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Old 03-10-2010, 06:27 PM   #1
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Default 99 miata blown head gasket

so i blew a head gasket at 50k miles, reallly bad and it warped the block a tiny bit. but i had the head shaved .037
so could i run a stock head gasket? or do i need a thicker one? i dont want my valves to hit. everything is stock
and i plan to turbo as soon as its together
i poured some liquid in exhaust side and intake side and like a few valves leaked a tiny bit on cylinders 2 and 3. so is that okay?????

i am in hawaii and some old hawaiin guy just looked at the head, shaved it and said ahhh its good. and that i should run it with a stock head gasket. and i was like you just eye balled it? and he was like look i been doing this for 40 years lol, he also had 2 cows in the front yard and car parts everywhere
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Old 03-10-2010, 06:50 PM   #2
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A lot of people who talk about 'doing this for 40 years' dont know **** in my experience.

What does the factory manual specify as the service limit for milling the head?

Leaky valves are not good. How much is 'a little' and over how much time did 'a little' leak?

Are you turbo-ed? Are you turbo-ing in the future?
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Old 03-10-2010, 06:59 PM   #3
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no turbo but yes i plan too. the car was perfect till it over heated because a stuck thermostat.
i have the factory manual but have not looked at it yet. yeah that guy knew nothing
and the valves were perfect untill this. just like maybe a slow leak of a few mm through the seats
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Old 03-10-2010, 06:59 PM   #4
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The service manual specifies .008" max for grinding the surface of the head and / or block. This seems a bit overly conservative to me. The stock head gasket is 1mm (or .039") so they're saying that the limit for grinding the head is one-fifth the thickness of the gasket.
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Old 03-10-2010, 07:18 PM   #5
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hmm so thicker head gasket....? i would think someone on here would have had something like this before
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Old 03-10-2010, 07:24 PM   #6
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Miatas are notorious for bent valves. It usually happens when the head is not handled correctly with cams in place. Remove the cams before removing the head, and you are less likely to have a problem.

Before you go much further in rebuilding the head, I would check with Mazda Comp to see how much racers are safely shaving the head. It will be very different than what the service manual calls for.
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Old 03-10-2010, 07:39 PM   #7
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yeah i did pull the cams before pulling the head
mazda comp?
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Old 03-10-2010, 07:49 PM   #8
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Quote:
Originally Posted by nickblackbelt View Post
yeah i did pull the cams before pulling the head
mazda comp?
Mazda Motorsports. I still have the habit of calling them Mazda Comp.

Go to www.mazdamotorsports.com Get their number and call for tech. They are closed today. I tried to call them to find out how much you can shave off a head, but got a recording.
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Old 03-10-2010, 07:50 PM   #9
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Quote:
Originally Posted by nickblackbelt View Post
mazda comp?
MAZDASPEED MOTORSPORTS DEVELOPMENT - Home Page
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Old 03-10-2010, 07:55 PM   #10
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sweet thanks, i will try and let ya know
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Old 03-10-2010, 08:00 PM   #11
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Mazda does some awesome stuff for enthusiasts racing their cars. Its one of the best things about ANY car maker IMHO. They will be the best surce of info on that much taken off a head.

Also IMHO, have all the valves and seats checked, and the head itself for true while you are at it.

And with the amount taken off (over 4 times the FSM reomended limit) I would go for a thicker gasket. If it ends up taking compression below stock, that will help avoid detonation when you go turbo anyway. Not that lower compression is neccesary, but it can make tuning easier in terms of ignition timing. This depends of course on a quality thicker than stock gasket and its availability. I have had crap luck with non-OEM gaskets personally.
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Old 03-10-2010, 08:04 PM   #12
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dang well i been looking for a thicker one but i cant find one. some one help me?
i payed like 40 bucks for prolly crap one off rockauto.com stock thickness
any one want it for 20? still in box
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Old 03-10-2010, 09:25 PM   #13
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Leaky valves from pitting are endemic to hi miles miatas.
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Old 03-10-2010, 09:28 PM   #14
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Leaky valves from pitting are endemic to hi miles miatas.
what?
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Old 03-10-2010, 10:50 PM   #15
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What I said. Every single miata head I've looked at with over 30k miles had some leaky exhaust valves.

Most miatas I've leakdown'd showed some exhaust leakage. Including a bone stock one with 35k miles.
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Old 03-10-2010, 11:19 PM   #16
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Quote:
Originally Posted by Sparetire View Post
And with the amount taken off (over 4 times the FSM reomended limit) I would go for a thicker gasket. If it ends up taking compression below stock, that will help avoid detonation when you go turbo anyway.
This is not necessarily so.

Yes, a thicker gasket will reduce effective CR. And yes, lowering CR is generally associated wit a decreased propensity for detonation. But when the compression is lowered by means of increasing the deck height (which is what a thicker gasket would do), you will often find that the engine actually becomes more prone to detonation.

A rather good discussion on this phenomenon took place somewhat recently. See posts 15 and 22 here: Engine management parameters... - MX-5 Miata Forum



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Originally Posted by nickblackbelt View Post
dang well i been looking for a thicker one but i cant find one. some one help me?
I've never seen one for the BP engine. HKA makes one for the 1.6, but I can't say I'd recomment it.



Quote:
Originally Posted by JasonC SBB View Post
Leaky valves from pitting are endemic to hi miles miatas.
Indeed. And fixing it is easy. Well, not easy, perhaps, but simple. Some valve grinding compound, a suction-cup valve lapping tool, and a lot of elbow grease.
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Old 03-10-2010, 11:24 PM   #17
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ohhh!! okay. yeah mine only had 50k miles it was just barley tho. both some on intake and some on exhust
yeah i understand all this but i dont care! i just want the valves not to hit
"Indeed. And fixing it is easy. Well, not easy, perhaps, but simple. Some valve grinding compound, a suction-cup valve lapping tool, and a lot of elbow grease." ------------and yes i am going to do this
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Old 03-10-2010, 11:32 PM   #18
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Make sure you do not in fact have a boat anchor before investing time and money into the head. Investigate the milling issue first, then fix the other problems.
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Old 03-10-2010, 11:40 PM   #19
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Quote:
Originally Posted by miata2fast View Post
Make sure you do not in fact have a boat anchor before investing time and money into the head. Investigate the milling issue first, then fix the other problems.
yeahh lol i been wondering this
there was a ton a burnt crap on piston number 1 and some water flew out when bolting the bolts holding the cams in
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Old 03-11-2010, 02:12 AM   #20
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Quote:
Originally Posted by miata2fast View Post
Miatas are notorious for bent valves. It usually happens when the head is not handled correctly with cams in place. Remove the cams before removing the head, and you are less likely to have a problem.

Before you go much further in rebuilding the head, I would check with Mazda Comp to see how much racers are safely shaving the head. It will be very different than what the service manual calls for.
Whaaaa? Details and noob decryption please. I had my assembled head shipped in a paper sack across the country to me. Cams were intact.
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