Low Compression, Help...

[timmay316]

I just bought a 92 talon tsi AWD, and got a decent price on it because I knew it needed some engine work. I got it home and did a compression test and got 50-152-149-155. Then I did a wet test to see if it was rings, but the compression only jumped to 53-155-155-160.

When the car is running, it seems like exhaust is coming out of the valve cover breather (passenger side of valve cover, the guy had the a long hose attached to the breather that dumped it to the ground), and it seemed like exhaust would come out of the dipstick tube when I pulled the dipstick out (wasn't bad enough to push the dipstick out on its own).

Any suggestions? I am planning on pulling the head today, I figure at this point it is probably either head gasket (hopefully) or ring lands. I am really freaking out at this point though, so please, any and all help would be great.

 

[freshlane]

no knock?...might be head gasket but no way to tell till you take off the head

 

[timmay316]

There's no knock, and the engine ran pretty strong, it just smoked a little and has that one really low compression number. I know a bad ring land would cause exhaust to come out of the dipstick tube, but could a bad headgasket cause this as well?

 

[ILLiCliPSE]

if there is pressure behind the dip-stick, that means that there is pressure in the crank case aka not the best thing in the world.

 

[timmay316]

Yeah, I know, that's why I am pulling the head (hopefully this weekend). But my question still remains, would pressure build in the crankcase with a blown head gasket? ( I know a bad ring land would cause this, I just want to know if a headgasket would too).

Also, if the headgasket is fine or isnt that bad, how will I know if the ring land(s) is/are bad? Is there any easy way to tell without pulling the piston out?

And this is sort of off topic, but what other parts would be good to replace while I have everything apart? I was thinking water pump (as far as I know it has never been replaced... someone told me they tend to go), timing belt...any other suggestions?

 

[dub2gsx]

Yeah, I know, that's why I am pulling the head (hopefully this weekend). But my question still remains, would pressure build in the crankcase with a blown head gasket? ( I know a bad ring land would cause this, I just want to know if a headgasket would too).

Also, if the headgasket is fine or isnt that bad, how will I know if the ring land(s) is/are bad? Is there any easy way to tell without pulling the piston out?

And this is sort of off topic, but what other parts would be good to replace while I have everything apart? I was thinking water pump (as far as I know it has never been replaced... someone told me they tend to go), timing belt...any other suggestions?

Don't know about the crank case pressure or checking for bad rings, but...
If your pulling the head you will need to get a new head gasket anyways, remember the head is mad of aluminum and it warps easy, so get it checked out by a machine shop before using it again. While you have it off replace the timing belt and water pump if you don't know the time frame the last was changed. Replace the intake manifold gasket if you take the intake mani off, block off the egr its really easy when the head is off. The valve cover gasket should be changed almost every time you take off the valve cover. Doing preventative maintenance is the best thing possible and saves a lot of time too.

Also plan on getting the bottom end rebuilt, with comp #'s like that a seal somewhere is out. I would be sceptical of putting the head back on untill you found out exactly what is causing the compression issue. My friend put his head back on thinking it was just the head gasket and it was the rings as well. It was a big waste of time putting it all back together for nothing.

Brian

 

[absolute_DSM]

A head gasket would not cause your dipstick to try and blow out. Your head gasket is above the pistons. Dipstick trying to blow out is cause by bad blowby which equals bad rings.

Oh and if youre taking it apart and want some "aftermarket stuff", well then... start searching the forums. Most of us started by "just taking it apart"

 

[timmay316]

Two more questions.

What does a bad ring land look like? Will it be obvious, or will I have to pull the piston out to tell?

If it is a bad ring land, and I have to replace the piston, is it okay to just replace one piston and its rings? What sort of break-in procedure would I follow (I've done break in on fully rebuilt engines before, but how would I do this?)?


On another note, when I put the head back on, should I buy a new set of head bolts, or buy head studs?

 

[timmay316]

ttt...

 

[absolute_DSM]

Shouldnt bump your own threads.

If you have a broken piston, you will know. There will be chunks in your oil pan and a loss of power at the least.

If you replace 1 piston, you will have to have the cylinder wall honed. To have the cylinder wall honed, you either do it yourself (if youre real good) or you pull out the rotating assembly and have it honed. Then you might as well put in all new pistons and rods. See how easy it is to turn on to higher boost?

Get some ARP head studs and a new 4 layer Mits or Cometic head gasket.

 

[timmay316]

Sorry about bumping, forgot.

I have no problem honing myself (I have done plenty of rebuilds on V-8s, this is my first experience with a DSM).

So If I do just replace one piston and obviously its rings, is that acceptable? Like I asked before, how would break-in procedure go in a situation like this? Would having slightly higher compression in one (the number 4 cylinder) cylinder bother anything? The rest of the cylinders are at around 150-155 (in other words, still very strong).

Is the above acceptable? Or should this warrant a whole rering job?

Whether I rering just one cylinder or all four, should I install new rod bearing(s)?

 

[timmay316]

Along with my other questions above, I was wondering, how much boost can a stock replacement head gasket handle? I have a stock replacement headgasket in the garage, and I would like to use it if I can. (I know three other guys who run about 15-18 psi daily and the occaisonal 20 psi at the track with stock or stock replacement head gaskets...now i know just because they do it, it doesnt make it safe, but is this reasonable?)

 

[timmay316]

I dont mean to make a repost or bump the thread, but I would really like to have these questions answered. I have searched, and I have gotten some questions answered, but I would like more input on my last two posts before this one.

 

[chanley talon]

Hello
It could be possible for the dipstick to be blowing out compression due to a bad headgasket. The reason being is there is oil passages both in the head and on the block itself that normally are sealed . If the head is warped compression could be leaking over and down into these passages . It seem strange though in your situaton that the compression doesnt slowly fall from one side to the other due to a bad headgasket letting out compression. You may have a burned piston. I personally have never done that on a dsm . But if it happens that piston will be leaking compression into the crankcase.
Let me know what you find please when you take it apart.

 

[telnut]

A cylinder leak down test would tell you where your loss of compression is coming from. If you get air leak at TB it intake valve, at the exhuast pipe it's a exhaust valve. at the dipstick tube or oil cap it's rings. There is a how to article on doing leak down test in one of these forums.

Telnut
"Motor oil in my veins and nuts and bolts in my brain."

 

[jking29]

Along with my other questions above, I was wondering, how much boost can a stock replacement head gasket handle? I have a stock replacement headgasket in the garage, and I would like to use it if I can. (I know three other guys who run about 15-18 psi daily and the occaisonal 20 psi at the track with stock or stock replacement head gaskets...now i know just because they do it, it doesnt make it safe, but is this reasonable?)

Is the replacement gasket you are talking about a genuine Mitsubishi gasket? If not, your guess is as good as mine how much boost it will hold. If it is a real Mitsu gasket I have seen them with ARP studs take 30+ lbs no problem.

 

[timmay316]

I finally got around to pulling the head, the headgasket was fine, so I pulled the valves out of the cylinder with the low compression. The exhaust valves seats and faces were both covered in black soot/carbon and they had large dull spots, not all shiny like if they were sealing properly. I can only assume this is my source of low compression? As for why there was smoke from the exhaust, there were two valves that were very wet with oil (bad stem seals). Could bad stem seals combined with the valves not seating properly cause the exhaust to leach into the valve cover and come out of the breather (the problem that I described earlier)?

The other thing I am now wondering about is the "exhaust I thought was coming out of the dipstick tube. Is there any way the exhaust migrating up into the valve cover could find its way into the crankcase? Or maybe it wasnt exhaust, in that case, would crankcase pressure blow out fairly strongly through the dipstick if the PCV valve was bad?

Two other just general questions, right now I have a Napa (victor reinz or something like that) head gasket. Should I use it, or should I go out and buy a mitsu (if I do, how much are they)? Also, I am replacing the water pump and all the belts while I am in there, are Napa belts and water pump as good as mitsu, or am I taking a big chance by using them?

Sorry for the long post, but I am really hoping that my problems will be solved with the head work and a new PCV valve, and I just want to make sure my logic is mostly correct.

Thanks

 

[94TalonTSI1]

Ugh, this post SCREAMED sticky valves.

You should have also done a vacuum test as well, it will tell you some more information along with a compression test.

Sounds to me like you have a sticky valve. This will cause you to have low compression and nothing change after a wet test.

Stock head gasket can handle a good 25+ PSI.

Good Luck!

 

[timmay316]

By sticky valves do you mean what I described (the carbon/soot buildup on the valve face)?

And anyone else have answers for the rest of the questions in post #17?

 

[timmay316]

anyone have some answers/opinions for me???

On another note, I called a local speedshop to get some price quotes on a valve job and new valve seals installed, and I also need an exhaust stud replaced (the guy I bought the car from snapped the stud off, tried to drill it out, couldn't get it out, so he just filled the hole with RTV and left it). and they told me 350-400 bucks. I dont know, this is my first experience with dsm work, but that just seemed outrageous to me. Is this what I should expect or should it be cheaper (a valve job on a set of small block ford heads is only 115 bucks, and I cant imagine drilling out that stud and helicoiling the hole will be that hard/labor intensive)?