New motor problems

[Jeep Craze]

I recently put in a new(well alright it was rebuilt) 360 in my J10. I have it running now w/ what I thought to be a carb problem, but Im not quite sure now. I hooked a vacuum gauge to it and at idle it vibrates very rapidly between 16 and 19. when accelerated and steadied at 2500 it moves up on the gauge but still shakes steadily very fast between 21 and 24. I tried everything that I can think of. Does this sound like weak spark(reason I ask is my timing light barelly lights up when hooked up(not sure why it always worked before) thought maybe the spark wasn't strong enough to trigger the light? Any thought are welcome....... Craig

[Chevelleguy]

Ignition m iss, blown head gasket, leaking valve or weak valve spring.

[Jeep Craze]

OK, I am thinking ignition too, I am gonna rule out the weak valve springs for now and the leaking valve, only because the ignition is easier. I will replace the coil and see what that does.

[Chevelleguy]

I had a friend ignore a miss on a 1 year old rebuild (I even pinpointed the cylinder for him). A week later he dropped a valve due to a broken spring. Messed up that motor real bad. He was loading it on a trailer to bring it to me because it was starting to make noise, then WHAM! Not good.

[carrotman]

On your timing light, the power for the light should come from your battery. The ignition just triggers the light on and off. Check the battery connection.

Chevelleguy is right about the oscillating vacuum. Oscillations at high RPM are due to weak valve springs. Rapid oscillations at idle are due to burnt or sticking valves, head gasket leak, or worn valve guides. Unless the rebuilder put in long duration cam.

[PhilSine]

Let us not forget that a cracked ring could also be the cause but then you would see a lot of blowby in the crank case distunguishable by a lot of pressure coming out of the oil fill tube.

[Jeep Craze]

Philsine: I checked that already, I have a slight suction on the oil fill tube.

Carrotman, I will try to get another light and see whats up

To chevelleguy, I am thinking it is a weak or broken valve spring, I am starting to get PISSED I just put this new motor in. Craig

[DjD]

Does you vacuum gauge needle action look like any of these?

http://www.users.bigpond.com/ergoff/vac1.htm

Be sure to look at the second page using the arrow at the bottom of the first page.

[hippymill]

try this to help you diagnose. i got this from a webpage, and pasted to a document so i'd have a record. don't remember the webpage, but here is the doc:

TuneWithVac.doc (http://howard.nebrwesleyan.edu/hhmi/fellows/lutkehus/TunewithVacGauge.doc)

[ March 04, 2004, 07:29 AM: Message edited by: hippymill ]

[Jeep Craze]

Thanks guys, I checked out those websites, and documents and what I can safelly rule out is worn valve guides(it says the needle will steady w/ rpm increase: mine doesn't) Mine shikes like its on speed all the time regardless of throttle or RPM. What I am not sure of is lifter bleeding down, worn or weak valve springs. I did a compression check tonight,
#1-152 #2-145
#3-155 #4-150
#5-152 #6-143
#7-155 #8-150

The even side bank seems like there are larger fluctuations. But They all pumped up at the same speed as the odd bank. would a compression test show me a weak or broken spring?I still can't get my timing light to work, so I am gonna buy a new one.....I had the timing set when I fire up the motor, i can't see why it would have changed.

Lost in the dark!!!
Craig

[Chevelleguy]

What you are seeing with the needle fluctuation is a small amount of compression leaking back into the intake. I would pull the valve cover and check check #2,6 very carefully. If you can't see a problem, try compressing the valve springs, on the intake valves, by hand. If one of them seems to compress more easily that the others, that would be your faulty spring. I have seen broken springs that are still closing the valve, they just allow the valve to bounce off the seat during closing.

[Jeep Craze]

ok, thanks I will pull the valve cover and check it out. I was kinda thinking it was something w/ those two low cylinders but figure there were more people out there w/ more knowledge than I. I will update as soon as I get more news. Craig

[DjD]

I can't see how you are having a problem with valves with such good compression results.

The compression specs I have for the 360 are as follows:

Haynes - 100 to 140 psi minimum with no more than 30 psi variation among cylinders.

1990 TSM - 120 to 140 min., variation 30

The Haynes book suggests a possible intake manifold gasket leak, you could try the carb cleaner/propane torch test.

I'm very interested in the outcome. Good luck!

[osceola]

COMPRESSION TEST !!!!!!!

[Jeep Craze]

OSCEOLA, I did the compression test already read through the entire post.

I am gonna do a leakdown test tomorrow to find out if the valve seats are good on those two cylinders that are lower than the rest.

DjD: I already used 2 cans of carb cleaner on everything including the carb and all vacuum lines and manifold joints. I was talking w/ the guy who redid the motor and he suggests that I do a leak down test on the two low cylinders and check spring pressures on those two intake valves. Its not that the compression is bad in those two cylinders, it is that they are the only two that are signifigantly different compared to the other 6.

[DjD]

You could build your own leakdown tester:

http://www.xs11.com/tips/misc/misc3.shtml

Does anybody have an account with Grainger's that I can use. hehehehe