The Stovebolt Site Forums The Shop Area Engine Shop Guys I need serious advice

I have a bad backfiring problem, it was sooooo bad it blew both ends out of my new Thrush eliminator muffler!!since my last post I change dist cap, change fuel, all wires on the right cylinder,I removed the timing chain cover by dropping the oil pan. The camshaft gear is a nylon one some wear but not enough to make it jump time. But there is enough wear I cannot for the life of me find the timing mark on the camshaft gear.everything is lined up,rotor on its mark for #1 cylinder ,marks line up on flywheel.I looked with a magnifing glass to find the mark!!Is there an alternate way of getting the camshaft gear off without disassembling the drive train and removing the grill to get the camshaft out??? :mad: :confused: :confused: :mad:

Alan

Sorry.What made you think this was a'Cam Timing' problem?
If you don't really have a good answer now you have a motor that is unrunnable and trouble shoot.
The first sportscar I ever worked on was a 250 Ferrari First page of the manual it said
'Keep the golden wrenches out'.......never forgot it.Fix what need fixin
I don't know much about thos short car motors but the GMC motors have a mark and spec to check problem without taking it apart!

[ 01-17-2002: Message edited by: J.H.Proffit ]

As silly as this sounds, are you 180 degrees out?
I've done it before. Bad sounds come out of the engine when you are .

Chris

Alan, first sorry to here of the headache. The method that I have sucessfully used when in doubt about a timing problem is, Take the spark plugs out. put your finger over the number one cylinder
(Front cylinder) have some one slowly bump the engine over until you get compression. On this compression stroke make sure the piston is all the way to the top (Feel screwdriver) then be sure the rotor button is pointing right at number one spark plug wire post, in the distributor. Double check that the firing order of the wires, are they in the correct places? Make sure it is correct with the way the distributor turns when cranking.
Again be sure you are wiring it the way the rotor turns when you crank it. If all this is done, it is in time. The backfire has always been a secondary ignition problem for me , not other stuff. Hope this Helps....Chb46

Nothing causes backfiring like exhaust leaks. Fresh air gets pulled in, unburned fuel mixes in exhaust and gets hot enough to ignite.
Also, leaking ex valves cause this.
Check the integrity of the ignition wiring (12volt side). Looseness at the switch or anywhere else will cause this too.
Best of luck!!!!!

Running an ignition coil that is designed for use with a ballast resistor on 12Volts after starting will cause backfiring as well.

Guys Alan HAS THE MOTOR APART!!!

Any you guys seen inside one a these car motors?
How do you GET the cam sprocket off!?

He CAN'T run the motor till he fixes this part and puts it back together

Alan, the gear is pressed onto the cam,you cannot remove the gear only, the cam has to come out. Its the same for a Chevy or GMC.Either pull the engine or pull off the front sheet metal. Your local machine shop can remove and install the new gear for you.There are two dots,one on each gear, line them up.the engine is not at TDC, when the dots are aligned so don't worry about dist timing right yet.If you have any doubts about the fiber cam gear condition, replace it.A better replacement is the aluminum cam gear used on 235/261 truck engines.Do you have a service manual? shows how to check cam timing without pulling the timing cover.Fun yet?

Alan, I just don't know what engine You have, but I it is a stovebolt, You can take the timing gear out of the cam with the cam in place, it's hard to do but it is possible. But You'll not drive the new one without taking it out of the engine.
You'll need a press to drive it to his place. If You just try to hammer it to the cam, it will make the cam expell the cam plug in the block rear side and an oil leak will occur. Also You can break something in the process. If it is already disassembled, take some time to remove it from the engine, and change it out. And You'll have to pull the grill out to make it happen.
But I don't think the trouble is there. Check the exaust valves, check the base ignition timing, plugs, wire plugs. Seems to me You're been through a ignition or valve stuff. Not valve timing.

What motor is this?? Changed the wires on the right cyl? Sounds like you have the wires on wrong. Did you happen to put the wires back on like they show in the books.Cause if you did and some one like me put the dist in your out of luck cause i just drop the dist in and do the firing order.The 235/261 firing order is 153624 and the rotor turns clockwise.#1 cyl is the front one next to the water pump and the cyl go 123456 #6 being the back one.Now pull#1 spark plug and turn it over with your finger in the plug hole till you hear comp air coming out.Now get a very small screw driver and keep turning it slowly till the piston is all the way to the top.(if you know were the timing mark is on the flywheel check to see it lines up) Now look at the rotor and try to rotate it so a plug term is dead nuts on it.Thighten the dist and put #1 spark plug on ,from ther you go clockwise on the cap 1-5-3-6-2-4 You can do this with out putting the motor back together.Just DONT let it run.Spin it over and see if it catches.Like i said dont let it run if you have the pan off cause it wont have any oil and that is BAD. I suspect your not talking about a 6cyl though when you say timing chain ,Is it a smallblock or??

[ 01-18-2002: Message edited by: Phat ]

This is the list of thingy I tried Before I took the timing gear cover off.

1 changed fuel
2 changed dist cap
3 aligned #1 cylinder by thumb over #1 cyl
4 made sure flywheel was aligned at this point
5 dist gear will be right or 180 degrees out only way it will seat
6 made sure wiring was correct
7 made sure #1 cyl at top dead center aligned with marks
8 removed valve cover to ensure #1 cyl valves were open at to dead center.
All of these things were correct and still it backfires is why I took the timing chain cover off.None of this was done in 10 mins.been messing with the timing externally for 2 complete days.

I didnt consider the electrically aspect side. I am running a 6 volt starter 12 volt solnoid, 12 volt coil, and 12 volt battery no ballast in the system.

Thanks for your help I still need it even ol Proffett who has such a way with words (laughing)

Sorry Phat meant to say timing gear and it is a 235.

Alan read #8 of your second to last post, If I read this right ,your timing is off. The valves should not be open when the cyl is firing on top dead center. I think you have timing 180 off. :o

Thanks Tommy

What Tommy Said and.............How did you get compression agenst you thumb with the valves open?
Does the coil have an internal ballest?
If I can find my old military manual I'll get Tony to post the Trouble Shooting page.It's very simple step by step.

Good luck Alan

I had a problem with our '68 Impala. I replaced the distributor cap and decided to just quickly label the wires 1-2-3-etc going clockwise around the distributor starting from the wire in the front. No problem but about a year later I decided to replace the wires. When I put the wires back on the cap, I hooked them up as if the labels (which were still there) were indicating cylinder number!!! I had to get the car towed to my trusty ol' mechanic. He promised never to tell anyone how stupid I was.

But then, my buddy once dropped a pencil down #1 spark plug hole while following the travel of the cylinder. Moral here is: Use a long pencil.

The valves have to be closed and the dist can go in many diff ways(you must turn the oil pump with a screw driver.) Get #1 an with the valves closed now look to see were the rotor is(DO NOT LOOK AT THE FRIGGIN BOOK)were the rotor is IS #1 no if ands or butts.Put the #1 spark plug wire on the cap to match up to the rotor placement(AGAIN FORGET THE BOOK)you may have to turn the dist a little to get the rotor matched to a post on the dist. Now just start form #1 plug wire and go clockwise on the cap 153624. Dont look at the diagram in the book. Timing rarely jumps on a 235 and you could have 6 burnt valves and it wont blow the muffler apart.YOU have the timing wrong.Did it happen before you changed any parts???Did you change vavle adjustment??? Keep us posted ,there are no dumb questions.

Phat I havent changed the valve lash at all. The dist gear will move freely? so far ive found it is slotted and it will seat is 2 postions opposite of each other only!!

Thanks for the help gonna put the the timing cover back on and the oil pan again. and start over. another note , when I did drain the oil it had a strong smell of gasoline is this from the backfiring??? Do I need to install a ballast for the electrical end of this Phat??

No the gas in the oil is from trying to start it.make sure you drain it and pull all the spark plugs and put a couple squirts of oil in each cyl and turn it over(you have washed the cyl down and will not get much compresion).Your spark plugs are most likly fouled out also so.....i know you dont want to hear it but go get another set. The slot in the dist drives the oil pump you can put a screw driver in the hole and turn the pump to get ti to were you want for the dist .The dist will go in about six diff ways. If you have spark dont worry about the ballast yet.BECAREFULL WITH ALL THAT GAS ARound.Do you have 12 volt or 6 volt???

[ 01-18-2002: Message edited by: Phat ]

[ 01-18-2002: Message edited by: Phat ]

Phat it is a 6volt starter,12 volt solenoid, 12 volt battery, 12 volt alt. dont mind changing plugs at all.Bought new gaskets reassembling the timing cover and oil pan. Ill have it back together tonite. and we will start over again thanks everyone I really appreciate your help
Alan

Well if its 12 volt make sure you have a 12 volt coil and a ballast resistor just before the + side of the coil or it will burn points.Get it back togeather and post back that ole 235 will run even if its got holes in some pistons

If the flywheel ball and pointer are lined up, #1 cylinder valves are closed, and rotor pointed to #1 plug wire, she'll fire up.

Phat is right. My 235 once ran with the #6 piston broken smooth in half. The piston crown was bouncing around in the cylinder like a beach ball, but she still pulled herself out of traffic.

chip

Immmmmmmm Back

All put together again did exactly as you told me phat step by step the frickin thing still backfires. If there arent any holes in it now I am about to put some 9mm ones in it (laughing)
Ok tag your it again

Alan:
This can be a very difficult problem. Lots a great advice you're getting, I always learn a lot from theses type of posts. Hopefully you will let us know what the resolution was. Just a thought, if you have points, have you checked them? Also, could there be some type of contaminant on the underside of the distributor cap (grease, etc. that could conduct electricity)? I'm assuming you changed the distributor cap before the problem. In any case, sometimes it is something simple. Good luck.

Thanks Don I have checked the dist cap and I have to quit for tonite , the neighbors are calling asking my wife if all is ok or has the crazy ol Nam vet's meds arent working. I do have a habit of shooting alot of rounds when Things are going bad (laughing) but no I havent shot the truck

Alan Does it run at all?

JH

Yes it runs but backfires so badly it really does sound like shotgun blasts coming from the engine.

Alan

I had a 216 that gave me trouble like this once , the cam gear had slipped on its bush . Looked ok cause the bush is keyed to the cam . but the bush is not keyed to the fibre part of the gear .

Let me ask this question a couple of you refered to.On my coil it states: use with primary resistance wire or external resistor. I have the ignition wired this way, I hope it is clear.Large red wire from battery center terminal of solinoid,
also red wire from ignition running to the same lug. On the coil I have the neg side running to dist and the positive side running to the ignition. on the right side of the solinoid I have another wire running to the ignition. No ballast inbetween the ciruit??? Could this be the problem??

Um,,, Phat the oil pump is a positive gear driven unit, it is driven by the camshaft gear, the oil pump gear has a slot in it , the distributor has a tang or blade that fits into the oil pump drive gear, so only two ways he can drop the distributor into the engine, Alan the only thing I can think if you have it running, set it up again for #1 cylinder at top dead center, check the timing marks that is the ball and pointer at the bellhousing, remove distributor cap see where rotor is, note its location, check to see if rotor isn't loose or free to turn on distributor shaft it should move a little with the distributor advance , check to see that #1 plug wire is inline with the rotor position when the cap is installed, make sure that your next plug clockwise from number one is number five and so on, what i'm thinking is you have a bad rotor or cap that is cross firing or firing two cylinders at once something of that nature, another thought is start it up in the dark and see if two plug wires are arching that is one wire sent a spark two another wire , well good luck,

jbennett
40 burb

Thanks j

I havent tried the rotor part but I have checked it all in the dark. So It only can be right or 180 out correct?

To check the cap you put it to your ear NOT TOO CLOSE and open and close the points you can hear it archin'
To cleck the points ...put new ones in

Hold the rotor and try to turn it

Bring it up to tdc with the valves closed!Move the dist in opp. rotation.When the points crack thats close

But FIRST PULL THE COIL WIRE AND LOOK FOR GREEN STUFF!!!!

Is the coil Hot?? That's bad!!!!!!

No offense to everyone that's trying to help, but shouldn't we start at the beginning?

First of all, what has Alan told us?

• It's backfiring through the exhaust system
• He's changed fuel, wires and dist cap
• He's checked all his alignments, including flywheel, dist, valves, cam, etc.
• He's running an external resistor coil with no ballast resistor
• The motor starts and runs

The cause of backfiring is timing. But timing means a lot of things, both mechanical and electrical. Alan's checked all the mechanical stuff, but only part of the electrical.

The motor starts and runs. What does that tell us? The mechanicals have to be fairly close to right. If you get the distributor off 180 degrees, the motor won't run. If the cam slips one gear, the motor won't run well. A couple of gears and it won't even start. If a valve breaks, the motor will run rough.

His runs, it just backfires.

Most likely cause? Points and/or condensor. The points are probably badly burned, Alan. The purpose of a ballast resistor is to drop the voltage from 12 volts to about 6 volts. This makes the points last much longer.

Don't forget, the amount of time the points remain open determines when the spark plug fires and how strong the spark is.

You don't need a ballast resistor if you buy a coil with a built-in resistor. NAPA sells them. They're much more reliable than the external resistors ever were. Get one. And while you're there, buy points and condensor. (I'm assuming you replaced the rotor with the cap.)

Now, let's clear up some misconceptions. The timing can't "slip" on driven gears unless one of the gears has plastic teeth (which his 235 does) and teeth are chipped off. I've seen this on the Pontiac 327, where the timing chain slipped because the teeth became brittle and broke off. But Alan said the teeth were worn, not broken. I doubt seriously that the timing gears are improperly located. Besides, the engine runs. If the cam slipped one tooth, that would throw the entire timing mechanism off by several degrees, which should be more than enough to at least make it very hard to start, and it would run very rough.

Second, jbennett is right. The distributor will only go in two ways. Either in the right place or 180 degrees off. If that was the problem, it wouldn't run at all.

Third, on the 235, the intake valve opens at 1 degree ATDC and closes at 39 degrees ABDC, and the exhaust valve opens at 42 degrees BBDC and closes at 9 degrees ATDC. So, if Alan had the motor at TDC, the exhaust valve would be open, not closed, if he was 180 degrees out. If he was 1 degree past TDC, both valves would be open, the intake on the intake stroke and the exhaust on the exhaust stroke. So what he is reporting is normal for the 235, if he's off just a hair or he's 180 out. Only Alan can answer that.

Finally, no one seems to have asked: Alan, has the motor ever run right? Has it always backfired since you've had it? Was it just rebuilt?

If you get it fired up again, pull one plug wire at a time and see what happens. If nothing changes put it back and move down the line. This could rule out one cylinder problem. I think the only way it can fire at the plugs is if the distributor tells it to fire. So you can probably rule out any coil or wiring problems. It has to be firing or it wouldn't be backfiring.

Will it run long enough to get hot? If not, this would rule out carbon build up. They have to be pretty hot to fire off of that. I would think the same is true for sucking air in the exhaust from a leaking gasket.

Is it running lean? How does the exhaust smell?

Are valves in the right position at top dead center. Are they closing and opening when they are suppose to be. Exhaust should be closing just as intake starts to open with piston starting on the down stroke. Intake should just be closing or aready closed as piston starts the compression stroke. The slipped nylon ring gear on the cam could of happened. You did say you couldn't find the timing marks.

Do you know anybody with a distributor machine? You can find alot about them real quick.

If you think it could be wiring to the coil, just unhook them and run a wire from the battery to the + side of coil. ( - ) side goes to distributor. Yes, this can burn out points but not in the few minutes it going to be run.

Did you check all of the rockers and push rods to make sure one of them isn't stuck ?

Does it ever pop out of the carburator? Blow fire or fuel out?
Joe

Just one thought, how's the clearance on the pushrods? Could be to tight.

Thanks Paul

For taking time to address my problems and I might add very enlightning. I am not the best wrench on here , but I was seriously worried about my memory ( laughing) The usual story "it ran when I drove it home 2 yrs ago" 70 miles from Chattanooga Tenn to Rome Ga. I have cranked it to move it to and from the garage, but not very long cause it hasnt had an exhaust system on it. To me yes it was very loud and some popping thru the exhaust running straight thru the manifold.But no where near what it started doing lately.And to blow the ends out of a new muffler is a pretty violent backfire.So I naturally assumed timing.
But I am weak in knowledge on the electrical aspect. I did install a new harness from Chevy Duty and was proud most everything worked the first time, But troubleshooting is my main weakness.So I paniced when I tried all of things to do and it didnt work. All of you have been great, and please keep feeding me ideas,although I am now sitting at my desk at work pulling 2/12 hr shifts over the weekend so it will be Monday or Tuesday before I realy can roll the shirt sleeves up again. She is close to getting on the road I was very disappointed when this problem arose. I cant say enough about you guys and all your info, I really appreciate you guys. Dont get swelled heads I appreciate my dog too!!
Alan

Hey Alan I bet when you get this fixed you will be one proud puppy. First off your getting some wrong info on the dist.Um....jbennett you better go back to 235 school cause your plain and simple WRONG(good natured ribbing buddy but i have done more of these motors than i care to remember).Baldeagle your in the same boat. :p The gear is on the dist .The oil pump can be turned and stopped any palce in 360 degrees.Its not uncommon to pull a dist and have the pump turn slightly .Presto it wont go back in with out turning the pump back with a screw driver or crankin the motor with the cam gear engaged till the pump slot lines up and drops in. Ok dont hook any wire to the solinoid,Its NOT NEEDED.Also dont use the internal resistor coil(done this for 30 plus years and they seem to fail at a higher rate)use a good balast resistor inline before the + side of the coil(its a great place to hook up the timing light)You need to go back and do as i said .GET IT TO #1 and put #1 spark plug wire on the cap to line up with the rotor.Next if you have not been using a ballast resistor i suspect the points are toasts.Replace and set to .016-.018 for now.Next change the condenser make sure the friggen screw holding the condenser tightens down or it will back fire.Last just for my personal mind set put a ground on the motor to the Neg batt post. I CAN NOT STRESS IT TO MUCH THE DIST CAN AND WILL GO IN MANY DIFF WAYS NOT JUST 180 out.(you were given wrong info) If you get real stuck during the day next week e-mail and i will give you my phone # and talk you through it.

Hey Phat

thanks I have grounded the motor to the frame and it did backfire still when I placed the dist in place where it set when i found #1. Ty I will email you and give you a call. I want this truck on the road before I die lol!!!

Alan

Any bets on the ballast resistor? Ever tried to run one of these motors without one? Can you spell S P L I T M U F F L E R ??? I was out one night and my truck stopped running, after about five minutes futzing under the hood I figured out the ballast resistor had opened up. No problem, jumpered it out, started it up and tried to drive it away . . . about two minutes, 50 feet traveled and one split muffler later I shut it down, pulled the ballast resistor off the firewall, found where the filiment was broken and unwrapped the wires and twisted them back together . . . re-installed, started it up and beat cheeks for home. Always carry a spare in the glove box!

Phat, I think we're not on the same page. I was assuming that Alan didn't turn the motor over with the distributor out. If he did, then of course all bets are off. While I have seen the oil pump turn slightly when removing a distributor, I haven't seen it often enough to think it's a big problem.

Secondly, NAPA makes an internal resistor coil, part number IC64, that Randy Rundle recommends, and I haven't had any problems with it. I certainly don't think it's less reliable than using an external resistor. Those are prone to burnout when trash gets in them, breakage when you drop them, etc., etc.

The rest of your advice, about the points, condensor and so forth, I wholeheartedly agree with. I feel certain his problem is related to: points, possibly condensor but they're so cheap I'd just replace it anyway, and the ballast resistor as Ken points out.