Calling 3RZ Pros...

Hey guys, I'm currently in the middle of a rebuild on my 3RZ and I'm looking for some advice from those of you that have done them in the past.

The head gasket popped on this motor a few months back and while I was in there, decided to venture into the block. I found two of the cylinders have slight damage as well as collapsed rings. As of now the build has been on a standstill with my machinist because there are a few routes I can go. I am calling on you guys for some insight.

The motor will need to be bored .5 mm over (20 thousandths) and piston selection seems to be the main sticking point. LCE seems an obvious choice but I do not want to use hypereutectic pistons. This leaves few options. I did find one overseas vendor that I can still get 95.5mm Toyota pistons and rings, but have not gone this route yet, and here's why. Wiseco makes a set for about the same money but they are 8+ weeks out in manufacturing. The wait is definitely not ideal, but is the route I would prefer to go. While on the phone with Wiseco, I was given some key details and mod options for the build. The stock deck clearance from the top of the piston is 2.5mm (100 thousandths) and he suggested machining it down to zero, as this would increase compression to 10:1. With a motor that makes such little power, this is certainly an attractive option. The stock head gasket is 1mm (40 thousandths) and must be at least this thickness for the rebuild.

Now here is where I'd like some help. My machinist brought up a valid point that removing the extra deck clearance will likely retard the camshaft timing out of spec. Being chain driven, it isn't just as simple as swapping for a chain with one less link, or putting in an adjustable cam gear. Plus not sure whether the tensioner would push the guides far enough to remove all of the slack. So for those that have done this, what have you run into?

 

I wouldn't machine the head to increase CR. If the head ever needs to be resurfaced again you'll need a new head. If you get wisco pistons you could probably have them increase the CR up to 10:1. I imagine that as long as you're in spec for head thickness and timing will be ok. Usually, it only takes 5 or 10 thousands to get the head straight.

 

Apologies, the cutting would happen on the block, not the head. The head merely got a skim coat to make it straight. The top of the piston to the top of the block has a 2.5mm gap. His suggestion was to cut it down to zero.

 

My bad I didn't read that right. It's more common to machine the head down for compression than the block. But to your own point, changing the block or head height significantly can cause timing problems. I'd recommend asking wisco to change the CR, especially considering it sounds like they are custom making them anyways. Make sure you don't go too high on the CR though as If you over shoot you might be stuck running premium.

 

Last time I was looking, Lce had some high compression pistons. They required an over bore though. Don’t remember how much though.

 

show us a picture of the damage in the bore.

When you took the top ring off the pistons did they spring back or did they stay collapsed. It just looks like caked oil making upper ring stick. These 4 cylinder Tacoma motors are pretty tough. Depending on the bore damage and if the pistons clean up and the rod/piston pin still rocks freely... I would hit it with a ball hone slightly, drop a piston in upside down attached to the rod and with a feeler gauge between the skirt and bore, check clearances. Kind of a quick and dirty way but it works, if Ok, put new rings and call it a day. If the clearances are too great what have you lost, the cost of a ball hone and 20 minutes?

 

Post #6 has some good advice. I did the same suggestion on a Ford 300 straight six many years ago. Replaced a couple of pistons, new rings, and the truck ran fine for years. Just depends on which direction you wish to go.