As Ricks79Duster340 said, the easiest way is to start diagnosing your problem is to measure the temperature at each exhaust manifold port. The IR guns are $25 at Harbor freight and they work great.
What's the best way to find a dead cylinder?
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You narrowed it down to an exhaust leak? Like your muffler has a hole in it or something? Really? Damn.
Dale Davies
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A few, guys pulling on the wires instead of the boots.
Dale Davies
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Exhaust leak?? NOPE. Now an exhaust valve is a possibility. Should hear a little kind of "pop" at the tail pipe.
Dodge73Dart
1973 Dodge Dart Sport restoration
And the mystery continues.
MILO
Well-Known Member
Easy to pull the valve cover start it up and see if all the rockers are working good
bcschief
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And while you're in there set the valve lash.
cruiser
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Okay guys. As promised, here's the data on my sick engine. The first six photos are the results of the leak down test on cylinders one through six. As you can see, several of the cylinders are way down from the 100 psi that was pumped in initially. The final photo is the compression values from cylinder six (top of the page) down to cylinder 1. Now I gotta decide what to do. Looks to me like a complete teardown. I do have a spare 225 engine from a 1974 Dart with only 83K miles on it. The dilemma is whether to rebuild the current engine (very expensive) of put the replacement engine in.
MILO
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I would put your other engine in it don't take too long
junkyardhero
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good lord. how was that even running with that amount of leak down.
anyway 6 & 3 are no bueno
it's a hard call with the spare motor. do you know if it was a good runner when pulled? how long's it been sitting? can you roll it over and get a quick and dirty compression check or leakdown?
if i could run some baseline on it and the test results met my criteria i'd be inclined to snap it in and run it.
anyway 6 & 3 are no bueno
it's a hard call with the spare motor. do you know if it was a good runner when pulled? how long's it been sitting? can you roll it over and get a quick and dirty compression check or leakdown?
if i could run some baseline on it and the test results met my criteria i'd be inclined to snap it in and run it.
cruiser
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Yeah, I was pretty amazed when I saw the leak down results. Remember, this is not the original engine from the factory. It is a parts store engine installed in 1988 at a repair shop in Portland OR. That's all I know about it. I can't attest to the quality of the rebuild job prior to putting it in my car in 1988. Kinda wish I had the original numbers matching motor. Anyhow, it's remarkable that the engine runs at all, but that's a testament to the durability of the slant six. My concern with the spare engine that I have in my garage is this: If I put the money into the engine swap (not going to do it myself because I don't have the tools and facility to do it with), what's to prevent something else happening to the replacement engine in 10K miles? Now, I just went and threw good money after bad.
Dale Davies
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OK, you performed a cylinder leakdown test. I notice the breather cap or oil fill cap are in place. I imagine the air filter was on and the throttle closed. When you perform a leakdown test, remove the breather or the oil fill cap and the air filter assembly and block the throttle open. This way when you find a low cylinder you can listen for hissing at the valve cover, carburetor and the tail pipe. This will indicate where the leakage is; rings, intake valve or exhaust valve.
When performing a compression test, again block the throttle open to allow full air in. 4 or 5 compression strokes are enough. After doing a "dry" compression test you can squirt a bit of oil in any low cylinders. A pump oil can works well and on a slant or Vee engine, a bit of hose on the end will let you get the oil to the high side of the cylinder wall. You need to fill the hose until oil just starts coming out to make certain you are getting oil delivered to the cylinder wall. Just 2 or 3 pumps is enough. If the compression pressure comes up, the problem lies in the rings.
If on the leakdown you hear no hissing, you could have a bad cam. Remove the rocker cover and use a dial indicator to measure how much the intake valves open to start with. Valves that open say 0.100" less indicate a cam lobe worn.
I recommend doing the leakdown again as I describe and then if notbing shows there, check valve lift. A bad exhaust will cause it to run rough but compression can still indicate good.
Nail the source of the problem before getting serious with the wrenches. If it turns out to be valves you just need to remove the head. You could think about larger valves and pocket porting while doing that. If it is the cam you can change it with the engine in the car. Radiator definately needs to come out. Pain in the butt getting the lifters out and degreeing a new cam, but then pulling the engine is a nusance also.
Oldiron440
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Exhaust manifold runner temp, check with heat gun or bottle of spray water.
junkyardhero
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it's a straight roll of the dice.
you can perform the same tests: cranking compression, leak down, scope down the bores, check the plugs, give a visual to the valve train, check the oil. pull the pan and check the bearings.
that would give you a better picture of were it's at, but it wouldn't necessarily tell you if the head gasket it going bad or the timing chain has an *** ton of slop in it. to get there, you'd need a tear down.
so armed with that info, you could decide if it's worth the risk to do the ol' rattle bomb rebuild (gaskets, oil pump, timing chain) and ship it or drop the coin and do a full tilt rebuild.
the cake cuts the same no matter how you approach it. spend a lot and get a sure thing with a warranty or some kind of assurances; spend a little and accept the risk involved.
Without seeing the inside of an engine, or building it yourself, there is no way to tell other than compression and leak down testing. But then, even if it tests good, like you say, how do you know how long it will last? Really only one way I would go.
junkyardhero
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nuthin' a 3/4 race cam, an 850cfm 4bbl and 3800 stall converter can't fix.
Having to pay for the swap complicates things.
Is there a trans or at least a flywheel and bellhousing on the extra engine? I've fired them up on the ground before.
I see 2 options, I've done both before at different times.
Swap out engines being you have another sitting there and rebuild the one currently in the car, swap back in when you get the one now in car rebuilt:
Or, rebuild the one on the ground and then swap.
Did you hear any air escaping when you did the leak down? Out the mouth of the carb? Out the exhaust?
Were you sure each was at TDC with the valves closed when you put the air to each hole?
Is there a trans or at least a flywheel and bellhousing on the extra engine? I've fired them up on the ground before.
I see 2 options, I've done both before at different times.
Swap out engines being you have another sitting there and rebuild the one currently in the car, swap back in when you get the one now in car rebuilt:
Or, rebuild the one on the ground and then swap.
Did you hear any air escaping when you did the leak down? Out the mouth of the carb? Out the exhaust?
Were you sure each was at TDC with the valves closed when you put the air to each hole?
Charrlie_S
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I bought a "supposedly" good used engine (V-8) for my truck (bad rod knock). Set it on the ground, put oil & filter in it. Installed oil pressure gauge, pulled distributer and installed a pump drive shaft, oil pressure at about 35 lbs. Pulled plugs, rigged up starter, cranked engine over. oil pressure good but took a 10 lb drop every revolution, then came back up. Compression good on 6 cylinders. # 1 & 3 zero. Leakdown showed exhaust valves. Pulled valve cover found two stuck valves, and bent pushrods. Engine not going in as is.
Actually decided to tear down. Most bearings had copper showing, Two pistons had broken rings. # 1 & 3 exhaust valves were bent, and seized in their guides. Didn't like the looks of the crank or wear pattern on the cam, so crank kit, cam and lifter kit with timing set, hone and rering. Valve job, and resize guides.
You can tell a lot about an engine out of the vehicle, without even starting it. So, check your spare engine to see if it is worth installing.
Actually decided to tear down. Most bearings had copper showing, Two pistons had broken rings. # 1 & 3 exhaust valves were bent, and seized in their guides. Didn't like the looks of the crank or wear pattern on the cam, so crank kit, cam and lifter kit with timing set, hone and rering. Valve job, and resize guides.
You can tell a lot about an engine out of the vehicle, without even starting it. So, check your spare engine to see if it is worth installing.
Dale Davies
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Dale Davies
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A simple way to check the timing chain for wear (stretch) is to bar the engine over to TDC. Then with the breaker bar, try gently rotating forward and backward feeling for the slop. The cam and valvetrain restrains the rotation. A new chain may have a couple of degrees back and forth, while a worn chain can have 10 degrees. Don't have to take anything apart.
cruiser
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Yeah, rebuilding the spare engine, then installing it when finished is looking like the best option right now. Yes, the valves were closed with the piston at TDC when the checks were made. Air was escaping around the pistons into the block.
MILO
Well-Known Member
If you were closer I would put the engine for you it is easy, usually the first thing to go on a slant six when the mileage gets high is the plastic gear on the end of the distributor and I have replaced a few of them other than that they will go a long way
chryslercruiser
Member
Do some simple tests on the spare engine, and find out if it actually needs rebuilding! Or Pay someone to do the tests to find out if you have an engine that needs to be rebuilt. Slant 6's are durable engines, and the likelyhood that you have two that both need rebuilding is uncommon.
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