A lot depends on when the intake closes ABDC. Don't forget that when you are cranking the engine to measure compression, the air is being heated as it is being compressed (think diesel) thereby increasing the pressure above what you would expect using the simple math of 14.7 X 9.5. This is exaggerated even more if you are testing compression on a warm engine. So if your intake valve is closing shortly ABDC, it shouldn't be a surprise if cranking compression reads higher that the expected number derived by simple math. All that said, 200 does seem to be quite high given the engine build specs you've given.
I don't know if this could be part of your problem but I had a set of heads redone with viton seals and the guy put on seals that were for a 1/32" larger valve stem. Kept fouling plugs, had knock, used a ton of oil. I thought it was a leaking intake gasket, when I pulled the intake there were puddles of oil on top of the closed valves and the gasket looked good. Change the seals and all is well.
the vac advance is only for fuel milaege on light throttle, forget vac advance, disconnect the line (Forget the vac advance!) set the timing with the dist to whatever max advance should be, when you have that what advance do you have at idle? when and only when you have everything else sorted out re plum the vac advance from a port on the carb, NO manifold vac for the advance has to be off the carb! stop mucking around with vac advance
Change the carb to one that is known to be good. I had my truck doing what you assay, replaced the carb with another one I had on the shelf which I thought was good, ran the same, I thought for sure it was distributor aft I rebuilt the carb and blew through every orifice. I did a complete tune up and still ran like shit. Threw on a Holley and now runs like a top.
There's a whole lot of information here But save yourself the frustration and aggravation and getting mad. Focus on finding out why your compression test is showing 200. Re verify that those numbers are correct, & if they are that's the root of your problem and showing many symptoms. Talk to your builder. You may have timing plate issues but that's not what you should focus on.
Don't use two PCV valves, only one on the opposite side of the breather, it will become a vacuum leak. What is your TOTAL mechanical advance at 2500 rpm??????? It should be all the way to max, change to lighter springs to bring it in faster. Your mechanical advance takes over when the manifold vacuum advance falls off. Venturi vacuum was used back in the 50's on distributors with no mechanical advance and Ford distributors in the 70's to retard the advance at higher rpms....... 210 compression.....mmmmm..... we had 225 and were running 14.5 compression (alky engine) sounds like you need to run straight 93 octane with no mixing. Or find 90 octane lawn mover gas (no alky added)
This is turning into a classic example of how to not solve a car problem! Bouncing all over the place, jumping from one thing to another. This is NOT how it is done. Need to slow down and work one issue at a time. If it did improve it would be hard to figure out what solved the problem. Set up a plan and address things one issue at a time. Do a little research so you understand what your doing. The vacuum advance is a good example, need to understand what it is and what it does before you start attempting to redesign it. The above advice on timing is good. First establish where TDC is, you have to have a place to start. Then plug the vacuum advance and forget about it! Now set the timing correctly and check it over the RPM range to see how it is advancing and where (RPM) it is max and what that max is. Now test drive the car and then move to the next issue, such as figuring out what your compression really is and why.
Here is the latest data. The engine runs (idles) much better with vacuum advance connected. Without the vacuum advance, the idle is low and crappy. I need to crack the throttle a little to get it to smooth out. When revving it, it runs better on full manifold vacuum, rather than ported vacuum. Either way it has a dead spot right when I crack the throttle well open. It has 15# manifold vacuum. By reading the adjustable timing light...I have 5 degrees initial timing, 15 degrees with the vacuum advance and 32 degrees total mechanical. After Revving it, it pops through the exhaust, with or without the advance connected.
EXCELLENT advice! Fix one issue at a time. 1. Establish TDC and put timing tape. Set the timing to what engine builder told you to. 2. What kind of distributor? Points? Get rid of the vacuum advance. Might need distributor advance re-worked. 3. Get the detailed cam specs (i.e. cam card) and post them up for us to see. 4. Stop being a tightwad and put the best high octane gasoline that you can find. 5. If it still doesn't run right talk to the engine builder and see if he can help you tune it up correctly. Just my 2 cents
I am working one issue at a time. 1. Fixed the oil suction problem from the PCV valve. 2. replaced oil fouled park plugs. 3. added 91 octane gas to tank (best available around here). 4. Set total timing and checked mechanical and vacuum advance. Since I can hear it popping through exhaust I am wondering if cam is going flat or if HEI module is bad or something else. The cam is small (RV style). The popping is a new symptom. It is more than a leaking header gasket, definite popping after revving it. I will pull the HEI Module off and have it tested at Autozone. I am also going to pull valve covers back off and check each rocker to see if moving correctly. I will also mark the pushrods as suggested and watch to see if they are spinning.
I agree. I don't see where the OP addressed the pushrods. If you have guide plates are they correct for the pushrods. As the pushrod rotates, if bent, it can hang up. Could explain the inconsistancies you are having
Yes indeed you need to baffle the PCV valve, you can buy a baffled grommet from Mr. Gasket that works well. Anyway tfeverfred is correct here as always. Pro-built is a nominal term in general and even more nominal term here in the mid-west where incompetence is the name of the game. It is unethical for us to bad mouth other builders so this is not a slam against your particular builder but the truth of the matter is that just because someone charged you to build it does not make it pro built. That said there is a reason that you broke a valve spring and that reason makes the whole engine suspect. Either someone cut corners on the springs, or they are binding or they are just not enough spring for the cam shaft. I would be in there checking them myself or have the engine back to the builder. Then you got the leaking timing cover seal, one of two things, it either was not changed and or torn when the balancer was installed or the balancer itself is worn where it passes through the seal. Something that a "pro engine builder" should not have missed. I would be to the builder before I went any farther and ask what parts he actually used and want to see receipts for them. let me tell you a story, when I first joined the HAMB I had a headache with a pro-built +.030 400 SBC. I was getting compression readings all over the board, it wouldn't pull a sick old woman off a bed pan and I could not tune it out of it. So I called the "Pro-Builder" and asked him about it. he couldn't tell me what he used for rings or pistons, his excuse was that he built a lot of engines in the last year. I had to call BS on that, I have a box of paperwork in the basement that represents 40+ years of engine building from my old man. Every last detail of every engine that passed through his business. Anyway I digress, my only option was to pull the engine down, mismatched pistons, chrome rings on some cylinders, cast on others, egged journals on the crank. I could go on but you catch my drift right? Do not mess around with it, go back to the builder and find out what was actually done to it then start from there. If he cannot tell you then you know that you are going to have to make it right yourself. OK sorry for the rant, something else to look at, check your rocker studs, are any of them sticking though the rocker farther then others? That indicates one of two things, flat cam or stud pulling out of the head. When you replaced the valve spring did you notice what kind of seals were used? Umbrella seals are your best bet even on new heads on used heads they are a must. I cannot tell you how many GM motors I have pulled apart that still had the little rubber bands in the valves, that will cause oiling of the cylinder every time.
This is spot on! Get your advance and curve dialed in before you mess with anything else. You should be looking for a total advance of about 36 or so, and stop screwing around with the vacuum advance, because in the situation you are dealing with it's simply confusing the issue. 4 or 5 degrees of initial advance is in my opinion a bit low for a small block, even if your compression is jacked up to the moon. What I have done before, and what I would tell you to do now is head out to Harbor Freight and drop about 30.00 on a dial back style timing light. Mine purchased ten years ago had an instruction sheet that read "Congradulation, you purchase velly fine timing right..." still works great. Then, get some one to help you and plot your timing curve. Check and record the timing events at every 500 RPM from idle up to 3000 or so. At least at that point you'll have a baseline so that you can see what needs to happen with your curve. Take the vacuum advance out of the equation completely for now, then reintroduce it later for it's intended purpose of adding extra timing in at light throttle applications for extended highway use and such. It's kinda hard to explain, but the way you have it set up now tells me that your engine is kinda happy at about 20 degrees of initial. The second you tip in, the manifold vacuum drops, and your vacuum advance goes away. Your mechanical advance starts to climb, but there is a point in all that chaos that it isn't getting a proper amount of either's effects. Go back, run some baselines and figure out what you need before you endlessly tune until your mind explodes...
The HEI module tested fine. I noticed the two separate wire leads were a bit loose on the tabs, so I will tighten them when I reinstall the module. I now have a different symptom, popping out of the exhaust when it is dropped off of a high rev. When I revved it to 3000 to check timing, and let go of the throttle linkage, it pops quite badly through the exhaust., with or without the vacuum advance connected. This was never a (known) issue before. Could a cam going flat cause this to happen? I will pull valve covers and check the rockers and push rods.
That could be an exhaust leak as much as anything else. If your dizzy is working then I wouldn't worry about what I am going to say, but just for information getting an electronic tested does not mean that it is correct. I chased a problem in a small block for about a week. It ran like it had a governor, *first thing I did was have the distributer tested. It tested fine and was a new distributer, but in my mind I knew that the distributer was the problem. Finally out of desperation I pulled the distributor out of my truck and dropped it in. The little SBC ran like a top. *The distributor was tested at a local distributer shop of good reputation. I would go back there for distributer work today.
Pull the timing cover, look for bad timing chain, rubbing parts and do the timing marks align correctly to cam specs at TDC
I double checked the valve adjustment on one head while I was inspecting the pushrod spin. (waiting for it to cool down to check other side) 1. All pushrods on that head spin, two were fairly quick (4rpm), but most were pretty slow (1 rpm). The valve adjustment was right on. I gave it time for the lifters to pump up and revved it a little between loosening and re-tightening the lifter, just to make sure they were pumped up. 2. Engine is running VERY rich. Black smoke from exhaust at idle. Is there something on a Quadrajet like a power valve, that I might have blown out? Did my removing the module to test it effect something?
Timing chain is fine. I've had two mechanical issues....1. Broke valve spring (seems to be repaired correctly) and 2. Loose distributer that spun and retarded the timing. The late timing is what I'm afraid might have done some kind of damage. When I accelerated onto the highway it blew black smoke out the exhaust for 3-4 seconds as I limped it home.
What do the slow spinners correlate to? Where Broken spring was? Side that's popping ? The odd ball slow ones are indicative of different circumstances than those that are spinning, could be adjustments, components, or wear patterns on lifters. But they should all spin noticeably equal not unequal.
Vicky, Sometimes a slow spinner is an indication of a bent pushrod, making contact with the guide hole in the head. A broken spring could cause more then just a damaged spring. Just adding to the thought process here.
As others have noted do the leakdown test it will show if you have bent valves, valves not seating, tight valve guides, rings not seating, being you had a broken valve spring that red flag would make me look at that cylinder and valve under extra scrutiny, a leakdown test is going show which cylinders have beyond acceptable leakdown percentages. Another question that is easy to check, it is common to overlook on a small block Chevy's is check and see that no.5 and no. 7 spark plug wires aren't swapped, especially if you have had the dist cap and wires off multiple times. Posted using the Full Custom H.A.M.B. App!
Bought a stop bolt to verify zero degrees. Since It seemed to be running rich, I looked down carb and there is no dripping. I turned idle adjust screws and it stumbled...hmm is it oil smoke and not fuel? I checked the PCV valves and they are clean and dry. Could it be oil in the headers from it sucking oil before? Or broken rings? Or manifold sucking oil? I'll check the plugs first. Then I will run a leak down on number 6 (the broke valve spring cylinder), and then on all of the cylinders. Still pops through exhaust. I also have a second (known good) distributer to swap in just to verify if mine is working correctly.
Swapped distributer, rotor, cap, coil and it ran the same, maybe a little smoother. Still popping through exhaust after rev, and smoking. Tailpipe feels oily inside. Going to Harbor Freight to buy a leak down tester. Could the popping be oil burning in the exhaust pipes? It does not pop at high rpm, but on the way back down, when the throttle is closed, and then only once or twice. On a side note - the engine sounds stronger than ever.
Caution. Harbor Freight leak down tester is only designed for 25 psi as are most of the less expensive ones. You need 80 psi to do a proper test.
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