3.0 OMC ignition problem

[6meter]

Re: 3.0 OMC ignition problem

OK. Remember you need fuel, spark, compression and timing, valve and ignition. Don't take the cam out. The crank will make two revolutions for every one camshaft revolution. Turn the motor so the timing marks are lined up next to each other. That will ensure your valve timing is good. Move your plug wires on the dizzy cap two spaces clockwise. Can't remember but did you put a timing light on #1 while turning the motor over to get timing close? If not do it. Just making sure dizzy is positioned close. Put your timing cover back on. You shouldn't have to do anything in there if the mark line up. Try it. Another thought, did you touch the rocker arm adjustment? Or is there one?

 

[[OBC]Patch]

Re: 3.0 OMC ignition problem

Here is an update of what i found when i pulled the timing cover. I put the motor to TDC with a compression gauge and pulled the valve cover just to make sure both valves were closed. When I pulled the cover i noticed the timing marks were opposite of each other. I thought this was strange since every motor i have built in the past (primarily 350's) have the marks together. I consulted my manual and it indicated the marks should be together as well as a machinist I gave a call to. He was surprised the motor even ran. I went through the firing order by turning the motor over by hand just to make sure I was in fact at TDC compression stroke and all the valves were working properly (at #1 compression stroke # 3's intake is still open but on its way shut). I have attached a picture of what i have found. I am not familiar with this motor so I am not going to attempt to move the cam until I get some feed back on this one. Thanks in advance!

That's it! The marks have to point at each other!!!!!!!!!!!

 

[Jessfly1]

Re: 3.0 OMC ignition problem

After much debate I elected to put the timing cover back on without changing the cam orientation. This is why... I wanted to make 100% sure #1 was at TDC compression stroke so with the valve cover and timing covers off I conducted a few tests. First I took the shrader valve out of my compression tester and just put the hose in the plug hole. With about 30psi of air supplied to the cylinder I rotated the motor by hand and when a valve opened I could hear air either escaping out of the carb (intake) or transom (exauhst) I then labled the valve respectively with a marker. FYI, my clymers manual had the valve orientation wrong!! I did this for all 8 valves. Once i knew without a doubt which vavle was what i rotated the motor again until #1 intake valve started to open. Once it was on its way shut I put a screw driver in the plug hole to gauge where the piston was. At the top of the stroke the intake valve is closed as well as the exauhst valve AKA TDC compression stroke! I verified they were closed by putting air in the cylinder and It was escaping past the rings not intake or exauhst. This proves the cam to crank orientation is correct! Timing marks orientation also wrong in my manual!

 

[Jessfly1]

Re: 3.0 OMC ignition problem

After putting it all back together with a new water pump (the old one started leaking for no reason NOT TOUCHED) I installed new platinum plugs with a gap of .40. I then leaned carb out as far as possible using the float adjustment. It was still running like crap and extreamly rich! I pulled the float out and bent the float tab up (first time I have had to do this on anything) so I would have more adjustment on the float. I then leaned it out even more and put both idle screw all the way in. That helped quite a bit. It now idles on its own and is no longer "blowing black smoke rich"! It is consistant but idles rough. I still dont think its firing on #2 because there are no indications on the plug. Also I pull the plug wire and nothing changes AGAIN! I am going after the distributor AGAIN to see if moving it around helps. Any suggestions? Thanks for all the input and i will keep you posted.

 

[[OBC]Patch]

Re: 3.0 OMC ignition problem

Your valve timing is 180* out, so your distributor is 180* out, so TDC #1 is 180* out. You have effectively changed the firing order, but it only works for 2 cylinders. You mentioned above you have compression in all 4, so you haven't bent any valves. Align the marks and crank it by hand with a wrench on the crankshaft so you wont fear bending valves, you'll see. Listen to the machine shop guy.

 

[bruceb58]

Re: 3.0 OMC ignition problem

Your valve timing is 180* out, so your distributor is 180* out, so TDC #1 is 180* out.

Not quite...TDC rotates twice as fast as the distributor and the cam so it would still be at TDC. For every 180 degrees rotation of the cam/distributor, the crank rotates 360 degrees.

 

[6meter]

Re: 3.0 OMC ignition problem

Float level won't lean out a motor. Turning your idle mixture screws in all the way is compensating for another problem. Turn them back out. Where is your ignition timing at? You need to set that correctly before you do anything. I still say that you are 180 out. Your valve timing is correct. The easiest way to get TDC on the comp stroke is to stuff a rag in #1 plug hole and click the engine over, click, click, click with the key until the rag pops out. Then turn it just a bit more by hand to line up the timing marks on the balancer.

 

[sqbtr]

Re: 3.0 OMC ignition problem

The pic is worth a thousand words, just move your plug wires two posts clockwise on cap and see how it runs

 

[6meter]

Re: 3.0 OMC ignition problem

The pic is worth a thousand words, just move your plug wires two posts clockwise on cap and see how it runs

I suggested that 2 days ago.

 

[[OBC]Patch]

Re: 3.0 OMC ignition problem

Not quite...TDC rotates twice as fast as the distributor and the cam so it would still be at TDC. For every 180 degrees rotation of the cam/distributor, the crank rotates 360 degrees.

Perhaps, I'm no engineer! My understanding is TDC is a reference to the pistons position in the firing cycle and the only moment when a spark is provided, not as it relates the piston position to the cylinder bore. I was referencing crank degrees since the cam is aligned to it, not the other way around; the cam in the provided photo is observed to be 50% off with the cams alignment dot facing away from the cranks alignment dot, which are supposed to face each other. 360* in cam degrees equals 1/4 of the crank cycle, or 180*.

It's my conjecture that allows 2 cylinders to work and fails the other 2. Don't ask me to prove it, I can't!

How come no one is backing on the alignment dots???

Has no one else here built motors before?

 

[bruceb58]

Re: 3.0 OMC ignition problem

My understanding is TDC is a reference to the pistons position in the firing cycle and the only moment when a spark is provided, not as it relates the piston position to the cylinder bore.

TDC is when #1 piston is at the top but it can be either compression stroke or exhaust stroke.

 

[chaparall villain 2]

Re: 3.0 OMC ignition problem

ok i have a stupid maybe question and i am sure you have checked it but when the cap is off when you turn the engine over is it clockwise or counterclockwise rotation in the distributor but worth a check if you havent ... good luck you got me stumped

 

[chaparall villain 2]

Re: 3.0 OMC ignition problem

ok i went thru the whole post and saw that it was already looked into ... oops

 

[Jessfly1]

Re: 3.0 OMC ignition problem

ok i have a stupid maybe question and i am sure you have checked it but when the cap is off when you turn the engine over is it clockwise or counterclockwise rotation in the distributor but worth a check if you havent ... good luck you got me stumped

Yeah...I just put the plug wires in the counter clockwise firing order just to see if that did anything and it wouldnt start. I am stumped as wall I have exhausted all my options, or at least everything i can think of, and its still not running right.

 

[chaparall villain 2]

Re: 3.0 OMC ignition problem

after some thinking i dont know that i wouldnt pull the carb and have it rebuilt and cleaned i have has carbs do weird stuff including making the engine miss then did nothing but change the carb and it was totally different ran perfect ... if the interupt switch has been disconnected which was my first thought as i had that happen to me one time with very similar results and everything i have read you tried i would go back to carb could be something in the idle circuit or main circuit casing the flooding to kill plugs before they get a chance to run ... good luck

 

[Jessfly1]

Re: 3.0 OMC ignition problem

Just accomplished a valve adjustment again. Turned them to 1/2 past lash and the problem is still there. I am still at a loss. After putting 3 sets of plugs, 2 sets of wires, 2 distributors and 2 coils Its not running right. I guess the only thing left is to adjust the cam to crank orientation. I am finding it hard to justify doing this because all my tests indicate it is correct. Also, I have not touched the crank, cam, or timing gears since i bought it. Im not saying someone else didnt screw it up but it still has the fiber cam gear with GM's logo on it. This leads me to believe that it came from the factory this way. You would think if someone took the time to replace the timing gears they would have went all steel.

 

[Jessfly1]

Re: 3.0 OMC ignition problem

after some thinking i dont know that i wouldnt pull the carb and have it rebuilt and cleaned i have has carbs do weird stuff including making the engine miss then did nothing but change the carb and it was totally different ran perfect ... if the interupt switch has been disconnected which was my first thought as i had that happen to me one time with very similar results and everything i have read you tried i would go back to carb could be something in the idle circuit or main circuit casing the flooding to kill plugs before they get a chance to run ... good luck

I am leaning more and more to the carb. I think I will look at the carb again before i mess with the timing gears.

 

[chaparall villain 2]

Re: 3.0 OMC ignition problem

i dont think i would do that yet i would still go to carb and redo it first just in case its causing the problem ... it doesnt sound like youve missed anything ignition wise at all

 

[Jessfly1]

Re: 3.0 OMC ignition problem

The pic is worth a thousand words, just move your plug wires two posts clockwise on cap and see how it runs

Yup...moved the plug wires two posts and it wouldnt run. Thanks though!

 

[wire2]

Re: 3.0 OMC ignition problem

When I saw the pic of the timing dots opposite, I thought "AHA!" But then quickly realized that they would coincide with 180? of crank.

Good compression numbers mean the intake is not blocked;
wet plugs in 1 & 2 mean they're getting fuel, so carb is prob ok;

I'd list the timing/ignition events on a paper as they should happen, according to the firing order. Then pop the rocker cover and the dist cap 1 more time.

Slowly turn the crank with a wrench, and watch the valve & dist events sequence. Do they match your list? A 2nd person watching will help.