valve lash

[zelatore]

Here's one for you Merc guys....

Got a carb'ed Merc MRE 7.4 bluewater in an '89 boat, but it has no identification on it - the only things I have found are some casting numbers, but nothing I can translate into exactly what Merc motor it might be. I'm pretty sure it's a replacement long block with the Merc 7.4 tin put back on it.

The heads are round port with screw in rocker studs - pic attached.

The reason I ask, my Merc manual says you don't set the valve lash, you just crank the rocker "bolts" down to 40 ft/lbs and your good to go. Now I know I'm not a Merc guy; heck, I'm not even a GM guy, but that just sounds too tight. Oddly, the book doesn't even say to set the lifter on the cam base circle....just crank 'em down to 40 lbs and go.

Further, I can find no refernce to screw in studs in any of my Merc literature. Again - I'm wondering exactly what this thing is. Looks like a Gen 4 7.4 (not to be confused with a 454, which is a different motor in Merc speak) but I'm sill not reconciling that with screw in studs.

On the back of the block, just behind the left head and the lifter valley are the following castings:
3935439
Conv2
GM hi-per

I suppose there should be a casting number behind the timing cover/water pump but I don't feel like tearing those off.

So....thoughts on valve lash? Could that 40 lbs actually be right?

[BUIZILLA]

the 40# spec is for the non-adjustable valvetrain

which you don't have

proceed as if it were a real Gen 4 engine

[Walt. H.]

I was thinking you were confusing the torque spec to tighten the rocker arm stud itself to the cyl head is 40-ft lbs where as the valve/rocker arm adjustment is tighten to zero clearance plus another 1/4 to 1/2 turn of the rocker arm nut adjustment for hyd lifters.

[zelatore]

the 40# spec is for the non-adjustable valvetrain

which you don't have

proceed as if it were a real Gen 4 engine

More or less what I suspected; I'm guessing at some point a 'generic' gen 4 long block went in to replace the stock 7.4.

Unless there was a 'real' Merc 7.4 with adjustable valve train and screw in (as opposed to press in) studs.

Seems to be a bit of a mix-n-match engine.

Walt - reading the books I too thought at first they were refering to the studs, but not the case.

BTW, I hate setting valve lash. I pretty much don't like anything that involves a feeler gauge.

[Walt. H.]

All big block Chev use screw in rocker studs, its the SBC that use both types of stud.

A feeler gauge wouldn't be involved since it's a hyd cam it would be tighten down to zero lash then another 1/4 to 1/2 turn when the lifter is on the heel of the cam lobe.

[mrfixxall]

that casting number comes up as late 60's 427 BB but a 454 crank will make it a 454..427 and 454 share's the same block.

like jim said,those are torque to yield bolts,just torque them down to spec and its done..l like to do them at zero lash or just make sure theirs no tension on the spring while torquing them down..

[MOP]

Up the turn down to 3/4 which is the book spec.

[Walt. H.]

Phil,
You're right but you'll get a little more perf in the upper rpm range by not going as tight and they'll still be clatter free at idle, that's why it's even better to adj them running hot at idle just to the point where the rocker quiets, of course you have to adjust them static cold during assembly and the reason why I recommended 1/4 to 1/2 turn after zeroing them. :wrench:

[silverghost]

On the old 88 MK IV in my skiboat I zero-lash adjused my rockers while engine was running at normal operating temp at idle to just where the ticking sound stopped and then just 1/4 turn tighter.
That way the hydraulic lifter tappet can adjust valve lash itself automatically and compensate for engine temp changes & metal expansion.
Tip:
I used a hose at my ear and at each rocker arm & valve stem top to actually hear each & every one from each other.

It's just a little messy with a small bit of oil splasing, but most oil drains right back into the head's oil drain holes.
The hard part was removing the nuts from the valve rocker cover studs that were very close to the center rise exhaust manifold elbow risers. It is a tight spot.

My engine is quet as possible now with plenty of power..

[Walt. H.]

Good to hear all is quiet, and to make adjusting less messy you can buy a set of spring clips at most auto parts stores that sell tools that snap onto the rocker arms that will deflex the oil spray and splash downward while you are running the engine with the valve covers off.

http://www.summitracing.com/search/Product-Line/Mr-Gasket-Rocker-Arm-Oil-Deflector-Clips/?keyword=oil+clips&autoview=SKU

[zelatore]

I used to set my small block Fords while running, and I had a set of rocker stoppers to at least keep the mess to a minimum. Still made plenty of mess though. I can still smell the oil burning on the headers...

This isn't a performance build in the least; it's a bargain basement refurb so trying for a little extra upper rpm gain isn't worth it. I won't be setting this one running. It'll be set cold. 1/2 to 3/4 turn. Quiet is more important than an extra 100 rpm so there it is.

[mrfixxall]

zel,,theirs is no adjustment on thepic of the rocker you posted..they are held in place with a sholder bolt..you torque them down and thats it!! no adjustment.

[Walt. H.]

Fix,
They look like jam nuts on those studs which would mean adjustable, not bottom out to end of thread.
I'm not aware of any other style with Chev eng's, when did Chev ever change to non-adj type rockers? :confused:

[silverghost]

Good to hear all is quiet, and to make adjusting less messy you can buy a set of spring clips at most auto parts stores that sell tools that snap onto the rocker arms that will deflex the oil spray and splash downward while you are running the engine with the valve covers off.

http://www.summitracing.com/search/Product-Line/Mr-Gasket-Rocker-Arm-Oil-Deflector-Clips/?keyword=oil+clips&autoview=SKU

Walt~
I've got a full set of those aluminum clips~
Have owned them since the 1970s.

But when I adjusted my rockers my boat was in the water in Ocean City NJ ~
And the clips were in my big toolbox in PA about 97 mles away.

It always seems to happen that just the ONE special tool that I need when down the shore~~~ I don't have with me~
And my car trunk has about 50 pounds of tools sitting in it at all times.

I can't tell you how many duplicate tools I now have from running out to Sears & auto & hardware stores while down the shore ?

I could start my own tool store.

[mrfixxall]

Fix,
They look like jam nuts on those studs which would mean adjustable, not bottom out to end of thread.
I'm not aware of any other style with Chev eng's, when did Chev ever change to non-adj type rockers? :confused:
MY Bad!! da,, i need to get some glasses..46 yep i guess thats the age it starts..

proceed with walts adjustments..

[zelatore]

Fix,
They look like jam nuts on those studs which would mean adjustable, not bottom out to end of thread.
I'm not aware of any other style with Chev eng's, when did Chev ever change to non-adj type rockers? :confused:


I can't tell you what year they changed, but I can tell you that MerCruiser service manual #16, GM V8 454/502 does call out non adjustable valvetrain on the 7.4, 454 Mag, and 502 Mag, with 40 ft/lbs for the 7.4/454 and 45 ft/lbs for the 454/502 Mag motors. (it's page 3A-1 if anybody wants to check:wink:)

And that's why I was a little surprised when I started putting it together. I hadn't paid attention when I took it apart, just set everything aside in order to put it back toghether later. When I started putting the rockers on I thought 'wait a minute.....'

That's also why it's not good to blindly follow the book sometimes.

[BUIZILLA]

the 40# spec is for the non-adjustable valvetrain

which you don't have

proceed as if it were a real Gen 4 engine revert to post #2

[Rumblefish]

Hello Don!!. Well its seems everyone right on this one.. the era of GM studs on big blocks toward the late 90's was a taper stud that resembled the old style with the only differnce being a severe taper to alow torq setting of 40lb and your were done.

Possible to see a mix in marine engines but trust me the taper is visually noticable and the rocker ball wont drop down.

Your photos show a standard screw in stud that you lash "zero lash plus 1/2 turn (ish)

Follow the firing order for the drop on the back of the cam and your good to go.

[BUIZILLA]

i've NEVER seen a tapered stud

can you post a pic or link?

[Rumblefish]

Well im half off. it was taperd bolt through and the torq spec was 45 lbs ..just torq them and you were done.

Only way to compensate loose lash settings was increasing push rod length.

[GeneD]

My business is Merc engines.
I've taken apart my share of stock BB Mercruisers and I've never seen this set-up before.
Normally, it's torque the rocker bolt down and forget it.
This appears to be a high-perf set-up.

[silverghost]

Not to hijack or get too far off of track here~
But
When did Chevy go to roller tappets in their Big Block engines.
My 88 MK IV is flat tappet as is the MK V engine in my 91 454 SS Sport Truck ?
Did the roller tappet style cam set-up start during the MK VI ; or as I always call them "Mark FIX" series of Chevy Big Blocks ?
And at aprox what year did roller tappets first appear ?

[mrfixxall]

Not to hijack or get too far off of track here~
But
When did Chevy go to roller tappets in their Big Block engines.
My 88 MK IV is flat tappet as is the MK V engine in my 91 454 SS Sport Truck ?
Did the roller tappet style cam set-up start during the MK VI ; or as I always call them "Mark FIX" series of Chevy Big Blocks ?
And at aprox what year did roller tappets first appear ?

when the vortec BB were introduced..Gen 6 and up..1996 was the first year..

[BUIZILLA]

when the vortec BB were introduced..Gen 6 and up..1996 was the first year..this would be correct in automotive, I believe the marine version started in 1997

[yeller]

i've NEVER seen a tapered stud
can you post a pic or link?Geesh..I can't believe you've never seen a tapered stud. Not studs (I don't have a pic handy), but there are a couple tapered bolts here. :rolleyes: (Check out the 4th and last pics).