When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Past Saturday I take my wife out for a drive in Miata I do minor hard driving for about 30 minutes. A mile from home not under boost about 30 mph I hear a sound it sounded like something coming apart, car dies had to get it towed home. I thought the timing belt snapped all this time, I waited until today to take the valve cover off to investigate the problem. Belt is fine still in perfect timing, I take plug 1 and 2 off, I feel a little resistance on 3, I get the plug off and it's smashed, the electrode is pushed in. The top of the piston from what I can see is marred with two indents I'm guessing the tang on the plug (not sure what the part where you pan is called). I'm thinking wrist pin? Please refer to pictures of the plug. Compared to a non damaged plug it's .21 inches pushed in.
I'm having a leak down test done on it tomorrow, waiting on Amazon to deliver a scope so I can see the damage in the cylinder. I'm hoping walls are fine, I just need new pistons and rods and head is undamaged.
What went wrong? Engine does not 100 miles on it, I was going to have the final tune today. I have forged pistons and rods, I'm hoping the head is fine, what can be due to fault of the builder I did pay him to put the head on. Pistons are 84mm, 1mm over stock.
Second of all, I'd wager the valve failed first and destroyed the plug. With only 100 miles, chances are a keeper wasn't seated perfectly.
Endoscope Camera with Light, Hijoy Two-Way Articulation Borescope, 0.33in Articulating Inspection Scope with Light, Perfect for Automotive & Aircraft Mechanics, 5.5FT https://a.co/d/78QKggV
I am up ***** creek with that one. No way to prove what you are saying is correct and I'm sure he will know you are correct.
He did use the old keepers. Like all machinist I can hear him now. "I done this for 50 years and I've never had that happen." Maybe I am being gloomy but I will call him tomorrow and bring it up.
I did buy those super tech valves from fab9 with the double spring, not sure if a warranty would cover it at this point.
Second of all, I'd wager the valve failed first and destroyed the plug. With only 100 miles, chances are a keeper wasn't seated perfectly.
further exam of the pictures the stem is still in its place. The valve head broke off, so much for super tech valves. I did email them asking what they would like me to do and included the pictures. Definitely worth a consideration of faulty valves due to materials. I did use their double spring valves springs and their pistons in the build.
I lost the head off a valve, way back, may well have been Supertech I know I used some of their stuff in that engine. The carnage was impressive, forged piston stood up well, as well as you would expect anyway, cylinder bowl stood up as you'd expect as well, which is to say not very well. Theory was that valve timing was out, allowing the valve head to get 'rocked' by the piston at TDC, supported by a series of small marks on the other piston tops where a valve might touch.
That was a damn good cylinder head, but not for a racecar anymore, so I had it repaired and sold it (with full disclosure) with no feedback/comeback from the buyer. That is an option, it was worthwhile for me because that head had been flowed, shaved, etc and what I got covered the cost of the repair with a good amount left over, numbers may not work for a stock head.
Don't do any more that you have, talk to your engine builder, he will want to see the engine untouched in the car (taking the plugs out shouldn't be an issue, don't touch the valvetrain).
The number one reason valves break is because they are contacting the seat unevenly which bends them every cycle. A good valve job is very important. New valves have to be inspected and I almost always have to grind them. There are very high end manufacturers that often can be run out of the package, but these are the exception. Valve seat to guide concentricity is very important. Many shops do not check this. As a secondary check I always vacuum check the head after assembly. The seat pressure is also important, but usually will not cause this failure unless it is substantially low.
Most parts manufacturers will say, "Yep, that valve might have failed. Here's another valve." But they don't pay for damage to everything else, generally. It's kind of a mess.
All of the pieces not still in the cylinder went through the turbine upon leaving, btw.
I lost the head off a valve, way back, may well have been Supertech I know I used some of their stuff in that engine. The carnage was impressive, forged piston stood up well, as well as you would expect anyway, cylinder bowl stood up as you'd expect as well, which is to say not very well. Theory was that valve timing was out, allowing the valve head to get 'rocked' by the piston at TDC, supported by a series of small marks on the other piston tops where a valve might touch.
That was a damn good cylinder head, but not for a racecar anymore, so I had it repaired and sold it (with full disclosure) with no feedback/comeback from the buyer. That is an option, it was worthwhile for me because that head had been flowed, shaved, etc and what I got covered the cost of the repair with a good amount left over, numbers may not work for a stock head.
Don't do any more that you have, talk to your engine builder, he will want to see the engine untouched in the car (taking the plugs out shouldn't be an issue, don't touch the valvetrain).
Originally Posted by LeoNA
The number one reason valves break is because they are contacting the seat unevenly which bends them every cycle. A good valve job is very important. New valves have to be inspected and I almost always have to grind them. There are very high end manufacturers that often can be run out of the package, but these are the exception. Valve seat to guide concentricity is very important. Many shops do not check this. As a secondary check I always vacuum check the head after assembly. The seat pressure is also important, but usually will not cause this failure unless it is substantially low.
Originally Posted by sixshooter
Most parts manufacturers will say, "Yep, that valve might have failed. Here's another valve." But they don't pay for damage to everything else, generally. It's kind of a mess.
All of the pieces not still in the cylinder went through the turbine upon leaving, btw.
Taking the whole motor to a shop tomorrow to look into what happened. Super tech wants the valves. Come to think of it there was always this ticking sound like lifter tick. I thought it was my injectors since they were much more output than stock. I only have 104 miles on this engine.
07-24-2024, 10:42 PM
Check this out.
0
