496HO Blowby
07-28-2008, 12:53 PM
#31
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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?
How much oil were you pushing through the dipstick?
Last edited by cloudmaster_321; 07-28-2008 at 01:08 PM. Reason: why not
07-28-2008, 01:22 PM
#32
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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!
Good luck!
Maybe Ray can hook you up with a discount for two sets this winter!
Good luck!
07-28-2008, 03:03 PM
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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 $$$ in it right now is making my stomach turn.
while the motor was out, I took the oppertunity to change impellers in both motors...now neither motor is pulling enough water pressure for me to even test...grrrr. Today ordered some new brass pump housing to replace these, which apparnetly worked well enough with the worn impellers, but won't seal on the ends of the new ones.
I would love a new set of short blocks from Ray which would give me the capacity to drop a whipple on top, however the thought of dropping a bunch more $$$ 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.
07-29-2008, 06:24 AM
#35
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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.
07-31-2008, 11:26 AM
#36
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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!
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!
08-01-2008, 06:40 AM
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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!
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:
- What is a anti-siphon fitting and where is this typically located?
- I thought the "smart" engines would monitor fuel rail pressure and prevent lean condition from happening if occured upstream of the injector?
08-01-2008, 07:43 AM
#38
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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.
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!
08-01-2008, 10:44 AM
#39
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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.
08-01-2008, 01:54 PM
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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?
