low compression SBC - HELP!

NYSpeed Automotive
1

i just finished the motor on my vette and after everything was said and done and we went to fire it nothing happened. Has gas, has spark, i ran a compression test and got about 25 pounds or less on every cyclinder. i decided to reuse the heads off of my old motor because they never have me a problem, 1.94 decked ported and polished with 1.6 roller rockers. they are tourqed to spec and the motor was put together the correct way. there was 2 bent push rods. the valves were correctly adjusted. am i missing something or is it possible i have some bent valves? im at the point where im sick of looking at the car because its been in the garage instead of being driven all summer. any suggestions let me know.

thanks
andrew

2

who did the bottom end? could be inproper ring size. I’ve seen so many people overhone motors for stock rings.

3

If every cylinder is that low, it’s likely not just a few bent valves…if it were valves, i’d think that would have to mean they were all bent lol, or at least most of them.

I’m by no means a mechanic, but i’d start with the simple things to check like spark and fuel, which you already confirmed…next i’d check to make sure the timing was dead on.

4

readjust the valves first

5

Cam could be way off. Are you sure the timing chain is lined up correctly?

6

^^^yea valves could be open at wrong time but depending on the pistons you have you could have smacked a valve with the cam being off and now have bent valves. also did you check ring gap when putting it together? if those cylinders are too big for the rings itll do no good.

7

What did you have done to the motor since the last time it ran? why was it apart?

8

You said there are 2 bent push rods. You found these after you tried starting the engine?
If you did, the cam is likely in wrong and the valves are hitting the pistons.

9

I’d def say cam timing.

10

sounds like the sam is off :gotme:

11

Yep, he accidentally the sam

12

he accidentally the whole thing.

13

to put it best… no more putting motors together while drunk… i put the timing chain on with out matching up the timing marks… it now runs great. thanks for all your help

andrew

14

lmao ya, timing chain not on right will def cause low/no compression, as well as not having your valve lash properly adjusted

15

Consider yourself extremely lucky that you didn’t seriously screw something up.

16

that damn sam…

17

im guessing its a pretty mild motor as nothing got fvcked.

glad to hear its running.

18

Good to hear you got it running…BUT, I would pull the heads and check for damage if I were you. You said you bent 2 push rods. At least 2 valves hit pistons. You may have bent/damaged valves that could fail down the road without warning. Usually, when a valve breaks it’s fairly catastrophic. I’d pull all the valves out too. Chuck them up in a drill press and spin them to check to see if they’re bent. Additionally, if you’re running cast pistons, you may have cracked a piston that you don’t know about yet. Just my .02, but I’d err on the side of safety