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Hi. I pulled the head off my M20B25 today and snapped a few photos. Here is a closeup of the 4,5 and 6 cylinders.
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Notice the color of number 6. I’m guessing water was getting into the cylinder but just wanted to double check with you guys.
Thanks for looking,
Mike
Interesting. Obviously an aluminum piston can’t rust so that would mean that rusty water kind of came thru and deposited the rust particles. It’s kind of surprising to me that the rust particles would adhere in that environment. Think about what it must be like inside of a cylinder…a slightly oily environment so nothing sticks, gasoline in there which is a fine solvent, then lots of pressure and heat.
The rust layer looks pretty homogenous too, not like it’s been participating on the piston face in thousands of explosions per minute. So maybe the rusty water got there after the engine was last turned off?
Note also that the coolant passages are not bright orange with massive water jacket rust. If the water in the water jacket wasn’t rusty as heck, then maybe the water that put the rust on the cylinder didn’t come from the water jacket?
None of that provided any answers, but since only you know the history of this engine maybe one of those puzzles might point you in the right direction.
An engine with a bad head gasket (or a cracked head) doesn’t have to sit very long to see that result. It is hard to tell in the picture, but ti sort of looks like there is some rusting on the cylinder walls. Which is not good and might mean the engine sat for quite a while.
Thanks for the replies.
I drained the water, removed the radiator and moved the car into my garage about 4 months ago. That was the last time it was running.
I was running water with a bottle of water wetter (no anti-freeze). I did not drain from the block, only the radiator, so there was most likely still water in the block.
The only way I see water getting into the cylinder is through the head gasket seal ring or the valves but the valves have been in the closed position the whole time.
Anyway I’m glad I decided to pull the head. This all started off as a broken rocker arm. I think I’ll clean it up now, soak it in oil and then rotate the engine to check the cylinder wall.
Thanks,
Mike
Because you didn’t drain the block, it and the head remained full of water. While there is some corrosion protection from Water Wetter, it is far from enough to prevent corrosion. Every winter when I replace the the water + Water Wetter with coolant for freeze protection the water comes out rusty.
Water got into the cylinder because the head gasket was bad or, the head is cracked. Pure and simple.
Thanks. I’m going to take the head to get inspected, pressure tested and resurfaced. Hopefully it is only a bad head gasket.
Good news is all the cylinder walls are smooth and crank rotates smoothly.
Hopefully I will have her all back together and running for CMP in Feb.
Thanks,
Mike