3.0 mercruiser valve adjustment

[Whitemustangman]

Maybe someone else has ran into this, I recently rebuilt my 3.0 and it runs good but really rich no matter I did, I did compression test and only 87-90lbs on all cylinders. I back the valve adjustment to zero lash with no preload on the lifters and get129-130 acrossed all cylinders…. Are my lifters defective and not bleeding down on adjustment? I’ve followed every procedure I find and it’s still the same. Hopefully someone can help!!

 

[Scott Danforth]

zero lash is the absence of movement up and down with your fingers

3/4 turn past zero lash

zero lash is not the absence of ability to spin. you can spin the push rods up to the point you start to compress the spring

130 psi across the board means your motor is low on compression. new and reman'd motors should be 150 psi

check your gauge

 

[Whitemustangman]

I zero lashed it till all up down movement was gone, not Couldnt spin. The stock compression is 110-130 per merc specs on that motor so I’m well in where it should be but only with the valves loose. I’ve built dozens of car engines and have never had this problem or on any of my other boats.

 

[Scott Danforth]

gm cranking spec for a 3.0 is 150 psi

its a 9.4:1 compression engine

 

[Whitemustangman]

gm cranking spec for a 3.0 is 150 psi

its a 9.4:1 compression engine

Under specs in my mercruiser manual for my serial num it’s 100 min 120-130 for “new”

 

[Scott Danforth]

Under specs in my mercruiser manual for my serial num it’s 100 min 120-130 for “new”

Same parts listed as 140 psi for 1997.

I trust the GM spec

 

[Whitemustangman]

Either way I can’t figure out why the valves are staying open if I put any kind of preload on the lifters. I can have maybe 20-.030 clearance and go 1/4 turn and lose compression

 

[alldodge]

Maybe your lifters are shot
Have you tried to adjust while running?

Do a leak down test

 

[Scott06]

Either way I can’t figure out why the valves are staying open if I put any kind of preload on the lifters. I can have maybe 20-.030 clearance and go 1/4 turn and lose compression

Were the block or head machined during the rebuild?

 

[Whitemustangman]

Maybe your lifters are shot
Have you tried to adjust while running?

Do a leak down test

They have 15 hrs on them

 

[Whitemustangman]

Were the block or head machined during the rebuild?

Yes, but only like .008 taken off head, nothing off block

 

[Scott Danforth]

They have 15 hrs on them

new lifters with a new cam?

or did you try to pair new lifters with a used cam?

 

[nola mike]

Under specs in my mercruiser manual for my serial num it’s 100 min 120-130 for “new”

Which manual are you using that covers everything from a 3.0 to an 8.2l?

 

[Whitemustangman]

new lifters with a new cam?

or did you try to pair new lifters with a used cam?

Everything internally is new, crank, rods, pistons, cam, gear , lifters ect

 

[Whitemustangman]

Which manual are you using that covers everything from a 3.0 to an 8.2l?

Seloc

 

[nola mike]

Seloc

I was being a bit tongue in cheek there (since no real factory manual covers everything ever built), but I'll be damned if the real thing doesn't spec 100 psi. I can blow through a straw harder than that.

 

[alldodge]

Note pressure list as 100 "Minimum". Every motor has to have at lest 100 to run. It won't run very well but it will run at 100

 

[Whitemustangman]

Note pressure list as 100 "Minimum". Every motor has to have at lest 100 to run. It won't run very well but it will run at 100

It’s running pretty good with 89-90 lmao it’s crazy, I tested my other boat with 3.0 and is 139-140 acrossed the board up

I was being a bit tongue in cheek there (since no real factory manual covers everything ever built), but I'll be damned if the real thing doesn't spec 100 psi. I can blow through a straw harder than that.
View attachment 352242I

I was being a bit tongue in cheek there (since no real factory manual covers everything ever built), but I'll be damned if the real thing doesn't spec 100 psi. I can blow through a straw harder than that.
View attachment 352242

Its crazy lol

 

[Scott Danforth]

GM spec is still 150. note, the 4.3 and 5.7 have the same bore and stroke.

 

[Scott06]

It’s running pretty good with 89-90 lmao it’s crazy, I tested my other boat with 3.0 and is 139-140 acrossed the board up

yeah your other boat is ok. I had a 3.0 for 20 years after 800 hrs pulling tubes and skiers still had 140-145 psi, which given how many hours it was above 4 k rpm is pretty amazing.

if you replaced the rockers, balls and nuts maybe you have a parts mismatch ? Maybe try a set of poly locks?