Misses when cold, goes away when warm... - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 12-20-2014, 09:18 PM   #21
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

Quote:
Originally Posted by sixshooter View Post
If you are using stock valve springs then it might be good to upgrade a little since you are boosted. The Volvo replacement springs are cheap - part numbers vs855 for a 1975 245, 244, or 242 2 liter.

They will give you 15-20 more lbs of closing force to help overcome the boost pressure trying to keep the intake from closing.
I bought everything from Supertech to decorate the "upstairs". That includes the springs, as well.
Godless Commie is offline   Reply With Quote
Old 12-20-2014, 09:33 PM   #22
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

Now, the truly interesting news...

I spoke with the guy who ported my cylinder head. He is a pretty cutting edge guy.
He tells me he has seen this happen way too many times with Supertech valves, and they simply erode away at the "angles".
According to him, cavities occur at the cut faces where they contact the valve seats, and he tells me has lots of pics to that effect.
He told me to get rid of the valves ASAP, and get different valves in there.

My question is, has anyone heard of or experienced premature wear on ST valves?
I was told I would just set myself up for another round of valve troubles if I repair this problem and continue using ST valves.

For the record, I have the following:

* Intake valves, Supertech brand, Part# MAIVN 1204

* Exhaust valves, Supertech brand, Part# MAEVN 1204

* Valve spring set, Supertech brand, Part# SPRK-MM18S (Springs, with retainers and seats)

I am running max 12-14 psi boost these days. The engine has seen about 18.5 psi last summer, when I was trying a much bigger pulley.
I also zinged the engine once on the track, and my maxi gauge tells me it went up to about 8250 RPM briefly when I was downshifting to 4th in panic, with a guy fishtailing in front of me at the end of a fast straight.

The car never overheated, not even once. Coolant stays below 110C, so does the oil. Those temps are actually at the 80-90C level most of the time. I do have a very good DIY reroute.

Any thoughts?
Godless Commie is offline   Reply With Quote
Old 12-21-2014, 12:01 AM   #23
Senior Member
iTrader: (3)
 
Join Date: Dec 2007
Location: Brownsburg,IN
Posts: 800
Total Cats: 58
Default

Most of that is taxes, the goverment there raised taxes on everything and laid off a bunch of employees in order to get bail out loans by the EU about a year or two ago.
Tough economic conditions for the average people.
HHammerly is offline   Reply With Quote
Old 12-21-2014, 05:39 PM   #24
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,365
Total Cats: 1,326
Default

Whoever cut your seats cut them too thin. I've run lots of ST valves and worked with a lot of motors with ST valves inside them, and there's no issue with the valves.
Savington is online now   Reply With Quote
Old 12-21-2014, 06:05 PM   #25
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

Quote:
Originally Posted by Savington View Post
Whoever cut your seats cut them too thin. I've run lots of ST valves and worked with a lot of motors with ST valves inside them, and there's no issue with the valves.
Does this mean the seats are wearing down?

In that case, that's a relief.
Godless Commie is offline   Reply With Quote
Old 12-22-2014, 08:21 AM   #26
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,669
Total Cats: 1,561
Default

Quote:
Originally Posted by Godless Commie View Post
In that case, that's a relief.
A valve relief?

A relief valve?

Sorry. I was required to insert a pun there due to my OCD.
sixshooter is offline   Reply With Quote
Old 12-22-2014, 10:07 AM   #27
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

Quote:
Originally Posted by sixshooter View Post
A valve relief?

A relief valve?

Sorry. I was required to insert a pun there due to my OCD.
More like a relief cut.
Godless Commie is offline   Reply With Quote
Old 12-22-2014, 11:18 AM   #28
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,669
Total Cats: 1,561
Default

If there isn't enough surface area where the valve contacts the seat, the valve isn't cooled enough and can wear prematurely. The valve is cooled by its contact with the seat.
sixshooter is offline   Reply With Quote
Old 12-22-2014, 11:28 AM   #29
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

Quote:
Originally Posted by sixshooter View Post
If there isn't enough surface area where the valve contacts the seat, the valve isn't cooled enough and can wear prematurely. The valve is cooled by its contact with the seat.
Does this mean you see a set of new valves in my near future?
I was really hoping I could save the valves.

The reason behind this hope is the fact that the engine runs well when it is warm.
If the valves were toast, they would fail to seal at all times, right?

I guess we'll know when I pull the head.
Godless Commie is offline   Reply With Quote
Old 12-22-2014, 01:38 PM   #30
Moderator
iTrader: (11)
 
sixshooter's Avatar
 
Join Date: Nov 2008
Location: Tampa, Florida
Posts: 15,669
Total Cats: 1,561
Default

The valves and/or seats may need to be reground. This is a common procedure for a machine shop to perform. The angles chosen and the widths of the surfaces at each of the angles when finished can be different.











Attached Thumbnails
Misses when cold, goes away when warm...-22491d1258097063-3-angle-valve-job-q-3angle.jpg   Misses when cold, goes away when warm...-valve_diam2.jpg   Misses when cold, goes away when warm...-3-angle-valves.jpg   Misses when cold, goes away when warm...-3-angle-drawing.jpg   Misses when cold, goes away when warm...-0703_impp_12z-head_and_valve_train-diagram.jpg  

Misses when cold, goes away when warm...-236381d1318626481-s2000-valve-job-advice-untitled.png  
sixshooter is offline   Reply With Quote
Old 12-22-2014, 02:07 PM   #31
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

Quote:
Originally Posted by sixshooter View Post
The valves and/or seats may need to be reground. This is a common procedure for a machine shop to perform. The angles chosen and the widths of the surfaces at each of the angles when finished can be different.
This is exactly why I found a decent machine shop and received the price quotes.

On the other hand, Supertech was very cool and responded to email immediately.

Here's their response, together with my initial email:



Hi there,

I have a 1998 Mazda MX-5 (identical to a '99 Miata), and the engine has about 17K miles since the rebuild.
(It was "built"as a precaution, not because of failure)

I used all Supertech components in the valvetrain:
* Intake valves, Supertech Part# MAIVN 1204

* Exhaust valves, Supertech Part# MAEVN 1204

* Valve spring set, Supertech Part# SPRK-MM18S (with retainers and seats)

After developing a severe cold miss, I checked the valve lash. 14 out of 16 valves are too tight, with the rearmost intake valve at "negative lash", meaning the cam lobe is pressing on the valve at all times, regardless of position.

Have you heard of any problems like this where the valve adjustment gets out of spec to the point of crossing over to "negative lash"?

I am in the process of pulling the head to lap (or replace, if necessary) the valves. Should I be worried they may wear once again in the near future?

For the record, the car is supercharged, with 10-12 psi boost. Engine coolant and oil temps never go hot, in fact they stay in the 80 to 90C range, with the oil occasionally going up to about 100C.

Please understand that I am NOT trying to get something from you. It's just information I am after.

Any information or ideas you'd be willing to share with me will be greatly appreciated.

Thank you,


------------------------------

Hi Hakan,
If when you put the new valves you also machined the seat inserts on the head, there are sometimes when the valves may have to adjust to the new machined seat and it will change the lash, so you will need a re-adjustment of the lash. But this will happen only once.

So you will need to adjust the lash and check sometime later to see if there any further change. There shouldn’t be.

Let me know any questions.

Best regards.
***** Tagliavini
Supertech Performance Inc.
3550 Charter Park Dr., San Jose, CA 95136

------------------------

(Paraphrasing my response)

Does this mean I do not have to pull the head, then?

I mean, I was fully prepared to do that.


-------------------------

Hi Hakan,
No problem.

At this time you don’t need to pull the head away. Re-adjust the lash and check them after a race of several hundred miles if you only drive it on the street. This is most probably what happened to you.

If you still have problems, it would be very rare, but then you will need to remove the head to investigate more the reason.

Best regards.



I guess I'll give adjustment a try...
Godless Commie is offline   Reply With Quote
Old 12-22-2014, 02:16 PM   #32
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,365
Total Cats: 1,326
Default

I disagree with *****. When valve clearances tighten up slightly on a new engine, it's a normal thing, but normal is losing .002-.003", not the entire clearance (.011+). If you lose all the clearance, something is damaged, and resetting the clearance is not going to solve the problem. You'll be back inside the motor shortly (like in another thousand miles or less).

The engine runs fine when it's warm because the aluminum cylinder head expands faster than the valve does, which slightly increases lash clearance and allows the valve to make contact with the head again.

tl;dr: pull your cylinder head and replace your damaged valves, then find a machinist who is willing to cut a seat wide enough to prevent this from happening again.
Savington is online now   Reply With Quote
Old 12-22-2014, 02:20 PM   #33
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,187
Total Cats: 2,583
Default

We've list of all the OEM shims posted here, they're like $3.50 a pop from mazda.
18psi is offline   Reply With Quote
Old 12-22-2014, 06:00 PM   #34
Junior Member
iTrader: (2)
 
Join Date: May 2014
Location: Arlington, TX
Posts: 328
Total Cats: 40
Default

Quote:
Originally Posted by 18psi View Post
We've list of all the OEM shims posted here, they're like $3.50 a pop from mazda.
Post a link to $3.50 Mazda shims?

Cheapest I can find them is $8.00 each, which is $0.80 cheaper than Rosenthal.
Dustin1824 is offline   Reply With Quote
Old 12-22-2014, 10:06 PM   #35
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

Machine shops do not necessarily use replacement shims.
They sometimes grind minute amounts off the tips of the valves to get the clearance correct.
Would you guys be opposed to this sort of procedure?
Godless Commie is offline   Reply With Quote
Old 12-28-2014, 05:52 PM   #36
Elite Member
Thread Starter
iTrader: (2)
 
Join Date: Jun 2009
Location: Istanbul, Turkey
Posts: 2,050
Total Cats: 433
Default

Here's a frame grab from a cheap scope I got a hold of:



Looks like the seat is toast.
What do you guys think?

I am uploading the video to Youtube as we speak. I will post that video as soon as it is ready.

Still waiting for the gasket set. There is no point in tearing the engine apart without parts on hand.
Attached Thumbnails
Misses when cold, goes away when warm...-hp8xil.png  
Godless Commie is offline   Reply With Quote
Old 12-28-2014, 11:08 PM   #37
Elite Member
iTrader: (21)
 
Join Date: Jun 2007
Location: Rochester, NY
Posts: 5,686
Total Cats: 558
Default

Yeah, that seat surface looks like the moon.
rleete is offline   Reply With Quote
Old 12-28-2014, 11:48 PM   #38
Senior Member
iTrader: (3)
 
Join Date: Dec 2007
Location: Brownsburg,IN
Posts: 800
Total Cats: 58
Default

Actually looks to me like carbon build up, and the good news is that it looks like the seat is not moving on the head itself, you can probably get by re grinding the seat and valve and re gapping valve lash
HHammerly is offline   Reply With Quote
Old 12-29-2014, 06:46 AM   #39
Elite Member
iTrader: (21)
 
Join Date: Jun 2007
Location: Rochester, NY
Posts: 5,686
Total Cats: 558
Default

Yeah, but why would it miss cold, then be okay warm?
rleete is offline   Reply With Quote
Old 12-29-2014, 08:29 AM   #40
Senior Member
iTrader: (3)
 
Join Date: Dec 2007
Location: Brownsburg,IN
Posts: 800
Total Cats: 58
Default

Quote:
Originally Posted by rleete View Post
Yeah, but why would it miss cold, then be okay warm?
It is not ok when warm, it is just not as bad...
HHammerly is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Hey everyone another n00b here Big_gumby Meet and Greet 80 10-05-2015 05:06 PM
Expected intake temps on the track? tazswing Race Prep 20 10-03-2015 12:04 PM
Leaky Wilwoods mx592 Suspension, Brakes, Drivetrain 1 10-01-2015 01:45 AM
Low oil pressure after 1.8 swap and new turbo setup JesseTheNoob DIY Turbo Discussion 15 09-30-2015 03:44 PM
Missing/knock at idle, can someone point me in the right direction? Mikel MEGAsquirt 4 09-28-2015 05:46 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 08:58 PM.