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Rebuilding 1HZ Motor

hr1hz80

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Feb 3, 2021
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australia
Hi guys

I have a 97 1HZ 80 series running a turbo. I noticed a knocking sound some months ago and have found it to be a singular piston.

While the vehicle has been pulled apart the head has been reconditioned.
My mechanic has advised me only 1 piston is in bad condition, and that the rest are fine. He also advised me that changing 1 piston is very doable, however I'm leaning towards changing all of them. Can somebody shed some light on this.

I do understand that the 1HZ was not intended to run a turbo however there are many getting around that have little to no problems.

Can anybody please advise me of any upgrades I can do while the motor is in pieces to safeguard the motor and better cater for the turbo.
- Can HDT pistons be used in the 1HZ block?, If not, are they other pistons/parts that can be used that are stronger then standard 1HZ pistons?
- Are there any other improvements that can be made to further safeguard the 1HZ with a turbo.

Thank you
 

MattT

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Feb 16, 2020
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south_africa
So I have the same model also running a turbo and I sent mine in for a compression test a few months ago and found there was zero compression on two cylinders. This ended up being a full engine rebuild including reboring and fitting larger pistons. I also had to replace the cylinder head as it had cracked in places. At the same time the mechanic replaced the radiator which was looking worn, the oil and water pumps, bearings across the board, all belts and so on. Con rods, crank and the cylinder head bits and pieces were all fine. This was my dad’s vehicle and he used to tow cattle with it, so I know the history of the car. He had the turbo installed back in 99 and never realised the damage it could cause under these heavy loads.

Having done the rebuild and fitting an EGT, my plan is to preserve the engine through driving style rather than anything else, though the turbo is running at minimal boost and the mixture is set lean. I think that I will get many years more from this guy before he’s done. That said, I’m not sure there’s scope for any additional reboring on this block so this is it’s last run.

My mechanic is a Cruiser specialist, and his advice was a rebuild = rebore and next size pistons up. I’d be wary of replacing just one.

I should probably introduce myself...
 

Jon_Tallis

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Jul 29, 2012
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wales
On what basis is the mechanic saying the rest are fine? Were compressions checked? Have bores been measured properly and found within tolerance? Have all pistons been removed, measured and visually checked for scoring? Probably worth crack-testing the piston crowns too.
If that has all been done and everything is within spec, then yes you can just replace one piston. You might consider new rings though while they're all out.
If compressions are OK but pistons are scored, then a new set of correctly sized pistons and rings.
If compressions are down or any bore is out of spec or scored (which out in any case to show up as low compression), then a re-bore and new pistons.
Obviously if you upgrade pistons you need to do this across all 6.

Going by post dates I guess it's possible this is already sorted but hope this helps
 

frank rabbets

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Mar 1, 2010
Messages
5,104
If you reuse the old bores remember to glaze bust their surfaces. If not the new rings will never bed in and engine will probo use oil. Done this mistake. (twice).
 

clivehorridge

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romania
AFAIK the 1HD and the 1HZ are completely different engines internally. They look the same on the outside, but I don’t think there’s many internals that are interchangeable.

Just the compression ratios alone are very different, 17:1 on the 1HD and 24:1 on the 1HZ... (don’t quote me, you can look it up) which suggests the pistons will be different, let alone other parts.

I‘ve toyed with the idea of fitting a turbo to my 1HZ, but I’ve heard too many disaster stories to go ahead. Done correctly, I know it can be OK, but unless you know what you’re doing (which you very well might) it can bite you in the ass.

Frank is spot on about honing the bores and I’d be wary of changing only one piston, but this depends on available cash to an extent, the parts prices are horrendous...

Best of luck...
 
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