Here's a little background: On dissassembly of my heads last night, i noticed that several of the umbrella type seals i used about 2 years ago on some World S/R torquers were brittle and cracked. One was completely missing. I tore everything down, and noticed that 4 valve guides had really bad wear, almost to the point of wearing completely through to the valve guide bore. The worst had almost 1/4" of play. These were all exhaust valves. (This explains what i thought was terrible blowby.) These were fine 2 years ago when this engine was put together. Its only been turbocharged for a few months. probaly less than 40 hours of actual run time.

I'm running 10psi of boost, so that means somewhere from 15-20psi of exhaust pressure. Probably closer to 20 at the top end since my turbine housings are on the smallish side.

So the question remains: Is the high heat/backpressure from the turbos wiping out my valve guides? What can i do to correct this situation so it doesnt happen again. I dont want to simply have new guides installed and have them go bad in 6 months.

Also, is it worth it to do this work to a mediocre set of iron heads? Ideally i would want aluminum heads with a large(72-76cc) chamber to keep compression down. I have flat top forged SRP pistons ready to go into a rebuild. Ideas??

 

I don't know how much help I can give you, but I did have a chance to check my heads out a bit when I had my engine out for a my restification last year. At that point, the engine was a totally stock L98 with 95k miles on it, 7k turbocharged at 6psi (with very small turbines- I probably had very high backpressure even at low boost). I decided to install 1.6 rockers while I was waiting for the body work, so I got a chance to inspect the guides. (The stock L98 cam seemed like it would be well suited to turbo apps because of the long LSA, but it needed more lift). The guides felt very good to me, though I didn't measure the them. I installed new seals, slotted the hpushrod holes, and reassembled it, and still haven't had any trouble.

FWIW, High MacInnes suggests in his book to just leave the valve seal off of the exhaust valve to improve guide lubrication and cooling. Maybe he knows something I don't.

 

I was using both the o-rings and the umbrella seals on the intake and exhaust valves. Is the heat the issue? The exhaust valves werent burnt at all, and i was running pretty safe AFRs the whole time.

I'm really stuck right now about whether i should pay to repair these heads that aren't too much better than stock, or to step up to a good set of aluminum heads.

 

Wow, that's pretty excessive wear!! I would check for proper valve train geometry first before spending any money.

 

If those heads weren't assembled by World they may have had sub standard Chinese valves installed which the majority of the time have terribly rough stems.

 

I'd have to assume the geometry is ok, its all stock stuff. What should be checked?

No idea of the history of these heads. I got them on a 350 block i bought. I thought they were just stock heads for a long time until i checked the casting numbers.

 

Well, it's going to be hard to check the geometry now on the bad valves, but you could go through and check some of the ones that aren't as bad. Basically you want to check how well the rocker tip runs across the face of the valve tip. You will also want to make sure the rocker body doesn't come into contact with the retainer.....this can cause extreme side loading of the valve stem. When you disassemble the heads, check the valve stem itself for any irregularities that may have caused the wear. On a final note, just because the heads were "completely stock" doesn't mean you shouldn't check for proper geometry. Bad geometry can come from th block if it has been decked in the past too.

 

nutshell answer for your orignal question... no, a turbo shouldn't have caused that kind of wear any more then anything else would.

as far as not knowing a previous history and looking for reasons, I'd put valvetrain geometry, oiling problems & knurled valve guides towards the top of my list of things to look for.