Author Topic: Broken pistons (Read 4973 times)

65714runner · « **on:** Mar 23, 2011, 09:32:26 PM »

I recently bought another 4runner for parts. I pulled the motor to put in my 85 runner but wanted to go through it first. The runner ran fine. I started into the motor and knew it had been into in about 10 min. Got it all apart and it has already been bored .75mm over and still has hone marks from the rebuild. My problem is all 4 pistons are cracked on the intake side of the motor and not sure what would cause this.

zippo · « **Reply #1 on:** Mar 24, 2011, 03:01:58 AM »

Thats crazy! Could it be just cheap pistons? What king of wall clearance do you have? Crazy timing/detention issue?

65714runner · « **Reply #2 on:** Mar 24, 2011, 06:41:07 AM »

It was a little lean on the intake side. The walls are still ok. Cheap pistons was my first thought.

superyota · « **Reply #3 on:** Mar 24, 2011, 09:01:49 AM »

post up some pics if you can.

Rocksnail · « **Reply #4 on:** Mar 24, 2011, 11:51:29 AM »

Are any of the valves messed up? kinda sounds like your Intake valves kissed the piston

junya92toy · « **Reply #5 on:** Mar 24, 2011, 11:53:58 AM »

Quote from: jimbo74 on Mar 24, 2011, 09:09:04 AM

that is a lot of overbore! but iwould think cheap pistons or really bad tuning..... the pistons are aluminum, so its possible they got too hot and cracked

He did say .75mm

65714runner · « **Reply #6 on:** Mar 24, 2011, 03:01:03 PM »

Yes valves are good. They all cracked on the skirt. I will try to get pics later.

superyota · « **Reply #7 on:** Mar 24, 2011, 03:10:42 PM »

if they cracked on the skirt, its probably from piston slap. your pistons are probably to small for the bore.

79coyotefrg · « **Reply #8 on:** Mar 24, 2011, 04:52:45 PM »

regardless you need new pistons. do the cracked ones fit tight in the cylinders??

zippo · « **Reply #9 on:** Mar 24, 2011, 06:33:02 PM »

So you are looking at .030" over.

Take it to a machine shop and get some LC Big Bore pistons. .080" over.

http://www.toyotacatalog.net/M1WebGear/ProductDetails.aspx?PartUniqueID=63847A79-E8FD-4BD1-92D3-71FD1778805C

79coyotefrg · « **Reply #10 on:** Mar 24, 2011, 07:36:56 PM »

Quote from: zippo on Mar 24, 2011, 06:33:02 PM

So you are looking at .030" over.

Take it to a machine shop and get some LC Big Bore pistons. .080" over.

http://www.toyotacatalog.net/M1WebGear/ProductDetails.aspx?PartUniqueID=63847A79-E8FD-4BD1-92D3-71FD1778805C

yea for $599

unless youve got money to throw away just get some good quality pistons and dont bore over .040 inch

79coyotefrg · « **Reply #11 on:** Mar 24, 2011, 07:38:06 PM »

fwiw i have .060 inch over size pistons (1.5mm) and finding a replacement SUCKS

65714runner · « **Reply #12 on:** Mar 24, 2011, 10:02:50 PM »

Here is a pic. All four are cracked in the same place.

65714runner · « **Reply #13 on:** Mar 24, 2011, 10:07:35 PM »

I need to check the piston to wall clearance, but i thought they were a little bit loose. I am hoping that .040 over will work hate to do .060 hard to find pistons and seems to want to over heat easier on the trail.

yotaneck13 · « **Reply #14 on:** Mar 24, 2011, 10:11:24 PM »

the motor was def boared more than the piston size had the samething happen to a buddy

superyota · « **Reply #15 on:** Mar 25, 2011, 08:05:50 AM »

Quote from: junya92toy on Mar 24, 2011, 11:53:58 AM

He did say .75mm

thats what i thought.

zippo · « **Reply #16 on:** Mar 25, 2011, 07:54:42 PM »

There is alot of scuffing on the skirt of the piston. How do the bores look?

65714runner · « **Reply #17 on:** Mar 25, 2011, 09:39:43 PM »

Bores are ok I am still taking everything to the machine shop to see what I need to do. Who ever build the motor after the last rebuild put is together dirty. The main and rod bearing had little scuffing on them but crank and rods are ok.

79coyotefrg · « **Reply #18 on:** Mar 27, 2011, 03:07:53 PM »

Jagdverband44 · « **Reply #19 on:** Mar 28, 2011, 11:21:01 AM »

What a crappy engine job. So many a 22r ruined by hack rebuilders. That skirt wear was caused by piston slap which eventually cracked the pistons. Some foo used the old pistons and stuck some new rings on em'.

Redbeard1 · « **Reply #20 on:** Mar 28, 2011, 12:43:25 PM »

Quote from: zippo on Mar 24, 2011, 06:33:02 PM

So you are looking at .030" over.

Take it to a machine shop and get some LC Big Bore pistons. .080" over.

http://www.toyotacatalog.net/M1WebGear/ProductDetails.aspx?PartUniqueID=63847A79-E8FD-4BD1-92D3-71FD1778805C

x2 Mine do great just make sure you get the pistons knotched for LC's largest cam just incase you ever decide to up grade.

65714runner · « **Reply #21 on:** Mar 28, 2011, 08:43:27 PM »

Droped it off at machine shop today the guy put .030 over pistons in a .040 over bore

.

zippo · « **Reply #22 on:** Mar 29, 2011, 01:24:59 PM »

That is the problem with unknown engine rebuilders! There are so many easy ways/tricks that get a engine running good for about 10k miles "Rering" then it dies. Good catch!

Glade it didn't destroy your block! If you were local to me i'de say bring her over and i'de help ya slam her back together. I enjoy building Engines.

twistedtoy92 · « **Reply #23 on:** Mar 29, 2011, 01:51:49 PM »

thats exactly why you need to measure the bore and do a piston ring end gap when building.... flippin stupid people..... at least they didnt come apart on you!

65714runner · « **Reply #24 on:** Mar 29, 2011, 03:40:55 PM »

Well I hope that the bore will clean up where its at if not the next step is sixty over and i really hate to go that big. I may try to find another block if that's the case. There are some that can build engines and some that can not. I thought this would just be an easy freshen up, looks like it wont be.

Wermz84 · « **Reply #25 on:** Mar 29, 2011, 04:30:01 PM »

Quote from: 65714runner on Mar 28, 2011, 08:43:27 PM

Droped it off at machine shop today the guy put .030 over pistons in a .040 over bore .

Sorry to hear that.

79coyotefrg · « **Reply #26 on:** Mar 29, 2011, 04:48:55 PM »

Quote from: 65714runner on Mar 29, 2011, 03:40:55 PM

Well I hope that the bore will clean up where its at if not the next step is sixty over and i really hate to go that big. I may try to find another block if that's the case. There are some that can build engines and some that can not. I thought this would just be an easy freshen up, looks like it wont be.

have him try some .040 over pistons hopefully they wont be too far out that you can do a good hone on the cylinders and run the .040 overs.

where are you ?? Mississippi?? Alabama??

65714runner · « **Reply #27 on:** Mar 29, 2011, 06:01:14 PM »

That's what we are going for. Since it still has hone marks might be ok as long as bore was good to start with. I'm in Missouri.

65714runner · « **Reply #28 on:** Apr 12, 2011, 03:40:11 PM »

Well I got my parts in. What i did not know was that toyota changed blocks from 84 to 85

So I am looking for an 85 or newer block that way I can put my efi head on it. I was told that there is a chance that I could put my fuel injection on the 84 head but I will still have to send everyting back and get parts for the 84. For now I will just try to find a different block. This is the reason you should research first.

79coyotefrg · « **Reply #29 on:** Apr 12, 2011, 09:37:04 PM »

yes they changed in 8/1984

newer pistons had a flat top and the block was shorter. 11.080 inches where the older one s were 11.280 inches

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