mercruiser 5.7 spark plug reading result

[Maclin]

Re: mercruiser 5.7 spark plug reading result

Check the timing in neutral.

Compression is held by the pistons and rings and the valves. The rings have to seal and the valves have to seal, pretty simple.

Adding some oil to the cylinder thru the sparkplug hole and trying the compression test again is a good way to test ring sealing. This is called a wet test. You may have done this already, pretty standard compression test item. If the numbers go up then it means the rings may need some help, but also gives a better indication of what is happening during actual running of the engine as the rings will be grabbing oil and holding better.

The valves have to seal well. The valves themselves need to be "lapped" meaning their sealing surfaces must be smooth and perfectly shaped to the opening in the head, called the valve seat. The seat also must be perfectly shaped and smooth. Lapping involves spinning the valve in the seat with some lapping compound, this is done with considerable "up" force on the valve. The machine shop should have done this or similar during the build process. If this was not done well then the valves may not hold compression well at higher cylinder pressures (higher throttle settings and rpm).

A leakdown test can help determine where compression might be leaking. This test is done with the cylinder at the top of a compression stroke, compressed air is sent into the cylinder thru a fitting in the spark plug hole. Then you listen to the intake manifold, if hissing is heard the intake valve is leaking. Listen to the exhaust, if hissing then exhaust valve leaks. Listen to the crankcase, if hissing then the rings are not sealing or a piston is holed. (I do not think any of your pistons have a hole, that would show almost zero psi on the compression test.)

There are also bench test for heads that can show improperly seated valves.

Again, the valves must be lashed properly or they may not have a chance to close and seal well at higher rpms.

Weak valve springs can also cause a higher rpm valve sealing or bouncing problem.

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

well said thanks much, i did not do the wet test on all cilinders i only did one , and that one from i think 120 to 140 if i remember right,

thanks again realy appreciate the help.

 

[littlebookworm]

Re: mercruiser 5.7 spark plug reading result

Hitting the valves with a wooden hammer is only done if you suspect a stuck valve. It breaks it loose. This is a newly "rebuilt" engine; you should not have any stuck valves. You really should be adjusting your valves with the engine cold and off, as explained in the manual. A quick and "dirty" check of spark advance can be done with your timing light. Make sure the timing mark, 8 degrees BTC, and the mark on the timing cover are painted white so they are visible. Start the engine and check that they line up at idle. That's your base mark. If not, move the distributor until they do. When they line up, have someone work the throttle to accelerate to about 2000 RPM. The timing marks should separate as you accelerate. if they don't, check your distributor. Either way, I think you really should get a marine mechanic, not the "engine rebuilder", to take a look at the engine. Something isn't right. Since I only have your description to go on, I'll reserve judgement on the rebuild at this time. Let us know what you find. Good luck. Hy

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

yes sir thanks the guy told me bang the heck out of those valve, on a new rebuild engine, what i realy wants to say i will just keeps it in my mind, all i know is that i am very unhappy, i am heading to the fishing ground on saturday glad i have sea tow.....

thanks everyone for filling in on long long problem,

 

[MikDee]

Re: mercruiser 5.7 spark plug reading result

IMO, The best way to adjust the valves, is with the engine warmed up, & idling, like bolo has done. All the parts are at normal operating temp, & working together in unison with each other, there's no slack, play, binding, mis-alignment, or guesswork as when doing static TDC adjusting. Static adjusting is only good for just getting an engine running for the first time, it should be followed up by final adjustment when running. I've been doing this for years, and it first began for me with a solid lifter cam, and this was the desired procedure. My favorite setting is 1/2 turn down from zero lash, But this must be done smoothly, & slowly, giving the engine a chance to even out, & run smoothly in between.

 

[dan t.]

Re: mercruiser 5.7 spark plug reading result

been following this discussion for a while now. lots of good ideas, consider this one. i ran across a 350 a few years ago with no power and only 120 pounds compression.to make a long story short, the rebuilder had put in a 327 large journal crank by mistake. this resulted a 327 with about 7 to 1 compression instead of a 350 with 9.3 to 1. iwould seriously question this rebuilders methods. a rebuilt motor should not have these problems

 

[dan t.]

Re: mercruiser 5.7 spark plug reading result

been following this discussion for a while now. lots of good ideas, consider this one. i ran across a 350 a few years ago with no power and only 120 pounds compression.to make a long story short, the rebuilder had put in a 327 large journal crank by mistake. this resulted a 327 with about 7 to 1 compression instead of a 350 with 9.3 to 1. i would seriously question this rebuilders methods. a rebuilt motor should not have these problems

 

[MikDee]

Re: mercruiser 5.7 spark plug reading result

been following this discussion for a while now. lots of good ideas, consider this one. i ran across a 350 a few years ago with no power and only 120 pounds compression.to make a long story short, the rebuilder had put in a 327 large journal crank by mistake. this resulted a 327 with about 7 to 1 compression instead of a 350 with 9.3 to 1. i would seriously question this rebuilders methods. a rebuilt motor should not have these problems

1/4" less stroke, Oops!, It would be ready for a blower then

 

[KJSmitty]

Re: mercruiser 5.7 spark plug reading result

final adjustment when running. I've been doing this for years, and it first began for me with a solid lifter cam, and this was the desired procedure. My favorite setting is 1/2 turn down from zero lash, But this must be done smoothly, & slowly, giving the engine a chance to even out, & run smoothly in between.

You performed this "running" procedure with your solid lifter cam?

Just curious - Cheers

 

[drrm123]

Re: mercruiser 5.7 spark plug reading result

I still think compression is normal 120-130lbs, you can check with person that rebuilt engine or if it was a long block, have them tell you the compression ratio if it's 8:1 to about 8.5:1 numbers your getting sound ok, if it's 9:1 or higher thats when 150 + would be normal. next time you pull the valve covers you can get the casting # of the heads to find size of chamber to figure compression ratio, i'm sure flat top pistons are in this engine. if you think you have a problem internally do a leakdown test, it'll tell you if valves are leaking or rings leaking or even blow head gasket(which you should not have anyway) but just gives you more info than compression test. if your having you pound valves to get them you release-close you have a problem with them. also design of cam(how much overlap) can have impact on cylinder pressure. also about the oil at the rocker arm tips i'd have to see it to be able to give an honest answer, but it takes very little oil to lube the rockerarms and valve tips, you actually dont want alot of oil on the top end of an engine, if oil pressure is ok your probably fine.

 

[MikDee]

Re: mercruiser 5.7 spark plug reading result

You performed this "running" procedure with your solid lifter cam?

Just curious - Cheers

Yes, I did, feeler gauge in hand, you develop a feel for it. I had to do it about every 2 wks, because I was young, & dumb, and this was my 1st hi-perf car, plus, I used to drive "pedal to the metal" all the time

I quickly learned what pinned, or screw in studs were, because I didn't have them

I also learned to stick with hydraulic lifter cams for the street

I will say this though, Once you adjust either type of lifter this way, and get used to it, you'll never be satisfied by doing it staticly, or by the book anymore. Feeling the pulse of your engine, and adjusting it, plus the sense of accomplishment is great!

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

yesterday, after i loaded up the boat with three big guys plus myself, bait, gears, and 40 gallon of gas i head out on the long run for the fishing ground, after i clear the no wake zone and put the throttle down i new imeadeatly the boat was running way better that the week before, now this is with the 15 pitch prop last time i have the 17 on. at 3000 rpm i was getting 16 knots that cruise took me to the fishing ground. on my way back i take it up to 3500 rpm at 22 knots . so with minor tuning i think i might live with that performance . i know in my hart the engine is no in my hart i got a bad reman engine, but i will live with that, it not the end of the world, but i am ****.

this is what i have done , as we all knows i did go over the valves adjustment , i tune the carburetor, last i change the fuel water separator. with that said i thanks everyone who help me out on this long thread , without you guys it wouldn't be possible for me to help myself with this engine, THANKS AGAIN.

after the trip my drive start acting up i had start a new thread on that instead of tapping on this one. please view it thanks.

 

[MikDee]

Re: mercruiser 5.7 spark plug reading result

Are you sure all your spark plug wires are on the right spark plugs?
Like I said, I've seen engines that appear to run good with crossed wires, depending on which particular ones, sometimes it's hard to tell! Please re-check this.

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

mikde thanks , yes i 100 percent sure, i gover it about ten times to make sure, i finally ask the yard mechanic to take a final look, thanks. so far it is running better. check out my next thread obout my drive problem thanks.