ShaneBuss2

I just dropped in a new 10.25:1 383 stroker with a 570 lift solid roller cam, and dart iron eagle heads.

It starts but sounds awful like its backfiring through the intake on one cylinder, so i only ran it a few seconds. I thought maybe a intake valve wasnt closing, but i rechecked all the valves and they are fine. (around .018 with a feeler guage). I have tripple checked all the plug wires and the distributor. Running out of ideas.

The engine did not come with a timing tab, so to find TDC i did this.

1.) buy 8" balancer timing tab from autozone.

2.)Removed #1 spark plug, and turned motor over by hand until i felt air coming out of the cylinder.

3.) rotated balancer clockwise until mark on balancer lined up with 0 on timing tab. (this happened soon after i quit feeling air coming out of #1 cylinder)

4.) installed distributor with rotor pointing at the #1 cylinder

Any ideas what could be going on here? I guess I am going to order a piston stop and find TDC the RIGHT way, and if it still doesnt run without backfiring thorugh intake i'll run a compression check. I have tried playing with the timing while its running, but it doesnt solve the problem.

My ears could be deceiving, but it does sound like its only happening on one cylinder, it is a very consistent backfire.

Thanks,
Shane Buss

radiateu2

Shane it sounds like a timing issue pull the valve cover off the #1 cylinder and look for both valve sto close on the #1 cylinder on the compression stroke. Then locat your timing tab on the 0 degree mark on the balancer. then reset your distributor. Try that and if anyone else has any suggestions please jump on in.
Ed

ShaneBuss2

Thanks for the reply. WHen i set it to #1 TDC, I did check and both valves were closed on the #1 cylinder. :-(

It's almost like a bent valve or something.. but heads and motor are brand new!

radiateu2

I am sure you checked the valve to piston clearance before cranking I think if it were a bent valve you would have more than one bent valve. If you checked your timing and think it is ok I would check my valve lash and check to see if all my valves where seating and spring binding. Let me know how you make out

F-BIRD'88

Three possibilities come to mind.

1.Check the rotor and cap to see if they are loose.

2. Do a compression check to see of all the cylinders are sealing.
Something could be holding a valve off its seat.

3. use some propane gas shoot down the air intake.
Of the motor won't start immediatly on propane, you got
compression , ignition or valve problems.

If it fires immediatly, you have a fuel problem.
It is very unlikely to back fire on propane.

ShaneBuss2

The motor was professionally built and shipped to me built from valve covers to oil pan. I REALLY hope its not a clearance issue ;-)

As far as the valve adjustment, i checked it today and it is fine. I really think its a timing issue.

I just ordered a piston stop. Tell me if this is the proper method to find #1 TDC.

Rotate engine until i feel AIR coming out of the #1 spark plug hole. Install piston stop. Rotate until it hits piston stop and mark position. THen rotate in opposite direction until it hits piston stop. TDC should be in the middle of the two marks.

Sound right? How do i know if i'm 180 out or not? If both valves on the #1 cylinder are closed at the TDC i find i guess it's right?

Then install the distributor pointing at #1 cylinder ?

:-(

p.s. The motor fires and starts easily, it just sounds like its backfiring through the intake when it runs. It will stay running unless i kill it.

next step will be compression check.

HiTech5

iTrader: (4)

Shane - It really sounds like a distributor problem. I'm sure it's been covered but do you have the firing order correct?

Should be 1-8-4-3-6-5-7-2 going clockwise around the distributor. If the rotor is anywhere near #1 while at top dead center, the motor will fire and be close.

www.geocities.com/dzperf

ShaneBuss2

i know it seems like a firing issue.. im hoping the distributor is one tooth off or something..

i know the firing order is correct and no wires are out of order.. checked it 23987275 times and had someone else check it to make sure i wasnt crazy.
thanks

89gta383

iTrader: (5)

You are off a tooth on the distributor gear. I have to play with mine for like a half hour before I get it right on. Remember, as long as the rotor and the #1 terminal on the cap are lined up, it doesn't matter where the rotor is pointing, just turn the distributor to the #1 terminal.

nosibear

Forgive me if I'm wrong here but, whenever the piston is at the top of either the compression or exhaust stroke....wont both the valves in that cylinder be closed...otherwise you would have clearance problems. You should pull the valve cover, and watch the intake valve on cyl. #1 ...once IT closes, check your mark on timing tab and bring it to zero (should already be close). If your bringing it up on the exhaust valve, it will definetly be 180 out.

evil t/a

People are making this harder than it should be. When you eyeball thetiming adjustment you can still be off by ALOT. The timing is most likely too retarded , making it easy to start but it will run like ****. By a bolt on timing tab for whatever size balancer you are using and set you timing with a tioming light.

radiateu2

when the piston is on compression both valves are closed and the piston is in the up position, on the exhaust stroke the valve is open on the exhaust position hense the name exhaust stroke this is where you could run into valve piston interference. I dont think this is the case here. He is off by a few teeth on the distributor. Evil t/a can you explain how you can just bolt on a timing tab and set timing? Well, you cant because the timing is already off you have to start with the piston on the compression stroke and both valves closed on #1

ShaneBuss2

I will verify TDC this weekend with a piston stop, set the timing to 10 BTDC, and try to start it. I have a good feeling it will do the same thing.

someone explain this "distributor off by tooth" theory. If thats the case, wouldnt it not be pointing to the #1 cyl? How do i tell?

Shane

p.s.

its on the compression stroke because i feel air coming out of #1 cyl spark plug hole, BOTH valves are closed, and i lined it up with the 0 on the timing tab. I tried adjusting the timing while it was running and it didnt fix the backfire through intake problem.

evil t/a

Yep I can explain so pay attention:

He doesnt have a timing tab , and he just eyeballed his timing. The engine starts and will stay running unles he kills it. There are timing tabs that bolt to the timing chain cover , if he gets one of those he can actually see where his timing is at now and where he should set it at. If he is way off or if the timing is right on and theres another problem he wont know it until he gets a tab AND a timing light.

evil t/a

\

There is no such thing as "One tooth off" , as long as you can rotate the distibutor body enough to line up the rotor with the correct post you can install your distributor any which way. Shane I would also double check to make sure that you arent 180 off , I know that you said you checked before but check it again . I have seen engines run like that.

radiateu2

shane I agree with evil ta on this one keep in mind that on the exhaust stroke you could still feel air coming out of the spark plug hole cause the exhaust valve and the cylinder hole are both open. The only way to be sure that you are close on your timing is to pull the valve cover and bolt on the timing tab. On the exhaust stroke there are 2 places for the air to go out the valve and out of the spark plug hole. so make sure that you are not on the exhaust stroke and on the compression stroke I have found the only way to do this without guessing is to remove the valve cover and look for the valve to be closed on the compression stroke.

ShaneBuss2

Guys i already said that i have a timing tab , and that both valves are closed when i found TDC. the intake valve had JUST closed, so im sure it was on the compression stroke.

thanks !

shane

HiTech5

iTrader: (4)

Shane - If the intake valve is just closing as you are bringing it to TDC, then your #6 is at TDC firing. You should not see the valve moving. Turn the motor over 360 degs more and reinstall the distributor. This is a common problem.

www.geocities.com/dzperf

ShaneBuss2

dude i hope you are right, because that would explain EVERYTHING..

im crossing my fingers!. cant i also just rotate the distributor 180 degrees?

evil t/a

You can but it would be easier to change the wires on the cap. If you are runing a large cap hei then you should reinstall the distributor with the rotor facing the right way.
And thats the best way to do it.

And you do know that if it was 180 off we are going to hang you from a tree and throw rocks at you for being so hard-headed , right?

ShaneBuss2

throw rocks if you can catch me in a near 500hp 383!

;-)

I just dont see why everyone says to find tdc rotate until valves are closed and air comes out of #1, if that can still be 180 off!

I have a large accel hei distributor, i will just pull it out, rotate motor 360, and put it back in.. ;-)

shane

HiTech5

iTrader: (4)

Shane - I agree with doing it the right way and pulling the distributor out and rotating it 180 degs. Remember that the oil pump drive probably won't line up. Have one of your buddies hold the distributor while you turn the motor over and it should drop right in.

HiTech5

iTrader: (4)

Give us an update!

Did you reinstall the distributor 180 degs?

ShaneBuss2

Well guys i got it running! I tried advancing it as much as possible and got it running. So i moved all the wires over one on the distributor (effectively it was on "tooth" off) and i think its good.

When i get the battery charged will see how it goes.. But it did start right up!

thanks guys

shane