Quick question about 8.9:1 4A-GZE pistons

[Rogue-AE95]

I just got my Lithia Toyota order, including my 8.9:1 pistons which include the wrist pins and clips. However, the wrist pin on the one I opened doesn't simply slide into the piston. Am I missing something? I thought the 20mm pins were "floating," not pressed, able to be installed & removed by hand.

[dr.occa]

"here WAS my original back-ass-wards statement"

[Rogue-AE95]

OK, thanks. So it gets pressed into the piston, but it 'floats' in the rod? Just seems odd to describe something as floating when it has to be pressed. I thought only the clips held the pin in place. Still learning about engine building...

[oldeskewltoy]

20mm wrist pins must be pressed in.

This is incorrect... ALL of the 4AG stuff using 20mm wrist pins should be full floating.

sometimes the fit is VERY tight...

[dr.occa]

removed my back-ass-wards recollection.

[oldeskewltoy]

Those pink rings are pin locks, or keepers... they snap into the pistons and restrict the pin from moving beyond the clip. In 18mm applications there is no such clip, nor groove in the wrist pin bore

[dr.occa]

I went through my various pistons and wrist pins upon arriving home and must correct my mistake. My 18mm wrist pins are the pressed type where as my 20mm wrist pins are full float. My apologies for the mix up everyone. Please forgive me

[Rogue-AE95]

No worries! I appreciate any help / advice. I only have a limited knowledge of engines, as I've been reading as much as I can in my spare time for about a year and a half. I've only had a few engines apart, like a RWD bigport 4A-GE, a '97 4A-FE, and a Honda D16z6. The bigport I have uses the 40mm/18mm rods, and those pins are pressed in. The '97 FE rods are also pressed in, but are 20mm (no locks on those pistons). So I was thinking those GZE pins ought to slide in by hand... odd that they're such a tight fit. This reminds me of something else...

One additional question, I was reading up on the piston differences and it seems these 8.9:1 GZE pistons are forged instead of cast. Does this mean the block bores should have some extra clearance to allow for piston expansion? Or don't I have to worry about this? I can only hope that I will find a competent machine shop to do the block work for me. But I would like to get as much info as possible before getting to that point. I wish I could just take this block to Loynings...

[oldeskewltoy]

One additional question, I was reading up on the piston differences and it seems these 8.9:1 GZE pistons are forged instead of cast. Does this mean the block bores should have some extra clearance to allow for piston expansion? Or don't I have to worry about this? I can only hope that I will find a competent machine shop to do the block work for me. But I would like to get as much info as possible before getting to that point. I wish I could just take this block to Loynings...

you might try using scotchbrite pad on the pin bores, this will remove any burrs, and should allow the pin to slip in. If not DON'T force it... tell the shop about it when you have the other machine work done and they'll get them fitted. DON'T mix up pins from one piston with pins from another...

Concerning machining the block. I would not automatically trust any machine shop to know what the 4AGZE specs should be, I'd do some research, try to find a FSM with the 8.9 GZE rebuild info... that way you will know definitively. If you can't find a FSM that shows the 8.9 engine over bore specs, I'd say you can use the earlier 8.0 GZE specs for machining purposes. I know a few of the MR2 sites have later (88 and 89) FSM so you should be able to at least find the specs for the earlier GZE.

[Crownvicman289]

The pistons are a different size IIRC, so the same bore specs apply. Also, the FSM prescribes heating the piston to 180 degrees then sliding the pin in. I just use a c clamp to slide 'em in cold, but you do have to be EXTREMELY careful starting it into the rod as it's extremely easy to start it crooked and nick the bushing.

[Illegal_Garage]

hit that one wrist pin with some #000 steel wool and polish it up a bit
see if that helps

Max

[Rogue-AE95]

DON'T mix up pins from one piston with pins from another...

I was thinking about this recently. Had to search to find where I read it, and it turns out to be one of my old posts. Anyways, is this advice for used pistons & pins? I have a brand new set of the 8.9 pistons & pins. I'm going to be sending out the pistons to get the skirts coated. I wouldn't be able to tell apart the pistons when I get them back, unless I scribe a letter or something on their insides. (I don't trust permanent marker to hold up to the process.) A couple months ago I sent out a set of new pistons (for another engine build) to get the skirts coated, without marking them. Then I sent the pins and some other stuff to my engine builder. He didn't raise any questions about them. Are pins matched to the pistons by the manufacturer?

Concerning machining the block. I would not automatically trust any machine shop to know what the 4AGZE specs should be, I'd do some research, try to find a FSM with the 8.9 GZE rebuild info... that way you will know definitively. If you can't find a FSM that shows the 8.9 engine over bore specs, I'd say you can use the earlier 8.0 GZE specs for machining purposes. I know a few of the MR2 sites have later (88 and 89) FSM so you should be able to at least find the specs for the earlier GZE.

I did manage to find the 8.0 GZE specs from the MR2 FSM, at another site. From what I've read, the 8.0 and 8.9 GZE pistons are both forged (or "semi-forged" depending on who is talking). Having a used set of 8.0 & a new set of 8.9 pistons, I can see that they're definitely not cast. Whatever they are, they look like the same process was used in their creation.

[allencr]

No piston has a pressed pin, only rods have pin that may or may not be pressed/clamped, pistons always slide/float.
The 'fully floating' phrase is just squirrel talk. Same with 'semi-forged'.
Just heating up the pin in your hand may have made it difficult to fit in a cool piston.
They have a beautiful tight sliding fit. Use Lube.
Yes, they may be hand/select/matched fit from the factory, but un-mixing them up shouldn't be too tough.
DO NOT go near it with any abrasive!!!!
Als