Valve clearances on a 99 head- Please check my math
Had a few questions about setting valve clearances on a 99-00 head. I found on m.net that the spec for setting the clearances is as follows:
IN: 0.18—0.24 mm {0.008—0.009 in} EX: 0.28—0.34 mm {0.012—0.013 in} Sourch: MX-5 Miata Forum - View Single Post - Timing belt tips? Currently my clearances for two are off, slightly. 1 inch= 25.4mm Intake #1 is .015 inches which is .381mm- Has a 3.370mm shim in it Intake #2 is .012 inches which is .3048mm- Has a 3.5mm shim in it I would like it on the lower side of spec, right? For # 1 ill want to add an additional .1778mm to my current shim to bring the clearance down to .008, right? For # 2 ill want to add an additional .1018mm to the current shim to bring it down to .008, right? Hows my math? Also, wondering if the clearances should be any different since i have supertech valves and springs in the head. |
Since you're running stock cams, I'd be inclined to run stock clearances. Cam geometry is generally the bigger factor what clearances you run moreso than valves/springs.
Your math is close enough... I got the same thing on intake 1 and .1016mm on intake 2. So you'd want a 3.548mm shim on 1, and a 3.602 shim on 2.
Originally Posted by thesnowboarder
(Post 479013)
Had a few questions about setting valve clearances on a 99-00 head. I found on m.net that the spec for setting the clearances is as follows:
IN: 0.18—0.24 mm {0.008—0.009 in} EX: 0.28—0.34 mm {0.012—0.013 in} Sourch: MX-5 Miata Forum - View Single Post - Timing belt tips? Currently my clearances for two are off, slightly. 1 inch= 25.4mm Intake #1 is .015 inches which is .381mm- Has a 3.370mm shim in it Intake #2 is .012 inches which is .3048mm- Has a 3.5mm shim in it I would like it on the lower side of spec, right? For # 1 ill want to add an additional .1778mm to my current shim to bring the clearance down to .008, right? For # 2 ill want to add an additional .1018mm to the current shim to bring it down to .008, right? Hows my math? Also, wondering if the clearances should be any different since i have supertech valves and springs in the head. |
Oh god...I remember doing this. 16 times. Makes simple math seem more complicated than it really is.
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My local dealership only has 3.4mm and smaller, where can i find a 3.5-3.6mm ?
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Originally Posted by thesnowboarder
(Post 496530)
My local dealership only has 3.4mm and smaller, where can i find a 3.5-3.6mm ?
http://img37.imagefra.me/img/img37/1...fm_0b2e4a8.gif Perhaps the dish in the follower is sufficiently deep that you could place a thin piece of material (such as a piece of sheet metal you've cut out) under the shim? 'Course, I'd hate to see what happens if a shim gets ejected from the follower because you stuck something under it. There's nothing in the FSM which tells you what to do if the thickest available shim won't get you where you need to be. |
Originally Posted by Joe Perez
(Post 496583)
There's nothing in the FSM which tells you what to do if the thickest available shim won't get you where you need to be.
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Originally Posted by thesnowboarder
(Post 496530)
My local dealership only has 3.4mm and smaller, where can i find a 3.5-3.6mm ?
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Originally Posted by thesnowboarder
(Post 479013)
I would like it on the lower side of spec, right?
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From a performance standpoint you want the thinnest shim possible in there to minimize mass.
In my experience you don't often have to do much adjustment once the head is past its initial settling in period after a rebuild, so I'd want to see it start at the mid-point of the shims available or smaller ideally. |
Originally Posted by MartinezA92
(Post 496588)
Find out why its so off. I personally think if its that far off that a head rebuild should be considered.
Could be cam / follower wear, but I'd think you'd notice the metal shavings. Valves generally don't get shorter over time. They stretch, but they don't contract. Horrible foulness built up on the mating surface between the seat and the valve? Lapping would answer that... I'm in the dark here as much as the OP. Last engine I had to adjust valves on was my '71 VW, and that thing was so random you'd think the valves really were growing and shrinking on their own. But instead of shims it used screw adjusters (like an American V8) so until you ran out of thread, there was no obvious min & max. And those adjusters were easily 1/2" long. How, I wonder, are the cam journals holding up? Seems that if wear has occurred such that the cams are now loose-fitting in their bores, this would cause a general increase in lobe-to-follower clearance. Any fix for this short of milling down the seating area for the caps and then line-boring the cam holes? Never been down that road...
Originally Posted by Rennkafer
(Post 496835)
From a performance standpoint you want the thinnest shim possible in there to minimize mass.
The mass of the valve, the follower, and the portion of the spring which is effectively unsprung is probably > 10,000 X. |
The motor was put together this way, if i were to yank the head would the proper adjustments be able to be made? I was under the impression the length of the valves was the determining factor for shim sizes. The valve clearances have not changed since the day i got the motor and the way it sits in front of my house. 200-300 miles since its first start.
If i can pull the head, adjust various things, throw a new head-gasket in, re set the valve clearances then i would love to do that. I would rather not invest more time and money into it if possible.
Originally Posted by Joe Perez
(Post 496583)
3.396mm is the thickest shim listed in the parts catalog.
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Originally Posted by thesnowboarder
(Post 496887)
If i can pull the head, adjust various things, throw a new head-gasket in, re set the valve clearances then i would love to do that. I would rather not invest more time and money into it if possible.
While the head is off, you might as well pull the valves and spend some time lapping them into their seats with valve grinding compound. It requires some sweat equity, but it's not rocket science. At a minimum, this will improve the valve sealing a tad. If you're lucky, and there's currently a lot of crud at the valve-to-seat interface, it may allow the valves to retract more fully into the closed position, which will decrease the lobe-to-follower clearance and just might bring you back into spec for stock shims. What boggles my mind is that i have a 3.5mm shim in the head now.. |
i take it this is just for the 99-00 head? it be great if someone made a youtube video of the procedure and what to do.
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Snowboarder, You may be able to stack two shims. See if there are two shims from Mazda that will give you the height that you need. Make sure that you go on the tighter side of spec to prevent a skinny shim from jumping out, and put the thicker of the two on top.
If there are not two shims that will give you the spec that you need, you can grind one of them down without any special tools at home. See if there are skinny shims available, and I will show you how to grind them if one needs it. It is a lot easier to do a valve job when the head is off the car. You will be taking the cam on and off many times, and it sucks when you are hunched over the fender all the time. |
I just looked at Joe Perez's diagram, and it looks like the smallest is 2.75. That would be a lot of grinding. I think I would lap the valve as Joe suggested. It would be faster than attempting to stack two shims and grind one down. You are so close, that valve laping should get you there. The only pitfall, is you will need to put the valve spring back on in order to get an accurate measurement.......If it is not enough that could mean: disassemble, grind, reassemble, check; disassemble, grind, reassemble, check.
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Originally Posted by miata2fast
If there are not two shims that will give you the spec that you need, you can grind one of them down without any special tools at home.
Not that I'd feel particularly secure about doing it. It's kind of like saying "If I were going to commit sodomy, I'd do it in the following way..." Just sayin' is all.
Originally Posted by miata2fast
(Post 497060)
I think I would lap the valve as Joe suggested. (...) The only pitfall, is you will need to put the valve spring back on in order to get an accurate measurement.......If it is not enough that could mean: disassemble, grind, reassemble, check; disassemble, grind, reassemble, check.
If you're still out of spec, I'd take the head (and the valves) to a machine shop and have them re-cut the valve seats by about 0.5mm or so. And then, of course, you have to re-lap 'em again.
Originally Posted by Hot_Wheels
(Post 497008)
i take it this is just for the 99-00 head?
it be great if someone made a youtube video of the procedure and what to do. |
He is off by what, a tenth or two of a millimeter? I think that a coarse lapping compound could get him there. But you may be right. I would call a machinist that is skilled in valvetrain to see what they think.
Here is another possibility. If you can get your hands on other lifters, there are differences in how deep the shim cup is or how long the contact point from lifter to valvestem is. The machining is not as precise on them, and you will probably find one that will use a thinner shim and get you where you need to be. |
Originally Posted by miata2fast
(Post 497149)
The machining is not as precise on them, and you will probably find one that will use a thinner shim and get you where you need to be.
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Originally Posted by Joe Perez
(Post 496875)
So, how does it get this loose?
Only thing I see possible is build up like Joe Perez said. If you end up taking this head apart Nick, pics or ban.
Originally Posted by Joe Perez
(Post 496923)
You might need to jimmy up a mechanism to lock the cams in place if you find that they want to autorotate to a position that does not align the lobe bottom with the follower, but everything else will be fine.
Originally Posted by miata2fast
(Post 497060)
I just looked at Joe Perez's diagram, and it looks like the smallest is 2.75. That would be a lot of grinding.
In my experience it took ages. And would be very hard to get exact. Shims are made of pretty hard material.
Originally Posted by miata2fast
(Post 497060)
The only pitfall, is you will need to put the valve spring back on in order to get an accurate measurement
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Several things...
1) Nicks head came to him from the engine builder this way... the valves were improperly machined. The right thing to do is take the head off, take it back to the builder and say "fix this". 2) You can't accurately grind the shims without a surface grinder, and they need to be flat. You simply can't keep them flat enough hand grinding. 3) I'd be suprised if there's enough variance in the lifters to be helpful, but it would be interesting to see Joes measurements... I have a set of 99 lifters out of a head at the moment I'll measure when I get a chance as well. |
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