bigbadboy

well did a leak down and comp. on my car and it came back really bad. here is wat it looks like.

#1 #2 #3 #4
170 100 145 170

when we did my leak down test on #2 we could feel the air leaking from #2 back into #1 and out the sparkplug hole. also we pulled off a vaccume source and we could hear some air going back into the mani but i think that is from the air that went into #1. do you guys think that it could be my HG??? my oil and coland are not mixing and its not smoking one bit. wat do you guys think the problem is? should i replace my HG and get new valves and stuff or just try to change my HG and see if that fixes it??

rmcdaniels

I've had that happen from a bad intake valve, the air leaks out into the mani and then to another cylinder through an open intake valve. I pulled the IM and then I could check each intake port to see where the air was really coming from.

spoolingb20

Well when you are doing the leakdown test if you felt any air coming out of the throttle or the exhaust that would indicate that you have an issue with valves seating ext. With the air coming back out of number one sparkplug from number two cylinder would have to be a blown headgasket.
I would pull the head and look over the headgasket, before you reinstall the head take a flat metal ruler and feeler guages and make sure that your blocks deck and head surface are all within spec.

Have you ever had the head off and what type of Head gasket is in there?

I know it may not apply but if you want to check the condition of the rings on those two low cylinders. Just do a wet compression test and compare your numbers to the dry test. If comp goes way up when you add oil into each cylinder then you have an issue with your rings or pistons...

thewrai6th

HG
What prompted the leakdown test?
Usually, two low (not 0) readings next to each other is HG.
Wet test those two for verification. A little oil can seal up bad rings. (It WILL smoke for a minute after the wet test )

rmcdaniels

If the throttle plate is closed, then air leaking past an intake valve will go back in the open (or bad) intake valve of another cylinder and come out of that cylinder's spark plug hole. It does not necessarily mean a bad head gasket, although it can mean that.


I wouldn't use a ruler to check the head and block for straightness, I'd use a machinist's straight edge.

thewrai6th

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rmcdaniels &raquo;</TD></TR><TR><TD CLASS="quote">If the throttle plate is closed, </TD></TR></TABLE>
That's a remote possibility that two sets of intake valves are bent. If that's the case, the car may not even run, and will surely sound like crap.
Anyway, the easiest way between cyl 2 and cyl 3 is a breach in the HG, that wouldn't really mean steam/overheating.
Good luck, HG's are easy and cheap

thewrai6th

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thewrai6th &raquo;</TD></TR><TR><TD CLASS="quote">
That's a remote possibility that two sets of intake valves are bent. </TD></TR></TABLE>
Would he even have 145 or 100 compression if the valves were not seating? Every time I see bent valves, there is 0 compression.

rmcdaniels

I'm not saying two sets are bent, I'm saying that while one set of valves is normally closed, another set is normally open, so if the throttle plate is closed, then the air will go out the bad set and through the intake manifold, then in an open set of valves, and out the spark plug hole for that cylinder.


I've had plenty of bent valves that had good compression, it depends how far they are bent.

What I wouldn't expect is #2 leaking through the head gasket to #1 when #2 shows 100 on a compression tester and #1 shows 170.

thewrai6th

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rmcdaniels &raquo;</TD></TR><TR><TD CLASS="quote">I've had plenty of bent valves that had good compression, it depends how far they are bent.

What I wouldn't expect is #2 leaking through the head gasket to #1 when #2 shows 100 on a compression tester and #1 shows 170.</TD></TR></TABLE>

I haven't seen a cylinder get any compression if the valves don't seat, but I'll take your word for it. I guess they could be slightly bent or loose.

The breach in the HG I was referring to is between 2 and 3 not 2 and 1...

The breach could, just as easily, be between 2 and the moat and 3 and the moat...but then you would push from the rad/overflow.

Just my .02. I would hope for blown HG instad of a mangled head.

bigbadboy

don't think its a bent valve because my car runs so good. thats the reason why i never did this test before. it runs great and it feels like it has a good bit of TQ and get up and go. we just couldn't get the a/f's right on the dyno. the reason i say its the HG is because i also had an oil leak in front of the block between #2 and #1 and then it sealed and stopped so i never changed the HG. but the thing abt the air in #1 is that, that was the only cylinder that air was coming out of. all the others where good. my friend bent his valves and he's car runs like crap and has no comp on like 3 cylinders. i'm going to try and replace the HG and see if it fixes the prob and if it does then back to the dyno. i figured air was going back into the intake mani was because of the air going into #1 then had a little bit escape through the open valve in the cylinder. the air was just rushing out of cylinder one when we did a leakdown on #2 all the rest where fine. the rings are great and new. we also didn't hear or feel any air coming out of the dip stick hole or anything like that. so we came to the conclusion that the rings where good. before i put the head on i had it upside down with water in it to see if the water would bubble (leak throught the valves) and it didn't. hopefully its just the HG. i mean the car runs so perfect you would never tell anything was wrong. will update with wat happenes when i change the HG this weekend thanks for all the help and reassurance