emeryz28

I started getting oil coming out of my dipstick tube as well as pressure buildup under the oil cap. The PCV system works fine. I did a compression check and all cylinders came in at 150 psi except #7, which came in at 38psi. I didn't have a bleed down tester but I did manage to pressurize the #7 cylinder with my air compressor with both valves closed. When I did this, I noticed the air was finding its way into the oil chamber because it was clearly coming out the oil cap.

Today, I pulled the heads off and the #7 cylinder wall doesn't seem to be in any worse shape than the rest. Looking at the pics of the #7 cylinder and head gasket (both top and bottom), is it possible that this head gasket could have been leaking in the area of the #7 cylinder and causing the excessive blowby? I don't see any signs of a failed gasket but just trying to rule out the head gasket (that would be the hoped-for culprit).

The only other culprit I can think of is a bad ring. The valves are fine and were done about 20,000 miles ago (although I can't see how a bad valve would cause blowby). The intake manifold gaskets seem to be in very good shape too. I think the coolant in the cylinder spilled out of the heads as I leaned the head towards the back when I removed it.

Thanks.

Jon D.

AlkyIROC

Your head gasket won't allow combustion pressure into the crankcase unless it was blown right out into the lifter valley. All the holes in the head gasket are for head bolts and coolant. Oil in the head is returned to the pan through the lifter valley and pushrod holes.

Bad valves will normally be noticed when popping is heard in the intake or out the exhaust pipe.

That leaves you with piston rings or a bad piston as the most probable cause of low pressure. You've gone that far, might as well drop the pan and remove the #7 piston for inspection.

emeryz28

Thanks. I didn't want to hear that, but I think you are right. The problem with dropping the pan is that I sold my engine hoist a few years ago (after replacing the pan and gasket) and there is no way to get the pan out without the engine being about five inches above the crossmember. Any idea how much an L98 short block weighs? Maybe I can get a friend to help unbolt it from the transmission and just lift it out with ropes.

emeryz28

I just happened to notice that the holes for my water jackets (L98 engine) are not the same size as my head gasket holes.

I guess I should have caught this when I installed it back in 2011. It's a Fel Pro gasket stamped 7733PT2. Could the smaller holes have caused the engine any harm?

AlkyIROC

Looks normal to me. They put smaller holes in the gasket to restrict coolant flow. If the coolant flows through the head to quickly, it can't absorb the heat.

emeryz28

Thanks again. BTW, as an experiment, I filled #3, #5 & #7 cylinders with water and found that after a few hours, the water level in #7 had dropped over an inch while #3 and #5 didn't budge, so I'm pretty sure at this point it's a broken ring. I'll have to take out the piston and replace the ring. If only one is broken, should I replace all of them?

AlkyIROC

You should replace the set but a simple ring replacement is only a short term fix. Without honing and deglazing the cylinder wall, the rings probably won't seal.

You don't want to hear it but a proper fix is a complete rebuild or engine replacement unless you plan on a patchwork fix to sell the car.

emeryz28

Thanks. Surprisingly, the engine seemed to be running okay even with only 38 psi on #7. To complicate the issue, I just ran it 1000 miles with an expensive ceramic additive in an attempt to fix the blowby, so I don't know how that would affect the sealing of new rings. If I can get the compression above 100 psi, I would be happy. Is there a possibility that the rings could have just worked themselves into alignment and created a gap, allowing blowby? I don't really see any damage in the cylinder wall.

paulo57509

Does the engine block assembly have +250k miles on it? If it does, that's the #1 reason for not patching it up and putting in a short block, IMO.

emeryz28

It does have a lot of miles. I drove this car off the showroom floor in 1992 and I have used Mobil 1 every 2000 miles (sometimes less). My days of seeing how much power I can get out of this car with 11 inches of boost ended in 1995 after I shattered three input clutch housings in a one-month period. Now, I just want to keep it running. It's no longer my daily driver. I do have two Mercedes 32-valve V-8s (mid-nineties vintage) with equivalent miles and those are our daily drivers. I know those engines are capable of 500,000 miles, if maintained, but not sure about an SBC. Is the L98 engine even available anymore?

sofakingdom

iTrader: (1)

I suspect there's a hint buried in there somewhere...

AMAZING how much clearer things become when, instead of yerbasic "what's going on" type of question, some ACTUAL HISTORY is supplied.


I don't see anything at all wrong with the head gasket; looks perfectly normal to me.

Most likely, you will tear it down, and find the ring lands on the piston all destroyed and broken off, right below the spark plug.

Of course not... the last car that used it is now AN ANTIQUE... since the 2017 model year is now out, 92 model cars are now 25 years old.

You can rebuild it easily enough; just beware of trying to go all-out cheeeeeeeep on it like seems to be most popular on this board. All "rebuilds" aren't created equal; and while paying a high price isn't a guarantee of "quality", paying the LOWEST POSSIBLE price, as is all too commonly the objective, pretty much guarantees a LACK of it.

emeryz28

Thanks for the input. Will a block from another engine (one that actually is in production) bolt up to my existing intake/heads? By the time I'm done rebuilding the lower end, and hoping I got it right, I'm afraid it could cost more than just buying a new one. I guess it's time to peruse the Engine Swap category on this forum to learn more about my options.

The blower hasn't been on this car since 1995. I learned the hard way that there's alway a weak link somewhere down the line any time you try to modify a car that wasn't originally designed for that kind of horsepower. I suppose if I could have found a stronger transmission than the 4L60E something else would have shown up.

sofakingdom

iTrader: (1)

Depends on what you mean by "in production".

Last engine that would, at least as far as ones installed in vehicles, was in 2000.

You can still buy new replacement short blocks, at least in the form of complete engines, that will however. The "HO 350" for example. You can easily sell those heads (Vortec) and re-use your existing ones on it.

Yup I feel ya about the weak link... you have no idea how many of those I've found myself, over the years.

emeryz28

Thanks. So the HO 350 block should mate up to my intake and heads without any modifications?

AlkyIROC

Unless you have access to a machine shop with proper knowledge to do a proper rebuild, it will be cheaper in the end just to buy a new engine. New engine should also come with a warranty.

One of the trucks I have is a 2004 F350 Superduty with a diesel. I melted a piston when an injector failed and got a new zero mileage rebuilt engine with a 3 year warranty installed for less than what I could have bought a new engine for. Engine also came with a lot of goodies like head studs, EGR delete etc. It was a $7000 engine replacement but I'll never have to worry about the engine failing before the rest of the truck does.

Search around locally for a shop to do the swap for you. You may find one that can do the swap in a few days. How much it costs you will depend on how much you value the car. A $1000 engine swap will probably use a junkyard engine. A proper rebuild on your own could easily push $3000 or more.

You can always buy a rebuilt engine and swap it yourself. Depends on how much time you want to spend doing it. Get the car back on the road in a week or a few months?

UltRoadWarrior9

I would've like to have known the original cause of 'blowby' and more important: the cause of the low compression on Cyl #7. Confirmed, with pics.
Helluva run for that engine. I've read rings rotate naturally, maybe they lined up or maybe 1 broke.

emeryz28

Thanks, AlkyIROC. I have to think about this. The car does have some sentimental value to me, but as a practical matter, even if I spent $3000-$4000 putting an engine in it, I probably couldn't even sell it for that afterwards.

Roadwarrior, my next step is to drop the oil pan and pop out #7 to see what happened. I will post pics when I do it. With all the rest of the cylinders at 150 psi compression (and that's a stone cold, dry test), I'm not sure I'm ready to throw good money after bad by replacing the whole engine. I have heard about rings lining up but I don't know if that's on old wives' tale; although I sure hope that's what happened here.

TTOP350

iTrader: (8)

Go to a GM dealer, buy a new 350 shortblock from a 96ish chevy truck for 1500.00ish dollars. put all your parts on new shortblock and enjoy.

Or, have your shortblock rebuilt for about the same cost and have the original motor still in your car.

emeryz28

Thanks, TTOP350. That sounds like a viable option. Will a short block from a 96-ish truck be completely compatible with my heads, intake and accessories? What specific short block would I be looking for?

TTOP350

iTrader: (8)

Yes, its the same late model 350 sbc from a truck/car/boat. The ones I have gotten came with Hyper-pistons, powdered metal rods and 4 bolt mains.
When GM says shortblock, they mean it. You will get, (all put together) block, pistons, rods, crank, rings, cam/crank/rod bearings, mains and main bolts.

emeryz28

Thanks. That sounds like an attractive idea. So, even though they no longer make the L98, I can still get a new short block that is nearly identical (maybe better) than my L98? I'm not sure I understand what makes it an L98 (roller lifters?). I've been told that the L98 wasn't ever really spectacular anyway.

sofakingdom

iTrader: (1)

The reason the L98 wasn't "spectacular" (or even .... competitive, past 87 or so) was because it had TPI on it.

In its day it was a pretty good long block. TPI may SUCK by modern standards; or even, the standards of, say, 1989; but when it was introduced, it was LIGHT YEARS ahead of the competition, but that only lasted for about 2 - 3 years - but the castings underneath were pretty good. The best in their day, competitive with the early 70s muscle car 350s. Good heads, reasonable compression. Too bad GM stuck with TPI while everybody else, Frod in particular, moved on, and DOMINATED GM in terms of power and speed for many years as a result.

All of the short blocks mentioned above - "HO 350", 96 - 2000 truck, similar years of boats - are IDENTICAL. The same same same same same. Part # for part #. Not only that, there are no differences.

emeryz28

Yes, in its day it was something. But just like computers, you can by the best today and next year it will be a dog that everyone laughs at. Still, I get comments or questions about my Z28 just about every time I drive it. The most common question: "Is that an IROC?" Then I have to explain that it is, but it isn't for the 91/92 year. The next comment is that they either used to own one, or had a relative who owned one and they remember how much they liked it.

Thanks for the confirmation on the short block part #. That's good to know.

emeryz28

Congratulations! You were right! Do you know if they sell pistons and rings separately?

paulo57509

Is this the result of detonation?

AlkyIROC

One piston bad. The other 7 are probably not far behind.

You can buy a single piston but the wrist pin will be pressed into the con rod meaning you won't be able to replace it properly by yourself and there's a good chance you'll damage the new piston trying.

A single piston will also have a different weight than the rest that are still in the engine and will likely cause a noticeable imbalance.

emeryz28

I had a serious problem back in 1994 with the blower and ended up having to do everything from injecting water into the intake to installing an MSD BTM boost retard. It turned out that the injectors were not delivering enough fuel. I took it to Arizona Speed & Marine in Phoenix and they burned a new EPROM that saturated the pulse-width of the injectors, giving me just enough fuel to tear up a few transmissions in a short period of time. Could this be the result of weakening that occurred over two decades ago? I don't know. I never had any detonation problems after I removed the blower.

Does Chevrolet actually balance the pistons by weight on production cars? I didn't realize that. These are the only identifying marks I can find on the piston. Anyone know the significance of these numbers and letters? I'd definitely have a machine shop press in the wrist pin.

sofakingdom

iTrader: (1)

How do the other 7 look? Can't think of many things more short-sighted than seeing one cyl destroyed that bad, and "fixing that one, but not even looking at the others.

The factory "balances" by accumulating enough similar-weight pistons, similar-weight rods, etc., as they randomly emerge from production; then matching a crank to them. They don't "balance" the same way a machine shop "balances" a single engine.

TTOP350

iTrader: (8)

I would bet money that there is more than 1 piston damaged.

IrocZonNos

I experiencing same issue with Blowby however car seems to be running ok.
How was your PCV system hooked up?

emeryz28

All the other pistons had good compression (150 psi). Even if this does happen to another piston, I had been driving this car with blowby for two years. I'll probably have plenty of time to deal with it if/when it happens. In the mean time, I'm not too excited about dropping a $2000 short block into a car that's probably not even worth $2000.

My PCV systme is fine.

TTOP350

iTrader: (8)

A few yrs ago, I pulled apart a Paxton supercharged 350 tpi motor. It ran smooth a silk but 2 cyls were way down on compression and the rest were fine. Had a blown head gasket and broken ringlands on 6 of the other pistons.

emeryz28

I think the damage was probably metal fatigue that started over 20 years ago when I had the Paxton on it. Just got back from the machine shop. He said he thinks he can find a replacement piston, but it's probably not going to be a Mahle.

UltRoadWarrior9

Seriously, thanks for posting about your engine. Tearing it down is some kinda work, a great many man hours of labor...
But when you speak of trying to replace 1 piston and associated hardware with that 1 cylinder, you are losing all credibility for any future build with this thing dude!

emeryz28

There will not likely be a future rebuild with this engine.

UltRoadWarrior9

Save the block if you are attached to it. Maybe a backup engine/project in the near or far future...

Galaxie500XL

iTrader: (1)

At a minimum, I'd see if the machine shop can hone all of the cylinder walls, and clean them up, then buy a new set of rings for all 8, and carefully set the ring gap to compensate for the slight bore change. Not ideal by any means, but it should buy you several years of infrequent driving.

OrangeBird

iTrader: (1)

Here you have three people who obviously know engines telling you that standard operating procedure here is to go through the entire engine and not to "just slap a piston into it and go" . Yes , it just may work . But OTOH it's just as likely to have one of the other pistons fail , could even happen a week after you spend all the $$$ fixing the one piston . Also , you mention the other cylinders having 150 psi and claim that proves they are fine , you do realize a fresh engine's numbers are up in the 190s usually , and that I have seen 100K mile engines with 170 to 180 on a regular basis ?

I'm not being a dick here , this may sound kinda dickish but I'm really not tryin to be , but just so you know when you come to a tech board , ask advice , and then cause you hear something you don't want to hear all of a sudden now you don't need anymore advice from anybody , it makes you look bad .

PS , if the car ain't worth it to you to fix it right , sell it to someone who will fix it right . No car deserves 1/2 assed repairs because it's owner won't pony up the $$$ .

sofakingdom

iTrader: (1)

Look at it this way:

You've got an engine with 200,000 miles on it. It was SEVERELY abused for some significant portion of its life. It has now popped.

Let that sink in for a minute.

200,000 miles would make it a senior citizen even if your grandma had only driven it to the store and to church on Sundays.

Boosting it puts inordinate stress on it even if it's brand-new.

Your motor has BOTH of those forms of life-ending history on it.

Your attempt at failing to face up to the reality of the situation is not going to work out well for you in the end.

There's a more accurate description of the outcome of replacing just the one piston.

Wish in one hand, and have a body function in the other, and see which one fills up faster.

How do the other 7 look?

emeryz28

The other seven look good, but as several here have warned, they may be weakened and fatigued due to things that happened over twenty years ago. The engine seems to be pretty clean. There was hardly any ridge to speak of at the top of the cylinders. Now that I went through the trouble of taking all the pistons out, I'm planning on replacing the whole set with new rings and probably new bearings. I do appreciate all the advice.

OrangeBird

iTrader: (1)

And when your finished putting it all back together you'll have an engine done right , and hopefully 200K or more miles for it to go .

emeryz28

I hope so.

emeryz28

Finally got it back together and running today. Thanks to everyone for input on this thread. I found a bent piston rod on #8. Who knows how long that was there. Probably 20 years. New pistons, bearings and rings (and one piston rod). No more blowby.