never seen any stringlets on the O-rings. Any suggested fixes for the head?

    Thanks for the input.

  4. #4
    carbuff91's Avatar
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    Wow, this sounds almost exactly like what happened to me at MUDBUG. I had a chunk of my piston missing on the exhaust side. I think my Advent may have been what caused it. Before I left for MB I was in my creek testing and my boat just died out. I wasn't getting any spark and nothing was coming up on the dash.

    After sitting in the creek for a half hour (thanks benny for getting me) I tried a few more times and the same...no spark. With the Advent I could actually hear the ignition popping when I had the boots off plugs.

    So, we got it back to shore and installed my stock ignition and it started right up. I didn't have any time to test and only after about a half hour or riding at MB...I seized the piston and it was missing a chunk. Granted I did have the wrong pitch prop on too. But, I'm going to be sending the Advent back to have it looked at.

    Keep me posted on your findings....

    Steve

  5. #5
    Moderator Insanediego Joe's Avatar
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    Throw the ada head into the trash and get a stock head thats milled. I have seen this on my tripple piped gpr. I cut my ada into 3 pieces and it seemed to lesson the Eating of the orings. After talking with hydro for hours and hours we have found the groove in the ada head where the oring seats is to shallow. The gpr shakes a lot and starts to fray the orings. Look at the orings closely to see if you can see any little hairs starting form on the outside of the oring. This damage wasnt caused by reed stuffers NO way.

  6. #6
    Crash Test Dummy Smitty's Avatar
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    Joe, if I'm not mistaken, I've got your old custom 3 piece head

    I've got new O-rings, I'm going replace them and keep an eye on it.

  7. #7
    Moderator Insanediego Joe's Avatar
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    Did you replace the orings when you first installed the head? There is another guy on the forum running a custom ada head but... we havnt heard from him. Smitty we need to figure out why that motor ingested water before proceeding. How many hrs on the orings in that head? Look for the little hairs on the orings. Last thing I want to see is you put a new piston in there and suffer the same damage. Did you use grease or something else to hold the orings in place when installing the head? The only safe thing to use is grease. If you used 1211 or anything else to hold the orings in place or nothing at all it going to spell disaster.

  8. #8
    Moderator Insanediego Joe's Avatar
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    On another note, if you ingested water from wave jumping this could all be an over reaction on my part!

  9. #9
    Crash Test Dummy Smitty's Avatar
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    Yeah, I put new rings on the head when I installed it, used grease even.

    I might have had water ingestion from that day in the surf; with no seal on the seat, no telling how much water sloshed in. Wish we had noticed that there was no seal on it before I went out that day.

    Like I said, we have found several issues that we have fixed; possible air leak, pop-off issues, questionable ignition problems, water injestion.... at this point, I think the best thing to do is to put it back together as tight as I can, then see how everything works.

  10. #10
    Robsauto2's Avatar
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    I did the same thing last year, same r-d ignition. I belive mine was:

    1. Went lean because of low fuel pressure, I rebuilt all 3 pumps, pressure now at 5 psi, was 1 psi before.
    2. Poor quality fuel.
    3. too much advance with r-d ignition.
    4. riding at 3/4 throttle, 6000 rpm, too long.

    I have the stock head with 165 psi, don't think mine was water intrusion.
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