Piston analysis

[Tor-Lein]

N/A 420A.


Got my old head off yesterday.
What i saw underneath, kind of made my jaw drop...
Here you see that there are alot of residue of some kind covering all the pistons..
(Better pictures will come)

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Other than the filthy pistons..
When the pistons are in bottom position ("bunn" in illustration),
there is a "halfmoon" (åpen halvmåne) opening behind the piston..
Game over, or is it the rod position that causes this?
If its game over, ill get a shortblock.. FAST..

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What compression ratio should i go for on new pistons? If i buy new short...
I can fill 95, 98 or 99 octane...

 

[delta448]

You should clean that ash mess really really good, disassemble and measure both the cylinder diameters and the piston diameters very carefully many times, paying special attention to the cylinder taper, ring gaps and PTW clearance. I'm thinking you're going to need to overbore this block at least 0.5mm and buy new oversize pistons in order to reuse it.

To me the mess on the pistons looks like ash from oil burning, but it's possible it could just be the additives in your high octane fuel. The only way I know how to tell which it is, would be to determine if the bottom end was out-of-spec (pretty sure it is, a visible gap between the rings and wall "Apen halvmane" is pretty bad) and therefore, probably burning oil.

Since you have 99 octane at the pump to play around with on the street, I'd go for between 10:1 to 12:1 compression for a naturally aspirated engine, or anything between 8:1 to 10.5:1 for a build that will eventually see a turbo, nitrous or a supercharger. With 99 octane I'd imagine you could run about 24-26psi on a moderately sized turbo and 9:1 CR with little or no knock, but that's just a guess.

 

[rstare]

That's close to what the top of my stock pistons looked like. There was build up but in lesser amounts. I would be more worried about that gap your talking about.

Did you do a compression test before you took the head off?
Can you actually see a gap between the piston ring and the cylinder wall?
How many miles are on the engine?
Were you noticing a loss in power?
Burning/leaking oil?
These questions can help you see if you have a bad pistons ring, and you can usually find out if it is a bad ring without taking the block apart and measuring like Delta said. If you can't find out without dissassembling then try what Delta said and measure to see.

If you do decide to get new pistons, then you have to determine your goals. Do you want to stay N/A, or are you going to go turbo down the road? N/A = 10.5:1, Turbo = 8.8:1, or you can just rebuild stock. It's all what you want to do.

 

[Tor-Lein]

Thanks for the replies guys.

First of all, the pistons did not have as bad gap as i originally thought.
Must have been the bad lighting that tricked me a bit. Nevertheless, I'll upload the new photos, so we can get a proper diagnostics.

One of the symptoms that i had before the overhaul started, was blue/gray smoke in the exhaust (only when idling) with burned oil smell, and lack of power.
And the intake manifold was very dirty inside, but it should be, right?

Did you do a compression test before you took the head off?
Can you actually see a gap between the piston ring and the cylinder wall?
How many miles are on the engine?
Were you noticing a loss in power?
Burning/leaking oil?
These questions can help you see if you have a bad pistons ring, and you can usually find out if it is a bad ring without taking the block apart and measuring like Delta said. If you can't find out without dissassembling then try what Delta said and measure to see.

1. Compression test: I did a compression test a while back, it was fine.
But the exhaust had smoke since i bought it.
2. As for the gap, you can make your own decision by looking at the pictures. =)
I seriously don't know how it should look..
3. 116.000 miles.
4. Yes, loss of power.
5. As mentioned, burnt oil smell in exhaust, when idling.

As for the overboring, that is more expensive here in Norway than buying a short from the US...

And, thank you again for helping me.

Photos:

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Intake manifold:

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I'll add more photos when I have cleaned up the block and cylinders.

 

[rstare]

I would say the gap is normal, but theres no real way to tell if the rings are fine without either disassembling it or doing a leak down test.
How was the headgasket?
Did you do a leak down test to see if the piston rings were bad?
How did the head (mainly the valves) look?
Was there any oil in your exhaust manifold?

My intake manifold wasn't that bad but it had some oil in there. I will let someone else decide if that is bad or not.
You could be burning oil from bad piston rings, head gasket, stem seals, valve.
All of those besides the stem seals also go along with your lack of power. But they would probably show bad compression numbers too.

How recently did you do the compression test and what were the exact numbers?

 

[david-b]

The oil in the IM can be from a bad PVC valve. Oil could have been coming up through the head into the IM.

And I agree the "gap" looks normal. I was expecting something totally different.

 

[Tor-Lein]

Thanks alot for helping me guys!

I would say the gap is normal, but theres no real way to tell if the rings are fine without either disassembling it or doing a leak down test.
How was the headgasket?
Did you do a leak down test to see if the piston rings were bad?
How did the head (mainly the valves) look?
Was there any oil in your exhaust manifold?

My intake manifold wasn't that bad but it had some oil in there. I will let someone else decide if that is bad or not.
You could be burning oil from bad piston rings, head gasket, stem seals, valve.
All of those besides the stem seals also go along with your lack of power. But they would probably show bad compression numbers too.

How recently did you do the compression test and what were the exact numbers?

Headgasket was very loose. I didn't even have to pry the head loose, I could just lift it off the block.
I didn't do a leakdown test, but i will when reassembled. Because i can't do that with the head off right?
As for the head, the core looks ok. As for the valves, you can judge yourself. Take a look at the pictures.
There was no oil in my exhaust manifold as far as i can see. But alot of carbon-like deposits. Like the debris on the pistons almost.
Compression numbers were fine, +-140-150 PSI. Isn't that good?
Vacuum test was also good.
I did the test about a year ago, the waterpump broke a while after, so the engine got somewhat hot, but not over the "redline".
It seemed fine because i got no other bad symptoms than what i had before, after that.

I checked the head for warpage by laying it down on a flat surface. In this case on a granite kitchenbench, which is very flat.. I could tilt the head about 2mm (0.08") to both sides.

With that said, here are some more photos!

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Washed the engine bay.

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Mouse attack?

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I thank you again very much for helping me, guys!
Please do comment the added info and pictures..

 

[rstare]

Everything looks fine really, dirty, but fine. That's normal after 100k miles though.
Why were you removing the head agian?
The factory compression numbers were between 190psi-220psi.
I have 170psi-180psi across the board in mine. Your numbers are low but even so it's not bad.
The stem seals are still a possiblity for the burning oil. But, they don't explain the loss of power.
Take the head to a machine shop have them look at it and clean it, they will be able to tell you whether its flat. And if it's not then have them machine it.

Just in case you don't know, your going to have to get some new head bolts or arp studs. The OEM head bolts are torque to yield. (That 1/4 turn it says in the manual actually streches the bolts, and then they can't be used agian.)

 

[delta448]

One of the symptoms that i had before the overhaul started, was blue/gray smoke in the exhaust (only when idling) with burned oil smell, and lack of power.
And the intake manifold was very dirty inside, but it should be, right?

Yes it is normal for the intake mani to get a little oily, and that looks to be about as bad as I've seen. I would question whether the engine was over-filled with oil, but it could just be because the bottom end is worn out and you're getting a lot of oily blow-by sucked through your PCV valve.

As for the overboring, that is more expensive here in Norway than buying a short from the US...

Get yourself a nice set of micrometers, pull the block, disassemble and start measuring. You may be able to reuse it, the only way to know for sure is to actually measure. Although I'm not a fan of it, you can always pick up a cylinder hone and refinish the cylinders yourself by hand if going to a machine shop is out of the question and the cylinders aren't in horrible condition. You'll just need to go slow, have a lot of patience and take lots of measurements very frequently.

Headgasket was very loose. I didn't even have to pry the head loose, I could just lift it off the block.

It was probably not sealing correctly.

As for the valves, you can judge yourself. Take a look at the pictures.
There was no oil in my exhaust manifold as far as i can see. But alot of carbon-like deposits. Like the debris on the pistons almost.

The valves themselves look okay to me from the pictures. Check the play in the guides, lap the valves to check their sealing against the seats and replace stem seals before you reuse the head. Also, there won't be any oil in the exhaust manifold because it will burn off and leave the carbon deposits you're describing.

Compression numbers were fine, +-140-150 PSI. Isn't that good?

The factory compression numbers were between 190psi-220psi.

If this is correct (sorry I don't know the factory 420a compression value), then you've found the reason you have a power loss, and you also know that you likely are in need of a rebuild pretty soon. Using the extremes here but, 140 is only 63% of 220.

I did the test about a year ago, the waterpump broke a while after, so the engine got somewhat hot, but not over the "redline".

I checked the head for warpage by laying it down on a flat surface. In this case on a granite kitchenbench, which is very flat.. I could tilt the head about 2mm (0.08") to both sides.

The overheating is a good candidate to be causing your current issues. Your head is warped, 2mm of warpage is a lot (although I'm not so sure about your method of checking that). Just because the stock gauge didn't hit red, doesn't mean you didn't get it hot enough to do some damage. We all know how wonderful stock gauges are, especially when there are no values written on them.

Mouse attack?

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Could very well be a rodent, but this also looks like it could possibly be steam/coolant spray damage from your very likely leaking headgasket. The brake proportioning valve stands out to me. Just wondering, did you ever have any problems with bad brake fade or with boiling off/losing brake fluid?

 

[Tor-Lein]

If this is correct (sorry I don't know the factory 420a compression value), then you've found the reason you have a power loss, and you also know that you likely are in need of a rebuild pretty soon. Using the extremes here but, 140 is only 63% of 220.

I read the compression test procedure, and I didn't open the throttle when testing.
How much does that matter?

The overheating is a good candidate to be causing your current issues. Your head is warped, 2mm of warpage is a lot (although I'm not so sure about your method of checking that). Just because the stock gauge didn't hit red, doesn't mean you didn't get it hot enough to do some damage. We all know how wonderful stock gauges are, especially when there are no values written on them.

I forgot to mention that I have a new head with core, which i got from CIMotorsports.

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Could very well be a rodent, but this also looks like it could possibly be steam/coolant spray damage from your very likely leaking headgasket. The brake proportioning valve stands out to me. Just wondering, did you ever have any problems with bad brake fade or with boiling off/losing brake fluid?

Im sure the coolant could be spraying. On the block, the right corner facing the firewall was washed clean. Im sure that was caused by coolant leaks. See image*
I have to pump the brakepedal before driving. And the brakes are very hard. I do have to change breaklines..

*Image:

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You can still see the honing in the cylinders, even where it's the most worn.

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As for a shortblock, how does this setup sound?

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[rstare]

For the compression test, everyone says it matters. But, I did mine with it closed and then with it open and I got the same results.
Pictures sometimes make it hard to tell because of the shadows and all. That is right where my headgasket was leaking though.

Looks like your right on track.
I would say if you got the money for the short block go ahead and get it.
Your goals determine how to build the bottom end. So ask yourself if you want to turbo, get more power N/A, or just rebuild stock.

 

[Shadow98]

If you want to keep the reliability of NA with a little more power, get the stock rods with 10.5 compression pistions.

 

[Tor-Lein]

Thanks guys.
I don't really have the money for it, so ill go ahead assembling the engine now.
Only new head w/core, gaskets, and oil.

But today im going to sandblast alot of components, like valvecover, passenger motormount, intake, steel water hoses, water filler thingy (where the radiator cap sits)...

Get things nice and shiny, and then paint it all with heat resistant clear.

New pictures to be added soon after!

Thanks again for the help guys!

 

[rstare]

water filler thingy (where the radiator cap sits)...

Thermostat housing.

 

[Locke]

A compression test with the throttle closed could potentially give a false (low) compression reading. While it may or may not show itself in this case, it is best to form the habit of doing it properly.

Shorten the bolt that goes in that corner where your HG leak occurred. It is the slightest bit too long and often causes leaks in that area.

 

[Tor-Lein]

Thermostat housing.

Of course....

A compression test with the throttle closed could potentially give a false (low) compression reading. While it may or may not show itself in this case, it is best to form the habit of doing it properly.

Shorten the bolt that goes in that corner where your HG leak occurred. It is the slightest bit too long and often causes leaks in that area.

I have new bolts, and im hoping that it should be leak proof now..

 

[Tor-Lein]

Update!

Now i have assembled the engine.
And, ofcourse some problems have come up.

It started at the first try, and im quite pleased with that.

Now, to the problems at hand.

1. It sounds like the engine is running at three cylinders, maybe one defect sparkplug or sp-wire. It runs somewhat coarse.

2. It runs at about 2100rpm, idling. Though, when i turn off the heater inside, it idles at 2900rpm. When i touch the throttle, like "tap" the throttle, it revvs and drops the idle down to 1000rpm, then it goes back up to 2100/2900rpm.

3. When running, it has a sharp suction noise comming from the airfilter/driver side radiator fan. I run with a cone Green filter.

Any good advice?
I'll add new photos later today.

 

[delta448]

Sounds like maybe an air leak on the intake side. Double check your vacuum lines, make sure everything is connected that should be and that any unused lines/ports/nipples are capped off or otherwise sealed.

 

[Tor-Lein]

EDIT: 3. When running, it has a sharp suction noise comming from the airfilter/driver side radiator fan. I run with a cone Green filter. The sound is LOUD. Almost as loud as the noise from the engine itself.

 

[Tor-Lein]

No one heard of this before?

I badly need some advice...

 

[bullettdsm]

Double check timing. If you have already, then triple check timing

2GNT.com - PROPER_TIMING_MARK_ALIGNMENT


For marks on a stand scroll down a bit to appropriate area;
http://www.2gnt.com/www/corbin/rebuild.html

Do you have any vac readings?

MB

 

[Tor-Lein]

Quadruple checked my timing, and it's spot on!

I used PCMSCAN to analyse my OBD-II. It says that injector #4 is damaged/clogged and cylinder #4 is misfiring. Because if the injector...

That explains the coarse idle, but not the high idle rpm.
And the sucking noise is still unexplained.

Any

 

[96TurboGS]

Quadruple checked my timing, and it's spot on!

I used PCMSCAN

I use it on all my cars; does work better then a hand scanner. Highly recommended for you ELM327 guys!!

That explains the coarse idle, but not the high idle rpm.
And the sucking noise is still unexplained.

Any

Get that injector fixed. Sounds like you have an vac leak somewhere; triple check all your lines. Follow the vac lines from the back of the manifold. Make sure your egr/vac tree/throttle body hoses are hooked up and everything is sealed properly around the TB.

EDIT: 3. When running, it has a sharp suction noise comming from the airfilter/driver side radiator fan. I run with a cone Green filter. The sound is LOUD. Almost as loud as the noise from the engine itself.

Still say its a vac leak

 

[Tor-Lein]

Thanks for that illustration!
I'll re-check my vacuum lines once more..

Injector #4 was loose! Fixed it, and now it runs great, except for the high idle and sucking noise..

I'll update later on today.

Allthough, the PCMSCAN does not register any fault in the system.. Wouldn't the PCM notice if a vacuum line was leaking or not connected?

 

[rstare]

No, there will be no CEL for a leaking vacuum line.
A vacuum leak will cause lots of funky things with idle, and with your "sucking noise" description I'm beting on a vacuum leak, just like the others.