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#1
Chris Ashcraft

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Hey guys, i have a customers 99 (street car) and it has 50psi on 1 and little to none on 2-4. Customer states that the car got HOT. All timing marks were spot on, took head off to verify no bent valves looks good. Has anyone ever seen one of these get hot enough to warp the head so much that there is this kind of compression loss, pistons 2-4 were definitely steam cleaned they look brand new, or are the rings toasted and welded themselves together making the engine a loss.

 

Thanks for the look

 

Chris



#2
davew

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I am not an engine builder, but here is what I suspect.

 

If it got hot and 2-3 pistons are clean, it got really hot. Head is probably warped beyond use. You may be able to make the gasket surface flat, but the cam journals are also warped. Causes drag on cams which cost HP. Rings are probably also junk. Oil may not look contaminated, as most of the water burnt off, but the water gets into the bearings. Water is not a good lubricant. Expect the bearings to be damage.

 

Short answer, start over

 

Sorry, Dave


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#3
Jim Drago

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Hey guys, i have a customers 99 (street car) and it has 50psi on 1 and little to none on 2-4. Customer states that the car got HOT. All timing marks were spot on, took head off to verify no bent valves looks good. Has anyone ever seen one of these get hot enough to warp the head so much that there is this kind of compression loss, pistons 2-4 were definitely steam cleaned they look brand new, or are the rings toasted and welded themselves together making the engine a loss.

 

Thanks for the look

 

Chris

these engines dont do well when overheated. It is likely a paper weight at this point from what you described above


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#4
Steve Scheifler

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Would have been nice to do a quick leakdown on it before pulling it apart just to see where most of the air went, but it's likely toast regardless. As Dave said, if the head is that bad the cams will bind too. I haven't attempted to have those re-sized/bored on a warped head though I guess it's possible. By the time you fix the head that way and get the necessary valve shims it would be cheaper to buy a good used one.
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#5
Erik Hardy

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I bought a car just like that a couple months ago for parts, it just needed a sensor....It started, sounded like a two stroke and barely moved. Similar minimal compression but the leak down test was comically over 80% on 3 cylinders (all out the exhaust). It was the first time I could spin the engine over like nothing while having 80psi in the bore. Pulled the valves out and gave them a quick lap just for kicks, not a chance in hell. To the scrap yard! 


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#6
davew

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Make sure you fix the original cause of the oveheat. Did the water pump fail? Coolant leak? excessive timing? Toooo lean? Small radiator?

 

I have seen many people fix the symptom, but not the root cause. It just allows you to practice doing the job again.

 

Dave


Dave Wheeler
Advanced Autosports, the nations most complete Spec Miata shop
Author, Spec Miata Constructors Guide, version 1 and 2.0

Building Championship winning cars since 1995

4 time Central Division Spec Miata Champion car builder 2012-2013-2014-2017

Back to Back June Sprints Spec Miata 1-2 finishes 2016 and 2017

5 time June Sprints winner in Mazda's

6 Time Northern Conference Champion Car Builder

2014 SCCA Majors National point Champion car builder

2014 SCCA Runoffs winner, T4 (Bender)

2014 Central Division Champion, ITS (Wheeler)

2013 Thunderhill 25 hour winning crew chief

2007 June Sprints winner, (GT1, Mohrhauser)

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