hey guys new to the group I have a freshly rebuilt Chevy 350, got it running yesterday but had some concerns, the timing was set dead on the distributor but it had a odd misfire. A friend told me that it could be the timing chain is off a few marks or the valves are closing how they are supposed to. Also having to have my distributor more advanced than what I would like and I also think there is a leak on my intake where it meets up against the head. I’m thinking about messing with the valve back lash but I am not sure. Thanks for any help.
Not sure on the misfire, check and make sure you have the wires in the correct firing order and that when top dead center on #1 that your rotor is pointed at the cylinder. You can also pull the valve cover to check the valve operation to check the timing chain is right as well with #1. As far as running it advanced that is determined by the camshaft your running. As far as the intake leak goes, make sure to put Teflon on the intake bolts, oil can work its way up the threads and pool.
The odd misfire could be a lifter handing up! Marvel Mystery oil could fix that problem if that is your odd misfire. Jimbo
Recheck the firing order, 18436572. If you are a true Chevy guy, memorize it. If you think you have a valve timing issue, check cylinder compression, it will be low across the board. Sent from my iPhone using The H.A.M.B. mobile app
Address the vacuum leak first. Run a compression check. are you plug wires good and in the proper firing order. you state freshly rebuilt. Did you break it in properly and not wipe out any camshaft lobes?
To check cam timing pull the easiest valve cover watch the valves on 1 or 6 depending on the cover removed turn the engine as the exhaust valve closes and the intake starts to open stop when they are both open the same amount look at the timing mark. It should be with in 5 degrees of TDC if more than 10 you are most likely off one tooth. Cams don't go flat during break in, the process only starts then if the break in is not done right.
I suspect we will see a lot more flat cams than in the past. Used to be Crane cams made the lions share of the camshaft cores used by all the big name suppliers. That equiptment went overseas when crane quit & sold out. Ive seen engines that had less than a hours running time with a new cam that wiped out lobes. Isky used to grind a groove around the lobes and fill it with molly.
Comp bought out crane some 3+ years back ,cams are not the problem ,it's spring pressures and oil and break in procedures that's wiping cams
Pull a spark plug wire one at a time at the cap if it is easier to do it there. Keep going until you pull one that doesn’t make a difference to the misfire that way you can try and isolate which cylinder is not firing. If this doesn’t help you can perform a compression check and look at the spark plugs when they are out to see what they can tell you. The compression should be even within 10 to 20 pounds per cylinder . If still nothing you could check for vacuum leaks. That’s somewhere to start.
Start with the basics first. Firing order. When checking rotor position at TDC it has to be on the compression stroke (#1 cyl.). Check the dist. cap for cracks or burnt terminals and the center carbon post. Check the rotor. The plugs could give you clues. A small vacuum leak will effect the idle and fuel mixture at idle. If you turn the idle speed out to compensate for the leak the throttle blade will not be in the correct position relative to the idle transfer slot. The intake and exhaust valves have to be properly adjusted as well. If it's points dist. you should verify the dwell. Timing. You just have to start eliminating one thing at a time.
For the most part I agree with the posts above. The only thing I have to really add is, if you have a vacuum leak, fix it first. Check timing in relation to #1 being at TDC compression stroke. Make sure the firing order is correct, if the misfire continues try to isolate it by removing a plug wire one at a time and seeing what it does to the idle. Another way to check is to use a an infrared temp gun on the header tubes to check for temperature at each cylinder as well. It will give you a clue but pulling the plug wires one at a time is my preferred method. If one cylinder is identified pull the plug, check the gap, check for cracks. I have purchased brand new plugs in the past and found them cracked after installing them when the vehicle ran worse than before plug replacement. The only thing new I have to add is does engine have an adjustable vacuum advance? It so, check to see when it is opening. Place a vacuum gauge on the line running to the vacuum advance. Note the reading. Then plug the vacuum line, place a vacuum pump on the vacuum advance and see what vacuum reading is on the vacuum pump when the advance opens. This check should be done with the engine running of course. For example, if the engine vacuum is twelve in/hg coming out of the vacuum line, and the vacuum advance is pulling at six in/hg the advance will already be open at idle and could cause a problem. Not sure what you are running. Hope this helps.
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