4.3 Mercruiser valve adjustment

[jdelisle]

I have a 2000 4.3 mercruiser mpi with a balancing shaft.

I need help solving the issue I'm having trying to adjust the valves on my mercruiser. Below is the background on the motor.

There was salt water infiltration in the motor (pistons/crankcase) which cause the motor to locked up. The motor had a lot of rust in it. I pulled the heads and had a stuck intake valve, replaced it, took apart the roller rockers and cleaned them, cleaned everything that I could get at, replaced exhaust manifolds.

I put everything back together and torqued down the valves to 20 ft/lbs. When I went to start the motor and wouldn't start and seemed hard to turn over. I then loosened the valve nuts to zero lash and then started the motor. It started up and then adjusted the valves wile the motor was running. The problem is that the nuts loosen up after a few minutes. Then I tried to tighten down the nuts until the motor starts to stall then back the nut off. The nut still wants to loosen up. This scenerio doesn't happen to all the valves but probably four of them. The oil coming out of the push rods only squirts out of on or two push rods and oozes out of the rest this is at 800rpms. (The motor has run for a total of 30 minutes so far). Oil pressure 38-40PSI

I'm leaning to a problem with the lifters. I didn't soak them in oil when I cleaned them. I only coated them.

This very frustrating and looking for any advice before I guess and replace the lifters.

Thanks

 

[Bondo]

Re: 4.3 Mercruiser valve adjustment

Ayuh,... Welcome Aboard,... If the adjustin' nuts are backin' off, replace the nuts,...

 

[jdelisle]

Re: 4.3 Mercruiser valve adjustment

Ayuh,... Welcome Aboard,... If the adjustin' nuts are backin' off, replace the nuts,...

This means that I don't need to torque the bolts down evan though I have a balancing shaft?

 

[mandmj]

Re: 4.3 Mercruiser valve adjustment

I've had a similar problem on a late model 4.3 truck engine in the past. It was bad lifters. The later model 4.3s require the rocker nuts to be torqued to spec. Otherwise they will come right off.

edited for spelling

 

[jdelisle]

Re: 4.3 Mercruiser valve adjustment

I've had a similar problem on a late model 4.3 truck engine in the past. It was bad lifters. The later model 4.3s require the rocker nuts to be torqued to spec. Otherwise they will come right off.

edited for spelling

Since I took apart the lifters that is the direction I'm heading.
It seemed before I started the motor I couldn't adjust the lifters more than 1/4 turn past zero lash when the motor was at TDC. After runnig motor I then tried adjusting from tdc and could djust to 3/4 turn past zero lash. Motor started but nuts loosened then tried torquing and motor wouldn't run.
I'm going to try running motor longer to see if lifters fill with more oil and then try torquing down again and see if the motor runs. If not I'll replace lifters.

 

[mandmj]

Re: 4.3 Mercruiser valve adjustment

Hopefully you can fix them, but I'm betting they have to be replaced. Good luck.

 

[Fun Times]

Re: 4.3 Mercruiser valve adjustment

I put everything back together and torqued down the valves to 20 ft/lbs.

You probably already know this, but just in case a quick reminder.

Torque rocker arm nuts to 22 lb-ft. No valve adjustment is required. Valve lash is automatically set when rocker arm nuts are torqued to specification.

And installing new nuts should be beneficial.

Hope it's something simple, Good luck.

 

[jdelisle]

Re: 4.3 Mercruiser valve adjustment

thanks

 

[jdelisle]

Re: 4.3 Mercruiser valve adjustment

I would bet on that also

 

[jdelisle]

Re: 4.3 Mercruiser valve adjustment

I fixed the issue by running the boat and adjusting one valve to zero lash, then adjusted it until boat starting stuttering then waited a few minutes to the motor smoothed out. I then repeated this process several times until the rocker nut was tight. I then repeated this process for every valve and once that was done I torque them all down.