Timing is retarded ;-)

[jimmbo]

Also, is there a way to identify when a part has actually been revised/redesigned rather than just changing the p/n on the same old part?

You would have to speak to the Manufacturer/Engineers, as they are the Ones who had their Reason(s) to change the Number.

 

[alldodge]

In most cases the change in part numbers mean nothing other than they might be getting the part from another manufacture.
Old numbers use to be 5 to 6 digits
Next Merc started adding a letter and then a number - 123456T01

Anything after the letter was just for separate the differences between manufacturers. If part was actually changed then they went with a new number

The 8Mxxxx numbers is just Merc starting a completely new record system. I would not expect to see any difference between the old and new parts. As example you can search the old number and new number at mercruiser parts and they both show up

 

[Scott06]

Latest Parts Lists usually show the updates

yes I think this is more a issue with the parts list the OP was looking at. Most site like marine engine.com have the old part number listed as unavailable then the new P/N as available

 

[gsbarry]

I decided to run a leak down test today. The results were apparently very good, I was getting ~4% leakage on all cylinders (72 psi cylinder on 75 psi air supply). This was done with all plugs out, WOT, and oil fill cap off. It was on a cold motor rather than warm (it’s a chore to get boat out of garage and on muffs).
View attachment IMG_7963.jpeg

 

[gsbarry]

On the downside, after running the motor the other day for another 30 mins or so, mostly at idle while I was checking the timing, the plugs don’t look very good to me. They’re not as clean as before, so they don’t look steam cleaned to me, but #2 and #3 look fouled to me. #1 and #4 seem normal. It’s kind of puzzling why the plugs look good but both compression and leak down tests are really healthy.
View attachment IMG_7967.jpeg

 

[gsbarry]

While I was at it, I put the borescope down each cylinder. I did see some signs of what could be relatively minor rust on the top of the pistons, although I suppose it could be some other kind of combustion deposit, not a great sign either way from the looks of it.

 

[Scott06]

On the downside, after running the motor the other day for another 30 mins or so, mostly at idle while I was checking the timing, the plugs don’t look very good to me. They’re not as clean as before, so they don’t look steam cleaned to me, but #2 and #3 look fouled to me. #1 and #4 seem normal. It’s kind of puzzling why the plugs look good but both compression and leak down tests are really healthy.
View attachment 405625

I would not worry about the plugs. My 3.0 always had 2 cylinder rich and two that looked perfect. same as you middle cylinders were different than the ends. I had the boat for 20 years…

Your piston deposits look normal still a nice cross hatch on the cylinders. Pistons are not steel and will not rust . Based on your numbers you have a sound engine. Stop worrying and run it.

 

[gsbarry]

On the downside, after running the motor the other day for another 30 mins or so, mostly at idle while I was checking the timing, the plugs don’t look very good to me. They’re not as clean as before, so they don’t look steam cleaned to me, but #2 and #3 look fouled to me. #1 and #4 seem normal. It’s kind of puzzling why the plugs look good but both compression and leak down tests are really healthy.
View attachment 405625

Meant to say why the plugs *don’t* look good. Appreciate the insight Scott. Could be how the fuel flows out the carb as to why the middle cylinders run rich. I may tinker with the timing by a few degrees, or possibly try another ignition module. But yeah I agree after all the testing I’m pretty comfortable as well the engine is solid.

 

[gsbarry]

Anyone on here ever tried experimenting with different carbs on the 3.0L?

 

[jimmbo]

Anyone on here ever tried experimenting with different carbs on the 3.0L?

Why?

 

[alldodge]

The plugs look wet and could be oil

Might be valve guides and/or seals
Don't see a need yet to try another carb

 

[gsbarry]

The plugs look wet and could be oil

Might be valve guides and/or seals
Don't see a need yet to try another carb

Wouldn’t that show up in the leak down test though?

 

[gsbarry]

Why?

I’d probably have to collect more data with an AFR gauge on the current carb to say if it’s performing ideally. Scott’s mention of 2 and 3 running rich on his motor (seemingly the same as mine) has me thinking perhaps there could be improvement with a different carb (either airflow or fuel delivery throughout the curve). Who knows, it could be the intake manifold design as well. I was just curious if anyone else had experimented already on this motor.

 

[alldodge]

Wouldn’t that show up in the leak down test though?

Leak down test is done when piston is at TDC, so both valves are closed and guides have no bearing on test readings

 

[gsbarry]

Leak down test is done when piston is at TDC, so both valves are closed and guides have no bearing on test readings

I think I see what you’re saying, some amount of oil could be infiltrating the cylinder through the valve train while the valves are open. Something to keep an eye on. I’ll keep a close watch on the oil level and recheck the plugs periodically.

 

[HiTekRedNek]

While I was at it, I put the borescope down each cylinder. I did see some signs of what could be relatively minor rust on the top of the pistons, although I suppose it could be some other kind of combustion deposit, not a great sign either way from the looks of it.View attachment 405629

 

[HiTekRedNek]

Have you checked the choke flap on the engine when hot to ensure it is moving freely and wide open as it should be? I had my long block replaced last summer and had lots of problems with the shop. My Sea Ray 180 sport topped out at 29 MPH (gps) with a brand new 3.0 engine. After my last run to the lake I took the flame arrester off and inspected the choke on a hunch. Yep, the shaft for the choke flap was stuck in a half open position. A little carb cleaner and some lube and the flap works freely now. I haven't had it in the water yet (Northern Wisconsin) but as soon as we thaw out I'll take her out. I'm mentioning this as your combustion deposits look like a rich fuel mix to me. My choke is electrically assisted so the coil on the carb that opens the choke could be at fault and result in an overrich condition. Just a thought!

 

[gsbarry]

Have you checked the choke flap on the engine when hot to ensure it is moving freely and wide open as it should be? I had my long block replaced last summer and had lots of problems with the shop. My Sea Ray 180 sport topped out at 29 MPH (gps) with a brand new 3.0 engine. After my last run to the lake I took the flame arrester off and inspected the choke on a hunch. Yep, the shaft for the choke flap was stuck in a half open position. A little carb cleaner and some lube and the flap works freely now. I haven't had it in the water yet (Northern Wisconsin) but as soon as we thaw out I'll take her out. I'm mentioning this as your combustion deposits look like a rich fuel mix to me. My choke is electrically assisted so the coil on the carb that opens the choke could be at fault and result in an overrich condition. Just a thought!

That is a good thought! I’ve been thinking about adding an AFR gauge, which would give me better diagnostic info on the carb performance. The carb on my motor is a TKS style choke (which replaces a typical choke plate with a heat actuated piston), so you can’t visually check operation while running like you can a choke plate because it is inside a bore in the carb. However, I was having issues cold starting. Suspecting the TKS module was the culprit, I bench tested it, and it operated correctly. I then throughly cleaned / sprayed carb cleaner through the TKS bore and a fine piece of debris was dislodged. This solved my starting issue. Another observation of correct function of the TKS module is an audible whistling sound at cold startup, which then goes away once the module heats up and is fully engaged, which mine does now. So, I don’t have any other indications the TKS module is not functioning correctly, but it is possible (they are stupid expensive for what they are at around $300, so not too inclined to swap parts on a whim). All that said, I could indeed have a carb that is running rich for several possible reasons. Something to think about.