4.3 Timing

[Caribeño]

In some info says that the TBDC for a 4.3l should be 8deg others say it should be 10deg

how do I know the proper timing for my engine?

 

[GA_Boater]

Caribeño Moved this into a new thread from a 12 year old archived thread.

Welcome aboard.

 

[Caribeño]

1987 Mercruiser 4.3l timing specs

I recently purchased my first boat for my family enjoyment. A1987 Marlin Rally with a mercruiser 4.3l 180 Alpha sterndrive.

Looking at plenty of manuals in the internet and here I am having a little bit of a hard time finding the correct timing Deg for the engine. Some say is 10Deg others say is 8Deg.

Some help would be greatly appreciated.

BTW while reading in this forum I noticed how cool and helpful people are. Good job on the moderators.

 

[alldodge]

What year, and is it carb or fuel injected?

 

[Caribeño]

1987 mercruiser 4.3l alpha double barrel carb

 

[alldodge]

8 BTDC
Idle set at 650-700 rpm idling in forward gear
Point gap .020
Dwell 34-38 degrees
MR43T or RV15YC4 plugs gap at .035
140 degree thermostat

The 10 degree is for TB-V ignition

 

[Caribeño]

Thank you very much!! I will adjust my settings and I’ll let you know the outcome!

 

[Caribenio]

Sorry I didn’t update before. I have been trying to access my other account and it is just imposible. The help from Iboats was not enough so I finally created this account. Kind of disappointed but I’m glad I’m back to the community.

Anyways, the engine now runs really well but it does not hold idle rpm’s that well do before I do something else i decided to test compression.

This is the result:

1 - 150
3- 140
5 - 150
2 - 155
4 - 110 - 115 < second read after a spoon of oil
6 - 155

I took the valve covers off because I need to replace them anyway. I notice that some to the rockers are not right on the center right on the top of the valves. Also some of them seem to be lose and some are kind for loud.

I decided to see if I could adjust the valves with the engine running. First valve it was loud so I losen it up and got louder. I tighten it until it was quite and then just a 1/4 turn more. Then I tried on an other one and as soon as I tighten that one the engine started to stumble so I losen that up and that was the end of my try.
I decided to change the oil. Put new oil and a bottle of -restore-
I started the engine and was running fine just like before. Al of the sudden a big tic tic care of for about a minute. I thought the engine was going to die. Then the tic tic went away. I let it run for about 15 min and then turn it off. I have not started the engine but I want to test the compression again after an other 15 min run.

This are the questions I have.
Should I adjust the rockers/valves or leave it as it is?

110 compression based on a manual say that above 100 is acceptable. Should I worry about that piston?
Muy seem to me like the piston that has the low compression is the one that has the rockers kind of lose.

The boat runs strong in the water

BTW this is a 1987 mercruiser 4.3l thunderbolt

thanks in advance for the advice.

 

[alldodge]

Might have some collapsing lifters, and the tic starting and then going away would be an indication. They are adjusted by getting them to zero lash (running or not running) and then an additional 1 full turn. When running, turn 1/4 turn then wait a bit, then 1/4 more until one full turn

The one cylinder I would not be to concerned, but keep check on the plug every so often to see if its burning clean and not pumping oil

 

[Caribenio]

AllDodge thank you! I
I was reading in an other site that they can be torqued to spec wich is 20nm. Is thay something that could be done as well?

 

[alldodge]

AllDodge thank you! I
I was reading in an other site that they can be torqued to spec wich is 20nm. Is thay something that could be done as well?

No, not for a 1987 model motor

 

[Caribenio]

Im a little unsure about the procedure.
So, I lose the rocker and the tight it enough until the push rod does not spin then 1/4 turns until I complete a full turn?

After reading so much info on different procedures I surprise by your comment that it does not matter if it is running or not. It does not matter if the valve if pushing the rocker or not? Would that make a difference in how much torque I need to apply with the ones that the valves are not pushing against the rocker?

What about the procedure where the cylinder one is all the way up and the after that you have to turn 120 deg to adjust the nest cylinder.

Dont get me wrong, i just don’t want to screw things up. I want to make sure to understand the proper procedure.

 

[alldodge]

It doesn't matter in reference to it is one turn more after reaching zero lash. Since you mentioned about how the lifters where being adjusted, I used short speak because figured you understood what I was meaning

When running, back off until it clatters, then turn down until clatter stops, then 1/4 turn at a time until there is one full turn

Engine off, use a grease pencil and loosen push rod that is fully up. Tighten down while rotating rod and also going up and down. Your feeling for the up/down and not the rotation. The slight rotation is just to make sure it doesn't stick. Once there is no movement up and down, turn one full turn down more. Mark rocker with grease pencil and rotate motor to other rocker until done

 

[Caribenio]

Long story short. After I adjusted the valves the motor ran very nicely. In the middle of the lake a valve retainer broke and now the engine is bad. I am in the process of buying a reman engine. Now my Boat is a project.
welcome to boating!! LOL

Thanks for the advices anyways. Now my

 

[alldodge]

That's a bummer