Compression Testing For Sticking,bent Or Burnt Valves?

[toofun]

Doing a compression test on my new motor because I have run into some major problems. SEE MY POST ON BROKE IN CAM NOW POPPING NOISE. Anyways I have decided to do a compression test on my cylinders because I have been told that it will let me know if I have a bent or hung up valve. The test on one side of cylinders was as follows #2 210 #4 210 #6 210 #8 190 I have not done the other side yet and did not warm up the engine before hand due to the fact that I cannot start the DAMN THING!!

So I guess I am asking if this difference in the #8 cylinder is excessive? Does this mean I have a bent valve or a valve that is hanging open? All the rockers are loose and the motor has 500 miles on it the heads, cam and rest is all new. If I had a bent or stuck open valve wouldnt the cylinder not hold pressure at all? Trying to eliminate the possibility of a stuck or burnt valve if I can help it so I can move onto the next thing.

Thanks
Mark
TOOFUN

[pushrod243]

it wont have any compression if it has a bent valve. The difference you see although not perfect but definitely not your problem. I like to use a leakdown tester for a more accurate way of seeing where i am losing power from. If you have leakage you can usaully listen to determine if it is going out the intake, exhaust or into the bottom end. If you dont have access to a leak down tester you can still put air into the cylinder and see if it holds pressure. Obviuosly you want to do this with the both valves closed. If you have leakage you will hear air escaping. if you hear it in the intake its a intake valve, exh=exh valve, oil pan=rings or worse

[yody]

Hey! take your head out of your butt, your motor is probally fine, you need to take care of the basics before jumping and thinking your motor is broken, this is a newbie reaction. Stop thinking so hard, and get the basics taken care of, then post and go from there, your compression is fine.(being hard on you but it will help you in the long run)

[Jagarang]

We all need to learn at some time and it's easier if your not embarrased when asking questions to probably one of your better resources. I see by reading the other post that your doubts have not been quelled by Yodys' advice.

Try this article Mark. http://www.popularmechanics.com/automotive/sub_care_clinic/1271886.html
Less than 20% between cylinders is usually OK. Less is better of course but that will give you an idea.

In your case 210-20%=168 . The 190 is ~10% down from your others.

Jitters when dealing with new motors are VERY understandable. When I built and installed the first 350 into my 69 back in.......1987 :eek: , I couldn't for the life of me figure out why the motor wouldn't run. My friends father came over and the first question out of his mouth before even touching the car was, "Did you adjust the valves?". Sure enough, a few turns of the rockers nuts to reach zero lash and another 1/2 turn and that motor ran like a champ for years.

I think I'll be on the verge of having a stroke when Frank and I start mucking around with the new motor for the first startup and breakin! :seizure: :seizure:

[toofun]

Definately can be frustrating. Takes alot to embarass me. I am the type of person who likes to learn. The more I learn the better off I am. I have done many projects on cars that I have never done before. I have made alot of mistakes but always learn from them and try not to repeat them. Books, manuals, experience and the internet are all good references. I try to use them whenever I can and sometimes look alittle too deep into things.... Yody, appreciate your comments as well as everyone elses. I will do what you say and try it again and let you know what I come up with. My problem is my time is limited because of work etc... so probably wont get to it until the weekend (Gotta wait till mid mroning or early afternoon though as my neighbors will have a heart attack if I get another backfire!! LOL)

Thanks to all

Mark
TOOFUN

[yody]

sounds good, also make sure the carb is getting enough gas, and putting out enough gas. that could also make it run lean and backfire, but get the basics done first, also check the mechanical advance on the dist. make sure the plates pop out and snap back, by pulling them with your fingers and watching them snap back. Also while your at it, you might as well do a compression check on the other cylinders, or better yet, re adjust the valves and then do your compression check.
1. Re-adjust valves
2. Re-time the engine(start from scratch like metnioned in other thread) check advance at the same time
3.Check carb
4. another compression test(if you feel like it)
5. post back after trying to run it again
Just remembe to keep an open mind and don't rush to opinions. We will figure out whats wrong

[MrQuick]

your valves aren't opening to there full potential.