New engine has loss of compression
- Thread starter DartVadar
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Inertia
Well-Known Member
Guages differ,, I have a Mac Tool,, a Snap-on, and a Walmart special,, none of them read the same..
Cheaper guages are usually used to find differences in cyl press,, not figuring comp ratios..
Cheaper guages are usually used to find differences in cyl press,, not figuring comp ratios..
bamamopar
Well-Known Member
I'm running a .30 over 360 with the eddy heads out of the box. Been running the car since 2005. Did a compression check and all are 185-190.
Gauge out of tune ?
russhal
Well-Known Member
Yea, somethings not right. If it was me, I would go ahead and tear the engine down and inspect. You know whatever it is you're going to have to tear it down anyway. I would want to see all the rings. I've used those pistons in a 360 before. Best piston for low budget build. Really gets the compression up. You should have 10.5 to 1 if I calculated right and the head cc' is correct. You can cc the heads yourself with a thick piece of plexiglass and suringe
There is a lot of thing that can affect compression check, weak or low battery, bad battery cables, bad/weak starter, BUT! even if you have all the problems mentioned above, it has still showed you have a bad cyl.
Yes, you should have had all spark plugs out, throttle wide open(I never have the throttle open when i do a compression check:violent1
and crank to the highest pressure.
If you do this, you will get a higher reading on you gauge, but you still have a bad hole............
Yes, you should have had all spark plugs out, throttle wide open(I never have the throttle open when i do a compression check:violent1
and crank to the highest pressure.If you do this, you will get a higher reading on you gauge, but you still have a bad hole............
that was a pretty good seat of the pants / good ear diagnosis . Gauge proved you rightWell I just finished doing the compression test and like I thought, I have a lame cylinder
1- 135 PSI
2- 134 PSI
3- 134 PSI
4- 99 PSI! I squirted some oil in and it went up a bit to 112 PSI
5- 133 PSI
6- 139 PSI
7- 131 PSI
8- 131 PSI
Number 4 is the issue here. Now because the PSI went up a bit does that mean its the piston ring? I assume its normal for a bit of blowby to occur. I will try to get a leakdown tester to see what is leaking though.
I dont think I would have noticed if I didn't have to crank it over so many times, well at least I found the issue.
Is there anything else I should do before I either take the motor out or start tearing it apart?
Is there anything else I should do before I either take the motor out or start tearing it apart?
moper
Well-Known Member
Edelbrock quality comes down to the guy who cares. I know many drivers that can't tell if the engine's skipping or not - then you have Vadar here that can hear the single weak cylinder...lol. If they get bolted on and they don't fail abd break something, and the engine runs as expected by the driver, were they bad? Case in point - my truck's engine has wrist pin noise. I've been driving it like that for almost 10 years now. I know what it is, but if i were to give it to someone they'd say the engine has a knock and stop driving it. Same engine - two different levels of knowledge and acceptance. Personally I've checked a few and they all had issues I would not consider acceptible. So all of them get valve jobs and milled now. I don't have to check - I want the best I can get for my money.
In terms of the compression test - what pistons are in it? What were the rings gapped at? 135psi may be fine, but the lower one obviously has a problem of some kind.
In terms of the compression test - what pistons are in it? What were the rings gapped at? 135psi may be fine, but the lower one obviously has a problem of some kind.
Inertia
Well-Known Member
If they're adjustable rockers,, back off both of those cylinder's pushrods till loose,, and recheck,, if pressure comes up,, was poorly adjusted rocker...
I honestly have no idea how I noticed that LOL but yea, I want to make it right, so even though it runs nice and strong now, I want to fix that cylinder. And who knows what other issues these heads have. I guess I just don't like to ignore problems.
And they are kb 107s, the top ring is gapped to 28thou and the second ring is 18 (I think) I just followed the instructions when I gapped the rings.
I do have adjustable rocker arms, but I also have a hydraulic cam so I wouldn't think that it would be holding open the valve, but its possible I wil maybe run another test.
Also the compression gauge that I used I tested it on an air compressor, it seems kinda low, and doesn't really seem too accurate the higher the readings get, so my numbers are probably all higher.
moparlover
Well-Known Member
a squirt of oil brings the pressure up... sounds like rings to me not valve
everyone blaming the heads lol
gonna have to pull the heads. check that cylinder for scoring. check the valves for seating problems.
you might be lucky, sometimes a head gasket gives out. you will know when you look at it
everyone blaming the heads lol
gonna have to pull the heads. check that cylinder for scoring. check the valves for seating problems.
you might be lucky, sometimes a head gasket gives out. you will know when you look at it
Inertia
Well-Known Member
If a valve was tight to begin with,, and the valve "pounds" in a bit,, you could lose the gap,, just eliminating a possibilty.. Believe me,, it wouldn't be the first time a valve was mal-adjusted,, caused a valve to be held open..
cheers
Okay so I think I found part of the problem. Somehow the spark plug threads got stripped, I don't really know how that happened but I want to fix that without dropping little pieces of aluminum into the cylinder. I had lots of anti-sieze on the threads so that caught what was there.
Also after cranking the motor over a few times I can hear a hissing noise coming out of the carb, could this be indicating a bad intake valve?
I cant really do a leakdown test because when I tried all the air just came out of the spark plug hole. I am also thinking that could be a reason that the compression gauge read so low, the threads didn't seal well enough, I do remember that it sounded like more air was coming out when I tested the low cylinder. But I put the tester on one of the good cylinders and it seemed to seal pretty well.
Also after cranking the motor over a few times I can hear a hissing noise coming out of the carb, could this be indicating a bad intake valve?
I cant really do a leakdown test because when I tried all the air just came out of the spark plug hole. I am also thinking that could be a reason that the compression gauge read so low, the threads didn't seal well enough, I do remember that it sounded like more air was coming out when I tested the low cylinder. But I put the tester on one of the good cylinders and it seemed to seal pretty well.
moper
Well-Known Member
Sounds like you might have cross threaded the compression tester... You can get spark plug hole repair kits - it's best to do that off the car by the way. Otherwise you can get most of the aluminum out, but you won't get all of it.
You set the gaps right at least by what you said.
Did the engine have any detonation issues? Could you hear any pinging at all? Did you pick up a load of fuel from somewhere you haven't bought before or some no-name mini-mart brand?
Noise in the carb could be a variety of thigns. I wouldn't call it important but keep it in mind when you take it apart. You definately should pull that head.
You set the gaps right at least by what you said.
Did the engine have any detonation issues? Could you hear any pinging at all? Did you pick up a load of fuel from somewhere you haven't bought before or some no-name mini-mart brand?
Noise in the carb could be a variety of thigns. I wouldn't call it important but keep it in mind when you take it apart. You definately should pull that head.
Yea seems that way..aluminum is so soft, didn't even seem like I did. And yea I think I will pull the head, not much more testing I can really do due to those bad threads without getting aluminum inside.
And actually yes it did. About a month ago I got some bad fuel, the car ran like garbage and started backfiring and all the plugs fouled. It also started to mis-fire out the right exhaust...so it would make sense that it could have been that cylinder. I usually go to petro-canada, but went to shell once instead, and that is when I got that bad batch, its all cleared up from that I think, but it possibly could have caused part of this issue.
It's winter , pull the head . You can fix the park plug hole and check the pistons . Don't take a chance some little piece of alu will fall in . While out inspect and test the heads , it will put your mind at ease next season .
I always worry when time to change plugs with Alu heads , is there anything that can be done to strengthen the plug threads ?
I always worry when time to change plugs with Alu heads , is there anything that can be done to strengthen the plug threads ?
The head is off, and the cylinder bores look really good, lots of cross hatching and no marks or scores in the cylinder walls. The head itself looks ok I think, I don't really know what I am looking for. The picture of the head is the cylinder in question, and I just took a picture of the bores for the heck of it.
But after looking at some of the lifters and the cam I am wondering if something isnt quite wearing right. And the one lifter picture is the only one like that, the rest have circular wear but not as shiny as that one, it is perfectly smooth as well. I always use a zinc additive for oil changes as well.
Lots of pictures!
But after looking at some of the lifters and the cam I am wondering if something isnt quite wearing right. And the one lifter picture is the only one like that, the rest have circular wear but not as shiny as that one, it is perfectly smooth as well. I always use a zinc additive for oil changes as well.
Lots of pictures!
Inertia
Well-Known Member
I'd move that piston down in the bore far enuff so I could cover the piston top with clean solvent,, and fill the other cyls as much as poss too,, if that cyl looses the solvent quicker than the others,, I'd suspect a ring problem.. If they drain evenly, look elsewhere,, That's how I test rings when doing a valve grind,, it's a good indicator..
Don't forget to change the oil..
What did the spark plug in that cyl look like, any different than the others..
cheers..
Don't forget to change the oil..
What did the spark plug in that cyl look like, any different than the others..
cheers..
Does this engine have adjustable rockers? It COULD have been as simple as the valves being out of adjustment. IMO, you never finished diagnosing it. You just ripped it apart. Did you not read my post about how to do proper diagnosis? You could have easily put air into that cylinder and found the problem. Now you cannot. I will never understand why people make things so incredibly difficult on themselves.
I tried putting air into it but I couldn't get it to seal because the stripped spark plug hole. I also re-adjusted the rocker arms, and tried a handfull of different attachments but none would seal, I then tried the same attachment in another cylinder and it sealed up and worked perfectly. I looked down at the threads and they were all messed up and dropping little bits of aluminum into the motor, so if anything I would have pulled it to fix the threads anyways.
So I tried to put air into it, I even got a partial seal but couldn't get much pressure in there.
Then try putting mineral spirits in that intake port with the port straight up. If that intake valve is not sealing, you'll see it quickly. You can do the same with the exhaust. In fact, I would do the whole head and if any of the rest leak, guess what? You should pull the other head.
Cuda68Scott
Well-Known Member
Well it looks like now you will have the opportunity to fully check your heads and rings, etc and put your mind at ease. Somehow I think your engine and heads were fine all along, and you inadvertently stripped the threads with your compression tester causing the low reading in that one cylinder, and your overall 135 reading in the other cylinders were due to the made in Taiwan tester being off. I have done the same thing trying to fix something!
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