14 replies to this topic

[Keith Novak]

Inspecting my cylinder head, it looked like there was a thick layer of lumpy carbon build up in the combustion chambers. When I started to try to scrape it off, I realized it was a thin layer of soot on top of lumpy aluminum. In places, the decked part of the head that is over the cylinders actually protrudes slightly into the cylinders and on other parts there are little grooves like tiny worms were eating the aluminum. It looks like the aluminum was burning and melting.

The history of the motor: 1 year ago it was a complete crate shipped from Mazda. The head has never been off but couldn't have come like that because a fly cutter would have decked off the taller material over the cylinders. It has about 22 races which is probably about 25 hours since most didn't have practice sessions. I always ran it about 14* of timing, checked it regularly and confirmed the timing marks against true TDC. I always used premium pump gas, usually from the same 76 station. It seemed to put out the right power for a crate. It never overheated (ran cool usually). Fuel pressure supplied by a stock regulator.

Could this be something caused by detonation for some reason like some bad gas that had low octane? Perhaps a fuel delivery problem caused it to run lean and caused a local overheating problem?

[DES4]

Sounds lean. What do the tops of the pistons look like?

[Keith Novak]

Below the bowl part of the combustion chamber they look fine, but at the sides where they're below the decked part of the head they have pits as well. Some are pretty deep. Some are long and thin, almost like bits of metal had been smashed in there but others are definitely burn holes.

[john mueller]

can you post some photos?

[Keith Novak]

Here you can see the pitting. All 4 cylinders have this on the head:



This is the worst looking cylinder (4) but they all have a bit of this:

[DES4]

What do the spark plugs look like? is there metal imbedded in the porcelain and/or noticable electrode wear or deformation?

Wow; because the damage seems heaviest at the tightest areas in the combustion chambers, it almost could be detonation or very extreme pre-ignition... but you'd expect the root cause of either of those to be something like overheating (hot spots) or low octane gas/too much initial timing.

An offhand guess (too early to do more than guess at this stage) would be hot spotting. Hot spots can be caused by not running a coolant or water tension-breaker (like Water Wetter)... it allows the water to boil inside of the cooling passages, and it aggravates hotspotting further as no coolant reaches the areas that are super-heating. A weak coolant cap will also allow water to boil inside of the engine, as the boiling point of the coolant will drop below engine run temperatures.

[Keith Novak]

The spark plugs almost look new but I did change them every other weekend if not every other. Except for the first few sessions with the stock NGK plugs with the break in oil then ran the same Bosch plugs Race Engineering recommends for their engines. I'd inspect them every change and they always looked good. Figured changing them so often was probably overkill. I used distilled and water wetter and my race temps never exceed 190 with the big Koyo. It's not even all that often that the fan turns on when I'm waiting for the scales.

I'll get 20 gallons of gas at a time so if it was bad gas, which I think I would notice in terms of power, after 2-3 days it would be another 2 weeks to a month before returning to the same station so I'd think it would be different gas by then. I start fresh each time emptying my tank and dumping the leftovers in my truck. I wonder if 6 sessions of bad gas could do that.

[john mueller]

WOW, that's a new one for me... Are all the cylinders damaged similar to this one?

I consistently use the cheapest crappiest fuel I can find & only change the plugs every 4 events (with a few 3-hr enduros tossed in too)... I just pulled my head ofter two seasons (50+ hrs) and everything looks perfect!

There is something else going on here. It looks to me like some metal shavings made their way into the cylinder.

[Keith Novak]

Yes, all 4 look the same. #4 has the biggest pit in the piston but all the others have some damage also, just not as easily photographed. I noticed what looked like metal debris damage in there too but once I saw definate irregular shaped burn holes I figure there's a good chance that's a byproduct of something else. I hadn't changed what I've been doing for years and a light dusting of soot was all I had seen before.

[Randy Thieme]

Keith,

Looking at the top photo some of the pits look more like dents to me. In that same photo look closely at the pits closest to the valves. They have very defined flat surfaces and edges, almost look they were made with a chisel or hard metal object. Almost looks like the head came off an engine which ate a valve.

[Keith Novak]

Randy, I thought that too when I looked at it. First thought was "Does Mazda recycle castings in their crates?" Then I started thinking that if they did, they would at least deck the head so that the lumps wouldn't stick up past the deck height. Plus, there are a few little irregular shape groves in the bowls about the width of a pencil line. If metal got in there or a valve let go, I'd expect damage in one cylinder, not the same thing in all 4. The most this engine has been apart since I bought it was removing the valve cover and plugs.

[chris haldeman]

I've seen this caused by debris left in the intake after blowing up a motor and not cleaning it out. You didn't happen the Grenade the previos motor?

[Keith Novak]

Aha. I bet that's it. The previous engine blew seconds after injesting a couple of birds in the radiator. I was sure I cleaned the heck out of everything before putting the new motor together since I had to clean bird parts out of everything. The intake may have been missed. Thanks everyone.

[KentCarter]

Aha. I bet that's it. The previous engine blew seconds after injesting a couple of birds in the radiator. I was sure I cleaned the heck out of everything before putting the new motor together since I had to clean bird parts out of everything. The intake may have been missed. Thanks everyone.

Birdstrike grenaded your motor? What is this thing? A PW5000???

[Keith Novak]

We couldn't conclude the birdstrike and loud bang 30 seconds later were related, just one hell of an unlucky lap. The result was astounding though. At least 2 robins chasing one another kamikazed me at about 110 mph. One sheared the Mazda emblem off the front.. Not really suprising. The other bent my tow hook down to the point where it cracked and pushed in my bumper cover. The bird went clean through the metal screen and finally stopped by the radiator...the big parts I removed with pliers. There were feathers and smaller bird parts everywhere in the engine compartment. Very gross clean up job.