Replacing the Heads on a L98 (86 C4)
 

I'm extremely new to the vette world and I need to rebuild the heads on my L98. I've been told that it was overheated by the previous owner and lacks compression. Possibly the valve seats are warped. The bottom end sounds ok when I turn it over and it only has 78K on the clock.

I don't want to dump too much money into it, but I'd like to get the best bang for my buck.

Should I rebuild the exsisting heads, get rebuilt ones, or is there some aftermarket heads I should look at? Jegs and Summit have a couple heads but I have no idea on compatibility.

I've pulled motors before but have never done a rebuild. Is there a good write up online to pulling the heads?

I've been searching, but I didn't find much on this topic.

Thanks in Advance,
Lucky Kid

Try this thread it should get you some basic information

http://forums.corvetteforum.com/c4-t...n-89-vert.html

Check CorvetteMike2004 link at the bottom

Hi Lucky and welcome to the Forum. Lets take this a step at a time: You didn't say what the car is doing now, does it run? if yes does it smoke? if yes, what color? Is there any sign of coolant in the oil? what does the spark plugs look like? is there a noticeable difference in # 5 and #7 and the remainder? Are your heads iron or aluminum? How you know? A magnet will stick to iron, not aluminum. Another way, if your valve covers have 4 bolts on the perimeter they are iron, down the center they are aluminum. Not likely your valve seats are warped, most likely your problem is a blown head gasket or a cracked head. Removing a head is not rocket science but a Field Service Manual, while not an absolute requirement, will be a big help. The cost of repairs will depend on what you have to work with. Give us, that's this bunch of experts, some more info so we can better suggest a course of action.

Muffin gives good advice.

Probably a good idea to plan on changing your head gaskets. I have an 84 I am rebuilding, replacing factory iron heads with Aluminum from Patriot ($895 with CNC proted intakes).

When you pull your heads, lay a machinists quality straight edge across the mating surface (bottom) of the heads. Lay it diagonally, length wise, cross wise, etc. See if you can fit a feeler guage in between the straight edge and the head...the tolerance will be in a manual.

Aluminum heads especially can warp. If so, the mating surface needs to be cleaned up at a machine shop. If it is really warped, your compression chamber will be smaller and your CR ratio will go up, so bear that in mind.

A good valve job will cost you $300 to $350 if your valves and springs are serviceable. Definitely have the machine shop clean the heads, do the valve job replacing the stem seals, and true up the mating surface if needed. This is half the cost of a new set of heads, but you will have factory performance.

Feel free to post more questions...the guys here have a wealth of knowledge.

Be careful with it. No compression doesn't sound good. If it got hot enough, you could have ruined the pistons,rings, and cylinders. With enough heat the rings will loose their tension. And if it get hot enough, it will scour the cylinders, and ruin the cylinders and pistons.

The car does not run, no coolant that I see leaking outside the motor. I haven't removed the spark plugs yet. I was told by the previous owner that he had sea foamed it, and since it no longer ran. Prior to that he said it would bearly run, unless it was hot. He said the heads are aluminim and checked the VIN. I will confirm.

I will run a compression test this weekend.

I like this idea and the price tag. How much more power could I get by spending another $300-500 for aftermarket heads? Any other head work I should do? Is it easy to swap the Cam while I'm down there?
When should I start to worry about torque on the drivetrain?

Any other seals/gaskets that I should replace on the short block once the heads are removed? I'd assume its easier to access everything with the heads and intake out of the way.

How about headers?

I'm not looking to build a monster, but if I can get 20-40 HP for a few hundred bucks, I might as well give it a go...


I've never worked with Push rods before. Anything I should be cautious of?

Thanks for all your help!
Lucky Kid

To begin...
one step at a time. You do not know at this point if your block is salvagable. Overheating to the point of loss of compression usually means seized rings or broken rings/glans from water in the cyl. A blown head gasket from over heating starts a domino effect of disaster.It does'nt have to leak outside...the leaks are internal and quite deadly. because they cannot be seen, people will assume that their car is ok after cooking it real good and fire it up and go for a drive...sucking in water and breaking things and doing more damage.
After ANY over heating event it is necessary to check all the fluids, and take note of any abnormalities...smoke, smells, misfires. All clues to bigger problems.

Find the exact problem first...diagnose, then treat.Like in an emergency room.:thumbs:

Compression test, look at spark plugs, water in oil,. vs versa.

Drain the oil and see what falls out.

In regard to your questions above...

$300-$500....none. That is what a minimal head rebuild will cost if your old springs and valves can be re-used. New performance heads...$1500-$2000 then all the things that have to go with the upgrade to make them perform well.
You can get your stock heads port matched, some mild porting and get some improvements, ONLY if you do the rest of the intake...plenum, runners and baseplate. Throttle body needs to be upgraded at that point to maximize the benefits. Get a K&N filter in the stock air box with a cut lid.
Trying to stick to a budget here...but that list is already at $1000+ using your old parts...

Cam...is much easier when the block is out. If you pull both heads, (Cannot rebuild one) its just as easy to pull the motor and do this work RIGHT, Clean, and look at the bottom end. Chain too,.
Nobody ever said you cannot use the old parts, as long as they are still good. Pistons, rods, crank. new bearings after a PlastiGauge won;t hurt and thats cheap.
Look at the lifters. I think yours is plain Hyd, later yr went to roller/hyd lifters. Might want to think about roller rockers for the heads...$300 to get a bump in performance similar to cam changes.

headers? yes, long tube offer real benefits. What you have now is basically a shorty header. Putting another shorty header don;t do much except advertise for someone.

If your block is solid, you might escape for $1500....If not, then I'd go buy a crate motor. The cost of a new block is cheaper than rebuilding and you get some warranty protection. Building a motor in pieces can be very costly. If you have to replace enough parts, that can easily justify a new short block, or long block if the heads are too beat up.

ID the damage first. Keep in mind that prevoius owners NEVER tell the whole truth when it comes to selling a damaged or broken engine.....It's likely worse than you were led to believe...:yesnod:

I had to do a head gasket a couple yrs ago and the simple repair cost around $300-$400 in parts and outside services. I had to buy a bare head 15 yrs ago, and that cost $1100....plus the labor and misc parts.

Because you;re new to the world of Corvettes...you;re going to get some surprizes along the way...
The worst being the "Corvette-Tax". Corvette parts cost twice as much as others just because they go on a Corvette.
The best thing is that you're now part of a family that takes care of each other, shares what they all know, and wants to help. Its more than just a car club,...its family.
Go find the local Corvette club and get some leads on parts thru them. They will know the local sources and what shops are righteous and which are rip offs.You're gonna need a machine shop...

Figure out whats broken and you'll get all the help you need here.
BTW...I'd go get on E-Bay and buy a Factory Service Manual (FSM) asap. About $75 for the 2 book set, used. Thats a must if you plan on doing work yourself.

Good luck. There are MANY guys that started out this way...with a car in a box. It may take some time and money but everyone thats done it has been glad that they endured the process.:cheers:

At this point you don't even know if there is anything wrong with the engine. Previous Owner may not have a clue what is wrong and just guessing at the problem. I'd be looking into why it doesn't run and going from there. It would have to be mechanically very bad before it wouldn't at least start and run.

Fair enough, Maybe I'll pull the plugs after work and take a look before I get ahead of myself.

First I think I'm going to drain the oil and see if I get any suprises.

I'll keep you guys posted with the results.

Thanks for your help!
LuckyKid

While removing plugs make sure you check compression and keep plugs in order so you know which cylinder they came out of. Check your fuel pressure with a gauge and check to make sure nothing is blocking your airbox (Mouse house, etc.). Check for loose connections or breaks on every wire you see. Take pics and share with the forum you will get a lot of help from some very knowledgeable people here. Remember if you have air, fuel and spark all at the right time and amount it should start and at least try to run.

Removed the plugs and everyone had some oil on the threads, not soaked, but nothing trivial. Similar to a tired but running miata motor I had. No coolant though. The plug wires are in the right firing order. Oil looked good, used for maybe a few hundred miles, no sheen, no fuel smell, and zero metal flakes/shavings. Intake and TB look good no blockage.

http://i1130.photobucket.com/albums/...g?t=1304560489

I will test compression and spark tomorrow, but so far I'm a little perplexed.

When I removed #7 I began smelling a good deal of fuel. Do these injectors stick open? I am assuming FP is good based on this.


I also have a wicked power steering leak. Maybe 1-2qts in a day. Not sure how it got on the lid, but its red and bitter.

http://i1130.photobucket.com/albums/...g?t=1304560552

It appears theres an sensor in each head and the one in the drivers bank was broken off.

http://i1130.photobucket.com/albums/...g?t=1304560610

Let me know if you guys have any other insight.

Thanks,
Lucky Kid

If the injectors are leaking then the fuel will run into the sump. Check your oil level. I ended up with 5 litres of fuel in the oil after the car sat for one week. Changed the injectors (and the oil) and fixed the problem.

Those spark plugs seem to be from iron heads the aluminum heads have gaskets and are flat on the seat not tapered

Make sure the correct plugs are installed and test compression.

Replace the broken sensor. That is (was) your aux fan switch. It's the second-line defense against high temps.

Many people assume these cars have over-heated when they get much above 220-230 degrees. That's not over-heated. They can take 250-260 before damage occurs (higher if iron-headed).

If you really want new heads, they can give you that 20-40hp gain you spoke of. But, so could headers and/or intake mods.

Choose wisely.

Wow, the heads are iron. I remember seeing the four bolts on the perimeter of the valve cover.

Well, I guess I'm back to the drawing board. What the heck could the problem be?

Going to check spark, and compression next.

Is fuel pressure a common problem? Its been mentioned many times in this and other threads.

If I can't get it fixed within the next few weeks, my wife is going to sell it... :toetap:

Thanks,
Lucky Kid

Do a fuel pressure leak down test to determine if an inj is leaking. These stock inj are famous for shorting out and when ONE fails, that whole bank fails. Bank-Fire inj system. The leak down should hold pressure from key-ON of about 40psi and hold 90% of that for an hour. Should hold at least 20psi for several hrs. If it does not, replace the set of injectors.

Broken off sensors will not keep the motor from running, but they will keep it from running right. Replace asap.
Rt bank head by dip stick is the temp gauge for your dash, left head is aux fan switch 238* . There is also a Knock Sensor in the lower rt block between freeze plugs.



The power steering leak is from the pump cavitating and foaming the fluid and blowing it out of the vent hole in the top. Clean it off and make sure there is not a pressure line leak thats just squirting oil up to that area. If the pump is cavitating its on the way out. Its a PITA to change, so do all the hoses at the same time. Check the condition of the rack. Often the rack seals go bad and contaminate the fluid, this is where/how the problem starts and can ruin the whole system. If there are torn boots or wet seals, its probably junk.
Good news, the whole steering can be replaced for $400 if you do the work. rack, pump and hoses.

You ask about fuel pressure and such. With an EFI motor it ALL matters. The computer controls the engine. It gets real time data from its sensors and makes adjustments 600 times a second. When the data is faulty the computer delivers faulty performance. The mechanical portions of the eng controls become that much more critical because the computer is operating off of a fixed set of parameters as far as fuel pressure and flow. Everything is metered, and needs to be within spec or the engine will not run. Its remarkably complex, yet simple when understood.

It's not grand dads Oldsmobile....

As others have stated, overheat is NOT 230....dangerous overheat is 260.
The fans were not coming on with broken senders and switches and Lord knows what else broken and missing. These cars NEED all that stuff to run.

Why people just let ($7) things break and not even attempt to repair tells me they either don;t appreciate what they have, don;t respect what they have, or they are too stupid to comprehend what they have. To treat a Corvette that way...should be a criminal offense. I hope the PO did'nt do too much damage.

Do your compression test, fuel pressure test with a good gauge and log the results. Also, learn the flash code trick and get whatever is stored in the ECM. That might offer a clue.

The plugs look fair, 2 look fouled. fuel or oil? The leakdown test will help tell which. You'll need the fuel pressure gauge with adaptor fitting for the GM fuel rail schrader valve. Might see about borrowing a NOID-lite also.

Got a full weekend worth of diagnostics ahead of you. many auto parts stores will rent you these tools if you do not have them.

do yourself a favor and sell it , buy one already running, you'll enjoy it more and your wife will like you for being smart enough to do that.

:D I got the car for $3K. I think I'd have to spend atleast 5-6 for a running one. She'd have my head if I did that.

The idea was that I get the car for $3K and pitch it to her as an investment. :cool:

So far so good! :cheers:

Once it running I'll try to convince her that its not going to lose any value and we might as well keep driving it for the summer.

Once winter comes, we can't sell it before winter, we'll wait for spring.

This keeps going until she forgets how we got it and just accepts that we own a Corvette.

The plan falls apart if I sell it now...

I'd spend a few hours attempting to get the engine running. Then drain the oil and replace. Do a compression check

THe iron head are pretty tough and will endure much more heat than the aluminums.

If your going for HP without spending lots of money then swap the cam.

Or just find a good running one and drive it for a year before you start modding it.

:cheers:

My .02 worth. Early C4's (84-91) should have the injectors replaced and when you have the heads off, that's the time to do it, because you're removing the plenum. I should've done it, when I pulled the heads off the 87'.

Secondly, while the plenum is off, you should replace the fuel pressure regulator and the EGR, because it's going to need it eventually and it is a real PITA to replace these two items.

http://i205.photobucket.com/albums/b...orvette020.jpg

Also, I am mechanically inclined, but it took me two months of weekends to get it done. That's because I took a whole lot of
pictures, tagged all the numerous lines and cleaned everything going back on. You could save a lot of time by having the numerous brackets and parts 'hot tanked' to clean them off, versus doing it yourself. I could've cut at least a couple o' weekends doing this.

Get an FSM! Also, get a whole lot of those blue parts bins to put the nuts and bolts in, while you're taking it apart. Buy a deck of 3x5 index cards and a permanent marker, also heavy duty zip lock baggies (the freezer bags already have a markable area, but the cards can come in handy for notes).

While this may sound overkill, this was the first time I did this. When I was done, the car started on the third or fourth turn. After adjusting the timing, it passed California Smog and has run for nearly three years without a leak or problem related to the top end. Better careful than sorry later on!

When you get here, you'll be glad you were careful, because now, you've got to put it back together!
http://i205.photobucket.com/albums/b...orvette037.jpg

You'll need to get the crud off the top of the pistons too
http://i205.photobucket.com/albums/b...orvette049.jpg

http://i205.photobucket.com/albums/b...orvette050.jpg

http://i205.photobucket.com/albums/b...orvette051.jpg

Look at how much stuff is on the Intake Manifold alone. Two of the sensors use exactly the same thread! You'll have to remove all of these to have the intake hot-tanked. It best go back together exactly the same way.

http://i205.photobucket.com/albums/b...orvette052.jpg

http://i205.photobucket.com/albums/b...orvette054.jpg