exhaust valve question

[cbarr300]

Hey guys, I've been trying to find out why I have only about 15psi in my number 7 chamber but the rest are 145-150. I've already changed the headgasket out and installed it properly but I still have hardly any compression.

The head isn't cracked and it's not warped. no bent pushrods or collapsed lifter and none of my cam lobes are wiped out. I don't see any valve seating problems either.

Now, I did notice that all of my exhaust valve stems have a white tint to them (the part you can see from the exhaust ports)...but my number 7 has a carbon/oily look to it. what would that indicate? btw, there wasn't any smoke out the tail-pipes while I was driving it home like that.

The only thing I can think of is that the compression is getting pushed out the exhaust side and it building up carbon. If that exhaust valve isn't the problem....then I can't see what else could be the problem aside from completely blown rings....but I can see the rings down in there

 

[bill302]

A wet compression test should be used when cylinder pressure reads below the manufacturer's specifications. It helps you to determine what engine parts are causing the problem. Pour approximately 1 tablespoon of 30-weight motor oil into the cylinder through the spark plug or injector opening, then retest the compression pressure.

If the compression reading goes up with oil in the cylinder, the piston rings and cylinders may be worn and leaking pressure. The oil will temporarily coat and seal bad compression rings to increase pressure; however, if the compression reading stays about the same, then engine valves or head gaskets may be leaking. The engine oil seals the rings, but does not seal a burned valve or a blown head gasket. In this way, a wet compression test helps diagnose low-compression problems.

Do not put too much oil into the cylinder during a wet compression test or a false reading may result. With excessive oil in the cylinder, compression readings go up even if the compression rings and cylinders are in good condition....repost results of the wet test.

 

[Dino Dino Bambino]

Bill's hit the nail on the head.

 

[cbarr300]

sorry, I forgot to mention the wet compression was the same. I guess one of my valves is messed up and it just doesn't look messed up...maybe it's sticking?

oh well, it's at the machine shop right now soooooo, I'll find out here shortly I suppose.

thanks for the input

 

[final5-0]

I just don't know what I'm gonna do with all you ... Young-uns

You always seem to make me dig ... way back
and
Bring back stuff I somehow or the other learned then

You can pour gas in the port
and
Check to see if it seeps past the valve & seat

You guys are making me give up
all my ... old ... hard learned ... tricks

Grady

 

[cbarr300]

I got some bad news....my head doesn't have a problem with it.

I got a .003" feeler gauge and moved it around the top compression ring...there's an area where it drops down a good inch or so...where as the rest of it only drops down maybe 3/8". The area is prolly about 3 inches long that it drops down. I guess I have some fuxed rings and or pistons...

time for that new engine hopefully

 

[final5-0]

Are the walls scored

Grady

 

[cbarr300]

there's a little nick in the cylinder wall where someone put the washer down in the #8 cylinder. It's not hurting compression or anything...but that engine was on borrowed time. I don't know what happened to the #7 area, haha..it just went.

I figure since I need a new block, I might as well get a fresh/stroked lower end. I'm sure a good one can be had for around 2000. I'm just gonna put the ported heads and the cam back on there and get a new intake once I can afford it after I buy the shortblock. I have a gt-40 intake right now.

btw, heads are perfect, rods are good, no valve problems, piston isn't cracked as far as a visual inspection goes, headgasket was on correctly (even tried with another headgasket just in case). When I turn it over by hand I can see some streaks made on the cylinder wall (#7). The streaks are made right around the area that I felt the drop around the piston ring.

 

[final5-0]

I don't know what happened to the #7 area, haha..it just went.

When I turn it over by hand I can see some streaks made on the cylinder wall (#7). The streaks are made right around the area that I felt the drop around the piston ring.

What Happened

Well ... lets play a little game
You guess the missing words

The fact you got a V****** means you got F***** induction

I'd submit those two mystery words
have something to do with the cause

Grady

 

[cbarr300]

you don't think that has anything to do with it..do you?

I haven't really been getting on it much the last couple months...which is what confused me. I guess the previous 3rd gear pulls beat on the rings a bit and over time things just wear.


I know WHY it went...I guess I should say, I'm not 100% sure HOW it went, haha. (as far as where I'm losing compression). I don't have an aircompressor around here so I can't push air into the cylinder....heads off anyway.

 

[reddy351]

If you have 3" of ring "unaccounted for", I'd say you'll prolly be surprised when/if you pull that piston out of the hole. The part of the ring that's missing had to go somewhere. I'll bet the ring lands are, at least, beat to "you know where". How bout some pics of that cylinder scoring? Maybe the piston, if you take it out?

 

[cbarr300]

I'm gonna put it back together and drive it about 10 miles to my old highschool's shop. One of my friends is the auto-tech teacher up there and he said it's cool if I use the shop/tools...which is great. I'm gonna start taking it apart once I get close to getting the short block.

should be quite the sight, haha