Need help. Just finished a rebuild on the 350 in my 75. Stock block bored .040, vortec heads, etc. Tried to fire her last night and no go. One backfire from exhaust, small fuel spitting from carb. Thought I had the distributor in 180 degrees off. Moved the wires around many times and got no better results. Engine was torn down completely and I installed the cam straight up. I rechecked for top dead center on number one cylinder and stuck my thumb over the spark plug hole and turned the engine. No compression! I didn't check any other cylinders, but the engine just didn't sound right when turning over. Like there was no drag on the starter and it spun too freely. I am not the world's most experienced mechaninc and my initial thought is I have the valves adjusted too tight so they are not closing on any cylinder! Installed the cam with the dot on the crank sprocket pointing north and the dot on the cam sprocket pointing south. Should this not have given me TDC on #1 piston? Could I have the cam in 180 degrees off? Before I start redoing everything, any suggestions?

Thanks!

 

You can't install the cam off by 180 degrees, either dot north or south doesn't matter as the cam spins at 1/2 the crank speed. The only thing that changes is the firing position for #1. It's easily checked if you are TFC during overlap or TDC for firing, if before & after TDC the exhaust valve closes and intake opens you're at overlap. It's pretty difficult to see when you don't move the crank, at overlap boh valves are slightly open but it is easily mistaken as being closed, that's why you move the crank to see what they do. ?If both remain shut you're at firing TDC .

Now, this all does not affect the compression, you have a leak somewhere and it's there on all cylinders which is weird. Make sure all the valves are not adjusted too tight.

 

TDC is when your (A.)timing mark on the balancer is at the zero(or close) mark on your timing pointer, (B.)#1 cylinder is at the top of the compression stroke (I use a straw inserted thru the spark plug hole to locate piston). C. The rotor is pointing to the #1 spark plug wire on the distributor cap.

If you balance is at zero but the #1 piston is not at the very top of the cylinder, you're not at TDC.

 

Too much lash. Your valves are hanging open.

 

Double check you valve lash, one valve might not be closing all the way.

 

open it back up and install the rings...

 

loosen up your valves just until the pushrod has the slightest play in it!

then fire it up and adjust them until you can hear the ticking just go away. I had this exact problem the first time I tried to adjust my valves by a book before I installed the motor.

 

Speaking from the experience of receiving a car after an inexperienced "mechanic" (professsional) tried to adjust the valves and set them too tight, go back and recheck the lash. Overly tight valve adjustment will hold the valves off their seats, resulting in no compression on any cylinders and a free wheeling starter.

And if you tightened them far enough for the valves too collide with the pistons, be prepared to remove the heads again to replace the bent valves. And pushrods:


Steve

 

I had my heads reworked when I rebuilt my engine and the valves weren't seating well and it caused a similar problem for me. I shined a light through the ports and saw light from around the valve seats.

 

Maybe off base here but...maybe the lifters were not pumped up when adjusted...

 

I can help you with part of the problem. The crank gear dot north and the cam gear dot south is #1 TDC EXHAUST position, not #1 TDC FIRING position. We had a thread about this common misconception a while back. With the dots the way you had them, you need to have the rotor pointing to #6, not #1 when you install the distributor. The other way to get the distributor firing right is to have BOTH dots pointing north. That is #1 TDC firing position. You use the dots pointing together to get the cam timed properly to the crank but after that you can rotate the crank 360 degrees and both dots will be facing north now. You can then drop the distributor in with the rotor facing #1 tower on the cap.

The other problem is probably the valve lash setting. Loosten all the nuts and wait a few minutes. Tighten them with one hand while you move the pushrod up and down with the other hand. Stop tightening when the pushrod stops moving up and down freely. then go 1/4 turn more. Rotate the engine 360 degrees and recheck for any pushrods that are now able to move up and down freely. Repeat the adjustment on the loose ones only. If this has been done propely you will be able to lean hard on the rocker arms and slightly compress any lifter that is all the way down on the base circle of the cam.

Do these 2 things first then see if you can get the cam broken in.

2000-3000 RPM for 1/2 hour with NO IDLING time at all. Add an extra quart of oil to put you a quart over full. Add a bottle of EOS purchased from the GM parts counter before start up.

And Good Luck!

-Mark.

 

You should NOT pre-fill or pump up new lifters with oil. Doing so can cause exactly this problem. If the lifters do not bleed down, you end up with a hydraulic lock. When you do lash the rockers, they hang the valves open until they do bleed down which, on some assemblies, may not occur for a very, very long time. When hydraulic lifters are installed, they are installed dry. Once you set the lash, it takes only a couple of turns of the crank to pump the lifters up and you'll have the .060(standard lifters or .020 with anti-pump ups) or so preload and an engine that actually runs. If the lifters are pumped up and you need to set the preload, then you have to do it with the engine running as described above.