Today's call from the PWC mechanic - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
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post #1 of 19 (permalink) Old 04-27-2017, 05:13 PM Thread Starter
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Today's call from the PWC mechanic

Took the 2001 Yamaha XLT 1200 to the PWC mechanic a month ago. It wasn't running as fast as my 2002 (which will hit 60 mph) and I wanted to add a new impeller, ride plate and free-flo air intake. The mechanic I took it to had rebuilt it in late 2012 and it had probably 25 - 30 hrs since the rebuild. It ran OK, just not as fast as the other. Just wanted to mod it out.

Mechanic called me up today and said:

fuel diaphrams in carburator are almost worn out

all three power valves are broken mid-shaft

bottom half of power valves fell into the engine and all 3 pistons are scored and have to be replaced

repairs will amount to $2,500!!!

This is all for a PWC that appeared to be running fine, if not fast, last summer

Mechanic says it is all due to ethanol in the gas, and not using high octane gasoline. He says you gotta add a $10.00 bottle of octane boost to every tank. Nothing was said to me after the rebuild that I had to use high octane fuel or the damage that would be caused by using low octane fuel. I add Yamaha Ring-free + and Startron to each tank.
And it very difficult to find gas without ethanol. That's why I used the additives.

Mechanic attributes the power valve failure to low octane gas that caused pre-detonation. Strange that my 2002, which was rebuilt in 2011, has been using the same gas and has had no problem.
Allegedly, when the 2001 XLT was rebuilt the mechanic installed heavy duty R&D power valves. The mechanic now says that there is a Yamaha edition 2 power valve that is new and improved and not supposed to break.

This machine has not been rough-ridden or mistreated. It did not run rough or miss or demonstrate any problem with running other than the top speed was only about 45 - 47 mph. It is very heartbreaking when you take the PWC to get mods and the mechanic says the engine is toast.

I told the mechanic I wasn't going to dump that kind of money in that old of machine, especially when it seems his rebuilds only last a few years. I plan to go get it this weekend, and may just tear into it with a mechanic friend of mine and see what we can do. We can't hurt it, as it's shot already.

So see, your day wasn't so bad in comparison, was it?

Any advice Rods?

ZARDOZ
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post #2 of 19 (permalink) Old 04-28-2017, 05:31 AM
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There are several things that have me po'd about this.
It ran fine other than no top end (from day one). Why is it just now something is broken that caused this ?
Did he do a compression check before tearing the engine apart ?
What led him to believe there was a problem with the power valves on a engine with that few hours ?
He went head deep into the engine, from what I can tell, without authorization from you. This is a huge one to me. if he did a compression check, or something else that led him that it needed to come apart, he is required by law to notify you before he does it. I'm a real stickler on this, and it happens all over the place, and pisses me off more than anyone knows.
Fuel diaphragms almost worn out ????? Lost on that one.
I have a very hard time believing that using non ethanol fuel was the contributing factor. Ethanol is very hard on the fuel system. The alcohol deteriorates the rubber components quickly. That is the reason race cars that run alcohol have components that are specifically made to handle it.
87 octane should handle up to around 150-155 psi compression depending on timing, and I don't believe yours is that high, unless he had the head milled to much. That's about a 9-9.5:1 compression ratio. I would recommend bumping to 89 though. It will help burn things off, and help the power a bit.
Pre-detonation is more detrimental to pistons than anything. It can cause holes in the top, and broken ring lands. If your timing was off, and the engine was pre igniting the whole time, could be the reason you had no top end or 3/4 to full throttle power.
I would call R&D and talk to them about the failure. If they are truly R&D, they might replace them.
You will have to look and see how bad the cyl's are damaged. If they are just scored a little, you can get away with a quick hone. I beleive your cyl's are plated, so you might want to check on this. If they are, you can only do a very light, quick hone. Just enough to scuff the walls.
Here's what I would do. Get it back, slap it back together real quick (without the power valves) and do a compression check on it. This is providing the pistons and rings are not trashed. If they are, when you get new parts, lube the cyl's with oil real good, and using the old head gasket, install the head, and do a compression test, and compare it to your other ski. They should be the same, if not real close. if it is much higher than the other ski, the compression could be to high from milling the head, and would require high octane fuel, and that could be the reason for the pre ignition. If the compression was high enough to require high octane, you should have noticed a difference in exhaust sound. It would sound raspier, and have more of a pop when each cyl fires.
I would like to see some pictures of everything, and curious as to what R&D says.
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post #3 of 19 (permalink) Old 04-28-2017, 05:47 AM Thread Starter
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The reason he looked into the engine was because he was going to check the pop-off to see if that was the reason for the low top end. Supposedly the cylinders are not scored, and look clean, as that's what he told me. It's the pistons that are damaged and the power valves that are only 1/2 there. The bottoms of the power valves have allegedly disappeared.

But my god, Rods, wouldn't a machine with pre-detonation and destroyed pistons run rough? The machine never had a problem except for low top end. Ran it up on the trailer at the end of the year without a problem.

Also, my 2002 XLT used the same gas, the same additives, the same everything; it was used much, much more, and was pushed much harder than the 2001. It will go from 0 - 60 in about 3 seconds. It doesn't make sense to me, except it was rebuilt in 2011 by someone other than MJD.

I plan to pick it up tomorrow. Sad day around here.

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post #4 of 19 (permalink) Old 04-28-2017, 11:26 AM
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Popoff will not affect anything over 1/4 throttle. If it was a carb issue it would most likely be a high speed circuit issue.
You would think trashed pistons should and would make it run lile crap due to low compression.
How in the hell does the valve part disappear ?
2+2 is not equaling 4 here.
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post #5 of 19 (permalink) Old 04-28-2017, 03:01 PM Thread Starter
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I reiterate, the 2001 did not run like crap. It ran fine, just slower than the 2002. I had no idea that there was anything wrong with the engine and thot that a few mods would take care of the speed issue. I'll try and post pictures when I get the machine back tomorrow. I have read though, that even with the power valves not functioning the XLT 1200 will still run decent as long as compression is not compromised.

Shouldn't a rebuild last longer than 4 yrs/30 hrs? And just for the record, the machine was not abused.

When talking to him on the phone the mechanic seemed disappointed that I was not going to have him perform the "necessary" repairs. I said for $2,500 I can buy a used machine, and mechanic said I may have the same problems over again by buying unknown used. I think it may be better to invest $2,500 in a used machine than to give the PWC MECHANIC that amount to rebuild. If I do get the machine repaired, I'm pretty sure that I am not going back to the PWC MECHANIC. I can't keep rebuilding every 4 years and that seems to be as long as their rebuilds last.

Hey Rods, wouldn't pre-detonation be noticed in the running of the PWC? The PWC MECHANIC says you can't tell with a 2-stroke and 4-strokes have sensors that prevent pre-detonation.

ZARDOZ

Last edited by ZARDOZ; 05-02-2017 at 04:09 PM.
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post #6 of 19 (permalink) Old 04-28-2017, 03:20 PM Thread Starter
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One more thing. I have a mechanic friend of mine who has rebuilt automobile engines and has his own auto service garage out of his home. We are considering tearing into the 2001 XLT just because we could possibly fix it and certainly can't do it much harm. He wanted to know if there is a Chiltons for the XLT, and I told him I had a service manual and thot that would work. A service manual is all that I can find on line. Heck, we might just tear into the other 2001 XLT that I bought last November. It has a burnt cylinder. I thot about using parts off of it, but if I'm gonna rebuild I'd rather use new parts as I do not want to do it again. Total engine rebuild kits run $1,200, so I could rebuild both for what MJD wants to charge. Of course, we're doing our own labor.

Do you think that an auto mechanic and a mechanical idiot can take the XLT apart, put in new parts using only the service manual, and get the danged thing to run again? Would it be better if the mechanical idiot (that's me) does not participate?

I would much rather not have these problems, but if I'm gonna have them would rather have them over the wintertime.

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post #7 of 19 (permalink) Old 04-29-2017, 07:41 AM
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ANY 2 stroke that is properly rebuilt and maintained should be able to go at least 120-150 hours before needing new rings. The cyl plating that is used on alot of stuff now, helps reduce the ring and cyl wear and reduce friction. I have heard of some going past 300 hours, not saying they probably didn't need a rebuild earlier. lol
Detonation is difficult to tell with a 2 stroke, as it is hard to hear over the engine. About the only way I know of is to remove the seat, and do a full throttle launch from a standstill. It will not burn off all the fuel at the designated time, and ping. He is right on a computer controlled 4 stroke engine, but the knock sensor and ecu can only compensate for so much. What it does is send a signal to the ecu, and the ecu retards the timing to the point that the sensor no longer registers it. You can check this systems function by tapping on the block by the sensor. It will register it as knock, but you need a diagnostic tool that shows the timing to see it happening.
Pre-ignition is two combustion processes happening in the chamber at pretty much the same time. One starts prematurely, and the other starts on time, or they both start simultaneously on separate sides of the combustion chamber. The result is that they meet somewhere in the chamber, and the collusion of the two is what you hear, so instead of it being a smooth combustion process, it is a very harsh, and violent process that can fracture pistons. It's the difference between squishing a marshmallow, and squeezing an egg to the point of breaking.
It can be cause by several problems. Lean fuel mix, hot engine from cooling system issues, or a lean condition, lower than required octane fuel for the current compression, timing is off.
It can run ok if the power valves are not functioning correctly, or at all. Depending on their position will dictate what your top end is like. If they are stuck closed, hole shot at part throttle will be decent, but anything over that will be crap. If they are stuck open, hole shot will be crap, but it should hit like a banshee in mid to top end when the power band comes in like the old dirt bikes did (a rich bottom end can act like this also as it gets to a point of enough air flow to lean it out some, like when a carbs regulator diaphragm is in backwards (don't ask lol)).
Your 1200 should be capable of easily getting into the 50's in stock form, with a good engine properly tuned. My 97 STX1100 is supposed to be able to hit 56 or 57 in pure stock form with a good engine, and this thing is huge.
If it is a actual service manual, it will have more information than a clymer or chilton manual.
Yes you can do it. It's not difficult.
You will prob not need a full engine rebuild kit, just gaskets, pistons, and maybe rings. It all depends how bad the damage is. This is going on that he had the crank rebuilt, and it is still in good shape. All the main bearing must feel like glass, and not have any excess play, and the rods must not have any vertical play at all, and also be glass smooth. This can usually be checked before splitting the cases but using the rods to spin the crank. Just be sure and don't let the other two rods just flop around. They need to be held, if nothing else so you can feel the bearings accurately. Not sure why he wants 2500.00 if the bores and crank are good. That and the crank are the two most expensive processes in that engine.
If you do split the cases, you will need some three bond 1211 to seal them back together, a flywheel puller, and a drive coupling remover. Just a real thin coat.
Get some carb kits from the jet ski store, and rebuild those carbs. Since it was running ok, I would leave the mixture screws in, but check the settings of them, and blow the passages out with low psi air. The kits are about 35.00 each. If you want to be super thorough, get a mikuni 100psi popoff gauge.
Once you see how simple all this really is, you will beat yourself up for not doing it before.
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post #8 of 19 (permalink) Old 04-29-2017, 07:42 AM
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Crap, that was a novel !!!! hahaha
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post #9 of 19 (permalink) Old 04-29-2017, 07:55 AM Thread Starter
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If it is a novel, it's a tragedy, not a comedy. Cry today, laugh tomorrow. I plan to leave in about 10 minutes to pick it up. Bringing my camera and packing heat. Never kno what's gonna happen.

Stay tuned for further developments.

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post #10 of 19 (permalink) Old 05-01-2017, 04:37 AM
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Just some info from R&D's website I thought you might find interesting.

"The new R&D Billet Exhaust Valves reduce the clearance between the valve and piston. This reduced clearance improves the seal which boosts the valve down compression ratio delivering greater bottom and mid range power. The billet engineered design is a direct performance bolt-on, guaranteed to never break in any application. Now being used by Factory Yamaha Racing."
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