I have a SBC 283 and I am troubleshooting a backfire problem, anyhow. I pulled the timing cover off to check the alignment of my timing marks on my crank and cam gears. My question is my cam gear looks like it could be plastic and I cannot see any marks, I also cant see any marks on my crank gear. I know I have #1 at TDC compression but I don't see any defining marks. Any ideas or thoughts? Anyone know of chevy using plastic cam gears?
yes, they were nylon teeth..and a poor idea and not worth a **** , most ended up in the oil pan. put a new timing chain with steel gears on
OK ,ya got it open then,replace gears and chain, cam and lifters,but before doing thatya should found the cam has a few or at lest one war out lobe=backfire as soon as you start adding gas hard. If it's way apart just rebuild it.
Backfiring could be caused by many things, not the least of which could be weak valve springs or a cam lobe goin' south.
It does backfire through the carb when I hit the gas. I have checked my timing, compression, valve springs and pushrods. It ran fine before I rebuilt the top end. What I find funny is that the timing mark on the damper was at about 12 instead of on 9 deg advanced. Thats why I am checking my gears and chain.
The nylon gears were installed at the factory to have the engine run just a tad quieter or so the theory goes. They usually give out somewhere between 60 and 100 thousand miles and then most mechanics swap in a metal gear with the new timing set. I have run across a couple of guys in the past who put plastic gears back in (especially in Pontiacs) for the repeat business in another 60/75 k miles. As the guys said. as long as you are in there go ahead and change the timing set. I think I would pull the valve covers first though and crank the engine over to make sure all of the valves seem to be opening right. If you have a flat cam now is the time to deal with it. Ok I just read what you typed while I was typing. It almost sounds like your accelerator pump is on the weak side and the engine is going lean when you open the throttle, especially when you open it quickly. If it pops, and then stutters for a second before taking hold and starting to pull that may be the problem but I'd still change the timing set too.
I think I found the mark on the cam sproket it looks like its pointing about 12 o-clock at TDC but I am still unable to locate any mark on the crank. Do you know if chevy used the keyway as the mark or is there some other defining mark?
Replace the chain and gears When motor is at top dead center No 1 .Gear marks Should align perfectly together.If your looking straight at motor They would align at bottom of cam and top of crank.The nylon gears had a tendenancy to jump timing. Answer to your question up top. Usually a dot Every motor has a mark on bottom gear Replace that first .When the chain goes you can bend valves.
Keyway straight up on a standard style setup http://www.edelbrock.com/automotive_new/misc/tech_center/install/7000/7880.pdf
Are you sure the Distributor is not in one tooth off. Also double check the spark plug wires are in the proper locations. Triple check the valve train you could have a rocker tightened down a little too much. Check the cap and rotor. If you didnt have the problem before you rebuilt the top end then that is probably where the problem is Gary
Ok so i found the mark on the crank gear it is straight up, and I think I found the mark on the cam gear it is off the nylon and on the metal little box with an ^ the cam was pointing at about 12 o-clock with the before mentioned mark. Now should I turn the cam to lign them up? I am stuck at this point and dont want to create more problems. As an answer to the post above I set the #1 at tdc using a compression tester to verify compression stroke and then ligned up the timimg mark on the crank to "0" and dropped the distributor to the #1 on the cap so I am sure that is not it also I have tripple checked the wires. I stated above that the timing was off before I started. When I put a timing light on it the mark was about "12 noon" not near 9deg advanced or "2 o-clock".
Hold on hold on hold on. First answer some questions so the rest of us know what you already know. Has this engine ever run right before your own 2 eyes? Is it a used engine? Have you done anything since you last knew it to run right? Have you investigated what's going on with the distributor? Bottom line, if this engine is used and those marks don't align they've jumped and you need a new $18 timing set before wasting one more moment on that timing set. good luck
It was running and driving. I bought it from a young kid who drove it from mississippi to salt lake. When I bought it it was running ok but it felt a bit off to me. I started looking around and found a few vacuum leaks and the valve covers were leaking. I replaced the valve cover gaskets the intake manifold gaskets the carb gasket and rebuilt the 2bb rochester. I I checked the timing when it was running and thats when I found that the timing mark on the damper to be way off. I have had the car running again and drove it around the block but as I said before at high rpm's I am getting a backfire through the carb and I am lacking power. I have done all the other troubleshooting as far as what I took apart. I am now looking at the timing of the gears to see if that is were the problem is. It looks like the cam gear is off but I am not sure what to do about it. any help would be apreciated
Be super sure the balancer ring hasn't slipped and the timing tab matches the balancer. Then replace the $18 timing set. That's my vote. Good luck
Good ole nylon gears....man....I thought everyone had change all these over by now.........Get a good doublerow chain............
Timing marks .smallblock After you change gears .crank 12 oclock cam 6 oclock,Some motors differ. But not this one. Intake valve on no.1 should of opened and closed .right before reaching these marks.
have you tried setting the timeing by ear, till you put the timeing cover back on it will be tough to solve the backfire issue, so your saying you checked the timeing before you worked on the engine just to get a baseline?, then you worked on it and now if you set the timeing back in the same spot it backfires?
And the cam marks line up when # 6 is on TDC not # 1. Knew a guy that bent a bunch of valves spinning the engine over with thevalves adjusted and the chain off. He was trying to time the cam off#1 . And yes the ring in the damper can and does slip. Any engine I deal with I use a piston stop turning engine both ways untill it hits the stop ,half way between these 2 points is actual TDC. Use # 1 to do this of course.
"Ok so i found the mark on the crank gear it is straight up, and I think I found the mark on the cam gear it is off the nylon and on the metal little box with an ^ the cam was pointing at about 12 o-clock with the before mentioned mark. " You have to turn the crank 360 degrees and then the crank and cam gear marks will line up.
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