So I can't find 3MZ pistons in the current Mahle catalog, nor could I find them in a 2009 catalog (when the engine was still being put into new hybrid highlanders). So either Mahle briefly made 3mz pistons between 2010-2020 and discontinued them or they are the original supplier to Toyota (which would be a surprise to me since these vehicles were produced in Japan).
I'd greatly prefer this be an original engine rather than a rebuild that has already gone bad (after an original engine went bad prematurely).
Quote:
Frequently Asked Questions
I have this part and it says MAHLE on it and I can’t find it in your catalog
We are sorry. Often customers have a bearing or bushing that says Clevite on the back or a piston marked MAHLE. In the majority of these cases, the part was manufactured only for the engine/equipment manufacturer and no aftermarket/service parts exist unless from that equipment manufacturer. The other possibility is that the engine you have is old enough that we have discontinued offering the parts, hence you cannot find a listing for it.
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The piston with the most worn skirt measured 3.6201-3.6202 (factory spec is 3.6211-3.6216). That cylinder bore measured 3.6220 on the piston pin axis and 3.6224 on the piston skirt axis (factory spec new is 3.6220-3.6225 with maximum service limit of 3.6272).
Standard oil clearance is 0.0013-0.0023 with maximum service limit of 0.0051. So that worn, 1 thousandth undersized, piston in the sloppiest part of that cylinder has 0.0023 oil clearance which is barely within factory spec but still well inside the service limit. Honing would probably increase that clearance another 1-2 thousandths though which would put me on the edge of the max service limit...
I cleaned up the machined flat portions of the block and measured for warpage. All but one were as flat as I can measure. The one slightly warped surface was one side of the oil pan surface and it was just barely off (less than 1 thou). So nothing that would explain the odd main bearing wear on #1.
Cylinder #5 was the one with the most worn crosshatching, but #2 was the cylinder with the blown head gasket. Maybe when it was misfiring severely on start-up it caused the bearing wear? I don't know. I'll continue cleaning and Mic-ing the remaining cylinders and bores this weekend and plan to take the block to the machine shop on Monday. I'm cautiously optimistic they'll be able to reuse it, but unless all the other pistons/cylinders are worn less than the one I checked I'll probably be looking at an overbore with new pistons. Unfortunately unless I want to spend money on custom JE or similar pistons, I'd probably be stuck with China-made DNJ pistons. They're probably okay, but not to OE standards...
The only other weird thing I noticed were these irregularities on the webbing of the block by #5:
At first I thought the rod must have somehow come into contact with the block, but the rod itself looked fine. And how could that happen without the rod breaking or bending severely? So I'm guessing it was some void from the casting process? None of the other cylinder webs have anything like it.
Interesting is that it appears Toyota smoothed the casting on the inside of the block. It wasn't quite polished, but definitely smoother than natural casting. Seems like a lot of machinework for an OEM to do to (presumably) improve oil drainage slightly.