Author Topic: Cold Engine Compresion? (Read 2942 times)

egspot · « **on:** November 23, 2005, 06:39:33 AM »

Before I go on and open a long block to rebuild it, I will like to know if I need to do so.

I got a long block outside. Can not get it started to warm it up and cant not crank it with a stater. I tried test the compresion anyway. The reading was between 40 and 45 psi.

Does anyone know what this translate to at operating temperatures. I know there would be a substantial increase but have no idea what the factor or formula would be?

Emilio

Cameron · « **Reply #1 on:** November 23, 2005, 11:24:32 AM »

Those numbers do seem kind of low, 40 to 45 psi. With a good starter and battery, properly adjusted valves, and the motor in decent shape, you should be able to get over 100 psi. I usually look for a difference in numbers. I would be concerned with huge differences, or one cylinder out of whack with the rest . A more accurate way of determining motor health is a \"leak down test\".

BUSDADDY · « **Reply #2 on:** December 03, 2005, 05:03:40 PM »

Just how did you test the compression if you can't crank it with a starter

egspot · « **Reply #3 on:** December 03, 2005, 05:59:09 PM »

Quote

Just how did you test the compression if you can't crank it with a starter

I turned the flywheel manually 5 turns, I figure the chamber was cold but sealed. (kind of stupid maybe.)

The one thing is that when the engine is hot the compresion will be much higher but, My old brain does not remember the physics formula.

Emilio

BUSDADDY · « **Reply #4 on:** December 03, 2005, 08:16:16 PM »

Wow, 40-45 ain't bad for cold hand turning. Big muscles!
Did all 4 cyls feel the same as you turned it (equal resistance/ compression) ?,If the spark plugs don't look all black and oily and are consistent color you might have a winner there. but what's happening in the bottom end? I've had engines that were heros for compression and power and didn't burn oil but had a loose bottom end (low oil pressure, hi oil temps, ticking rods decelerating, etc,)
If it was me and it's out of the car and bare, at least pull a head and the cyl's off of one side and peek inside (don't mix up the cyl's and pistons) You can remove a rod and see how much the bearing is worn and generally get an idea how black and gooey or clean and new it is inside the case. Check for a ridge on the cylinders too.
Iv'e seen engines that have been sitting awhile contaminated with rust flakes from the con rods ( kinda looks like coffee grounds) that craps worse than sand and considering you likley don't have an oil filter it goes around over and over and.... Well you get the picture. now's your chance to flush it out. Don't forget to lap the barrels in the head and change the mainseal while you are at it.
IMO better to spend a few extra hours now then many hours sitting on the side of the road.

kit · « **Reply #5 on:** December 05, 2005, 05:14:17 PM »

if i remember correctly the compression was in the green on this motor but cant remember the numbers, this motor was supposed to be a rebuild but didnt look very clean so i took it out and went with a turnkey to save myself some headaches, good luck eggspot. did you take out all the plugs before your test,you need a starter and at least five cranks per cylinder

egspot · « **Reply #6 on:** December 05, 2005, 08:05:46 PM »

Yes I took the plugs out to test but did not have it mounted on a trany.

I have made a shot block to inspect it. I was about to split the case. The piston and the ring look very good with the exeption of evidence of oil and carbon. Just like Kit stated. I may just clean the pistons, put new rings, and get the heads clean and the valves seats done. and put it toguether again.

Then I can find someone to guide me in rebuilt my AE block Which the more I plan the more I want on it.

Thanks Kit

Regards,

Emilio