12HT engine rebuild (1 Viewer)

[ozcrusier]

I brought this engine a few months back for my hj75 and was told it had 280'000 K when started it ran on five cylinders and then cut to six after 30 seconds with mild blue/grey smoke. I done a comp test and found cold.
1 320
2 340
3 285 wet 420
4 360
5 230 wet 330
6 360
I pulled engine and lifted the head and found number five cylinder has slight scores probably caused from broken rings with number 3 looking good with good hatch.
I'm getting my engine stand sorted this week and hopefully be able to check the BEB bearings and decided what way I'm going full rebuild or a full kit with main bearings.
If you check the pics you can see how the pistons are out off the bore so will give them a good clean and spec + old head gasket thickness for squish on rebuild

 

[Freewheel]

How tight are the ring grooves? cylinder number 5 seems to go fairly often - in my 2H the rings were eating through the piston, which is a common problem- not sure if the 12HT shares that issue or not.

 

[Gengis]

Yes, all the Toyota pistons did this, but you wont get Toyo replacements and all good aftermarket pistons have alfin inserts, a metal band around the top ring groove. You will be pointed towards Engine Australia for these but there are a few others, but getting info on them is difficult.

if this is your only problem, then order a set of first oversize, get a re-bore replace the big and small ends and away you go.

Oh and a gasket set too. To fit and forget, genuine Toyota oil seals on the back and front of the crank, and please torque the crank pulley nut up properly to speck. Bloody tight is not good enough.
G

 

[ozcrusier]

We pulled number 5 and found 1st ring broken and 2nd ring shattered quite surprising as I have never seen a ring like this.
The bore is looking very good with some slight scores and big ends are in great condition. We caught her at the right time before one of those rings pieces tried to exit.

 

[ozcrusier]

The cross hatch is still visible in all cylinders so the guy I brought it from told me it had 280.000 so its close. Also all the pistons where 10 thou out off cylinders if anyone is interested.
Happy days

 

[HoJo 61]

Fun project. But that's bit odd the rings broke at 280k. Normally they go after 500k, don't they?
Cross hatches were still visible in my +600k 12H-T so..

 

[ozcrusier]

Thanks mate been searching high and low but not much info on these unicorn engines so thought I would post some photo's.

 

[Michael B]

Oz,
Thanks for this thread. I have recently bought and installed a 12HT that the PO had just rebuilt but never installed. Since I have never owned of these before I'm keen to learn all that I can about them. You are providing me with a lot of good information.

 

[ozcrusier]

No more broken rings but check the end gaps.

 

[ozcrusier]

The full standard rebuild kit arrives tomorrow and my local engine shop will mic the pistons to spec and mill if needed then fit little end bushes, pistons rings etc. I need to buy or borrow a ridge reamer as there's a small ridge on the thrust side of number 5 where the broken rings done some damage I would hate to hone it and have a engine tic or worst case break another ring.

 

[ozcrusier]

The engine kit arrived through the week now waiting on the snap on ridge reamer.

 

[Oldtoy74]

What are they stinging for kits, and did you use engines australia or someone else, and if don't mind me asking what's your budget to get this completed,
Looks like fun, I would like to rebuild mine one day, but I've only got 208k on clock, so I've got some time to learn etc

 

[ozcrusier]

Oldtoy74
It's a engine Australia kit just under $1000 including postage.
Not sure on overall costs won't know till it's finished possibly $2000 on the engine.

 

[Oldtoy74]

No more broken rings but check the end gaps.
View attachment 1224225 View attachment 1224226

Can I ask a couple questions, when you say "check out the end gaps" is that the ring end gaps on piston, you are referring to, and are they too wide ?
Also the ridge reamer what does that exactly do, and what was the reason you need it for ?.
Look forward to learning some lingo and insight to a rebuild.
Cheers

 

[HoJo 61]

@Oldtoy74 Download this manual and read it from cover to cover and you are good to go!
Dropbox - Engine_manual_2H_12HT.pdf

 

[northumbrian]

Ooooh this going to be a good one

 

[ozcrusier]

This is the flex hone where going to run through the cylinders for the 45 cross hatch needed for new piston rings.

 

[ozcrusier]

I had some off these photo's on my hj75 build thread but decided to put all the engine related stuff in the diesel section for people who may have the 12ht engine or considering buying one.
Exedy Safari tuff clutch for when I swap engines.

 

[HoJo 61]

Is that clutch the 40% stronger one?

 

[ozcrusier]

25% from my understanding but never opened the box and seen the clutch specs.