AMC WBX cylinder heads

Here’s the dope on AMC wbx heads as of summer ’17 when I last processed them, this should cover most of the questions and swat down most of the BS I’ve seen on this subject:

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The castings are excellent, better than VW’s, they have much more material across the upper half where the VW heads are known to develop cracks from the stud and spark plug holes. VW never did make very good heads, so the bar is set kinda low, but AMC makes some of the best aftermarket castings for all kind of heads and the wbx heads are no exception.

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The machining registration always results in a small overhung edge inside one exh. valve port, which should be cut smooth with a burr. Apart from that, port and polish work is optional according to your goals. Like the OEM heads, the ports are well-sized for velocity so don’t go hogging out much unless you’re building a huge engine (like over 2400cc).

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The valve seats and guides are also good quality, and the basic one-angle seat machining is always dead on. If you’re tooled up for it, it’s easy to improve performance by cutting additional margin angles above and below without even disturbing the existing seat angle, it’s sufficiently wide that it can afford some margin loss and still have good seating width.

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The intake valves provided are fine for use as-is, because an intake valve runs very cool so doesn’t require super-quality metallurgy. However the stems aren’t as hard as a VW intake’s, and that’s why the stem grooves hammer out when keepers are used unmodified. It isn’t a matter of VW vs. AMC keepers, both are well-hardened, and both lock together before clamping the valve stem to allow the valve to rotate independently of the spring. This “feature” isn’t really required, though, the spring dynamics will cause spring and valve to rotate no matter how the keepers fit. But when keepers are fit to the AMC intake valve in the original loose-clasping fashion, the small amount of play between the grooves of the valve stem and keepers will allow the stem ridges to get deformed and hammered out to eventual failure. There are two solutions: either grind the keepers to fit with small gaps so they clamp the valve stem , and/or use a reground VW intake valve.

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You could also buy a new top-quality intake valve, but there are better places to spend your money when you can have the stock ones reground for 2 or 3 bucks each.

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The exhaust valves provided are a 2-piece welded valve just like OEM, but not of top-quality metallurgy. The valve sourcing hasn’t changed since I started buying these heads in ’06. I’ve seen some folks say they have changed, I can say they are wrong at least as far as summer ’17. These valves often begin to burn by about 30k miles. This doesn’t mean that will definitely happen, but there is a clear pattern. An exhaust valve is the hottest part in the engine so metallurgical quality is critical. So for insurance of long life it’s best to bin the AMC exhaust valves and replace with a KS/TRW valve, which are OEM for the wbx. These valves have stems sufficiently hard that gapping keepers wouldn’t be strictly necessary, but I’ve always done them all that way because it does eliminate play in the keeper fit and the stock fit isn’t necessary for valve rotation.

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GoWesty is now also using Eaton exh. valves, a top shelf manufacturer, but I can’t vouch for those having not used them.

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It’s fine to regrind intake valves, but some people claim that you should regrind the VW exhaust valves and use them instead of the AMC ones. I would advise strongly against that, grinding and re-using any exhaust valve is pennywise and pound-foolish.

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The factory seat machining is good enough that lapping isn’t needed, you should see good leakdowns using them out of the box, but I tended to do a light lap just to confirm full contact and to speed seating-in when the engine is first run.

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Summing up: minimum work for longevity is replace exh. valves, grind keepers to have small gaps.

2 Comments

  1. Steve Johnson

    Thanks for providing recent experience for us to consider.

    Reply
    • Chris

      My pleasure Steve, thanks for stopping by.

      I wouldn’t want anyone to view this as “recent experience” though, that I think reflects the common perception that these things change fairly often, when in fact there’s been no change at all in over a decade and there’s not likely to be any anytime soon. That perception is usually the root of common mis-information this post is meant to counter, things like “I heard they changed the valves and now they’re OK”, when they’re still not OK. I mentioned the last time I bought these just in case anything does change, as unlikely as that is. Since 2006 I’ve bought and used over 200 copies of these heads and nothing has changed except the boxes they’re shipped in. AMC has no good reason to change the product, as far as they’re concerned the valves they supply are adequate because they do actually provide several years of service for most users before any problems come up, and since quality exh. valves are very expensive, including really good ones would require raising their prices substantially and cutting into sales. This guide would have summed up my advice ten years ago, and will probably be just as pertinent ten years from now.

      Reply

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