496HO Blowby
 

Starting this year, one of my 200 hour 496 HOs is pushing oil out the dipstick tube. When the boat was put away at the end of last season, I had no issues, but since the boat has been put back into service this year it has been a huge problem.

I have pulled the fill caps off both motors to compare vacuum. With a paper towel held over the fill tubes, the good motor has a slight vacuum, creating a consistent dish shape in the towel. The motor that is pushing oil will cause the towel to fluctuate between vacuum and pressure.

These are bone stock, naturally asperated motors with the only change between last year and this year being the oil change and motor fog. Do these motors have a history of sticking or broken rings? I have begun removing the interior in preparation for a leak down test later this afternoon.

Any suggestions would be greatly welcomed.

do a leak down and see which cyl. is causing the problem.
hopefully it is just a stuck ring and not something more serious.

Thanks, kinda what I am hoping for...any magical suggestions for correcting a stuck ring/rings other than surgury?

if it's the ring, you could try filling the cyl. with a product called PB Blaster, get it at wally world, spray it in and let it sit, hopefully it will free it up.

Got out to the marina last night and pulled out all the plugs. All looked pretty much the same with a golden brown color over the insulator except cylinder #1; it was damp and oily. We started with the cylinders on that bank doing compression tests:
#7 = 160 psi
#5 = 165 psi
#3 = 165 psi
#1 = 0 psi :(

This wasn't good...stuck ring would at least get me something I would think.

Before prepping the engine for a pull, we quickly pulled the valve cover on that side to see if there might be a bent valve or other tell tail....nothing. Everything on the upper looked good.

The only thing that makes sense now is a burnt hole in the piston. If anything had broke or hit, I would think I would have heard some noise when it is running or the spark plug would have shown signs of debris in the combustion chamber.

Having the motor pulled today and hopefully by this weekend will have some good new to report. Anyone heard of these cast pistons burning from normal asperated usage?

There could be a number of things that could cause a piston to burn even on a N/A engine. Could have been sucking air in from somewhere or could be an injector issue! I would think you would get something on the compression test if just a stuck ring.

well I guess my idea is out, hopefully damage is not to bad, good luck on your quest.
Larry

I'm leaning (no phun intended) toward a fuel problem as well, but if this is the case aren't all these (496s) ticking time bombs then?

Well again a number of things could cause an injector to not work properly. Does not mean all 496 are going to blow up.

I was just thinking out loud that this would pose a potentially small margin of safety if it turns out to be a burned piston from a faulty injector...however, i won't know anything until the heads are off later this week.

So as suspected, the piston is burned thru. We haven't pulled the report from the onboard computer, but suspecting it will support a fuel delivery problem in #1. While we are at it will run the report from the other engine and I am keeping my fingers crossed...I thought these "smart" engines where supposed to protect themselves from problems like this?

http://www.intored.net/images/496/49...ons_003-50.jpg

http://www.intored.net/images/496/49...ons_004-50.jpg

http://www.intored.net/images/496/49...ons_001-50.jpg

http://www.intored.net/images/496/49...ons_005-50.jpg

Naughty kitty , I had the same problem last year. My piston looked exactly like yours... I'am just getting mine back in the water I feel your pain...

What did you attribute the failure to? For giggles, I contacted my insurance agent (statefarm) and was told that contaminated fuel is a specific exception in coverage.

Leaned out cylinder, assuming bad injector. Never tried ins claim. Just for my own knowledge how many hours were on your motors???

200 hours...really hurts

it looks like there is one spot on the edge that is burnt thru, that would make me wonder about detination in that cyl?
looks like there is a lot of black on there for it to be lean? lets see what some other have to say. sorry for the loss, we've all been there.
larry

I think the black is a post trama sign...once the burn got down into the ring lands, oil was free to get into the combustion chamber. What struck me strange was the relative area of clean on the head. It almost looks like a coolant leak.

What you are seeing on that piston is the result of a piece of the top of the piston by the valve relief that sometimes breaks off on the 496's with detonation or a lean burn condtion. t
This piece will bang around in the cylinder and make the marks you see on the top of the piston and cylinder head quench surface. Obvoiusly from the overall damage to the piston side and ring pack the motor was run quite awhile after this event occured.
If your interested in a new short blcok with forged pistons,HD rods and such, give us a call and we can get you pricing and delivery on an a short block and such.

Best Regards,
Ray @ Raylar

Thanks for the input Ray. If the respected builder (PowerSource) in my area had not been so responsive, my next call was going to be to you. I don't believe it was detonation as the other 7 pistons all look good with no signs of peening on the head. so this points to the injector, which we will look closer at this week.

To prevent this problem from re-occuring in this or the other motor, can someone recommend a decent fuel additive to clean injectors?

I was out at the builder on Saturday. The block was sitting in the honing tank and looked like the .030" oversize bore cleaned up the damage. I also noticed the new pistons have a symetrical head, with valve relief on both sides of the wrist pin. Is this a newer design, or just unique to this manufacturer?

http://www.intored.net/images/496/496_Pistons2-50.jpg

http://www.intored.net/images/496/496_Pistons1-50.jpg

http://www.intored.net/images/496/496_Pistons3-50.jpg

ny codes or tell tale signs of this happening?

Rough running or ???
Good luck and keep us posted.
I tohught the earlier HO's had better internals. like the 2002 and 2003 496 HO's? (forged)

Dennis

Sounds like a great oppuertuity to upgrade to some Big Power Raylar heads!

not to my knowledge did any of the 496s have forged pistons, although Ray might be able to confirm or dismay this.

I had no indication of the problem, other than a slight oily residue around the dipstick flange. The engine didn't make any strange noises, there was no noticable vibration and it was very difficult to see the small amount of oil in the exhaust steam.

We are going to pull the codes from both the damaged motor and the remaining one this week. I'll keep ya posted on the progress...
Jeff

If it wasn't the middle of our boating season, I would have been looking to pull both motors and drop in Ray's forged pistons.

I forgot your dealing with twins...Big difference. Were you able to salvage your heads...because there are alot of those take offs sitting around these parts.

Yeah, the heads look fine, but if pressure testing reveals a problem, I might hit the boards here to find a couple.

Dropped the motor back in yesturday, however the builder told me he tested all the injectors without finding a problem. We will be firing the motor this afternoon and pulling the ECM data logs in hopes of finding some clues.

I did purchase several cans of Sea-Foam and plan to remove the water sepparator fuel filter, pouring out 1/2 the fuel and adding Sea-Foam to clean the system on the remaining motor. Any thoughts on this?

http://www.intored.net/images/496/49...ons_006-50.jpg

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I've done Sea foam in the filter with diesels...But it won't hurt a gas engine...It will smoke like nothing you've seen before. It will also be hard to start...If it was me I would start it up first on gas and make sure everything runs smooth then hit it with some sea foam.

The new motor I am only planning on adding the Sea-Foam to the tank, but the untouched motor (with 200 hours) I was going to try the Sea-Foam in the filter.

Mind if I ask what kind of oil you were running and looks like a NAPA filter. Looked like lots of pitson scoring on the cylinder wall.

I only use the Merc 25-40 and merc filters, but i'm not sure what the builder used for oil and yes he installed a napa filter. You can see in the first picture of the last group the merc water/fuel filter that I installed at the end of last season.

Didn't you notice power loss with only 7 pistons running. I would have figured you would notice a WOT speed being slowwer??
How much oil were you pushing through the dipstick?

That piston looks exactly like what mine looked like last year... I've learned there is a difference with different brands of gas and now only run Sunoco. I can't say that's the reason it happened, but I do know all my injectors were working correctly, as yours were.

Maybe Ray can hook you up with a discount for two sets this winter! :D Good luck!

As far as power lost, it isn't as if I was getting zero power from that one jug...probabaly still pushing 40%, just a guess based on the relatively small void in the head (most damage was on the side. So to have one jug out of 16 not operating at 100% is really not too noticable. Any depreciation in speed I attributed to a change in my trim angle, air temperature or changes in the water condition.

I would love a new set of short blocks from Ray which would give me the capacity to drop a whipple on top, however the thought of dropping a bunch more $$$ in it right now is making my stomach turn.

while the motor was out, I took the oppertunity to change impellers in both motors...now neither motor is pulling enough water pressure for me to even test...grrrr. Today ordered some new brass pump housing to replace these, which apparnetly worked well enough with the worn impellers, but won't seal on the ends of the new ones.

How much oil were you actually pushing through the dipstick, just curious?

Hard to say, because at >3,500 RPM it wasn't noticable. On the 496 however, the dipstick tube opening is right above the serpentine belt so it didn't take much oil to look like a mess. Reflecting back on this whole situation, I can remember last year seeing a small oil residue around the threaded flange on the top of the tube on that motor...that was the tell tail.

Slow burn down on 496's
 

Lets face it, in some boat builder shops the rigging isn't always as foresighted as it could be. Can"t always blame the builder as they just get the 496's out of the crate, ready to run and drop them in, hook'em up and deliver the boat!
There job is really not to figure out what size fuel line the particular engine should be fed with. Mercury should specify and probably does in the fine print of the installation instructions that most installers don't read!

If you notice in your pictures and on the motor, the fuel line inlet bard to the cool fuel system at the primary suction pump looks to be a 3/8" line size, which has about a net 1/4" inside opening at best. A 425HP -496HO at WOT is using about 45 gallons of fuel per hour minimum or about 3/4 of a gallon a minute! Try sucking that much water thru a straw that is about average 4 feet long with fuel line to tank average and you can see that the engine is probably going to strain and run lean at WOT with that type of fuel feed!
Couple a marginal fuel flow rate to the pump with our marginal new gasolines, the hotter weather boating days, the average condtion of the fuel water filter and you can see its possible to put the fuel delivery on this engine in a close to marginal or even a less than needed delivery and you will under big loads especially at WOT slowly lean burn the engine. This will raise cylinder temperatures to the extreme edge of minimum requirements and the resulting condtion will most of the time cause the pistons to heat up excessively, swell tighter in the bores and start scuffing bores, skirts and rings. If the condition gets at the limit for the piston usually the top piston above the ring groove will start to lift and either the ring will fail or is as usual in the 496 because of the stock piston thin top dimension of top of the piston over the top ring, this top edge of the piston will start to melt away or crack and break off!
When this happens the motor is toast! and usually when it happens its a catistrophic failure of the rotating assembly!

496's are great engines when set up right the actual failures are a very small percentage versus the number of 496's out there about 40,000 or so at last estimates. This is a strong engine and they will run wounded on 7 cylinders very well and in a twin installation its even harder to see or feel a wounded 496 until it gets obvious with blowby, power loss, etc.

The bottom line is make sure the fuel feed lines from your fuel tanks to the 496 fuel pump inlet location are 1/2" size on both lines and fittings and that if your boat has anti-siphon fittings at the fuel tank, that they are also 1/2" size instead of the 3/8" size we see on most boats, even those with 1/2" fuel lines. Remember its not the OD size of the line that counts, its the ID size that flows the fuel!!

I realize I ramble on a bit but being the college professor and the educator teaching basic 496-101 class I try to be instructional with my comments. Hope this information helps and saves other 496 owners similar damage!

Great information Ray and I really appreciate your insite into this problem/motor. I will definately look into the hose size this weekend. I do have two questions that maybe you or other board memeber can help me with:

1. What is a anti-siphon fitting and where is this typically located?
2. I thought the "smart" engines would monitor fuel rail pressure and prevent lean condition from happening if occured upstream of the injector?

There is a repair kit avail from place in Havasu (search old threads) so you don't need entire new housings.
Was it not pulling enough water off hose or backed in at ramp? Merc Mechanic told me only test at ramp, using hose will just burn good impellers. Good luck!

Anti-siphon is located at the tank pickup-it looks like a hose barb and the hose is mounted to it. You can either punch out the check ball or replace it with a brass barb fitting.

Any idea what the purpose for this device is? From the description and location it is intended to prevent fuel from running away from the engine's fuel delivery system back to the tank?