1998 Merc 4.3 burnt piston

[H60Chopperdr]

Hi all,

New to the site. I'll try to make this as brief as possible. Motor developed a knock noise last year. Decided to run it to it's death as I have twin engines and the other can bring me home. Well, knocking stbd engine lost most power and decided it had enough. I ordered a new base engine and swapped over the external parts. Pulled old engine apart and found one piston had a 1/4" x 1/16" spot worn away on outer edge. Combustion blew past the worn away edge and annihilated the rings and upper 1/2 outer piston (ring groves and lands) and skirt surface. This of course caused blow by and fouled plugs but that is not the issue. My issue is this. Now that I have the new engine about ready to install I am worried this can happen again. I suspect detonation. What could have caused the detonation? I used good fuel with Seafoam. It was not an octane problem. Is my timing off? It is a TBI with what I believe is TB V ignition. The distributor does not hold the ECM or KSM. I think my KSM is mounted to the left riser elbow. Could it be a bad KS? Any advice is great. I don't want a repeat of this $3K shenanigan.

Additional info:
About 600 hrs on motor
Exhaust manifolds were nearly corroded shut (put new ones on new engine and port engine)

One other question. New base engine has a much larger threaded hole on the LH lower block where the knock sensor was mounted on old engine. Now my knock sensor won't fit. Why? How do I remedy this?

Thanks.

 

[dan t.]

Re: 1998 Merc 4.3 burnt piston

Hi all,

)

One other question. New base engine has a much larger threaded hole on the LH lower block where the knock sensor was mounted on old engine. Now my knock sensor won't fit. Why? How do I remedy this?

Thanks.

Pipe bushing.

 

[Bondo]

Re: 1998 Merc 4.3 burnt piston

I suspect detonation. What could have caused the detonation?

Ayuh,.... Water in the fuel, causes a lean condition....

Check the contents of the fuel filters...

 

[H60Chopperdr]

Re: 1998 Merc 4.3 burnt piston

Excellent point. I did indeed have water in the fuel a couple of years ago that was causing problems. I drained the tank and have used Seafoam since. Fuel filters were also changed then. I hope that was the cause because that was remedied. Any other possibilities before I run this motor?
One other point...this may be totally unrelated but maybe not. The stbd tach (upper and lower) (flybridge boat) both starts bouncing eratically and wildly (nearly pegged sometimes) after about 3000+ RPM. There is no audible fluctuation in the engine's actual RPM. I read on a differnt forum that it was related to a faulty ICM and spark advance issues. Thoughts?

 

[Bondo]

Re: 1998 Merc 4.3 burnt piston

I did indeed have water in the fuel a couple of years ago that was causing problems. I drained the tank and have used Seafoam since.

Ayuh,... The fuel filters are at a minimum an Annual service point...

It's called Preventive Maintenance for a reason...

 

[Don S]

Re: 1998 Merc 4.3 burnt piston

Not only should you be changing those filters yearly, you need to check the contents of the old filter to make sure you aren't picking up water again.
After you get the engine back together and running, you also need to verify the static timing, and advance timing. Being a 98, you have Thunderbolt V ignition that needs to be in base timing mode to set the timing.

 

[H60Chopperdr]

Re: 1998 Merc 4.3 burnt piston

It's been a long time coming but finally got the engine in and running. Sea trialed today but ran into some issues. First is starting. It seems to labor a little harder than it should during cranking. Once it fires it runs okay but the idle slowly surges but smothes out when warm. This is unlike the port engine which is smooth from the get go. Anyway, the idle tends to be too high (1050 rpm). Checked linkage and all is normal. The idle will also sometimes be fine as it was when we launched. I ran the boat at idle for awhile and all was well. Advanced the throttle to 2000 rpm (per break-in procedures) and noticed significant detonation pinging. Sound is best described as a sock full of marbles being shaken. The detonation starts at about 1850 rpm. I did not run the boat any further up the rpm scale until I get this detonation thing under control. I am suspecting ignition/timing issues. Here are some other facts. I do not have a timing scale on the front of the motor. Just two index marks on the crank pulley and one on the block. I used that mark for setting the initial distributor position on installation. I keep reading about setting the base timing but am having trouble finding a good easy to understand procedure. Can I do this without a scan tool or timing index on the motor? Finally, could a knock sensor be the culprit? I don't think so since this is obtuse detonation. I would think that severe detonation is first and foremost a bad timing issue, so much so that the knock sensor could not compensate. Advice anyone?

 

[Lyle29464]

Re: 1998 Merc 4.3 burnt piston

To much initial advance in timing can cause the starting problem and detonation.

 

[dubs283]

Re: 1998 Merc 4.3 burnt piston

did you install new tune-up parts with the new long block?? plugs wires cap rotor sensor filters etc...?? rebuilt carb??

you need an oem manual for your engine, if you post a serial number there are folks here who can post a link to download one

you can then follow the procedure for properly setting the timing, with no index on the motor i suggest using an advance timing light to set base timing, then check total advance throughout the rpm range

to test the knock sensor just rap the block next to the sensor with a hammer at 1500-2000 rpm an listen for an rpm drop

 

[H60Chopperdr]

Re: 1998 Merc 4.3 burnt piston

All new ignition parts. TBI is fine. I have both the Mercruiser and Seloc book which are nearly identical. The problem is the procedures in the manuals for setting base timing don't make any sense. First off, my distributor looks like the EST type as seen on pg 10-45 of the Seloc manual just with 6 terminals not 4. The manual does not make any mention of this setup on a v-6. Second, even if I have a TBIV, it mention on pg 10-50 to set to an initial setting of 8 deg but as I mentioned before my new motor (old motor and port motor as well) do not have indexed scales on the block. I can only assume a scan tool of some sort might display actual timing, although this in NOT mentioned in the book. I believe a scan tool is required for the TBV as per pg 10-50. My distributor (either engine) does not look like any of the distributors on pg 10-53 which indicate TBIV and V. If it is an EST, the procedure for timing on page 3-23 (again for 3.0 eng only) makes use of a timing scale. I do not have a timing scale. Both engine distributors look to be OEM original 98 distributors, not some frankenstein job. So which ignition system do I have and what procedure do I use to set timing? Left eng ser # is OL28120, Right is OL278080.
On another note, I read another thread of a guy that had a similar sounding problem, pinging, erratic tach. Turned out to be his shift cutout. Should that be an area of concern?

 

[achris]

Re: 1998 Merc 4.3 burnt piston

....the Mercruiser and Seloc book which are nearly identical.

Not in a million years!!!

The problem is the procedures in the manuals for setting base timing don't make any sense. First off, my distributor looks like the EST type as seen on pg 10-45 of the Seloc manual just with 6 terminals not 4. The manual does not make any mention of this setup on a v-6.

Stop using the seloc. Throw it in the bin, burn it, use it as hand wipes. Anything you like but get rid of it!!!

Second, even if I have a TBIV, it mention on pg 10-50 to set to an initial setting of 8 deg but as I mentioned before my new motor (old motor and port motor as well) do not have indexed scales on the block. I can only assume a scan tool of some sort might display actual timing, although this in NOT mentioned in the book.

You need a timing light that has the ability to retard the flash. That's how you check the spark timing. Set the timing light to retard by 8 degrees, then set the marks together.... Then you have your engine at 8 degrees BTDC

I believe a scan tool is required for the TBV as per pg 10-50. My distributor (either engine) does not look like any of the distributors on pg 10-53 which indicate TBIV and V. If it is an EST, the procedure for timing on page 3-23 (again for 3.0 eng only) makes use of a timing scale. I do not have a timing scale. Both engine distributors look to be OEM original 98 distributors, not some frankenstein job. So which ignition system do I have and what procedure do I use to set timing? Left eng ser # is OL28120, Right is OL278080....

Your engines are 1999, so you should be using manual #25...

They were only supplied with Thunderbolt V. If you have anything else in there, it's after-market and you need to identify it and go back to the manufacturer of the ignition system. For TB-V you need to set the system in 'Base Timing Mode' before you can set the timing. The procedure for that is on page 5, section 4B of the GENUINE manual....

Chris.....

 

[Pete104]

Re: 1998 Merc 4.3 burnt piston

They also are using the "1 time covers" (plastic) and those marks are tough to see! Yellow/white chalk get it done.

 

[Lyle29464]

Re: 1998 Merc 4.3 burnt piston

I know reverse turn v6's were very rare but they do exist. If you have one the timing must be set on the left side of the mark on the dampener or the right side of the plate.

 

[dubs283]

Re: 1998 Merc 4.3 burnt piston

I can only assume a scan tool of some sort might display actual timing, although this in NOT mentioned in the book. I believe a scan tool is required for the TBV as per pg 10-50. My distributor (either engine) does not look like any of the distributors on pg 10-53 which indicate TBIV and V. If it is an EST, the procedure for timing on page 3-23 (again for 3.0 eng only) makes use of a timing scale. I do not have a timing scale.

post #9 paragraph 3

use an advance timing light, like chris mentioned in his post too

 

[H60Chopperdr]

Re: 1998 Merc 4.3 burnt piston

Sorry it took so long to respond. Busy life and only occasional weekends to work on it. I was off a tooth or two when initially stabbing the distributor. 55 deg of advance. I am amazed it ran at all. Anyway, the timing is adjusted. Took boat for test/break-in run and all is well. The new engine pulls like a freight train. I just wish the port engine would pull as hard as stbd. Time for a compression check on that motor. Thanks to all who helped out. As long as I own a boat I know I'll be back to this site!!!