The Delphin Rat

[eyagel]

IMO those are wristpin gouges ... but im not sure how high up in the block that the piston will travel in a m20 to make a gouge that high

wrist pins run parallel with the block dude

[TwistyTunedE30]

Oops, I didnt see the orientation of the block in the pic. Good call

[itsbrokeagain]

broken ring if you ask me...causing some scoring. Time for a fresh teardown and rebuild...


I would definetly add a catch can, and route all possible oil vapors to outside the engine..it will keep the intake manifold very clean and free of the gunk. Those scratches look deep..I dont know if the block can still be honed out enough to get rid of them (do these blocks have cylinder liners??)

If you do not want it to be a stroker, your best bet is to find another M20 out of a low mileage car, tear it down, do the seals in it, pull the intake off and get it cleaned out, and just do a gasket set and away you go....

[Hallen]

Well, there are no broken rings. They all seem fine to me. I only checked ring gaps on the #1 piston so far, but they were within spec.

But, there is plenty of other goofiness to go around.

Something here is wrong, can you spot it? One of these things is not like the other...





Yep, one of the end cap bolts is a different type. It was the only one like that. It was on the #5 piston and that was the cylinder with the biggest scratches. Coincidence?



All the pistons except the #6 showed scratching on one side. It was the same side on all of them. This is the #5 and it was the worst. None of the others really had that gouging above the rings like this one did.



All the pistons shown above. You can see how the scratching is on one side of each piston but not evident on the other side.

The end caps and rods were not all lined up in the same direction either. It was a bit of a mishmash as to which direction the numbers would be aligned. It says in the manual that they should all point the same direction.

I also noticed that when I slid the rod back and forth on the pin, it would bind up. It took a lot to unbind it. They would all spin and I don't feel any slop axially, but you couldn't slide the rod back and forth. The #6 piston assembly did allow the rod to easily slide back and forth on the rod pin.

The #6 had been replaced separately later on. The PO had told me that they had found a piece of metal of some sort in that cylinder so they replaced that piston. This was after the original rebuild that another owner had done.



The crank seems to look OK though.

It looks like whomever rebuilt this engine before either started with junk and left it that way, or had no clue as to what they were doing. I suspect that with the mismatched alignment of the end caps and rods and the weird rod bolt and the sticking piston pins, that there was an out of balance condition in the engine causing things to slap around.

Anybody else have any ideas?

What is the prognosis for those pistons? I suspect that all of them should be replaced and probably the block too. What a waste. Stupid people who shouldn't ever touch a wrench, and I end up with a car maintained by one of them. :(

[eyagel]

i would say pistons are fine, if u want i have a full set out of my parts car...pm me for details.

[Sean]

Even my rebuilt motor that I rebuilt 30k ago has carbon builup on the pistons - valves good, but pistons were pretty black. Pretty sure it's just the nature of an M20.

you may have to bore out that block and use custom pistons to get rid of that nasty scoring. That's what I would do.

[h82crash]

What is on the sides of piston #4? Was that something that the engine ingested? I would have bet my paycheck the rings were broken. I've had cylinders look like that and when I pulled the pistons the rings just fell off in 2-3 pieces. Perhaps the scratches look worse in the photos. Good luck with the project.

[Hallen]

What is on the sides of piston #4? Was that something that the engine ingested? I would have bet my paycheck the rings were broken. I've had cylinders look like that and when I pulled the pistons the rings just fell off in 2-3 pieces. Perhaps the scratches look worse in the photos. Good luck with the project.

Piston #4 is just all scratched up on the sides like 4 of the other pistons were. It could have been something nasty the engine ingested, really dirty oil, sand and grit sucked in through the K&N filter that was on the car before, or it could be the rods sticking on the wrist pins that allowed the pistons to get cocked a bit. I dunno. The #6 piston is newer than the rest and it looks fine. So whatever was causing it did not occur after the #6 piston was installed. The #6 cylinder does have a scratch in it like the others though.

Yeah, now it is a question as to what I can do with it. It will come down to money and availability of parts and if those scratches can be honed out. That one scratch is probably about .2mm deep but I don't have anything to measure it with.

[eyagel]

tell u what..ill give u the pistons. just pay shipping

[Hallen]

tell u what..ill give u the pistons. just pay shipping

Thanks!

Sent you a PM.

[eyagel]

didnt get it?

[Hallen]

The block and head got dropped off at the machine shop this morning. We'll see how the measurements come out. I suspect that the score marks were responsible for a lot of the oil loss. The measurements should tell though.

I am prepared to go to over sized pistons if I need to. I found a set from MaxSil on BavAuto for $500 that includes rings and pins. That is a heck of a lot less than the $160 per piston that I found other places or the $190 per for OEM or the $140 per for over sized ones I found on Pelican.

[AndrewBird]

Were the cylinders bored once before? Piston slap is usually caused by the pistons being too small of diameter in relation to the diameter of the cylinders. Maybe the previous owner had it bored and then used stock size pistons?

[Hallen]

Were the cylinders bored once before? Piston slap is usually caused by the pistons being too small of diameter in relation to the diameter of the cylinders. Maybe the previous owner had it bored and then used stock size pistons?

Yeah, that is a possibility.

I know that the engine was "rebuilt" by a previous owner, but I don't really know what exactly was done. It was definitely honed though. The car has 260k miles on it so it wouldn't surprise me if the bore had gotten too big for stock pistons. If they just honed it and installed the same pistons, they yeah, there probably would be a problem.

Hopefully when the machine shop gets the precise measurements done, we will know a bit better how to proceed.

[Hallen]

Well, I am back at it. No pictures or anything major to post this time though.

I have had a break with working on the car because work has been very busy and the track season is over. So I have all winter to mess around with the car.

Also, my job situation has been resolved so things are nice and solid there once again. It is quite a relief.

You can read the full details on the blog (direct link to the post): Back At It

I have had the block worked on a bit... I just had it honed. However, now that I have more time and can be a bit more liberal with the money, I am considering other things. A friend who built high performance engines for a living is back in town after a military deployment and is willing to take a look for me. We'll see how it goes.

Also did a bit of other work on the car... and managed to screw things up yet again. ;)



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