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Old 08-09-2008, 05:05 AM   #1
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Default Keep losing valve clearance!! OMG HELP!

Well - ok this sucks.

I had the head put together, like, a year back. Maybe two. They messed up doing it, redrilled the cam holes, got them all out of round, but it was a head with some money into it, so I decided to keep it.

Well, a while later, I noticed my motor stumbling a lot at idle. Well, the valve lash was tight in some sports. New shims, odd I missed that, normally I don't have issues.

Later, the stumbling comes back. Turns out the valve lash was low on cyl one (like, 5 or 6 mils low), and another cyl had none. ****. Put in new shims (this time the next to smallest size mazda makes). This was four months ago.

Recently, it's been stumbling again, of course I didn't even think about it, but checked valve clearance for laughs, and low and behold, everything on the whole motor is awesome, except that one intake valve, no clearance at all. Put in the 3 mil smaller shim - the smallest made - and yep, can't get a one mil gauge in there.

After spending hours dulling bits, wearing out my arm, sanding, using stones on the lathe, everything I can think of.. I managed to get 0.0025 thousands off a shim, and gave up.

I know I can pull the head, have a shop take 0.030" off the valve stem, and be good to go. But, is it worth it if things keep getting worse like this? My guess is the valve seat isn't holding up. They are "+1mm" valves (more like +0.5mm), and if the shop couldn't even put the caps on right for the cam, can they actually DO a valve job? The work on ferarris, but, that doesn't mean they know what they are doing, only that they charge a lot.

Anyway, there's a run tomorrow, I guess I'm missing. If anyone knows how to get 20 thou off a shim in a hurry, I'd love to hear it. Otherwise, I'm just trying to figure out what to do with the head, etc.

Sucks, too, since the car's been running awesome aside from that. Best it's been in months.
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Old 08-09-2008, 01:25 PM   #2
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i wonder if maybe your valve job isn't concentric to your valves and as they spin, the clearance changes because they seat differently. were they lapped in?
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Old 08-09-2008, 01:33 PM   #3
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Don't really know - I assumed they were - and don't have a lot of reason to doubt it - it was a proffesional shop, even if they don't know which way to face the cam caps on a miata.The other time I'd had the place (under different management) do work there, it was first rate.

It's hard to spin the valve from the outside. :-) I've learned that tapping the valves with a hammer (via a punch on the lifter) will usually get them to read the lowest clearance, I assume they don't seat perfectly, or bind slightly on the guides. I replaced the guides last time in the hopes of fixing that, but it didn't really change much. When doing a leakdown you have to tap each valve. Which I thought was crap till I read a few sites from pro tuners who said this was typical. Learn something every day. :-)

I'm going to bring the shim to a friend in a shop, see if he can come up with a way to thin it, if not there's another autoshop I really like - they don't do custom work but they do day-in-day-out stuff the best of anyone I've seen and don't charge anything crazy for it.

Still kinda at a loss. I don't want to put a lot more money into this head, but don't want to put all the money into the new head I'd have to to bring it up to speed.

Perhaps I can copy the porting if I have them both in front of me, but I doubt it.
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Old 08-10-2008, 03:11 PM   #4
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Ok, so like... After quite the adventure making my own valve shims just a bit thinner.... to go on a run, then pull the head later, I found.... METAL SHAVINGS. Damnit.

First I thought the oil pump was spewing them, but 1) they were all alum, and 2 running the pump didn't do much.

So I look closer, find this:



Pull the guides out, about half are so afflicted:


And it corresponds to damage found here:


Overall, here's the look:



My question is, a while ago, a shop worked on this head, put in biggie valves I'd bought, new guides, etc. They'd line-bored the cam journals with half the caps on backwards. I was livid since I have a lot of money into this head, they gave me this and sent me home:



Does anyone think I have a leg to stand on for getting a new head out of these guys?

The long version of the story is in the next post.
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Old 08-10-2008, 03:20 PM   #5
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Backstory. A while ago, I overheated the head when one of the water lines broke. Nothing seized, but it wasn't too pretty. I bring it to a shop, the only one in town I found to do good work, it was recommended to me by a friend who runs a BMW shop.

Unbeknownst to me, they were under new managment, and also, the guy I specifically brought it to since I liked the work he did gave it to some new guy.

Well, since I needed new valves, I got some "plus 1" (really only about 0.5mm over) valves, which were still cheaper than mazda ones. They say it'll be a couple of days. I call them up 4 days later, they say one of the cams won't turn, they have to line bore it. What? I don't think so, I remember stuff looking ok. I tell them to double check it.

Two days later, they call, say they need to line bore it. I ask if they took it all apart, etc, and put it back together, lining up the little marks. They say yes. I say check it again.

Another couple days (now two weeks without a car, or more) they say they are basically just storing my head, waiting for permission to line bore it. I tell them to please, double and tripple check it, I know it's fine, but if they are SURE it needs it, do it.

So, they line bore it. Charge me for it as well. When I get there, half the caps on on backwards. They used the cast marks not the stamped ones for orientation. MAN am I pissed. After lots of arguing (they offer to give my $200 back or whatever, on a head with $850 in work on it, $500 of intrinsic junkyard value, and $300 or more in new guides and big valves I just put in. Oh, **** them, you know?

So they give me this warranty.

I check the cam clearance. In one dimension, it's right on - factory spec, as tight as it would be new (only ~50k on the motor). In the other (kinda 10 o'clock?) it's right at the wear limit. I mean, RIGHT at it. So the cam can wiggle in one direction and the factory manual is staring me in the face with "replace head".

So I put it together. The valves, I find, are tight, way tight, in places. I have to tap the valves to get them to come up fully. Ok, new shims. This happens a few times, over the year or so it's been (1.5) since I had them work on it. This time I needed a shim thinner than mazda makes. So I make a shim, thinking I'll have to pull the head next week.

So, yeah - the valves don't close, so they burn. That's where I'm at. I'm sure the seats are toast too, but I don't have them off yet.
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Old 08-10-2008, 03:46 PM   #6
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I'd make them stand behind that warranty they gave you. Nothing to loose by trying. This sure does suck.
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Old 08-10-2008, 04:56 PM   #7
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This may not apply to Miata heads, but the overheating may have something to do with your current issue.
It is my understanding, from previous experience, that once an aluminumn head is overheated, the qualities of that metal change. In my case, the valve seats were more soft than a non-overheated head. After 40 dyno runs, 250 miles and one two day drag event (this car was shifted at 9800-10200 RPM), the car did not idle right. Turns out the guides were shifting in the head as well as the valves were tearing the seats apart.
The change in metal properties could apply to you, and maybe not. Worth some research.
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Old 08-11-2008, 03:06 AM   #8
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Wouldn't surprise me if that's part of it. I would have hoped the valve guides being all fresh might have helped. I don't see excessive wear in the cam journals, and I've yet to come up with a good reason why their being loose (or unsymetric) could lead to the buckets going sideways.....

Either way, 1) it hurts, and 2) there's not much I can do to save this head I'd bet. I could fill it and redrill it maybe but is it worth it?
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Old 08-11-2008, 01:41 PM   #9
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Did you rearange the cam caps after they line bored? If so there's your problem.
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Old 08-11-2008, 02:28 PM   #10
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No way, I was ultra religous about every cap, shim, bucket, valve. Everything lived its life in an individually labeled bag, etc.

Still no real ideas. I want to check and see what the valves look like. Tonight I will. So far the best argument I've heard is the off-center-line cam lobes made the parts come up at an angle.
-Abe.
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Old 08-14-2008, 02:09 PM   #11
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Update, not that it's much of one. Took it to the shop a couple days back, told them it'd been ticking since I got it, they are "checking it out".

In the mean time, I'm trying to decide between a new head or a new motor, then build up the motor that's in there and sell it or maybe keep it as a space. Dunno.

Looking at that GTX motor Dr. Nick is trying to unload, but without NB manifold compatibility it's odd....
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