Compression test only at 90 psi max, timing chain off?

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zig

zig

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I had a post a few weeks back about not being able to start my car. It is a 340 Duster that I had machine work done, I assembled it with a book to put everything to spec. I just ran a compression test and maxed out at 90 psi on almost all the cylinder. I had 2 that were only about 75. I don't believe this is high enough. It sounds like combustion doesn't happen until a minimum of 90. I did add some oil to each cylinder and tried again, had luck on a few, but still nothing higher than 90.

So next step, could the timing chain off affect the compression? I am going to tear into the front to get at the timing chain and check that. The heads were done at a local machine shop. I installed the rings per instructions and put plenty of oil on them.

I hope I didn't screw something up, but it's not looking good... Hopefully it's only the timing chain. I did install a comp cams XE274 and am using stock pushrods. Could that affect anything?

Any guidance is appreciated for my first build...
 
Something to check would be cam timing. Almost everything in the world has the dot on the cam gear and the dot on the crank gear lined up and facing each other at 6:00 on the cam gear and 12:00 on the crank gear. Not so on a smallblock Mopar. The dot on the cam gear should be at 12:00 with the crank gear dot also at 12:00. They won't fire if they are 180 degrees off. Hope this helps.
 
I'm not sure the compression numbers mean anything since the engine hasn't run and the rings have not been seated? Did you try swapping the dizzy 180* as was recommended in the last thread?
 
grumpuscreature said:
Something to check would be cam timing. Almost everything in the world has the dot on the cam gear and the dot on the crank gear lined up and facing each other at 6:00 on the cam gear and 12:00 on the crank gear. Not so on a smallblock Mopar. The dot on the cam gear should be at 12:00 with the crank gear dot also at 12:00. They won't fire if they are 180 degrees off. Hope this helps.
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Line it up dot to dot, put the distributor on #6............
 
And the cam and crank dots face each other, NOT at 12 and 12. It doesnt make any differance though, if you set the cam at 12 o clock and the crank at 12, turn it one crank revolution, and they will be lined up.. I would check pushrod length first, and check your compression gauge in a known good engine before tearing anything back apart..
 
How much run time on the motor? Did you try a leak down test? Do you know the compression ratio? 75 psi should be enough to fire gas, the thing I see that stands out is the pressure difference between holes.
 
I did rotate the distr 180, still no luck... It is a brand new engine, never fired. I can try the gauge on my car. It is a brand new gauge though... I thought I had the dots lined up to each other at 12 o clock, but it has been several months and I am second guessing my self. I am going to order a tool to measure push rod length tonight from summit... I get fuel and spark otherwise... just no ignition...
 
grumpuscreature said:
Something to check would be cam timing. Almost everything in the world has the dot on the cam gear and the dot on the crank gear lined up and facing each other at 6:00 on the cam gear and 12:00 on the crank gear. Not so on a smallblock Mopar. The dot on the cam gear should be at 12:00 with the crank gear dot also at 12:00. They won't fire if they are 180 degrees off. Hope this helps.
Click to expand...

I just re-read your post... I am pretty sure I lined up dot to dot. Maybe I am 180 off on the timing chain? A friend of mine with more experience on this is coming over sometime this weekend, I'll have him check it out more..

Thanks for the replies.
 
grumpuscreature said:
Something to check would be cam timing. Almost everything in the world has the dot on the cam gear and the dot on the crank gear lined up and facing each other at 6:00 on the cam gear and 12:00 on the crank gear. Not so on a smallblock Mopar. The dot on the cam gear should be at 12:00 with the crank gear dot also at 12:00. They won't fire if they are 180 degrees off. Hope this helps.
Click to expand...

OldmanRick said:
I'm not sure the compression numbers mean anything since the engine hasn't run and the rings have not been seated? Did you try swapping the dizzy 180* as was recommended in the last thread?
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Seems like both orientations would be correct since the cam spins at half the speed of the crank. The dots will line up at 12:00 - 6:00 and again at 12:00 - 12:00.

I would position the distributor so the rotor points to cylinder #1 when #1 is at TDC.
 
I've got the distributor lined up with #1. I do have stock rockers, pushrods, just upgraded the came with new lifters. Heads were redone with new springs for the .480-.500 lift. Still no fire..
 
I used KB hyper. stock '73 340 block, stock rods, crank, pushrods, comp camXE274 with new lifters, j heads with valve job and 2.02 intake valves put in. Air gap intake, rebuilt thermoquad... Nothing to crazy...
 
Are you checking for spark from the coil wire, or the spark plug wires? Could be a chance its not making it to the spark plugs.

Here's another good one to check, because I had Spark & Fuel on my '74 Duster the last time I dropped the engine in the car (after more upgrades and a new Accel 300+ Ignition System). Like I said, it had Spark & Fuel but I couldn't get the engine to fire no matter what, not even a sputter.

My dad walked over, looked under the hood and immediately pulled the spark tester off, slapped a spark plug in and set it on the intake and told me to hit the key. No Spark with a Spark Plug (but it showed up great on the tester). He laughed and said "Your ignition box isn't getting a good ground." Sure enough, I changed the Ground Wire from the Body (Where the Accel Instructions told me to put it) to the Battery and the engine fired right up at the tap of a key.
 
zig said:
I used KB hyper. stock '73 340 block, stock rods, crank, pushrods, comp camXE274 with new lifters, j heads with valve job and 2.02 intake valves put in. Air gap intake, rebuilt thermoquad... Nothing to crazy...
Click to expand...

Even un run you should have more cranking psi than that.

I run those same pistons with an int closing of like 52 and have about 155-160psi fwiw
 
1wild&crazyguy said:
Even un run you should have more cranking psi than that.

I run those same pistons with an int closing of like 52 and have about 155-160psi fwiw
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my 360 only had 60psi,dot to dot.it has 160 cross the board now .the cam was 4 degrees off.
 
I'm betting with numbers that low it's gotta be either timing or pushrod length. I wouldn't even worry about the spark and or distributor timing until you get the psi figured out.
 
Thanks again for all the replies. I definitely have spark at the plug. I check each one when doing the compression test.

I am thinking timing chain also. I am going to tear in to it this weekend. I remember using an edelbrock timing set and the instructions were confusing to me at least. It seemed like a generic set and said point timing marks at this for this motor, that for a different motor, etc... So I probable lined up to the wrong mark. It has been 8-10 months since I did it, so who knows what it is...

A guy at work is bring me a timing wheel and push rod tool to measure that also. It is worth a try, but trying to figure out how the push rod length could have change. Unless they decked my block or heads more than the machine shop really told me...

Next round of trouble shooting...
 
You don't need to tear it down to confirm cam timing.

Use a piston stop to confirm where TDC is

Get a degree wheel. Get an indicator OR JUST USE YOUR EYEBALLS and see where some of the timing events are happening
 
Some of you guys are gonna have this guy so screwed up making a big deal about the "line it up to 6 and 12 O'clock" or "line it up to 12 and 12 O' clock" or it won't be right. As pointed out by replicar and 65Dart GT the cam spins at half the speed of the crank (that's why the cam gear is exactly twice the size as the crank gear) and if you do line up the dots at 12 and 6 O'clock and spin the engine exactly 1 revolution the dots will magically be at 12 and 12 O'clock. When their at 12 and 12 O'clock that's TDC #1 firing (compression stroke). When the dots are at 12 and 6 O'clock the engine is at #1 TDC exhaust stroke. Remember guys our engines are 4 cycles so there is 2 top dead centers per combustion cycle.

Zig my guess is the cam timing (timing chain) is off a tooth or 2 or maybe you got an improperly ground cam. That's why all cam's should be degree'd in upon install. It eliminates any guessing. I'd first verify the new compression gauge is accurate and if it is you have 2 options, do like 67Dart said and see if it looks close or take off the front cover to verify things. When the engine is in the car it's not the easiest thing to look down and see if the dots are lined up so I use a straight steel ruler held on the center line of the crank and cam to see if the dots are lined up. And if it does happened to be lined up I'd degree it in to make sure you didn't get a junk cam. It doesn't happen often but it does happen.
 
Hard starting engine washing down the cylinders with fuel probably doesn't help with compression
 
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