1984 5.7L heads are cracked, repair options

[tfret]

This is a follow up to an earlier thread. I started a new one since now I know my problem and want to discuss repair options. After pulling my heads to diagnose a high leak down rate, I determined that I have cracked exhaust seats on both heads. The last 3 digits of the cast number is 664. After doing very little research, I have learned that this head number is famous for cracking. Now to the repair options. I can find a decent set of good used heads to bolt back on and go. That's what I'm hoping to do although I may avoid the dreaded 664 heads. Several folks have recommended upgrading to vortec heads (1996 - 2000??) and get a new intake. I'm open to that option but wonder if these heads will have the same bolt holes needed for the accessories??? And finally simply replace the engine with a good used truck motor. I'm currently looking for all of these of C.L. and ebay. My only two real questions are: Will my accessories bolt on to the newer vortec heads if I go that route? And, other than vortecs, are there other heads that would be better than the original 664's. Thanks for any advice.

 

[Bondo]

Re: 1984 5.7L heads are cracked, repair options

This is a follow up to an earlier thread. I started a new one since now I know my problem and want to discuss repair options. After pulling my heads to diagnose a high leak down rate, I determined that I have cracked exhaust seats on both heads. The last 3 digits of the cast number is 664. After doing very little research, I have learned that this head number is famous for cracking. Now to the repair options. I can find a decent set of good used heads to bolt back on and go. That's what I'm hoping to do although I may avoid the dreaded 664 heads. Several folks have recommended upgrading to vortec heads (1996 - 2000??) and get a new intake. I'm open to that option but wonder if these heads will have the same bolt holes needed for the accessories??? And finally simply replace the engine with a good used truck motor. I'm currently looking for all of these of C.L. and ebay. My only two real questions are: Will my accessories bolt on to the newer vortec heads if I go that route? And, other than vortecs, are there other heads that would be better than the original 664's. Thanks for any advice.

Ayuh,... It would be easier to answer if ya included the whole castin' number,...
With only 3 digits, lookin' 'em up for specs ain't so easy ya know...

Yes, the Vortecs are possibly a plug, 'n play swap, with the manifold.... Bolt holes are All there...

Without the specs on the 664s, I donno how they compare to the Vortecs...

Chamber volume affects compression ratios, 'n valve size, 'n intake runners affects flows...

There's No doubt there's Lotsa other head castings that'll work, but again, donno what yer startin' with...
can't look 'em up...

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

462624. I believe they are 76cc and the valves are the smaller type, 1.94 and 1.5 inch. Good to know the vortec heads have the same bolt holes for the alternator, p.s. pump, etc. I'm told that virtually any year head will phisically work up to around year 2000. I'm guessing I want to stay with the same volume and valve size. Basically I just need to know what "won't" work or what to avoid. Thanks for any and all advice. I'm not exactly a motor head, so I appreciate all the pointers.

 

[Bondo]

Re: 1984 5.7L heads are cracked, repair options

462624. I believe they are 76cc and the valves are the smaller type, 1.94 and 1.5 inch. Good to know the vortec heads have the same bolt holes for the alternator, p.s. pump, etc. I'm told that virtually any year head will phisically work up to around year 2000. I'm guessing I want to stay with the same volume and valve size. Basically I just need to know what "won't" work or what to avoid. Thanks for any and all advice. I'm not exactly a motor head, so I appreciate all the pointers.

Ayuh,... You'll have to do the math to see where the compression ratio comes too,...

Vortecs are 64ccs,.... Shoot for 9.5:1, or under...

Head gasket thickness can be used to alter it abit...

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

uuuh you lost me there....can you teach me how to do the math and what my concerns are? I confirmed mine are 76cc.

 

[Silvertip]

Re: 1984 5.7L heads are cracked, repair options

Each cylinder in the basic engine block without heads or head gaskets, has a cylinder volume expressed in cubic inches, cubic centimeters (CC) or liters (L). For reference, 1 liter = 1000 cc = 61 cubic inches. So therefore, a 5.7 engine cylinder (3.48 inch stroke and 4 inch bore) has a volume of Pi x 1/2 bore squared, x stroke so 3.1416 x 4 = 12.5664 x 3.48 = 43.73 cubic inches. Multiply that by 8 (there are eight cylinders) and you have a 349.848 cubic inch engine. Divide that by 61 (cubic inches per liter) and you have a 5.7 L engine. Now you add the volume created by the hole in the head gasket. For history purposes steel shim (very thin) head gaskets were used on some GM engines. Those present very little extra cylinder volume. Composition head gaskets are much thicker and therefore alter cylinder volume and hence compression ratio since they increase the volume. Lastly the combustion chamber volume has the same effect. So decreasing head gasket thickness and decreasing combustion chamber volume raises compression ratio. We could also get into dished, flat top and domed pistons but that's for another time and place. So the long and short of this is that when making mods to an engine, you need to do the math. Too high a compression ratio requires ignition advance modification and higher octane fuel.

 

[Bondo]

Re: 1984 5.7L heads are cracked, repair options

Each cylinder in the basic engine block without heads or head gaskets, has a cylinder volume expressed in cubic inches, cubic centimeters (CC) or liters (L). For reference, 1 liter = 1000 cc = 61 cubic inches. So therefore, a 5.7 engine cylinder (3.48 inch stroke and 4 inch bore) has a volume of Pi x 1/2 bore squared, x stroke so 3.1416 x 4 = 12.5664 x 3.48 = 43.73 cubic inches. Multiply that by 8 (there are eight cylinders) and you have a 349.848 cubic inch engine. Divide that by 61 (cubic inches per liter) and you have a 5.7 L engine. Now you add the volume created by the hole in the head gasket. For history purposes steel shim (very thin) head gaskets were used on some GM engines. Those present very little extra cylinder volume. Composition head gaskets are much thicker and therefore alter cylinder volume and hence compression ratio since they increase the volume. Lastly the combustion chamber volume has the same effect. So decreasing head gasket thickness and decreasing combustion chamber volume raises compression ratio. We could also get into dished, flat top and domed pistons but that's for another time and place. So the long and short of this is that when making mods to an engine, you need to do the math. Too high a compression ratio requires ignition advance modification and higher octane fuel.

Ayuh,... To go along with ST's excellent post,... Have a look at this Hot Rodder's comp. ratio calculator...

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

excellent info, thanks alot guys!

 

[artificialreef]

Re: 1984 5.7L heads are cracked, repair options

At the risk of sounding like an idiot. What about having a machine shop replace the valve seat with a better than oem quality. You will then have the stock head with an oem improvement. That is of course as long as the rest of your head is not cracked. Putting another identical head in will glean the same results probably. I am not familiar with the history of that head and whether it is a paticular port prone to cracking or all of them. If you have to replace them all then i recind my comment.

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

yeah artificialreef, that was my first thought: I'll just clean these up and lap in the seat real good and away we go. Unfortunately, the cracks go beyond the actual seat surface and into the combustion camber surface. I did speak to two machine shops that both told me they are not repairable. Or at least, that a repair wounld't last long. They recommended going with the previous generation head which numbers end with 882. These are basically the same head before GM tried reducing the weight of the heads by 8lbs each. That is why they crack. But the older heads don't have hardened seats originally because they were made when gas still contained lead. So a set of 882 heads would work but only if they have had hardened seats installed. At least that is what the machine shop is telling me. I'm by no means a motor head. I'm just trying to learn something, and get the boat fixed with minimal fuss.

 

[Bt Doctur]

Re: 1984 5.7L heads are cracked, repair options

pm me . got a set of heads

 

[Bondo]

Re: 1984 5.7L heads are cracked, repair options

But the older heads don't have hardened seats originally because they were made when gas still contained lead. So a set of 882 heads would work but only if they have had hardened seats installed.

Ayuh,.... It's debatable 'bout the hardened seats,...

The odds are 'bout a Million to 1, that you'll ever run the hours it would take to cause problem, from the exhaust valve seats...

In other words, it's pretty much a non-issue...

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

Bond-o, do I understand you to say not to worry about the 882 seats being hardened or not? That would be good news since they are fairly common to come by. Yes, I'm cruising CL and ebay daily. Hoping to find them local on CL to avoid the shipping cost. Ebay is a good tool to see what prices things are going for.

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

I found a good deal on CL on a clean set of 14079261 heads. I think they are 1986 and what are called "swirl port" TBI heads. From what little I can find about these, they are designed to have better, more efficient combustion, and are good for lower end torque up to around 4000rpm. I think my WOT is 4200 and I never run there. This boat is for skiing, tubing, wake boarding etc. I think these might be a good option for me, but I seem to recall someone else saying they aren't good for boat applications. What do you guys think?

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

today a guy gave me a free set of heads just because he didn't want them laying around any more. I checked out the cast numbers and they are mid 80's 305 heads. The valves are smaller than my original heads, and the chamber volume is 60cc which is much smaller too. They appear to be in good shape, but i'm guessing the smaller valves and the much high combustion ratio (I haven't calculated it) would not work too well?? What do you think?

 

[Bondo]

Re: 1984 5.7L heads are cracked, repair options

would not work too well?? What do you think?

Ayuh,... Yer Right,.... They're No good to ya...

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

Any opinions on the "swirl port" heads?

 

[MWG2600]

Re: 1984 5.7L heads are cracked, repair options

"swirl port " is junk also. get a set or vortec heads and a new intake manifold and be done with it. That is the best option, heads should be under $300 intake $150 You will have to check the timing spec of a vortec boat engine, i think the vortec heads run a few degrees less timing.

 

[RogersJetboat454]

Re: 1984 5.7L heads are cracked, repair options

Agree on above assessment of the swirl port heads.
They don't really offer much benefit over what was originally on the engine, and most guys looking to make upgrades on a TBI engine usually ditch them. Either find old style heads like the ones that were on it, or step up to Vortecs.

My .02?

 

[tfret]

Re: 1984 5.7L heads are cracked, repair options

Yeah I've been looking for the easy way out with a simple bolt on solution. I know going with any number of the older heads it will work and the cost will be minimal. However, as suggested by many, since I'm already into it, upgrading the heads and intake to the newer vortec style will give me better performance. I guess I'm just a little intimedated by what issues I may run into with raising the C.R. and how to properly address that. I'm a novece at this and don't want to screw up. I'm looking at the cost and thinking an engine swap might be the smarter way to go, especially considering the age of my motor. If I stick a newer truck engine in there what adaptations are needed?