Hardened seats or Stainless valves?

[FSJunkie]

Install hardened seats

The first engine I rebuilt was the AMC 232 I6 from my daily driver. I was a sophomore in college and taking engine's class that semester. I decided to rebuild my own 116,000 miles engine for my class project.

The professor advised me of course, as did the owner of the local machine shop. They had 80 years of experience between them.

I wanted to install hardened exhaust valve seats and new valve guides. They were worn and I knew I needed this engine to handle lots of interstate driving. Both of my advisors said this was unnecesary and that the engine would "probably be fine" if I just reground the original seats and left the guides alone. I followed their advice and built my engine as they told me.

Fast-forward to my senior year, 15,000 miles later. Cylinders start dropping compression. I determined it was from leaking exhaust valves, so I pulled the cylinder head off my brand new engine and sure enough, those exhaust valve seats were pounded out wider than the valves themselves, recessed back into the head, and oval-shaped because of the worn guides. Not sealing worth a darn. Now I was pissed off. Fortunately I was taking advanced engines that semester. I carried my 60-pound cylinder head into the college machine shop and did what I should have from the beginning: installed hardened exhaust seats and all new guides. I also installed all new valves, all new springs, all new keepers, and touched up the intake seats. I cut no corners. I put $300 into that cylinder head with top-quality materials and I did it all myself because at this point I didn't trust people any more and I was pissed.

That engine has run fine ever since.

I put hardened seats in everything after that fiasco. I learned the hard way. I'm also more skeptical of advice now and trust my own judgement more.

[SC/397]

Take it from a guy who has built a few of these engines.. LOL!
Seriously, In 160 cylinder heads I can only remember cutting and installing new exhaust seats in one pair of cylinder heads that had been reworked once already. We have never had to replace the intake seats. This includes all of the cylinder heads casted before they started induction hardening the seats. Sometimes the valve stems wear out and valve guides wear out but even this is not near as common as other makes engines of the same time period. Like mentioned above, even brand new valves will have to be ground to match the correct angles etc. Make sure the machinist laps the valves to assure a good 360 degree seal at the right contact width. Another key thing to look for is cracks in the cylinder heads at the front and rear corners. This is much more common than having to replace valve seats.

[levelhead]

SC/397 Would you go with valve guide inserts the machine shops seem to be pushing these days or replace with new cast iron guides?

[SC/397]

SC/397 Would you go with valve guide inserts the machine shops seem to be pushing these days or replace with new cast iron guides?

Great question. If you have to replace them, the machinist that I have used for the past 20some years prefers cast guides on a street engine. He is picky and also polishes some of the stainless valve stems because they are kind of rough. He told me that he hasn't had to do that to the stainless valves that I have given him. He also hones the guides to get the correct clearance. Not all machine shops do this.

I an now using a second machinist and he likes to use bronze sleeves. I asked him about that and he says that he has never had a problem with them - whatever that means.



I am not a metalurgest but maybe a stainless valve would play nicer with a bronze bushing and a non-stainless valve would play nicer with a cast guide. I honestly don't know.


Rambling on here and sorry, not answering your question directly, I have been leaning towards in putting positive type valve seals in everything. I usually use the nylon umbrella seals on stock stuff but sometimes those seals don't fit the valve stem tight. It costs more of coarse but may be worth it in the long run.

[wiley-moeracing]

I always cut the valve stem so I can uses the better valve stem seals, lasts longer and a less oil leakage. I would just do a quality valve job and pay attention to the valve guides. The hardest part is finding a good honest machine shop now. Kind of like finding a doctor, when you do stick with them no matter if it costs more.

[rang-a-stang]

... The hardest part is finding a good honest machine shop now. Kind of like finding a doctor, when you do stick with them no matter if it costs more.

I'm with you Wiley-Moe!!! I KNOW I am paying a lot for these heads to be done. ALOT. But I trust this guy. Almost every person I have talked to at car shows here in Ventura County either recommended a shop that has shut it's doors or Jim Grubbs Motorsports (the shop I am using). Those are folks with engines from all the Big 3. It's very rare to find an AMC engine at a car show here.

I am paying for the viton positive seals now because I figure either do it now, or do it later and it really isn't to much money.

[Ristow]

SC/397 Would you go with valve guide inserts the machine shops seem to be pushing these days or replace with new cast iron guides?

its gonna be inserts either way. apparently cast iron and stainless don't play well together.i seem to recall i had stainless valves in cast iron guides but my memory may be failing me on that one. in that case it may have to be manganese bronze.

[FSJunkie]

New guides come in different types.

There are the thin wall "guide liners" usually made of bronze. The guide is reamed out slightly oversize and the thin liner is installed. I am not a big fan of those. Bronze is good at resisting scuffing from lack of lubrication, but it wears out quickly and has a low melting temperature.

Then there are what I refer to as actual guides. Calling them an insert isn't really correct. They have an outer diameter of about .503". The existing guide in the head (which is just the iron of the head itself) is reamed out to .500" exactly and the guide is hammered into place then trimmed to length. The guides are already the correct inner diameter for proper clearance to the valve stem, but unfortunately hammering them into the head collapses them a little and they have to be reamed back out to proper size. These guides come in steel with a smooth inner bore or steel with a partial spiral groove at the top to let oil get into the guide except for the very tip near the valve head. I prefer the spiral groove guides. All my engines have them.