Low compression on 1HZ

[tantor]

First post.

Recently inherited my old man's 1996 HZJ75 troopy. It was in a bit of disrepair when I got it, but I fixed a few things up and took it to the mechanic and asked for a compression test. All cylinders are at 300-320 psi. Manual says this is well below limit (384 psi?), mechanic says "about the limit for what we would call a ‘healthy’ engine".

So, is 300 psi on the verge of dying or just being unhealthy? And is the best path forward to get a engine rebuild and the cylinders rehoned?

Cheers for any advice.

 

[Rigster]

In my experience, not all shops are the same... Not to throw shade on the shop you are going to, but did they do a bore scope? Or a top down leak test? Is there blowby if you remove the oil filler cap? This could be just be a head refresh job, and not necessarily a complete engine rebuild. If so, I would still do the BEB's while the head is being redone.

Best advice would be to decide if you love this truck, and are going to keep it, or will it be a burden you are hanging onto for sentimental reasons?

If you love it, prepare for a complete engine overhaul and be pleasantly surprised if it is just a head rebuild. It also makes a huge difference if you are going to do the work yourself, or pay a shop to do it. But more information is probably the way to go for now to ascertain what is necessary. Whatever your decision, I wish you all the best in this endeavor!

 

[JuanJ]

Hello,

A simple test to determine whether it is a piston ring issue.

Add a small amount of engine oil into the cylinder and check the compression. If this results in a better value, then the piston rings and/or the cylinder are worn.

As mentioned above, prepare for a complete engine overhaul. Expect the worst but hope for the best. Sentimental value is worth a rebuild of any size.






Juan

 

[tantor]

Thanks rigster, juan,

Bought a compression test kit to verify myself. Very keen to give as much as I can a go myself.

It seems to run fine generally. I replaced leaking water pump and the timing belt at the same time. Thermostat, radiator, radiator hoses as well. Going to change fuel injectors because of some black smoke and age of engine.

If I keep driving it with that low compression (if I verify it is that low) do I risk getting it to the point it's beyond saving? In other words can I kick the can down the road a bit on the refurb or should I pull the trigger on it now if it's that low? Has 317k km on it.

 

[JuanJ]

Hello,

If your test confirms the data you got, then continued driving may worsen whatever wear and tear your engine has.

Tired engines have this habit of giving up the ghost when you least expect it, with a lot of damage.

Plan for the worst, hope for the best, and pull the trigger.

Chances are that, down the road, you may not have enough time, resources, or patience.





Juan

 

[Rigster]

Thanks rigster, juan,

Bought a compression test kit to verify myself. Very keen to give as much as I can a go myself.

It seems to run fine generally. I replaced leaking water pump and the timing belt at the same time. Thermostat, radiator, radiator hoses as well. Going to change fuel injectors because of some black smoke and age of engine.

If I keep driving it with that low compression (if I verify it is that low) do I risk getting it to the point it's beyond saving? In other words can I kick the can down the road a bit on the refurb or should I pull the trigger on it now if it's that low? Has 317k km on it.

View attachment 3975344

317,000km is not much on a 1HZ, but of course there are a lot of caveats to that. Primarily maintenance history and use case. You might have a good understanding of these as it is coming from your father (condolences, btw)

It is a good idea to verify things yourself. It is hard to find a good and reliable shop these days. See what you find with your tests, but as @JuanJ stated if it is actually this worn, if something catastrophic breaks internally, it could ruin the block or crankshaft, and you are looking at a larger bill.

With that low of compression, I would expect harder starting, and a significant loss of power. Does it use oil? Do you have any others around that you could compare it with?

For reference, my 1HZ has close to 290,000kms and it still does not use any oil. Good luck with the testing!

 

[AussieHJCruza]

If it starts well, I'd suspect that compression to be an error.
Do your own test, and add a few ml of engine oil to the cylinders if it's low, and test again. If you see an increase, your issue is rings, if not you either have some head/valve work to do, or you have a hole in a piston or something, but doubt it's that if you're getting 300+ psi.

Remove all the glow plugs to give the best cranking speed and disconnect the fuel cut solenoid on the pump to stop diesel spraying everywhere.