Re: mercruiser 5.7 spark plug reading result
baileysboat thanks very interesting, yes it was a long block with heads , i install the old intake from the old block, i spray carb cleaner all over the intake gasket area with the engine running it did not make the engine runs different. about the egr port maybe i got it wrong so that is ok. it idle ok its a little coarse sounding shake just a tiny bit, now about the valve lash, Siam almost a hundred percent sure that these rockers need more tork, why because the way i got the engine the rocker nuts was screw down more on the bolts. if that is the case will that kill my compression?? because i know i should be getting at least 150 on all cylinders . so you are saying i should tork the rocker nut 1 1/4 from just where the rocker stop rattle??
if i found a bent pushrod on #8 is it easy to install another without pulling the head ? last what is the diffrent with adjusting the valve with the engine off the way the guys do it in the shop before the engine runs, and doing it with the engine running?? thanks
This is a "new" motor right? Long block? Came with heads(new cam, lifters, guides, valves etc)? How many hours? Kind of funny about the EGR passage, as was previously stated shouldn't be on a marine engine. Was the intake changed?
The compression readings are a lot lower than I would expect (150-160) with a "new" engine. Are you checking the compression with a warm engine and the throttle wide open? The difference between # 8 and the other seven is not significant, but the generally low readings bother me.
Now, you said you adjusted the valves. Why? I'm a licensed auto tech and run a big car shop (wish it was marine), and providing the initial setup was done correctly valve adjustment is not normally required on a Chevy small block (same thing right?). Were you getting noise?
The correct adjustment is done with the engine off, zero valve lash plus specified number of turns ???. I don't have a Mercruiser spec, but 1/4 turn seems a little light, I would expect at least 1-1/4. Someone else in the forum can answer that.
Is the idle ok? What does a vacuum gauge show at idle and high idle? Steady at 16-18 (normal), regular downtick of 4 hg will indicate valve not opening correctly (worn cam or valve lash incorrect) or burnt valve. Rapid /vibration at higher rpm indicates weak valve springs. Fluctuating at idle but going away with higher rpm is valve guides.
Regarding the plug, I would be looking closely at a lean condition on #8. Pop the valve cover and check if the intake valve is opening. If its not could be a bent pushrod caused by improper valve adjustment or cam lobe worn off. Verify the exhaust valve as well.
If this looks ok go ahead and verify the valve adjustment. Considering the valve cover is off you might as well do all 8on that side. When I do this adjustment the engine is off as the manual states (But I'm a car guy). Try it running if you like, but it's not as exact and messy.
If all is well to this point, look at the intake manifold. A long block comes without an intake. Was the Intake checked & cleaned? Usually it has to be machined to match the new block. It could be the gasket is out of position. We use a plumbers propane torch with a small diameter vacuum hose attached, and with a low flow through the hose look for an rpm increase as it is passed over the suspect area. Not a good idea on an inboard so don't try it, but you can get the same effect by spraying a little bit of WD40 around the intake runner. If the idle jumps up or changes you've nailed it.
baileysboat thanks very interesting, yes it was a long block with heads , i install the old intake from the old block, i spray carb cleaner all over the intake gasket area with the engine running it did not make the engine runs different. about the egr port maybe i got it wrong so that is ok. it idle ok its a little coarse sounding shake just a tiny bit, now about the valve lash, Siam almost a hundred percent sure that these rockers need more tork, why because the way i got the engine the rocker nuts was screw down more on the bolts. if that is the case will that kill my compression?? because i know i should be getting at least 150 on all cylinders . so you are saying i should tork the rocker nut 1 1/4 from just where the rocker stop rattle??
if i found a bent pushrod on #8 is it easy to install another without pulling the head ? last what is the diffrent with adjusting the valve with the engine off the way the guys do it in the shop before the engine runs, and doing it with the engine running?? thanks