Head/Valve work... what would you do?

Caver Dave

Caver Dave

Just holdin' it down here in BFV
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Mar 10, 2005
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Hooterville (24171)
Had a leaking exhaust valve (cyl #2) on the 304... pulled both heads (as 1 more head gasket ain't anything after having everything else off to get at the heads :rolleyes:) and toted them to the shop.

Local guy (years of experience) shows me the seat (case hardened = pre-unleaded fuel insert type) is fried, valve appears unevenly worn, caused by guide/seat. Appears to have been a slight vac. leak around the intake on that cylinder, which says would account for the single failure. Besides machining for new seat insert, possible valve, guide, & stem seal on that valve, he recommends a minimum hot tank, tear down, stem polish, valve/seat grind, & new seals across the board for both heads. I agreed based on the price (estimated 200-250)...

However, several experienced AMC builders are cautioning me against having anything done other than having him repair the single fubared seat/valve... saying that the other 15 valves are bound to be leaking slightly and any increase in compression gain (from fresh head work) is likely to cause other issues... namely blowby.

Engine was supposedly rebuilt by Rausers in Salisbury 10 years ago, I got it 5 years ago w/ approx. 5K on it, and have put about 7K more on it. Doesn't burn any oil that I can tell, though it does drip a bit out the bottom/back :eek:. I didn't do a compression check on it before I pulled the heads, since the issue was localized to the single cylinder and the others appeared to be fine.

So, lets hear the arguments for one way or the other... :beer:
 
The vacuum leak on the one cyl would have caused a lean condition, causing the valveface/seat to over heat, so yes, very likely and possible.

As for NOT doing the rest, thats foolish, you have them apart, do it all. YES the compression will be a little better, but with fresh valve work the possibilty for blow-by is at the rings.

it's a gamble (all be a small one), but unless the engine has major miles or abuse on it since the last refresh, there shouldn't be an issue.

Having just the one vavle set redone is asking for an uneven running engine, as the compression will be up on that one cyl, due to the better seal of the valves.

I never have figured out how folks can justify only doing 1/8th the work when doing the whole job NOW will save having to go back in later in most cases.
 
DITTO with Blkvoodo.

Low to no risk of creating blowby. Guy at the shop is too conservative and I would question his decision making skills.
 
I would swap in a straight 6...:flipoff2:




If you have the heads off already, why not check out the cylinder walls/ ring conditions and see how it looks. If the walls aren't scored and the rings seem good, I would redo both heads completely.
 
Blkvoodoo said:
As for NOT doing the rest, thats foolish, you have them apart, do it all. YES the compression will be a little better, but with fresh valve work the possibilty for blow-by is at the rings.

it's a gamble (all be a small one), but unless the engine has major miles or abuse on it since the last refresh, there shouldn't be an issue.

,I agree it would be foolish to not do both heads and do them correctly,and with that few miles on the engine i dont see blow by as a issue,

I've taken sbc's with well over 100 k miles on them and changed the heads to higher compression ones and changed the cam and timing chain to preformance stuff and sprayed nitrous to them and went drag racing and never had a problem,question your guy at the machine shop about his decisions
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Dave, Head work is what I did most when I worked at the machine shop. If this head was a DD'er and was gonna see a lot of miles, I would say go through it all. That would be the thing to do. That said.............

He can check every valve guide and only repair those that need it. He can replace the valve seat, and any others that need replacing. It does need to be checked on the intake surface to make sure there was no erosion where the leak was and that the surface is good. Just to insure there won't be another failure.

Replacing guides isn't replacing at all. They have to be cut down, drilled out, and new guide inserts put in. The new guide has to be hones to fit, and or clearance the valve stem. The benefit to this is being able to use a better valve seal. AMC only uses the umbrella type seals.

After the valve grind, and I would have them all done, vacuum will be pulled to check the valve seat. At that point it may or may not be necessary to to lap the valves in. This is done pre assembly so there is no spring pressure on the seat at all.

Before any work is done to the head or heads, I would pay the extra to have them magnafluxed to make sure you are not dumping money on a worthless head.

Fell free to give me a call if you have any questions on the how's or why's
 
Hold on, if I udnerstand the OP correctly, it is the machinist who suggests complete redo on all 8, and the "several experienced AMC builders" who suggest doing only the one.
Uglyjeep has a good point. If the heads are off, you should be able to get at least a righ feeling for teh cylinder/ring condition. If its decent, as I'd think it would be after only 7k, I would see only good thinsg to come from a complete redo.
$250 for both heads? Curious, which shop?
 
Just to reiterate:
The shop owner said to go thru them both at a minimum. It's Rotating Dynamics in W-S. He runs an alky rail in the sportsman classes and judging by his lack of advertising/web presents, is a word of mouth business for the past 15-20 years

It's others that have worked on more AMC mills than most of us have seen saying to patch the bad valve & move on...

Also, shop was only going to replace what's bad (it's VERY obvious on the "bad" valve that it'll take a seat & guide minimum and possibly valve) during the rehab.

He described the process:
- "hot tanking" (though his is a rotary pressure type)
- "bead blasting" (I realize this is not true "magnafluxing", but won't any cracks show up still?)
- disassembly (checking for additional worn parts = guides, seal, etc)
- polish the stems
- cut the valves
- cut the seats
- lap them in
- reassemble & test for seal
- check the mating surfaces for anything that'll require additional work (don't recall when in the process this is done)
- call me to bring him $$
 
Caver Dave said:
Just to reiterate:
The shop owner said to go thru them both at a minimum. It's Rotating Dynamics in W-S. He runs an alky rail in the sportsman classes and judging by his lack of advertising/web presents, is a word of mouth business for the past 15-20 years
It's others that have worked on more AMC mills than most of us have seen saying to patch the bad valve & move on...
Also, shop was only going to replace what's bad (it's VERY obvious on the "bad" valve that it'll take a seat & guide minimum and possibly valve) during the rehab.
He described the process:
- "hot tanking" (though his is a rotary pressure type)
- "bead blasting" (I realize this is not true "magnafluxing", but won't any cracks show up still?)
- disassembly (checking for additional worn parts = guides, seal, etc)
- polish the stems
- cut the valves
- cut the seats
- lap them in
- reassemble & test for seal
- check the mating surfaces for anything that'll require additional work (don't recall when in the process this is done)
- call me to bring him $$
Click to expand...

Hot tanking is a tank just for it to soak in and then pressure the crap off.
Bead blasting is nothing more than blasting it with metal beads to clean it up, while it looks really good, to answer your question, no, it WILL NOT show up cracks! Only magnafluxing will show up cracks. Usually in the combustion chamber but could be anywhere. There is no substitute for this unless it is pressure tested and sometimes pressure testing will not show a leak when there is a crack!
The valves being ground is a definite plus, stem polishing.... well I don't agree. a good cleaning of them in a tumbler and you will be fine, this is of course pre grinding.
On the valve seats if he tries to say there is a difference in a 1, 2 or 3 angle seat cut he's blowing smoke. Same process for all three, and no extra work for him at all.
If he knows how to cut the seats and not let them chatter, then little or no lapping will be required.
The "test" is a simple pull with vacuum to see if they seal.
The mating surface check is done with a machinist straight edge, and a feeler guage. Anything more than .003-.005 should be surfaced. You have three surfaces to be concerned about. the combustion side surface, the intake side surface, and the exhaust side. At the shop I worked at it was IIRC, $38 for each surface. and this is done before being assembled.
Did he mention cutting the stem heights to match? Important on an AMC since there is no adjustment.
 
Drew does good work. I've known of him to build motors successfully that other "race shops" kept screwing up on. I'd trust his judgement. Every motor I've seen come out of that shop was spotless, which is amazing considering the condition of his shop! Definately old-school, but he knows what he's doing. If you're worried about blow-by, how hard would it be to do the rings while you've got the heads off? Not very.
 
I ask you this...

How much is your down time worth ? can you afford the full head rebuild ? or is this your 'spare' offroad vehicle..

I'd fix them all and also take a look at the cylinders as mentioned..

How many miles on this Craptastic 304 ? :flipoff2:

If it were mine if it had over 100k I'd have the heads done, and do a quick freshen on the bottom end, slap some new bearings in and rings some new gaskets to clear up any leaks for a few weeks and call it a day..

From a shops perspective, their advise should always be... what will make you the most happiest in the long run. (or least likly to return anytime soon) IE doing 1 valve will not ensure another one won't go bad in 6 months... Doing them all will..

Also as mentioned this is not a DD... But a vehicle thats used sporadically and when used its driven hard (as hard as dave can drive) and likely ran hard all day, dipped in some puddles on occasion.. etc.. my .03
 
check the crosshatch in the cylinders if there is any left, it will be fine fixing one valve is piontless to me. i would redo the heads if bottom end is suspect at all, i would put rods and rings in it, mains if your feeling froggy a pain int he ass but possible at least on toyota not sure on a 304. if you do put rings in it you can hit the cylinders with some stones to give it a good sealing surface
 
upnover said:
Did he mention cutting the stem heights to match? Important on an AMC since there is no adjustment.
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He did & I knew that Chip.

catfishblues said:
Drew does good work. I've known of him to build motors successfully that other "race shops" kept screwing up on. I'd trust his judgement. Every motor I've seen come out of that shop was spotless, which is amazing considering the condition of his shop! Definately old-school, but he knows what he's doing. If you're worried about blow-by, how hard would it be to do the rings while you've got the heads off? Not very.
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I got the same read from him Mark. This ain't his first rodeo... he's kinda the anti-"Super Shop" type (if anyone remembers those tards?). While well equipped, it looks just like my space does now! :lol:

yager said:
How much is your down time worth ?
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Little... wasn't planning to ride until Labor Day at the earliest

yager said:
can you afford the full head rebuild ? or is this your 'spare' offroad vehicle..
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Yeah, I can pay the toll, but I only have one rusty POS Jeep

yager said:
How many miles on this Craptastic 304 ? :flipoff2:
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I guesstimate less than 15K miles on the rebuild, probably closer 12-13K... Since there's zero indication of anything wrong with this mill other than the valve/seat on #2, I ain't touching ANYTHING south of the decks! Head work & fresh gaskets is all she'll get for now.

I just did Royal Blue on 7 cylinders without any problems...

yager said:
and when used its driven hard (as hard as dave can drive) and likely ran hard all day, dipped in some puddles on occasion.. etc.. my .03
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Thanks! :flipoff2:
 
Caver Dave said:
I just did Royal Blue on 7 cylinders without any problems...
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He's a MACHO MACHO MAAAAAAAAAN!

acover6.cduniverse.com_MuzeAudioArt_210_215013.jpg
 
You guys are so cute when you fight. LOL
 
Do a complete valve job. If the bottom end of the motor had unknown miles or very high miles then you might run into a problem with blow by. I've done valve jobs on cars with 300k plus on the bottom end and sometimes it just doesn't work out throwing a Darrel Hannah head on a George Burns bottom end. But in your case I'd have no worries.
 
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