Overheated this weekend - 0 compression in 5 and 7

[CJD]

If its soft, I bet it's just a gel from oil and water mixing. Neither of those should be inside the cylinders in significant quantities. The water can come from either the riser, a crack in the head or block, or a blown head gasket. The oil could come from bad rings or a bad head gasket. So, let's hope the common factor is the head gasket.

Is there a reason you think the lifters need cleaning?

[pridekit]

Not particularly, just because I have access to them I figured I would give them a cleaning. I don't plan on pulling the intake off again any time soon, and figured I should take advantage of the easy access


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[pridekit]

According to the machine shop the loss of compression came from the valve seats. They were corroding away and would no longer seal. They suggested that I replace both heads and the exhaust manifolds. I can't quite swing heads and manifolds, and feel that I can still get at least another year out of the manifolds (they are going on 2 years old right now). The suggestion for doing both heads came from the idea that it if it has corroded on one side, it is likely corroding on the other, and I'm inclined to only pull this motor apart once (preferably ).

What is everyone's thoughts on this?

[CJD]

You mentioned coolant...so I assume you have a fresh water cooling system. If so, I can't believe the heads can't be freshened up for a reasonable cost. Look on the Summit website, as they have really good prices for either the parts (SS valves, guides, and seats), or entire heads. Small block Chevy heads are common and interchangeable.

The risers do see salt water and will eventually corrode from the inside out. I'd still use them until they blow out from rust, though.

[pridekit]

Yes, it's got a fresh water cooling system. He is asking $330 for each head (each one would be rebuilt on new castings, using a mix of whatever he can salvage from my heads and what he has collected over the years).

Did the vehicles and boats use the same heads? I called my family mechanic to see what kind of price he could get.

[pridekit]

Here are some pics from the shop (they are a couple hours away so I'm not able to take my own).










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[CJD]

Yes...the car and boat heads start the same. For a boat, it is preferable to use bronze valve guides ( you'll note that yours have iron guides) and stainless steel valves (yours did not have stainless). I would avoid aluminum heads, since you are running in salt water.

There are 3 choices in valve sizes you will see. The 1.88" intake valves for low performance motors. The most common heads are set up for 1.94" intakes...which is mild performance, and likely what yours has currently. And finally 2.02" intakes, for best flow and performance.

The 1.88" are junk, as the intake runners are also tiny. The 1.94" can be opened to take the 2.02" valves, but the runners are not quite as good as factory 2.02" heads, which are often referred to as "double hump" (for street heads), or "Bowie" (for Chevy performance heads). Chevy is so popular with racers that there are a dozen aftermarket heads too. I'd avoid these, as they sometimes alter the exhaust ports so they may not fit your risers. But if you check the shape and position of the intake and exhaust ports, there are some that will work.

I have rebuilt heads that looked a whole lot worse than yours. You need guides and valves. If you go with the next size up valves, you could even get by with the original seats. New, hardened seats would be better...but then the price starts to go up, if you replace them all.

$330 a head is not unreasonable. Be sure he is using SS valves...and ask if he plans to use iron or bronze guides, and if the seats are being replaced or not. Insist on the SS valves...the other stuff is preferred, but not necessary if price is a factor to you.

What I find interesting is that the damage I see is not from overheating, but long term corrosion. In your salt environment you should probably start fogging the intake before shutting down the engine anytime it will sit for a week or more. That should prevent this from happening again. Also...are the flapper valves on your exhaust still working? You could be getting more back flow up the risers than you should.

[pridekit]

I was thinking about buying the stainless valves and giving them to him so he has no excuses. I'm kind of entertaining the idea of doing the work myself, I'm a bit nervous though as it seems like a rather important job to do right Also, I've never rebuilt a head before, but as I've said before, I'm not afraid to get my hands dirty.


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[CJD]

Head work is very specialized, and not so much a do it yourself item. The seats have to be cut with special grinders (old school), or cutting tools (modern). You can buy the valves...but check the heads first. With a new Guides, you want standard size valve stems. If it is a used head, it is common to ream the old guide oversized, and then use valves with oversized stems. If it already has oversized stems...then you have to replace the valve guides.

The seats are similar....you can cut the old seats for larger valve heads, or use the same valve head size and cut/fit new hardened seats.

Now, once you have the shop do the work on the valve seats and guides, it is an easy job if you want to assemble the heads yourself. In fact, it's so easy that most shops charge the same whether you or they do the final assembly.

[pridekit]

Thanks! I'll get in contact with the shop then. I was doing a quick Google search and noticed that there are some z28 kits that come with new springs and all. Is it worth spending the extra for the springs or just get the stainless valves?


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