Help!! My Intake Valves Keep Wearing Out! - Page 5 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-23-2015, 11:17 PM   #81
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Most things point to thin seats and not enough spring pressure. I would like to hear from Hornetball and K24 and any others that had this issue and have some time on the changes that were suggested for the fix. I have been using a stock head as I burned the engine that the modded head was on and am just now getting around to going with a modded head again.
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Old 05-24-2015, 01:20 PM   #82
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Quote:
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Any chance you guys are wearing out the valve guides and that is allowing the valve to move around a bit on the seat? This happened to me years ago on a honda engine.
+1 loose guides will cause rapid valve wear.
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Old 05-24-2015, 02:34 PM   #83
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Guides aren't loose.
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Old 05-24-2015, 02:36 PM   #84
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Think about the surfaces that could "wear".

Cam to lifter: not likely, huge surface area.

Lifter to valve stem- very small surface area, for sure this spot COULD show wear. If the stem isn't perfectly flat, it could wear flat over time.

Valve to seat- very small surface area again, and gets exposed to lots of heat. This is likely where the problem is. This spot also requires specific angles and seat widths, again, a spot for error.
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Old 05-24-2015, 03:31 PM   #85
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I have not put any hours on the new setup yet. I'll have some more info later this summer.
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Old 05-24-2015, 07:02 PM   #86
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I took a junkyard head to a different machine shop and had it put together. Had the ST light doubles and Ti retainers transferred over. Other than that, just a thorough refresh. Been beating on it ever since with no issues.
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Old 05-24-2015, 07:19 PM   #87
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Thanks Rick Sounds like with a proper seat width and spring presure the ST intakes work fine. Did you have the stock shims installed also? I suppose you have checked the lash adjustment and are satisfied that it's not changing.
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Old 05-25-2015, 12:34 AM   #88
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Yes, the stock shims were installed with the ST light doubles. I've tracked it a lot this Spring and have been keeping an eye on things. It's stable (thank goodness).
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Old 12-16-2015, 10:01 PM   #89
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How is every ones ST intake valves doing, I would like to hear some updates. As far as mine went, it wasn't any different. I installed the double lites from the singles and the stock shim also along with grinding the seats to a stock width and the same cupping took place on the seat face on the valves. I think the alloy is inconsistent in their makeup as a few look pretty decent and others to varying degrees are cupped. Maybe running high boost has something to do with this and the valves aren't able to take it.

Please post your results after changing things, thanks
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Old 12-17-2015, 11:15 AM   #90
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I have no updates for you. Spent the summer working my butt off and had no time to run the car. I plan to get more use of it this year.
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Old 12-17-2015, 12:27 PM   #91
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Quote:
Originally Posted by jmann View Post
How is every ones ST intake valves doing, I would like to hear some updates. As far as mine went, it wasn't any different. I installed the double lites from the singles and the stock shim also along with grinding the seats to a stock width and the same cupping took place on the seat face on the valves. I think the alloy is inconsistent in their makeup as a few look pretty decent and others to varying degrees are cupped. Maybe running high boost has something to do with this and the valves aren't able to take it.

Please post your results after changing things, thanks
I'm running the heavy double supertech springs and supertech valves, 10-30 conventional castrol oil, stock shims. They have seen 8,800 RPMs about 200 times, over 8,000 god knows how many times, about 150 passes at the 1/8 mile, about 7-8 thousands street miles thrown in there. Clearances are exactly as I set them when I built the head (top end of spec), and spraying brake parts cleaner into the port shows they do not leak at all. Valves are quiet on cold start/hot start too.

I cut the seats with carbide cutters from Newway, 5 angle intake, 4 angle exhaust, and I set them conservative since reliability is more important than 3 more hp. It works for me. I made sure and set the angle that contacts the valve on the outer perimeter of each valve to maximize contact surface area, as that has several benefits.

EDIT: Also I'm running all the boost.
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Old 12-17-2015, 12:43 PM   #92
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Sounds like yours are doing fine. Mine gets run alot of track days and very hard, maybe the difference is yours is short spurts down the drag strip verses 25-30 min. sessions on the track. Mine was also ground to the outer surface of the valve seat face.
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Old 12-17-2015, 01:23 PM   #93
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I have mentioned this elsewhere but thought it worth repeating in this thread; valve springs are consumables in a race engine.

Your pro engine builder should record seat pressure when first assembled and at each refresh. I don't personally know what percentage loss in seat pressure is acceptable at what time interval but Keegan does. In very high rpm high dollar race engines (not BP's), valve springs get replaced at very short intervals. If you have enough spring for the rpm/cam/duty cycle/valvetrain weight, etc, the springs should last a few seasons or until the rings and mains are done. The harder you push the mechanical limits, the faster the springs degrade. On a BP at least, there is little penalty for using a little too much seat pressure. We have taken to recommending ST singles up to about 7200rpm, light doubles up to about 7800rpm and heavy doubles for anything above that. That doesn't mean you should run heavy doubles on your OEM N/A rebuild though.

We have never experienced any problems running a bit too much spring but certainly experienced and heard reports of issues with running too little. Valve and valve seat wear has ended up being one of the most common causes of premature rebuilds I have seen in performance BP builds. Only a few of ours, mainly friends and others. So that's been one of key points in our engine development over the last 10 years. Thus the formula: stock width seats, properly hardened seats, adequate spring pressure then stay below 9000rpm. If F/I, then SS exhaust valves. Inconel exhaust valves increase safety margin for high duty cycle F/I builds. This stipulation for F/I is independent of power. A 210whp, 14psi GT25 turbo on pump gas on a Roval will cook exhaust valves where an 300whp GT30 14psi turbo autocrosser on E85 can run stock valves without a problem.
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Old 12-17-2015, 02:05 PM   #94
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Thanks Emillio The car had the lite singles in 2014 and cupped the intake valves which had narrow seats without the stock shim installed. So for 2015 the head was redone with stock width seats and the double lites bought from you with the oem shim installed back and new intake valves. Same thing happened, the seats in the head are fine, it is the valve seat face that is bad. They are still sealed as I poured gas into the chambers and they didn't leak, but the gap on a few is down to 1 thou and the others vary.
The inconel exhaust valves have never had any issues even with a narrow seat grind. Think I'll go back to oem intakes with the +1 inconel exhaust, never had an issue with oem intake valves, was just after a bigger intake valve.
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Old 12-17-2015, 03:49 PM   #95
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I highly agree with his post on it being better to have too much valve spring vs not enough. Very well accepted advice in the motor world.

And jmann you are right, I don't do long track days so my engine doesn't see the abuse yours would. But I have pushed it in the RPM department without any sign of degradation.

jmann, my advice is that you need more valve spring if the machining is right. What seat width are you running? You can always bump it up some for reliability and stop worrying about it if giving up 2-3 hp is an option for what you do. Mine is a street car so a tiny loss for reliability is no issue.
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Old 12-17-2015, 07:05 PM   #96
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Im sending mine to Calico for their DLC treatment. If thst doesn't work.....I'm building a spare head.
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Old 12-17-2015, 07:13 PM   #97
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I shift my car around 6800 to 7200 rpm as the power curve fall offs much above 6800. The rev limiter is set to 7500 so it never sees above that and seldom that much unless I'm just short of making a corner entry at the above rpm's. As I posted above after the issue in 2014 and being in on this thread last year I went to a stock ground seat with a stock seat width. I told the shop no fancy multi angle cut, just do it as if it was stock street engine. Brand new dbl lites with the oem shim.
I still am of the opinion that the ss valves have a metallurgy issue under extreme heat conditions. The inconel exhaust have the same grind and springs and in 2014 had a 5 angle grind and no issues and they see alot more heat then the intakes do. Thanks for your opinions but I think stock intakes with inconel exhaust is in for next year.
Emillio have some inconel intakes made and solve this problem, I and others that I know would buy them as they aren't that much more in the greater scheme of things.

Last edited by jmann; 12-17-2015 at 09:27 PM.
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Old 12-17-2015, 07:41 PM   #98
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We'll see how mine wore with the heavy doubles. I had about a minutes worth banging off the rev limiter at 8500rpm this season due to the 6 speed 3.63 combo and a little more power. Thats about the amount of time I spend on the heavy singles the previous two seasons and the intake valves opened way up before I put in the inner springs in and reset the lash. I'm going to check it at some point, maybe this weekend.
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Old 12-17-2015, 09:29 PM   #99
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Did anyone figure out what exactly is causing the intake valve cupping?
potentially some combination of rpm and lack of valve seat area?
I am curious as the '95 head I just pulled has the same problem with cupped intake valves on the factory valve job. It only had 63k street miles and was on an auto trans car.
It seems to me that the valve seats are the problem here but I do not want to rule things out.
(was trying to save money by lapping valves instead of paying a machine shop to cut new seats for my rebuild)
In for answers
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Old 12-17-2015, 09:40 PM   #100
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So if I understand, you say the head is original oem intake valves, not ST ss valves? I've never heard of oem intake valves having a problem. I've ran oem under pretty extreme conditions without issues.
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