bk26008

[IMG][/IMG]Hello All,

I took a short cut and just replaced the Intake gasket after having coolant mixing with oil.. The compression test at the time was 165 across the board except #7 was roughly 138 to 140. Anyway got the intake gasket replaced and replaced numerous other things trying to solve rough running and rough idle.. So after this driving it around and the coolant mixed with the oil again so I thought maybe it was some of the old residual and changed the oil again.. Then test drove it again and had faint white smoke from exhaust then killed it and parked for a few days then went back out cranked her up and it looked like the bat mobile and had left a white smoke screen behind it bellowing out and looked at the oil and really milky this time so I though well heck and went ahead and yanked the driver side head off and I could see where the gasket looks like it had degraded around the number 7 no blows between the sealing ring all fine on that so what do you think is it possible for this to leak at that spot even though it was sealing around the piston with no obvious signs of a blown spot? I have not pulled passenger side yet but gonna change them both.. Also is it necessary to have the heads resurfaced on these motors? here are some pics of what I have also the number one spark plug electrode was smashed to the insulator part what would cause that ? it was on number 1..



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black88z51

If there's no damage to heads then no you don't need to resurface, besides looks like you found the problem with the gasket. Good idea to change both sides.

bk26008

Ok thanks for the reply.. I cannot see any obvious damage to the head thus far but have always been told better have aluminum heads resurfaced not sure why they always say that.. I can get a straight edge and check for warp I guess. How can you check for a cracked head without using a machine shop? Any Ideas as to why the number one plugh electrode was smashed closed? I guess I could have done it after installing agter compression check

Baller

I'm doing this right now as well.



Good ole #7...

Baller

There's a dye kit you can get. Hot tank the heads and then apply it. My guy said that unless the car overheated to the point of stalling he wouldn't bother as he can usually see any cracks pretty easily.

And FWIW, I'd spend the bucks and get them decked and valve job while they're off.

bk26008

I was thinking wow looks like that number 7 is a problem Why is that anyone know? Also this is going to be a stupid question how can you tell a L98 from a LT1? this is my friends vette and he thinks its an LT1 and I said no its an L98 but how can you really tell (Intake design? TPI vs ? on the LT1

bk26008

Yea think I will for sure get them resurfaced not sure about valve job though because this thing could have bad rings also Had the puff coming out of the oil fill hole and pressure pushing out dipstick(some oil spew) but I was thinking that also could have been from the added pressure from the coolant getting in to the cylinders?

Baller

Got to do with the design. As I understand it the back cylinders get the least help with getting cooled, 7 being the worst. I've also heard some mention made of coolant holes being too close to the bore.

L98 is TPI and while have the long runners that cross under. LT's have short runners and optispark (no distributor in the traditional spot at the rear of the engine. The LTs also make use of a reverse cooling that flows through the heads first and provide more power and eliminate? the head gasket issue (not quite sure about that last part. It's what is claimed but I don't know if real world supports that).

How many miles does it have on it? Mine's at 96K and there's no real appreciable cylinder wear, the bores still smooth with no ridge above the top ring travel. That said if you've got that kind of crankcase pressure it could be something to consider re: not doing the valves...

Edit: Does anyone know of some way he cold perform a leakdown test?

bk26008

It has 188k and I think that the pressure could have been from the bad gasket issue IE plugging up the PCV system etc but I have heard that if the rings are in question and you do a valve job then the increased pressure could make this worse I dunno if I believe that because there should not be any pressure loss through the valves anyway.. The bores in the cylinders are clean and smooth bit slight ridging at the top part of the bore at top travel.

Baller

Yeah, that's right at the point where it could go one way or the other. My guess would be that if the blown gasket was allowing compression gases to leak into the lifter valley then that would have definitely contributed to it. How was the smoking, etc... prior to the gasket going? IOW, did both symptoms start at the same time or was there the puffing, etc... prior?

If the rings are the cause then the increased pressure from a valve job can worsen the problem. Of course then you have an excuse to re-ring it and of course if you're going to do that then you may as well get a stroker crank and build a 383 and if you're going to do that then you may as well.... And that's how the slide down the slippery slope gets started. $6K later you look up and go "What the hell just happened???"

bk26008

I love that Slide funny how things always go that way.. This is my friends vette and he brought to me with running rough and then I began the diagnosis at that time I rolled the dice on just being an intake gasket failure and it still had lots of residual oil mixed with coolant but and the oil on the passenger side was also leaking (minor spewing out the dipstick(which was replaced because had bad seal) but looked like it might have been pushing out the VC also? only on passenger side.. Think its all related

phat87

Don't use caustic cleaning on an aluminum head. Them chemicals just LOVES that aluminum. Eats it up like breakfast cereal.

PS Don't use Simple Green on aluminum.

Baller

I use the term hot tank more as a generic one for when they use a heated solution versus cold. The local guy I use does everybody's aluminum blocks, heads, etc... and uses a non-caustic formula. I'd guess with the proliferation of aluminum components nowadays that most do as well but to the OP I say this is a good reminder to double check with your machine shop and make sure they don't use a caustic agent on aluminum.

BTW, just as a tip, if you have badly oxidized aluminum or anodized aluminum that's been pitted, oxidized, etc... an alkaline cleaner or draino is a great way to strip off the bad layer so you can polish it.

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cv67

Machine shop would have to pull the valves and really clean the heads to find cracks. You can only magnaflux cast iron

With 188k resuraface and valve job would be a must have. Fresh springs could restore some lost power. Springs are cheap.

SunCr

Head gasket is a common issue caused by galvanic corrosion (yours, though visible on the gasket, doesn't look too bad) caused by leaking intake gaskets (per GM) corrected in '91 (per Service Bulletin) with counterbored intake mounting holes on the heads allowing for intake gasket retainers. That maintains gasket alignment and stops the leaks which supposedly stops the corrosion. Anyway, check the deck of the block. These things would weep as early as 25,000 miles and put a crevice in the deck which isn't going to allow the new gasket to seal meaing you or some other owner will be replacing the gasket again. Flush the block, radiator and heater core of old coolant and crap.

bk26008

Ok I appreciate all the replies here is the passenger side pics did not look as bad as driver side but gasket looks old!!! Also on this side I had another spark plug that the electrode was pushed in ?????? detonation on only 2 cylinders??? maybe the coolant was being compressed and pushed the electrode shut? Anyway I am afraid to do a vavle job I will get the heads resurfaced but doing valve job (and the engine having possible bad rings I do not want to risk the extra pressure and maybe cause the rings to get worse I had blow by already and little spew coming out of dip stick and may have been leaking between the head gasket as well not 100% sure). Also anybody use corteco gasket set? I will probably go felpro but if corteco is good then I can get a set for 50.00 also I see head bolts are recommended to replace for 30.00 buck I guess it would be good measure to do so. Anybody know what happens if I remove that air injection system will it cause it to fail inspection?

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bk26008

Also you talked about the intake gasket and counter bore where can I find complete info on this? The intake gaskets are the 1st thing I changed and got a good seal but if there is an update and I can do it in the garage then I will before reassembly.

Thanks

Baller

Removing the Air Injection System will cause it to fail a visual if they do that where you live. They actually don't eat up much HP. The stupid part is that they only actually function for a couple of minutes until the car warms up. After that everything is vented to the atmosphere.

bk26008

Yea here in Texas I think it would pass Visual but it if it has anything to do with any emissions and they still probe the Tailpipe here and test the emissions so if it will cause any issues there then I will leave it.

I called a local machine shop that I have used before and maybe they are under new ownership or someone was new but I asked how much to pressure test the head since they are aluminum and magnaflux will only work on Iron heads and they said 30.00 per head on resurface and 35.00 to pressure test but then they went on to say that if I had coolant in my oil and can see it on the dipstick its more than likely not a head gasket because the head gasket would cause it to leak external I said no you are incorrect they can leak external and internal but these HG were not blown between cylinders and were more detioirated around the coolant jackets so I may check somewhere else....

SunCr

You can use the newer ('91) intake gaskets by finding a set and taking them to your machine shop to have the outward intake bolt holes counterbored for the retainers, or you can buy current production 113 heads which include this feature. They were somewhere around $800 to a Grand depending on Dealer.