HELP! bad compression...
11-07-2005, 10:28 AM
#1
Old Polish Lady Lover
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Location: Cheektowaga, NY...land of nothing but a mall and 10,000 old Polish ladies
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HELP! bad compression...
so #6 has low compression, and i have the infamous valve lifter tick as well, but from #4 i believe...i'm not worried about the tick because numnerous z owners have told me it can be a common thing...i'm just worried about my head gasket now though...
i dyno'd the car saturday, with 2.5" downpipes and testpipes, the rps flywheel, and ur pully...and only made 190whp...
it can't be in safety boost because i bypassed the det sensor with a resistor...but the guy that did the pull on the dyno says the car creeped slowly and barely hit 7psi...which sounds exactly like safety boost...
i'm going to run another compression check soon, last time we did it was before we even got the car running properly...and i'm also going to try to listen for any vacuum leaks...but the power curve on the dyno looks bad, 220 tq 190 hp, and it peaks around 5k i think...dropping down after that...
any suggections as to how much labor (hour wise) is included in changing a head gasket? if i'm better off just getting another engine, and where BESIDES Z1 to go to get that engine? what would be cheaper...this engine supposedly only has about 60k miles on it, so i dont want to trash it if i dont have to...i have plenty of very knowledgable friends that work for dealers and what not, and would be able to help me out with the project...but incase none want to get involved in what has become known locally as the "hell swap," what can i expect as a quote from a shop on the labor involved in changing the head gasket? and i have my spare NA motor still, so i will be using that as a parts source for the new valve lifters that need to be replaced...
SIDE NOTE: i was also told that it may not be a head gasket...even though head gasket problems can be tricky to find, i was told it may also be a bad or damaged piston ring because my oil is not milky looking like head gasket problems usually would make it...i have a diagnostic sheet in front of me on how to check compression, then put oil in the spark plug chamber to see if that fixes it...and if it does ist most likely a piston ring, if not it could be a bad sitting valve or a head gasket...
what do you all think?
i dyno'd the car saturday, with 2.5" downpipes and testpipes, the rps flywheel, and ur pully...and only made 190whp...
it can't be in safety boost because i bypassed the det sensor with a resistor...but the guy that did the pull on the dyno says the car creeped slowly and barely hit 7psi...which sounds exactly like safety boost...
i'm going to run another compression check soon, last time we did it was before we even got the car running properly...and i'm also going to try to listen for any vacuum leaks...but the power curve on the dyno looks bad, 220 tq 190 hp, and it peaks around 5k i think...dropping down after that...
any suggections as to how much labor (hour wise) is included in changing a head gasket? if i'm better off just getting another engine, and where BESIDES Z1 to go to get that engine? what would be cheaper...this engine supposedly only has about 60k miles on it, so i dont want to trash it if i dont have to...i have plenty of very knowledgable friends that work for dealers and what not, and would be able to help me out with the project...but incase none want to get involved in what has become known locally as the "hell swap," what can i expect as a quote from a shop on the labor involved in changing the head gasket? and i have my spare NA motor still, so i will be using that as a parts source for the new valve lifters that need to be replaced...
SIDE NOTE: i was also told that it may not be a head gasket...even though head gasket problems can be tricky to find, i was told it may also be a bad or damaged piston ring because my oil is not milky looking like head gasket problems usually would make it...i have a diagnostic sheet in front of me on how to check compression, then put oil in the spark plug chamber to see if that fixes it...and if it does ist most likely a piston ring, if not it could be a bad sitting valve or a head gasket...
what do you all think?
Last edited by Riz Z Speed; 11-08-2005 at 11:34 PM.
11-07-2005, 11:05 AM
#2
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I agree, it's not necesarily your HG. Go to NAPA and get a combustion gas tester. It tests to see if there's combustion gases in your coolant. This will help you figure out for sure if it's your HG or not.
11-07-2005, 02:44 PM
#3
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Location: Naperville, IL
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Just so you know, if your power fell off that early and you only hit 7psi, you could also have vacuum leaks causing that (and, if the compression is really bad, your engine might have trouble even making the full 9psi)
As for your compression, it's pretty rare that a 300ZX blows a headgasket; cracking ring landings or wearing out rings is much more common... but what do you mean by it supposedly has 60k miles? Is this a JDM engine? If it is, I'm sorry bro, but it's probably a ring or piston problem. I say this because 1) there is no Japanese equivalent for carfax, so you really have no guarantee of the mileage of your engine, 2) In Japan, you have to either replace the engine or the car every 100k kilometers (or something like that), so if you had a car that you knew you were replacing the engine on anyway, how would you treat it? They're generally beat to ****. If it comes back that it's a ring or piston problem, don't put another JDM engine in it, get a USDM engine or rebuild that one. There's too much uncertainty with JDM engines, and that why Ultimate Z (at least when I worked there) won't deal with them.
As for your compression, it's pretty rare that a 300ZX blows a headgasket; cracking ring landings or wearing out rings is much more common... but what do you mean by it supposedly has 60k miles? Is this a JDM engine? If it is, I'm sorry bro, but it's probably a ring or piston problem. I say this because 1) there is no Japanese equivalent for carfax, so you really have no guarantee of the mileage of your engine, 2) In Japan, you have to either replace the engine or the car every 100k kilometers (or something like that), so if you had a car that you knew you were replacing the engine on anyway, how would you treat it? They're generally beat to ****. If it comes back that it's a ring or piston problem, don't put another JDM engine in it, get a USDM engine or rebuild that one. There's too much uncertainty with JDM engines, and that why Ultimate Z (at least when I worked there) won't deal with them.
Last edited by Riz Z Speed; 11-08-2005 at 11:36 PM.
11-07-2005, 03:26 PM
#4
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I highly agree with zlover as far as jdm motors. they're hit or miss. They're like a box of choclates...ya never know what your gonna get. Do some diagnostics, then fix the problem, if it's a rebuild, at least you'll learn a lot about your motor and have peace of mind afterwards.
11-08-2005, 12:32 PM
#5
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how hard is a ring problem to fix as opposed to changing a head gasket? i know neither is easy by any means since both require a full engine pull and disassembly pretty much...
and when rebuilding, what do you all recommend i do? what i mean is, other than fixing my valve tick and the compression problem, what else should i look into while in there? while i have it apart, i know there are other things i should probably check and replace to save myself the labor later...what are some recommendations? and if possible, can i get some price/time quotes on some of this work?
what i dont get though, is that the car drives real smoothe...not jerky, not loud, not bumpy...it's a real good ride...which is a relief because at least i know i dont have any rod problems...
and when rebuilding, what do you all recommend i do? what i mean is, other than fixing my valve tick and the compression problem, what else should i look into while in there? while i have it apart, i know there are other things i should probably check and replace to save myself the labor later...what are some recommendations? and if possible, can i get some price/time quotes on some of this work?
what i dont get though, is that the car drives real smoothe...not jerky, not loud, not bumpy...it's a real good ride...which is a relief because at least i know i dont have any rod problems...
11-08-2005, 01:26 PM
#6
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I was just looking at your mod list....do you have an upgraded ECU?! If not and you're running 12psi, I'm sorry. On your winter mod list, you have weisco pistons, you can do the rings then during that rebuild.
11-08-2005, 01:31 PM
#7
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well, the quality of normal driving won't necessarily be sacrificed with a "blown" engine (in my book, blown = bad compression for whatever reason, or any other internal problem that diminishes performance and requires a rebuild to be resolved).
For instance, when I blew my first engine (technically, my second engine, but whatever), it was from a 26psi overboost. Car fired on all six and I really didn't have any drivability issues, infact I'd go as far as to say it performed exactly like it was supposed to, but when I'd boost high (I think 12psi is about the point where this would happen) it'd shoot the dipstick out and blow oil all over my engine (the boost was getting past the piston into the crankcase, and it was more than the PCV valves could handle, so the only other place to escape was the dipstick). Compression came back as 75psi in the 2 cylinder (and I can tell you exactly how everything happened and why that cylinder died the way it did to top that off), and it turned out I had a cracked piston...
as for cost, that entirely depends on what you have done, who you pay, and how well you/they do it. If you can do all the work yourself, a minimal rebuild could cost $500 (assuming there's no cylinder wall damage)... on the flipside, I could easily spend $15k on my engine if I had the opportunity (I've already figured out how I'm going to spend $5k on the heads alone...and that's without any porting/polishing or other machine work).
For my rebuild, I did a .020 overbore with Wiseco pistons (polydyne coated), reground and micropolished crank with oversized bearings, all new gaskets (duh), and no headwork. Start to finish it cost me about $1500. I had a machine shop do the bore/honing and the crank work (~$600 total) and I did everything else (pulled the engine, stripped it down, put it back together, and reinstalled it). However, the machine shop I went to was very cheap compared to others, and I now know why... they're sh!tty. They overbored my overbore and I again have an engine with bad compression (will be rebuilt this winter for anyone who cares). For the same work at a quality machine shop, it would've cost about $800+.
A normal rebuild will cost upwards of $4,000 if you're paying someone to do all the work for you. The cost rises really quickly if you do headwork or get more expensive pistons (Wiseco's - $585, JE - $800....), rods, and all the other goodies. If you can get by with replacing the rings and it'll solve your problem (meaning there's no cylinder wall damage and it's just a cracked ring), expect it to be close to $4k though.
What would I recommend doing while you're in there? That depends on your goals with the car. Eagle rods ($400 IIRC), Wiseco pistons, and new lifters and valve springs with all the proper headwork would be really nice and your engine would rev like a mutherf*cker, but it just might not be realistic for you.
important stuff...
-have the crank sonic-tested (I think that's what it's called) for cracks
-have them check its balance
-have them mic it to make sure it's within spec (and if it's out of spec, make sure to get it reground and oversized bearings to match)
-if it's just one bad piston and the cylinder wall is fine, just replace the piston... if the piston is fine and it's just the rings, replace the rings. If you can afford the extra money, replace the pistons and rings though, because it's better to be safe than sorry.
-gaskets... get an OEM Gasket Kit (about $250-$300 IIRC), but that's a given with a rebuild
-lifters, because that's probably what's ticking on you
-have the heads checked while you're in there (if you can afford it). It's probalby not necessary, but it could be a contributing factor and again, it's better to be safe than sorry. Re-deck the heads if need-be.
that's pretty much it... like I said, I didn't even go that far into it, but my lifters weren't ticking and I know my heads were fine; I just did the overbore with Wisecos and made sure the crank was fine and put it back together with all new gaskets.
Hopefully, for your sake, it's just a head gasket... but it's not that likely. If it isn't, and all of this (cost and work) scares you, like I said before, just get a USDM TT engine and swap it out...
For me though, this winter.... hahahaha..... Wisecos are going into a new block with Eagle rods, lots of headwork, and the GT2530's will be resurrected once again... (I <3 building VG30DETT's)
For instance, when I blew my first engine (technically, my second engine, but whatever), it was from a 26psi overboost. Car fired on all six and I really didn't have any drivability issues, infact I'd go as far as to say it performed exactly like it was supposed to, but when I'd boost high (I think 12psi is about the point where this would happen) it'd shoot the dipstick out and blow oil all over my engine (the boost was getting past the piston into the crankcase, and it was more than the PCV valves could handle, so the only other place to escape was the dipstick). Compression came back as 75psi in the 2 cylinder (and I can tell you exactly how everything happened and why that cylinder died the way it did to top that off), and it turned out I had a cracked piston...
as for cost, that entirely depends on what you have done, who you pay, and how well you/they do it. If you can do all the work yourself, a minimal rebuild could cost $500 (assuming there's no cylinder wall damage)... on the flipside, I could easily spend $15k on my engine if I had the opportunity (I've already figured out how I'm going to spend $5k on the heads alone...and that's without any porting/polishing or other machine work).
For my rebuild, I did a .020 overbore with Wiseco pistons (polydyne coated), reground and micropolished crank with oversized bearings, all new gaskets (duh), and no headwork. Start to finish it cost me about $1500. I had a machine shop do the bore/honing and the crank work (~$600 total) and I did everything else (pulled the engine, stripped it down, put it back together, and reinstalled it). However, the machine shop I went to was very cheap compared to others, and I now know why... they're sh!tty. They overbored my overbore and I again have an engine with bad compression (will be rebuilt this winter for anyone who cares). For the same work at a quality machine shop, it would've cost about $800+.
A normal rebuild will cost upwards of $4,000 if you're paying someone to do all the work for you. The cost rises really quickly if you do headwork or get more expensive pistons (Wiseco's - $585, JE - $800....), rods, and all the other goodies. If you can get by with replacing the rings and it'll solve your problem (meaning there's no cylinder wall damage and it's just a cracked ring), expect it to be close to $4k though.
What would I recommend doing while you're in there? That depends on your goals with the car. Eagle rods ($400 IIRC), Wiseco pistons, and new lifters and valve springs with all the proper headwork would be really nice and your engine would rev like a mutherf*cker, but it just might not be realistic for you.
important stuff...
-have the crank sonic-tested (I think that's what it's called) for cracks
-have them check its balance
-have them mic it to make sure it's within spec (and if it's out of spec, make sure to get it reground and oversized bearings to match)
-if it's just one bad piston and the cylinder wall is fine, just replace the piston... if the piston is fine and it's just the rings, replace the rings. If you can afford the extra money, replace the pistons and rings though, because it's better to be safe than sorry.
-gaskets... get an OEM Gasket Kit (about $250-$300 IIRC), but that's a given with a rebuild
-lifters, because that's probably what's ticking on you
-have the heads checked while you're in there (if you can afford it). It's probalby not necessary, but it could be a contributing factor and again, it's better to be safe than sorry. Re-deck the heads if need-be.
that's pretty much it... like I said, I didn't even go that far into it, but my lifters weren't ticking and I know my heads were fine; I just did the overbore with Wisecos and made sure the crank was fine and put it back together with all new gaskets.
Hopefully, for your sake, it's just a head gasket... but it's not that likely. If it isn't, and all of this (cost and work) scares you, like I said before, just get a USDM TT engine and swap it out...
For me though, this winter.... hahahaha..... Wisecos are going into a new block with Eagle rods, lots of headwork, and the GT2530's will be resurrected once again... (I <3 building VG30DETT's)
Last edited by Riz Z Speed; 11-08-2005 at 11:45 PM.
11-08-2005, 01:36 PM
#8
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my quick summary (for those wondering how mine only cost $1500)
Wiseco pistons, coated - $585
Machine Shop work (crank, overbore, hone, bearings) - $600
gasket kit (with my discount at the time) - $250 IIRC
plus various other supplies (RTV, brake cleaner, etc)
Wiseco pistons, coated - $585
Machine Shop work (crank, overbore, hone, bearings) - $600
gasket kit (with my discount at the time) - $250 IIRC
plus various other supplies (RTV, brake cleaner, etc)
11-08-2005, 05:44 PM
#9
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my mod list isn't exactly accurate...that's what i was supposed to be at, but i never even got around to hooking up the boost controller, and still run stock boost, and yest still have the stock ECU...
$4k will be way out of my price range...i know i can pull and put back the engine myself with the help of some friends...that will save me a lot of labor cash....parts i will most likely get all OEM and used where i can...my dad is a machinist, and i'm sure he knows some automotive machinists that could help me out if i do need machining done...i'm hoping i can get it all done under $2k
$4k will be way out of my price range...i know i can pull and put back the engine myself with the help of some friends...that will save me a lot of labor cash....parts i will most likely get all OEM and used where i can...my dad is a machinist, and i'm sure he knows some automotive machinists that could help me out if i do need machining done...i'm hoping i can get it all done under $2k
11-08-2005, 09:17 PM
#10
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$1500?! When I just did a HG on my poopra, it ended up costing me $700+ and the machining only costed me $75. All the little stuff like a new water pump, new hoses, vaccum lines, etc added up! The upgraded HG and arp headbolts added a quick $250 too.
11-08-2005, 09:58 PM
#11
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well, I also saved on the timing belt and water pump (and related parts) because I had done a 120K only 11 months prior, so all those parts I reused.
90NA300ZX - like I said, it can probably be done for less than $1500 if you can do most of the work yourself. Pulling and reinstalling the engine saves you upwards of $1600 alone. Stripping down the engine will save you a few hundred as well. Either way, though... good luck!
90NA300ZX - like I said, it can probably be done for less than $1500 if you can do most of the work yourself. Pulling and reinstalling the engine saves you upwards of $1600 alone. Stripping down the engine will save you a few hundred as well. Either way, though... good luck!
11-16-2005, 10:24 AM
#12
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will be pulling and and putting back the engine myself...with the help of some friends in the spring, winter's coming fast up here in Buffalo so i'm not gonna even bother trying to start the project now...just do a lot of homework and reading and talking to people that have done it before, so i'm ready in the spring...also, i have my old NA engine sitting at my dad's shop, ready for me to practice taking apart...if i feel comfy with it after trying out the disassembly on the na motor, i might just do the whole thing myself, and like you said, save myself close to 2 grand...that'd be nice...even though i'd just end up spending it on other **** for the car that i want, and dont need...
Last edited by Riz Z Speed; 11-16-2005 at 12:55 PM.
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