Engine blown or not blown. Is Mechanic right

[Guest ekomike1]

Hi guys.

I have been going through a nightmare . I got a 280zxt picked up in Fla. The old owner decided to turn the Turbo off (in his altimate wisdom). He told my pick up people that it couldn't take the long trip with the Turbo on. He cranked it all the way in. I paid an extra $2000 and got it shipped not running (not including original pick up expenses ($1000). I got it checked and was told that the head gasket was blown by a local mechanic.The frost plug blew out . closest to the upper block by the water thermostat.(is this a frost plug?) I spent the next 2 weeks tearing down the top end , sandblasting , checking and repainting all the parts.The head was perfect , and the way that i slid the head off , damaged the gasket on removal. I couldnt tell if it blew or if it was just damaged on removal. Put the engine back together. It wouldnt start. All cylinders were low compression. 90 psi. Took it back to mechanic.He said that the engine block must have a hole in it the size of my fist. Its hard for me to believe. He changed timing and still couldnt get compression. His final comment was that he poured water into the plug hole (where the plug blew out). He said that the water went right into the oil pan as fast as he poured it into the water jacket. My question is two fold. First. Is it possible that that part of the water jacket is actually casted to attach to the oil passages? and not to the water jacket at all? Its a 25mm plug. Not 32mm like the rest. second , any ideas on why compression is so low , if in fact there is a possibility that my theory may be correct. Others have told me that it is almost impossible to blow a hole through the block internally. I should mention that the head was perfectly straight and everything looked good in the cylinder walls and piston tops except for cylinder 3. It had coolant in it. That backs the theory of the head gasket being blown.Why are all cylinders low?

[Warren]

Not to be contrary, but you need to find someone who knows what they're talking about, much less what they're doing, i.e., another mechanic.

 

His final comment was that he poured water into the plug hole (where the plug blew out). He said that the water went right into the oil pan as fast as he poured it into the water jacket.

 

Uh, wait a minute...the 25mm hole under the thermostat housing would be where the PCV pipe originally went. Apparently, the previous owner used a plug to block it off. It SHOULD go straight to the oil pan, it's an engine block airway passage.

 

Now, that being said, you clalim that the head was perfectly straight and everything looked good in the cylinder walls, etc... How about the block? Did you check BOTH surfaces with a straight edge, or did you just eyeball it after removing and cleaning up the old gasket material? Did you or he use the proper head gasket? The 82ZXT uses a P90 head and the older gaskets won't seal the water passage between #5 & #6. Go to the dealership and get the right gasket.

 

Also, since the timing on a ZXT is NOT adjustable, according to the FSM, and is controlled by the ECU (ECCS System), I'd like to know how he performed this little miracle.

 

I'm no expert, but I'm willing to bet that it's nothing more than a blown head gasket, probably due to the engine overheating, and nothing a proper rebuild by a competent mechanic who uses a real machine shop (even using your old parts) wouldn't fix.

 

Advice: Buy a factory service manual, read, read, read. Get to know what the engine is supposed to look like, what it's supposed to do, and how it's supposed to be rebuilt. They can be purchased through Courtesy Nissan or downloaded free from Carfiche.com when it's available.

 

Then, take the FSM, if it's in CD form, print it out, and go beat that mechanic over the head with it until he goes unconscious. When he regains consciousness, explain to him that you're donating that copy of the FSM to him for his own educational use later in life, with the hopes that he'll actually read it and stop advising people that they're motors are completely blown when all they really need is a proper head gasket replacement.

 

I don't think I totally understand how you turn a turbo off. That's a new one to me. If you're referring to adjusting the wastegate actuator to a non-operating position, that should have been one indication that the previous owner didn't know what he was talking about either.

 

Excuse the sarcasm above, as it was intended to humor a bad situation. Just find a mechanic that has worked on L28's before and knows what he's talking about. The one you're using obviously doesn't and that can be VERY costly.

 

Warren

[woldson]

warren said it well, their is a lot of stinky on this one. is compression consistant across all the cyn?

[Guest ekomike1]

Thanks for the Sarcasm. I am not that sensitive and needed some good laughs. Your response was very informative. I am new to the Z world. I am very mechanical ,but only now getting familiar to this engine. What a way to start. You have convinced me that my theory of this 25mm hole going straight to the oil pan is actually true. Thanks for that. Furthermore your suspicions of the gasket being the wrong one could be true. I did take the Head into a reputable shop and watched the runout on the dial indicator myself.It was very straight. I am guilty of not putting a straight edge on the block.I did buy this gasket from the Z store.I never would have thought that they would ship me the wrong one.

Timing.... He didnt really adjust the timing. He repositioned the cam gear to what he said was the proper notch.I did read the manual on that part , plus got good info off of this site. I thought that i had it right , but i could have been wrong. The old owner was an idiot , your right. He has small adjuster to the turbo.Could be to the gate.(remember i have never seen this thing run nor do i claim to be an expert on Z s or Turbos). Sounds like the mechanic is a loser as well. He showed me a screen of some sort that he pulled out of the 25mm hole. It had Oil residue on it. This is what made me think that he was wrong ,and this hole was in fact connected to the oil pan..Duh..

Thanks for the quick response. I have already given him the go ahead for pulling the engine. You may have saved me a lot of time and money. You can be as sarcastic as you want with good technical advice like this.

1 more thing. If the head gasket is wrong...... Is that the reason that every cylinder compression is low? He said 90 - 95 psi.I have to trust that he at least knows how do a compression test. Finally. what exact info should i need to order the proper gasket? The cylinder walls were perfect and the pistons tops looked new. It didnt make sense to me.

Hopefully you guys can help me cut my teeth in this new Z world. I will get some photos up soon. Shes a Beuaty...... Mike

[Guest ekomike1]

he said that they were a;ll around 90 - 95 psi

[Warren]

Pistons look new, clean and not nastied up, could mean that the previous owner, changed them to the wrong ones (unlikely though). Just guessing on this one. That would account for lower compression. Like I advised earlier, get the FSM and go through it. It'll teach you ALOT about the car.

 

The screen that he pulled out should be inserted from the bottom, with the oil pan off, it actually has a sheetmetal cover that stops it from dropping into the oil pan. Please replace it properly when you go through the engine. There are 2 phillips screws that hold the cover on. Be sure to use some threadlock on those, if they fall out, you'll be rebuilding it again.

 

The info you need to get the proper head gasket is the model number (S130), the month and year of production (found on the driver's side B pillar tag) and a dealership who knows how to look up the right gasket. There was a modification of the part number done by Nissan some time ago. The head gasket that the car came with has been superceded. I'd have to go through alot of paperwork to get you the right part number, but the dealer should be able to get the right one for you with the above information.

 

Please be aware that this site is geared more toward Hybrid Z's, meaning swapped engines and highly modified powertrains. All of the information regarding the stock configurations can be found on the web in various places. This site has an extensive amount of information on both stock and modified engines, but you MUST use the search engine to access it. Your questions are basic enough that other places may have more info available regarding them. Welcome and enjoy the ride!

 

Warren

[Guest ekomike1]

Thanks for that advice. I am planning on modifying drive to Hybrid.Thats why i joined this site.I looked at your mods. Thats the way i want to go. Bigger Turbo , Injectors , exhaust , tranny , clutch ,etc. My goal is to get a 300+ H.P. reliable car.It alreday has an intercooler and 3" stainless exhaust ,Electonic fuel pump. Electronic msd ignition with fireball coil.I would prefer to go with whats proven. Does my dream sound like reality? what is your experience with your Mods? I am also prepared to do brakes as well.I have the funds. I just want to do it right. Mike

[Guest ekomike1]

what happens if i leave that screen out? they pulled it out from the hole. Would i have to take the engine out to replace it?

[SHO-Z]

Just a quick look at the 90 psi per cylinder. A L28 TURBO with a P90 head has 7.38 to 1 compression ratio acording to the Lengine program. With 7.38 CR the cylinder should have around 94 psi on a test from my calculation.

 

I would do a pressure test on the cooling system to start with.

[woldson]

kinda waht i was pondering due to the consistancey. fyi thotal must be wide open for acuate pressue test!

[ShaggyZ]

Just a quick look at the 90 psi per cylinder. A L28 TURBO with a P90 head has 7.38 to 1 compression ratio acording to the Lengine program. With 7.38 CR the cylinder should have around 94 psi on a test from my calculation.

 

Really? I have a '89 Merkur XR4Ti (turbo Ford 4cyl) and my compression readings are around 175psi across all 4 cylinders. I think the compression ratio is around 8:1. 94psi can't be right unless I'm missing something.

[Warren]

It's NOT right. The FSM lists the compression specs as 142 Max, 100 Min @ 350 RPM. I would go by the specs in the FSM. Don't rely on a computer program that was written 20-25 years after the engine was built, for calculations. It doesn't take into consideration all of the variables and changes from year to year involving the block and head differences from year to year.

 

BTW, I don't think it's possible to turn the motor to 350 RPM with just the starter and since there would be more than 1 cycle of the piston during the test, the values above would have to be an average.

 

If you want to hear a horse, go to the horse, not the zebra. All of the information you need about the car is in the FSM. The rest of the info you desire about the mods you can make are listed (if only by reference) on here.

 

You can literally spend 3 months reading the search results here and find more than enough information, with reasons, before you even touch the engine and be so well versed on the engines, you'll know what works and what doesn't and why, but always refer to the FSM and microfiche for stock specs.

 

Sorry, meant to add 2 cents worth and dropped a dime instead.

 

Warren

[SHO-Z]

I used the perfect gas formula.

 

PV/NRT=PV/NRT get rid of the NRT on both sides and PV=PV

 

V/V= Comperssion ratio or change in volume.

14.7 is the absolute pressure at sea level

Gauge pressure is PSI - 14.7

 

So 14.7x CR = PSI in cylinder-14.7 is what you get in your compression gauge.

[savageskaterkid]

You sure this is right? Because if I took that formula and switched it, I could use in reverse. PSI divided by 14.7= C.R. My compression numbers came out to 150 across the board. Divided by 14.7 and I get about 10:1. Does this sound right for a stock N42/N42 motor? I think the formula is wrong.

[Sparks280zt]

Savage, your numbers appear to be in the correct range.

[drzed]

First, as said above get a FSM and read. For the most part they are filled with facts! Until you find a FSM, research via this and other sites but beware - not everyone who posts on these sites knows what they are talking about so the facts seem to get skewed. On the other hand there are many people on this site who consistently provide good info - Warren above seems to be this type.

 

Second make friends with someone local who knows Z's (or at the very least vehicles in general) and have them look at this car before you do anything else or spend any more money. There are lots of good guys in Ontario (Doug??) who could help you out.

 

Now for what we know. The first owner sounds like an idiot and this mechanic might not be much better so who knows what else they have screwed with. The cranking pressure is dismally low but even across the board. There is no formula (at least that I know of) that will give cranking compression from static compression ratio - the reason is that although related there are many other factors that come into play. In your case it could be the wrong head on the wrong block (unlikely) or the cam to crank timing is out (more likely). When you get your FSM you will want to check this out.

 

Now the compression being low on all cylinders and your (potential) water problem are probably not related. After checking out the cam to crank timing you and your new Z friend could pressure test the cooling system but at this point it will run leaking or not. As a side note did you have the head pressure tested when it was off? This is important on L series engines due to the high possibility of cracked heads.

 

Also, once you get this thing running confirm whats going on with the turbo to make sure that the previous owner didn't damage anything.

 

As for the screen just leave it out for right now. If you end up pulling the engine it can be easily replaced from below as Warren said but if you get the engine running an alternate oil baffle system might be required (to save pulling the engine).

 

Good luck with your new project.

[aarang]

When was the last time this mechanic had his compression tester calibrated, or even knows how to use it properly???

[Tony D]

I'm going to cross post on this thread, as I addressed this same query at another forum...

First, the compression. My statement at the other site was "did your mechanic do a proper compression test"?

 

Well, this is a prime example of what I referred to: someone doing a calculation and coming up with a totally wrong conclusion.

 

Warren is correct in his 100 minimum, 150 normal statement---first off it's out of the FSM which is final arbiter on conflicts like this, and because he reveals the problems of mechanics not knowing how to take a compression test.

 

I stated in the other post "is that a one-pump number?"

 

Well, the theoretical measurement people are touting here is a one pump reading! Yes, the compression ratio is 7.38:1, and ON THE FIRST PUMP AT SPEED, the gauge should come up to around 90 psi.

 

But a compression test does not consist of only the initial compression pump!

 

The first pump will tell you if there is any DRAMATIC issue with teh cylinder like a burnt valve, holed piston, etc. This is why it's critical that you use a screw-in compression tester, and obsaerve the way the pressure rises.

 

Yes, the first pump will be around 90, but the second time that piston comes around to compression stroke, it should jump up further to at least 135, if not 150. And by the third pump it should stabilize or make the final rise to 150. Most good mechanics will then let it pump once or twice more to see what happens, but only if the compression is not rising.

 

See, if the thing jumps to 100, then 150, and holds there. Then everything is hunky dory. If it takes three pumps to make 100psi, and doesn't rise to 150 by five pumps, the cylinder is tired, maybe a bad valve seal leaking...whatever, further diagnosis (like a leakdown test) will be required.

 

If it cranks and cranks and takes a everything it has to get to 90 psi, chances are good there is a bad ring land. This is where the follow on "Wet Test" will confirm if it's bottom end, or top end. I have had Toyota 3C engines pump 60 after 10 pumps, and then on a wet test jump to 120psi in two pumps: classic worn ring scenario.

 

On an L, if you don't get that compression right away, and it's taking five pumps to get to 90 psi, then there is something wrong. If it's there at one pump, and doesn't rise.... then there is also something wrong, just a different thing!

 

The key is to watch and observe the test to see how the number is arrived at. If this guy is using a 'hold it in and push hard while cranking' compression tester...well that is about useless as they generally leak as much as they take in. If he's doing a "one pump" it's not a full diagnostic reading.

 

Of all the threads NOBODY has asked what the "Wet Test" results were, and apparently the mechanic is condemning the engine WITHOUT doing a wet-test!

 

My wife's 260 had 150-150-100-100-150-150 on a five pump style test. EXACT SAME RESULTS DRY AND WET. That told me the RINGS were FINE.

There was (my assumption) a bad head gasket, though when I pulled it I saw no channelling. So quickly I examined the valves while the head was off, and found some debris on the #3 & 4 valve sealing faces. So a quick shot of lapping compound on all the exhaust valves, slap it together, and run it. Compression was up to spec across the board, so the next day I took it on a three week 18K mile run around the country with my son as co-pilot.

 

Thing is, without a dry and wet test, and knowing the methodology around the test, everyone is guessing. No conclusions can be drawn form the numbers given, as IMO the WET TEST has to be done and results presented BEFORE a condemnation can be given.

 

But back to the "theoretical compression"---yes, 7.38:1 will give you that compression on the first pump, but like an air compressor you will keep pumping against that deadhead and should gradually build, over several pumps, a peak pressure. This is why reciprocating industrial air compressors have relief vavles, they are positive displacement pumps, and it wil lkeep cramming air into a spac till it goes boom given proper inlet conditions. The thing is with a starter driven compression test, the dynamic filling of the cylinder can not be taken into effect because the engine is not turning fast enough to have ring sealing, valve overlap, etc, give you what you are really getting in the cylinder at idle speed. This is why the FSM gives you a number higher than "static" theoretical compression. This is what the FSM gives you, and is a direct result of testing on the engines when new. Basically one pump will not dynamically give you the proper reading regarding ring seating. There is more to it than that, as I have explained above.

 

When aarang said 'or even knows how to use it properly???" I thought "at least someone else wonders about technical competence"---that is a big issue these days. Mechanical training is sorely lacking and like I said in the post elsewhere, old timers are set in their ways---and in many cases never received proper training in the first place. It's the old "I've always done it this way" argument---to which I will always reply: "If you screwed your sister for the last 20 years, that doesn't make it right!"

 

Hope this helps out, and clears up some of the theoretical tangent. 90 psi is NOT a correct pressure. Warren is correct on that, 100%!

[Warren]

If you've been reading this thread from the beginning, please note that I edited my earlier post to include the fact that the specs in the FSM also state "@ 350 RPM".

 

Nissan, in their engineering and development stages actually turned the engine over with an external device of some sort to come up with the 142 Max and 100 Min "@ 350 RPM", and as stated earlier, that obviously cannot be done with just the starter.

 

TonyD is right on the money. It takes more than just single cycle to get the correct pressure reading. Wet tests will ALWAYS increase the compression numbers, but leakdown tests will tell you alot more about the condition of the internals.

 

Now, getting back to the original question in the poll, there is not enough correct information provided by a simple, wet or dry, compression test to tell whether or not the problem is being caused by the rings (oil passage) or the head gasket (water jacket).

 

NOTE: I'm assigning the rings to "oil passage" and the head gasket to "water jacket" for the purposes of this poll only.

[Tony D]

Yes, as Warren stated "@350" (which I thought I read) adds to another oft overlooked compression testing mistake by technicians who are not...er...."melticulous"... A fully charged battery is required for the engine to crank at that 350rpm from the starter.

I have had customers come in after doing their own compression tests screaming that one of the shops rebuilds "took a dump" because they couldn't get proper compression.

 

They were, in one case, cranking a STONE COLD engine, in an UNHEATED GARAGE (and we're talking -20F cold soak, with them going out and firing up the heater in the shop, and rolling the car from unheated storage to the shop and immediately testing while everything is still -20...), and just not understanding how I got the numbers I got the prior week when doing my compression tests.

 

Battery Condition, Engine Warm or Cold, Throttle Plates Blocked Open, ALTITUDE OF THE TESTING FACILITY....I mean the list of variables are endless, and many times people just disregard them, and you can't do that and expect any test to provide any usefull information!

 

Crossing the "T's" and Dotting the "I's" is the hallmark of a good technician. Unfortunately, through no foult of his own, Ecko is probably being fed inaccurate information from the tech, who has a vested interest in performing more heavy maintenance to cover his initial warrany costs after the come-back on the initial head gasket replacement.

 

Sad to say that, but in the reality of today, this is more often the case than not.

 

The thing to be aware of is that at least two more tests need to be accomplished: A WET compression test, and a Leakdown Test.

 

Wether the compression comes up or not on the Wet Test, a leakdown should be performed.

 

But that all comes back to Testing Methodology. If this bozo is doing a "one pump" test, all of it is out the window, as the test results are useless!