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Recently I've been looking into the need to redo the head on my 83zx/non. I've been told by some of the head rebuild shops not to rebuild unless I'm willing to rebuild the whole engin. They've said a rebuilt head will "blow out the bottom end". Could somone explain to me what they mean by this ? Rings ? Pan gasket ? Front and rear mains ? Main bearings ? or all of the above. I could deal with gaskets and seals but not sure I want to deal with rings and mains at this time.
 

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That doesn't sound right to me unless you change your compression ratio. Bottom ends on the ZX are really strong. By bottom end, I mean mains. I rebuilt mine with pistons, rings, connecting rod bearings (left the mains alone) and head work. It is at 15k and very strong.
 

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<b>RE: definition please</b>

I did a top-end job on my brothers 70 Corvette Sting Ray some years back and suggested strongly to do the bottom-end while we had it apart. He insisted that it had only 50K on the motor. When we ran the motor it smoked real bad. the motor in fact had 150K and the compression now being kept in the head was leaking past the worn rings (blowby). Depending on the mileage on the motor you might consider bottom-end work. Hope this helps.
 

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I know what he's talking about

Mechanics that do general repair are skeptical of putting a "tight" head on a mileaged bottom end. They are for allot of reasons primarily that they will end up eating the job. In some cases the rings may be in such wear that a good tight head *may* cause ecxessive blowby past the rings. When you are working on commission you try to stay away from jobs that *might* bite you in the ass, and create an unhappy customer. No one likes to work for free, which is what they are afraid of most. This is a general rule of thumb when you are a all purpose Auto repair shop.

From an ex general repair auto mechanic

Ken
 

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<b>There is Truth In Those Words</b>

I have seen that exact problem happen on three different engines (none of which were mine)after I advised friends to not do the top end without doing the bottom end when the rings have a lot of miles on them. You can take your chances, but I would recommend doing the complete job.
 

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RE: There is Truth In Those Words

On an overhead cam engine and specifically on the Z cars that is not a problem. I know of tons of people who have bought completely new heads, rebuilt heads and have taken the head off cut bigger valves, basically performanceing the head out and placing it back on the motor. No problems, the Z and the ZX or I should say the L28E and the L28ET are extremely strong in the block area, in fact I have never seen a bad lower end on one of these cars myself, EVER. About the only internal engine problems I have observed is blow head gasket (seems to be the weakest part in the Z motors, but only a little). On the Turbo motors the **** hydraulic lifters tend to clog up tapping a few mins in the morning when it is cold. Outside of that, or valves going out of adjustment on the standard Z's I have not seen hardly ANY internal engine abnormalities. Most Z's I have seen and owned were retired due to body rust, a bad wreck, or the rest of the car falling apart around the motors, they are just EXTREMLY STRONG. If you were not burning oil, and you get no bearing noise from the crankcase. I would not worry about it, you should be fine. It is ALWAYS a better idea to do all of it, but I would judge that on your budget. If you do not want to mess with it, buy one of those Japanese 40,000-mile engines, and rebuild this current one over time. Just my opinions, but the L28 engines are part of the reason I am such a fan of the Z car, I have not seen many engines that offer the power, economy, durability, and upgrade ability that they offer for there price, just well engineered
 

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<b>Don't worry about it!</b>

I had a N42 head shaved 75 thou and had a $1000.00 port/polish/combustion chamber work job on the head, put on a wild cam, headers and Webers on a stock bottom end L28 with 180,000 kms on it. It ran REAL strong till about 220,000kms. It then started to lose some compression and get some blow-by under Full Throttle. That might not seem very long but I did autocrossing and LOTS and LOTS of friday/saturday night drags with the car. So I was quite pleased...till...I got beat on the highway by a friend with a 280hp N/A 300zx. But that is another story.
ZR8ED
 

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<b>RE: Don't worry about it!</b>

Seems like there are lots of opinions out there, which is the value of these forums. However, I take issue with the generalization:

"On an overhead cam engine and specifically on the Z cars, that is not a problem"

Each of the three engines I referred to in my previous post were overhead cam engines, but none of them were Z engines (one was a 4 cylinder Nissan 200 SX). While I too am a huge fan of the L series Z engines, my '77 L28 is now running at about 130 psi compression with 105 K on it, which means I will be doing the rings fairly soon. To imply that the bottom end of Z engines never have problems indicates a lack of experience. The longevity of the engine has a lot to do with how the engine was treated during its lifetime. Things like oil changes, driving style and environmental conditions play a big role. My previous owners did not take good care of the engine (I bought a rust free body with a great paint job).

I'm not saying that rebuilding the head without doing the bottom end will definitely cause problems. In my opinion and experience, there is about a 30% chance that you will have a problem. Given the time and expense of the head work, those odds are not something I would be comfortable with myself. So, in the immortal words of Clint:

"Do you feel lucky today?"
 

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<b>RE: Don't worry about it!</b>

Seems like there are lots of opinions out there, which is the value of these forums. However, I take issue with the generalization:

"On an overhead cam engine and specifically on the Z cars, that is not a problem"

Each of the three engines I referred to in my previous post were overhead cam engines, but none of them were Z engines (one was a 4 cylinder Nissan 200 SX). While I too am a huge fan of the L series Z engines, my '77 L28 is now running at about 130 psi compression with 105 K on it, which means I will be doing the rings fairly soon. To imply that the bottom end of Z engines never have problems indicates a lack of experience. The longevity of the engine has a lot to do with how the engine was treated during its lifetime. Things like oil changes, driving style and environmental conditions play a big role. My previous owners did not take good care of the engine (I bought a rust free body with a great paint job).

I'm not saying that rebuilding the head without doing the bottom end will definitely cause problems. In my opinion and experience, there is about a 30% chance that you will have a problem. Given the time and expense of the head work, those odds are not something I would be comfortable with myself. So, in the immortal words of Clint:

"Do you feel lucky today?"
 

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Right now while the engine probably doesn't have excessive wear, you may be able to hone the cylinders, and put new rings, and bearings in it. With the head off, you have a good part of the labor already done. Get an estimate to do this, if you don't feel confident in doing it, and then make your decision.
We, also just had an 89 Sentra come in, with an $1800.00 repair bill from another shop for head and timing chain work that was smoking so bad, you couldn't see behind it. The cure was to hone it, and re-ring it, passed emissions, and ran perfect. The owner said it started smoking 500 miles after he had the head done. Joe
 
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