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Old 03-25-2010, 11:57 AM   #1
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Default Replace valve guides when rebuilding head?

I think I've decided I want to rebuild the head on my '95 since I've come to blame my oil consumption issue on bad valve seals, and I'm trying to figure out the best way to go about it, doing all the necessary work but without spending an arm and a leg.

I'm at 183k miles on the stock motor, so I want to take care of as much as possible in one shot to avoid problems down the road. So far I have the following plan.

- Fully disassemble head and get hot-tanked, do a mild porting job, clean and lap valves
- Valve seals
- Valve guides
- Cam seals
- MLS head gasket
- Timing belt and water pump
- Replace or have lifters ultrasonic cleaned
- Spark plugs, and misc other bits and pieces

Am I missing anything? Should I skip the ultrasonic cleaning and just get new lifters for the peace of mind? Keep in mind that I'm not boosted and probably won't be for quite some time, so I'm just looking for a solid refresh and maybe a little something extra from the 'ol butt dyno.
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Old 03-25-2010, 10:19 PM   #2
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dam my valve seals went out also it sucks
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Old 03-26-2010, 01:15 AM   #3
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I would measure (or have your machine shop measure) the valve guides before doing a wholesale replacement of all of them. If they are egg-shaped or overly worn then get them replaced. I'd also get a quality multi-angle valve job done rather than just lapping the valves in the seats; at nearly 200K miles..I question the quality of valve seal you'll get by only lapping. I'm not sure if the stock Miata valves are single piece (the SS aftermarket valves are) or two piece (head welded onto stem). Depending on your budget, replacing all the valves with oversize valves would give you better airflow and fresh "higher" seat cut. I'd also get check the open closed seat pressures of all the valve springs.

There is an article (on Miata.net) detailing how to dissassemble and clean the Miata hydraulic lifters; if you are on a budget this can save you the cost of the ultrasonic cleaning or lifter replacement.

Last edited by sn95; 03-26-2010 at 01:17 AM. Reason: added lifter comment
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Old 04-05-2010, 05:32 PM   #4
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they are cheap and if you are going thru the head definately replace those with 183K miles on them without question
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Old 04-06-2010, 11:30 AM   #5
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You can see on the valve seat a unique wear pattern if the guides are bad. Also the valve will rock in your hand back and forth in the guide.
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Old 04-06-2010, 12:00 PM   #6
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You can pull the valve train and check the guides with the head still on the block- while you do the seals. If you do need new guides, you'd be better off buying a low mile NB head. Replacing guides is a lot of work and you'll still need to cut the valves/seats.
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Old 04-06-2010, 12:11 PM   #7
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I'd think its safe to safe that any motor with that many miles needs the guides replaced. Especially a head that old.
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Old 04-06-2010, 01:19 PM   #8
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I pulled a 96 head with 170k on it this fall and it had no measurable wear on the guides or valves. Same thing on a 90 head I pulled apart a year ago. They don't seem to wear that bad as long as they are maintained well.
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Old 04-06-2010, 02:07 PM   #9
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Quote:
Originally Posted by sn95 View Post
There is an article (on Miata.net) detailing how to dissassemble and clean the Miata hydraulic lifters; if you are on a budget this can save you the cost of the ultrasonic cleaning or lifter replacement.
Not much to it; they pull apart, give them a bath in seafoam and push them back together.
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Old 04-02-2015, 11:45 AM   #10
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I'm in the process of rebuilding a head. It's a 99 with 120k miles according to the seller. I'm using new +1mm intake and +2mm exhaust super tech valves.

The exhaust valves seem to be pretty loose in the oem guides. I can get a decent amount of wobble in it. When I measured the clearance they all fell on the upper edge of the allowable clearance to falling just outside the spec by a couple thousandths.

The intake valves seem to fit well with the proper clearances.


For those experts in the field, do you typically replace valve guides when rebuilding a head? Is it something that should always be done as a security measure or only as required based on millage and wear. would it be fine to just replace the 8 exhaust valve guides or should I do the intake as well while I'm at it.

So far I've found these option:
OEM-$10 a guide through mazda motorsports development
supertech - $7 a guide
miata roadster - $90 for all 16 guides


has anyone tried the miata roadster one or should i just stick with the OEM?

http://www.miataroadster.com/miataro...i-1964291.aspx
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Old 04-02-2015, 12:01 PM   #11
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Valve guides a typically measured and replaced as needed by machine shops.
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