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Where has my valve lash gone ?

 
Old 07-11-2018, 07:44 PM
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Default Where has my valve lash gone ?

Bit of a mystery, to me at least , recently rebuilt 2001 cylinder head . New inconal + 1 exhaust valves , Super Tech springs , ground the factory intake valves and all was good. Iíve put on about 8000 Km since the motor went back together and recently picked up a cold start miss. Oddly the miss would go away as soon as there was some heat in the engine . 30-60 seconds of running and I have all the cylinders back. After much head scratching and cursing Iíve managed to rule out spark and fuel. Further investigation revealed that 3 of the intake valves had zero lash and the rest had closed up significantly from the factory clearance . Exhaust side seems good. New valves have been ordered and I resided myself the fact that the head has to come off again . Does anyone have an idea what I did ( or more accurately my machine shop did wrong) ? It has been suggested that grinding the factory intake valves removed the hardened layer causing excessive wear. Just trying to avoid a future reaccurence . What say yee all ? Fredb
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Old 07-11-2018, 07:58 PM
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Read away!

https://www.miataturbo.net/race-prep...ing-out-82462/

In my case, changing to a more careful machinist and telling him to make the valve seats FAT fixed it for good.
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Old 07-11-2018, 11:55 PM
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Thanks , that an interesting read. Iím curious to see how wide the margins on the valves and seats were cut . I probably shouldnít have cheaped out . It would have been a lot easier to put in inconal intake valves while I was there the first time ..... Something about hind sight being 20/20 Another hour or so and Iíll have the head off. Thanks Fredb
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Old 07-12-2018, 11:58 PM
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Crap. Following.

I've got 1200 street miles and 3 track hours on mine and just had the same thing happen last weekend at the track. Took hours to get it started Sunday morning, and I limped it 120 miles home. Found very low compression, had 6 intakes at or below 0 lash, exhaust completely unchanged. I ordered shims already so I'll find out this weekend if I burned any valves or not.

Mines a mild n/a build, ~160whp, vvt head with volvo springs, stock valves and seats were both machined. Only occasional revs to 7500 so far.
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Old 07-13-2018, 02:11 AM
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If the lash was set properly when you built it, and it has closed up to zero "or less" DO NOT just reshim the valves. Take the head off and have it rebuilt

Your intake valves look like this if you have lost ALL your lash.


Last edited by TNTUBA; 07-13-2018 at 12:15 PM.
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Old 07-13-2018, 11:36 AM
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Also of note, setting the lash prior to torquing the head down means sometimes it needs to be redone after it is torqued down. See Tony Montana's build thread.
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Old 07-17-2018, 12:18 AM
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Welp, you all are certainly right. My intake valves are trashed.



Interestingly, the valve seats don't really look worn or damaged. Granted I don't really know what I'm looking at there.




Does anyone have experience with the generic brand stock replacement valves? I haven't been able to find any in the NB 102mm length, only ~101.3mm ones for NA8. Using the shorter valves would put me at the upper limit of available shims.
OEM and Supertech are basically the same price - any reason not to go Supertech for a mild N/A HPDE motor?
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Old 07-17-2018, 12:45 AM
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Factory replacements were easiest /fastest and cheapest answer for me. Iím dropping the head off at the machine shop tomorrow, guess Iíll find out shortly how bad mine are. Not that it matters with all new going in.
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Old 07-17-2018, 12:48 AM
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Tuliped OEM valves are indicative of too little valve spring and/or too much RPM and/or too narrow a valve seat. FYI
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Basically I've come over to the camp of "If something is a reliability problem on the track, just ask Andrew and do what he says".
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Old 07-17-2018, 01:48 AM
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Thanks , I suspect my seats were ground too narrow , some investigation is required . Definitely hasnít been too many rpm . Hopefully new factory valves will solve the issue. My last motor was NA and I spun the bejesus out it with ground factory Valves with no issues . Fredb

Originally Posted by Savington View Post
Tuliped OEM valves are indicative of too little valve spring and/or too much RPM and/or too narrow a valve seat. FYI
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Old 07-17-2018, 07:17 AM
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There is no downside to running more valve spring pressure than you need, You have found he downside of too little. Spend a little extra money and put a good set of valve springs in it.
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Old 07-17-2018, 07:21 AM
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And from the pic you posted, those seats look decent and the 45 doesn't look to be what I would call "narrow"

I installed new valves over seats like that with just lapping them in, cleaning the seats, valves and guides THOROUGHLY and upping the seat pressure and that same set of valves have been in my motor for going on 3 seasons now.
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Old 07-17-2018, 08:25 AM
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I experienced this as well on my 2002, twice. The first time was my fault, not instructing the machine shop to use OEM intake valves. I replaced these valves replaced with Supertech SS valves and 54# springs. Seven thousand miles later, I have the same issue. Machinist number 2 replaces all valves with inconel valves from FM and raise the spring pressure to 74#. Fingers crossed these valves live a long life.

Bottom line, I hate my VVT head. Between valves failures and VVT actuator issues, the VVT system is way more trouble than what itís worth. My car is a turbocharged street car. No track time. Yes, my torque curve is a bit wider than a standard head, but not enough to justify the aggravation. Sorry for the rant. I feel better now. 🙂
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Old 07-17-2018, 01:23 PM
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I think you'll want to go the Volvo VS-855 spring route. They are very cheap ($3-5 per spring) and provide 66lbs or spring pressure vs. the stock 40lbs. I second the opinion that your valve seats look plenty and that it is likely you are seeing valve flutter causing the valve wear (inadequate spring pressure). You also will want to make sure you are perfectly nailing the valve clearances.
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Old 07-17-2018, 07:39 PM
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Im not at all a fan of the Volvo springs. When installed they have decent seat pressure but they fatugie as quickly as a paperclip when used at elevated RPM.

valvesprings are a wear item...I don't run stock cams, But I'm over 100psi on the seat and am seeing zero valve wear. And everytime we went up in seat pressure....the car made more power.
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Old 07-17-2018, 11:35 PM
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Interested.. I'm right at the cusp of deciding supertech vs Volvo. It is very hard to pass up $3 x 16 = $48 vs $400 for the other options. Is it truly worth 10x the price? Not to have this thread devolve into the Valve Spring thread.. but are there any others out there with opinions?

If I run at high hp, but not race conditions (extended high rpm runs) and lower rpm (<7500), am I OK with something like the Volvo spring? I'm about to run 20-25 psi with a 6758, so I need to choose wisely.
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Old 07-18-2018, 12:10 AM
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EIBACH has valve springs for a reasonable price. I bought the single springs but can't remember what % more they were than OEM.

Found the specs -: 66 lbs @ 39 mm 200 lbs @ 27 mm
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Old 07-18-2018, 01:56 PM
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edit: sorry, didn't see it.

Last edited by albumleaf; 07-19-2018 at 02:37 PM.
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Old 07-18-2018, 02:49 PM
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Originally Posted by albumleaf View Post
VS855 fits the bill too

This was already mentioned above as well as input from those who've used them.
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Old 07-18-2018, 08:53 PM
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I'd try the eibach. The supertech arent much better than the volvo ones. Pacalloy springs from one of the companies that make springs out of them would be the real go to setup. I gave up on all this bullshit and just put in a motor that wasnt trash.
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