Why this motor failed (w/pics)

[TimmyG]

I will post pics of what I found and explain. Let me know why you think it failed. I have a few ideas, but not totally sure. 

 

I bought an '84 720 with z24 not running. I was told it needed a head gasket. I tore into the motor to find out what it actually needs... I'm still not exactly sure why the motor failed so here we go...

 

What I found:

(Lots of pics because why not!)

 

Oil under the valve cover looked like mud. Drained the oil and significant amount of coolant came out first. Magnet into drained oil collected zero metal shavings.

 

No coolant level visible with radiator cap off, but about 2-3 gallons drained out from radiator. 

 

Removed the head. One head bolt was curiously loose and very easy to remove (bolt between cylinder 3 and 4, exhaust side, second from the rear-most head bolt). 

 

Some of the cam lobes are brown and not shiny. Honestly don't know the significance of this...? Did the head get too hot? No clue if the motor was ran hot. 

 

 

Head gasket did not show any obvious major failure point. Some wear noticeable near a cooling passage in same area as loose head bolt. Possible failure point?

 

Intake manifold had brownish/tan oil/coolant mix inside mostly the #4

runner and some in #3 runner. Other two runners on intake manifold had none of this goop at all. Intake manifold gasket could've been leaking coolant into cyl 4 (and sucking it thru intake manifold into cyl 3 as well). Pics of #4 runner.

How does this goop end up inside the intake manifold runner? I'm confused about the oil/coolant mix getting into the intake runner. 

 

Pics of other two runners. Clean inside.

 

What happened?

 

Maybe a leaking intake manifold gasket allowed coolant into combustion chamber causing the head to lift from excess pressure on compression stroke, loosening the head bolt(s), possibly warping the head from being run hot with low coolant...then causing the head gasket to leak more coolant into cyl 3 and 4 on exhaust side? (The head gasket looked worn near a cooling port in this area as mentioned before. Same area as loose head bolt.)

 

At this point I'm thinking the intake manifold gasket failed at least, and possibly the head gasket....but I'm confused as to why there is oil/coolant mix inside the intake manifold runner? 

 

What do y'all think?

 

[wayno]

My guess is blown headgasket and then it sat outside for a while and rain got into the intake manifold, check the head and block for flatness and if flat clean it up and install new headgasket, but this is all a guess as the Z24 is known for blowing headgaskets.

[TimmyG]

6 hours ago, wayno said:

My guess is blown headgasket and then it sat outside for a while and rain got into the intake manifold, check the head and block for flatness and if flat clean it up and install new headgasket, but this is all a guess as the Z24 is known for blowing headgaskets.

What's the best way to clean the deck of the block and check for flatness at home? I think given the situation I will probably have the head checked at a machine shop to rule out cracks.

[datzenmike]

Looks ok, just clean and assemble. The brown and most of the other is from lack of proper oil changes.

 

Loose bolt is from not re-torquing the head bolts every year or so. The Z24 has a chronic problem with blowing head gaskets when it gets to 100k. A simple loosening of each bolt and tightening to 60 ft lbs, one at a time, is the preventative measure for this.     

 

The cooling system looks like it was run often without or a poor mix of antifreeze and not changed every 3-5 years. Wouldn't hurt to flush the block and rad later.

 

The above are normal for a truck this age. Probably on the 5th or 6th owner and no one wants to spend any money on something they got for so cheap and they drive it into the ground.

 

 

 

Blocks almost never warp but you can check this when you check the head... which is aluminum and can easily warp if overheated. You'll need a straight edge that can be trusted and some feeler gauges. A professional straight edge is like $75 and up, maybe you can borrow one. Clean the head and lay the straight edge diagonally in an X along the length and try to fit a feeler gauge under it to find any low spots. If you can get a 0.004" feeler under it, it really should be leveled. For major or minor warp there is an inexpensive way to fix this at home.

 

Never lay the head down with the valves pointing down. If one is open far enough you can easily bend one by accident.

 

Smart to remove the head with the intake on. Saves a lot of unnecessary work.

[TimmyG]

1 hour ago, datzenmike said:

Looks ok, just clean and assemble. The brown and most of the other is from lack of proper oil changes.

 

Loose bolt is from not re-torquing the head bolts every year or so. The Z24 has a chronic problem with blowing head gaskets when it gets to 100k. A simple loosening of each bolt and tightening to 60 ft lbs, one at a time, is the preventative measure for this.     

 

The cooling system looks like it was run often without or a poor mix of antifreeze and not changed every 3-5 years. Wouldn't hurt to flush the block and rad later.

 

The above are normal for a truck this age. Probably on the 5th or 6th owner and no one wants to spend any money on something they got for so cheap and they drive it into the ground.

 

 

 

Blocks almost never warp but you can check this when you check the head... which is aluminum and can easily warp if overheated. You'll need a straight edge that can be trusted and some feeler gauges. A professional straight edge is like $75 and up, maybe you can borrow one. Clean the head and lay the straight edge diagonally in an X along the length and try to fit a feeler gauge under it to find any low spots. If you can get a 0.004" feeler under it, it really should be leveled. For major or minor warp there is an inexpensive way to fix this at home.

 

Never lay the head down with the valves pointing down. If one is open far enough you can easily bend one by accident.

 

Smart to remove the head with the intake on. Saves a lot of unnecessary work.

Thanks for the reply. I am still unclear on what that crap is inside the #4 intake runner... you're saying it's just old neglected coolant gunk that made it's way in there from leaking intake gasket?

[datzenmike]

Probably and probably the head gasket isn't blown. Coolant leaked in and got past the rings. You can clearly see the #4 piston top has been steam cleaned of deposits. No big deal just clean and assemble with new HG. 

 

 

 

 

[TimmyG]

20 minutes ago, datzenmike said:

Probably and probably the head gasket isn't blown. Coolant leaked in and got past the rings. You can clearly see the #4 piston top has been steam cleaned of deposits. No big deal just clean and assemble with new HG. 

 

 

 

 

What solvent do you suggest to clean the piston heads? That #4 has been difficult to clear of those deposits with carb cleaner, toothbrush, and credit card scraper. 

[datzenmike]

Wouldn't even bother, they'll be just as dirty in a month. You can lightly wire wheel the combustion chambers if you turn the cam to close both valves. Be sure to return to the TDC valve position when done. A good running engine in tune is pretty much self cleaning.

[TimmyG]

How long are the valves and springs good for? I would think now is the time to at least replace the oil seals.

 

 

 

Edited August 12, 2019 by TimmyG
Pics

[Stoffregen Motorsports]

5 hours ago, TimmyG said:

What's the best way to clean the deck of the block and check for flatness at home? I think given the situation I will probably have the head checked at a machine shop to rule out cracks.

Do you have a gasket scraper? If not, get one. Remove the dowels (don't lose them), scrape the gasket off, then wrap some 180-220 grit wet/dry sandpaper around a 1x2 block of wood (I use a 2x2 block of stainless), lube the deck with WD40 and then sand the surface clean. If there are low spots, you will see them, but even if you see low spots, they're probably not a problem. You can use the emery cloth/sandpaper on the head too.

 

NEVER use a Roloc disc on an angle grinder to clean the gasket surfaces.

 

Remove the gasket from the intake and do the same emery cloth/sandpaper cleaning method.

 

I would also run a ball hone down the cylinders a few times to clean up the bores a bit before you reinstall the head. Using WD40 and a battery powered drill set on low speed, count one-one-thousand per stroke. Clean with a towel and then squirt it down with WD40 again. Rings can rust to the cylinder walls, and sometimes this is fatal to the rings. Often times, it just leaves a ghost-like stain in the cylinder wall, which can affect ring sealing, so ball honing is a good idea.

 

Wire wheel the pistons and combustion chambers. Do this lightly so you don't erode any aluminum.

 

Can you feel scratches on the shiny cam lobes? If so, your cam is probably toast. You can shine them up with the same emery cloth/sandpaper if you like.

 

Hate to say it, but if you're this far in, pull the front cover and inspect the chain guides and tensioner. Pull the pan too. Install the head first, then the timing set followed by the front cover. Torque the head, adjust the valves, then install the oil pan with "The Right Stuff" RTV.

[TimmyG]

9 minutes ago, Stoffregen Motorsports said:

Do you have a gasket scraper? If not, get one. Remove the dowels (don't lose them), scrape the gasket off, then wrap some 180-220 grit wet/dry sandpaper around a 1x2 block of wood (I use a 2x2 block of stainless), lube the deck with WD40 and then sand the surface clean. If there are low spots, you will see them, but even if you see low spots, they're probably not a problem. You can use the emery cloth/sandpaper on the head too.

 

NEVER use a Roloc disc on an angle grinder to clean the gasket surfaces.

 

Remove the gasket from the intake and do the same emery cloth/sandpaper cleaning method.

 

I would also run a ball hone down the cylinders a few times to clean up the bores a bit before you reinstall the head. Using WD40 and a battery powered drill set on low speed, count one-one-thousand per stroke. Clean with a towel and then squirt it down with WD40 again. Rings can rust to the cylinder walls, and sometimes this is fatal to the rings. Often times, it just leaves a ghost-like stain in the cylinder wall, which can affect ring sealing, so ball honing is a good idea.

 

Wire wheel the pistons and combustion chambers. Do this lightly so you don't erode any aluminum.

 

Can you feel scratches on the shiny cam lobes? If so, your cam is probably toast. You can shine them up with the same emery cloth/sandpaper if you like.

 

Hate to say it, but if you're this far in, pull the front cover and inspect the chain guides and tensioner. Pull the pan too. Install the head first, then the timing set followed by the front cover. Torque the head, adjust the valves, then install the oil pan with "The Right Stuff" RTV.

I rubbed some oil inside the cylinders to prevent more rust. Do you think the rings will rust to the cylinder walls? Motor turned freely before. 

 

If I remember, the cam lobes feel slick. 

 

I would rather not pull the timing cover, etc. I'd like to keep this rebuild solely in the top end for budget purposes. I may not keep the truck very long, and if I do...I'm not opposed to tearing the whole motor down again for full rebuild. Just not yet. It's not a primary vehicle. Just a side hobby. 

[banzai510(hainz)]

ck behind the waterpump to make sure the front cover didn't cavitate(hole)

[Stoffregen Motorsports]

12 minutes ago, TimmyG said:

I rubbed some oil inside the cylinders to prevent more rust. Do you think the rings will rust to the cylinder walls? Motor turned freely before. 

 

If I remember, the cam lobes feel slick. 

 

I would rather not pull the timing cover, etc. I'd like to keep this rebuild solely in the top end for budget purposes. I may not keep the truck very long, and if I do...I'm not opposed to tearing the whole motor down again for full rebuild. Just not yet. It's not a primary vehicle. Just a side hobby. 

If they rusted to the cylinder walls, but you can move them by turning the crank, the damage is probably minimal. You will see the dark stains left behind, and it is best to hone those stains out. This light honing will help the rings re-seat too.

 

Understood. Budget. Hate that word.

[TimmyG]

7 minutes ago, Stoffregen Motorsports said:

If they rusted to the cylinder walls, but you can move them by turning the crank, the damage is probably minimal. You will see the dark stains left behind, and it is best to hone those stains out. This light honing will help the rings re-seat too.

 

Understood. Budget. Hate that word.

It is what it is. Thanks for the tips.

[G-Duax]

Would seriously consider Stoffregen's suggestion to pull the pan.

If it sat long with coolant in the pan, or had been run a long time with a failing head gasket, then you may have rust on the rod & main journals.

A lot of the older Toyota Supras had head gasket issues, that ended up with water in the oil,, and after head gasket replacement, lost rod bearings just because the bearings were not checked, and they had a little rust in them.

 

A pan gasket costs little, and if the bearings are bad, they are cheap also.

If you inspect them, and they are good, then all it cost you is the pan gasket.

If they are bad, and you don't check them, failure will come, but at a much higher $$$ costs once the bearings fail, and the rod hammers the crank.

 

I think the old saying is Don't build to last on weak, and shifting sands.

 

That comes back to spending a few bucks on a complete gasket & seal kit, as you should be replacing the valve seals anyway, and when bought in a full kit, the crank seals, and front cover gaskets don't end up costing much more.

 

 

Not quake related, just built on soft ground.

[TimmyG]

30 minutes ago, G-Duax said:

Would seriously consider Stoffregen's suggestion to pull the pan.

If it sat long with coolant in the pan, or had been run a long time with a failing head gasket, then you may have rust on the rod & main journals.

A lot of the older Toyota Supras had head gasket issues, that ended up with water in the oil,, and after head gasket replacement, lost rod bearings just because the bearings were not checked, and they had a little rust in them.

 

A pan gasket costs little, and if the bearings are bad, they are cheap also.

If you inspect them, and they are good, then all it cost you is the pan gasket.

If they are bad, and you don't check them, failure will come, but at a much higher $$$ costs once the bearings fail, and the rod hammers the crank.

 

I think the old saying is Don't build to last on weak, and shifting sands.

 

That comes back to spending a few bucks on a complete gasket & seal kit, as you should be replacing the valve seals anyway, and when bought in a full kit, the crank seals, and front cover gaskets don't end up costing much more.

 

 

Not quake related, just built on soft ground.

I was thinking today I really should drop the oil pan... it's not that I'm too cheap to buy the gasket. I just know I might get carried away and not planning on keeping the truck long at this point. I will definitely drop the oil pan after talking with y'all and thinking about it more. 

 

When I check the bearings, should I just remove the rod bearing caps one by one to visually inspect...and the same with the crank main bearing caps? 

 

4 hours ago, Stoffregen Motorsports said:

If they rusted to the cylinder walls, but you can move them by turning the crank, the damage is probably minimal. You will see the dark stains left behind, and it is best to hone those stains out. This light honing will help the rings re-seat too.

 

Understood. Budget. Hate that word.

I definitely don't disagree with the advice you gave, so hope I haven't come off the wrong way. However, if I can't turn the bottom end after removing the head with timing chain wedged then I can't hone all 4 cylinders. I'd have to strip the whole block, remove the timing cover and reset the tensioner, etc

Edited August 12, 2019 by TimmyG
I said something dumb and fixed it

[TimmyG]

8 hours ago, datzenmike said:

 

...Never lay the head down with the valves pointing down. If one is open far enough you can easily bend one by accident.

 

I just realized I did this.... what a noob. Hopefully that cyl 3 exhaust valve that's open a little isn't bent. I've only laid the head down on that rubber horse stall mat.

[G-Duax]

22 minutes ago, TimmyG said:

...... should I just remove the rod bearing caps one by one to visually inspect...and the same with the crank main bearing caps? 

 

 I can't hone all 4 cylinders. I'd have to strip the whole block. 

 

I would just check one of each, unless it was a race engine.

If one is bad, they all are, most likely.

 

I have honed cylinders with the crank in, by laying rubber from an old inner tube, or sheet plastic over the rod journal, with the outer edges next to the main bearing webs turned up, so honing debris runs down past the crank.

Just slide the hone in so it's just shy of the crank, make a mental picture of how far the drill chuck is from the head surface, so uoi don't run the hone into the crank or main webs, and hone away.

 

And it doesn't have to be a perfect hone job. The bores in my engine now had rust in 2 cylinders from sitting with coolant in it (previous owner abuse), and I didn't even know it until compression, and oil consumption forced me to finally take a look.

Honed until one just had a shadow in the bore, and the other was at about 95%, with some pits still showing, and it runs fine for a street engine.

Edited August 12, 2019 by G-Duax

[TimmyG]

2 minutes ago, G-Duax said:

 

I would just check one of each, unless it was a race cylinder.

If one is bad, they all are, most likely.

 

I have honed cylinders with the crank in, by laying rubber from an old inner tube, or sheet plastic over the rod journal, with the outer edges next to the main bearing webs turned up, so honing debris runs down past the crank.

Just slide the hone in so it's just shy of the crank, make a mental picture of how far the drill chuck is from the head surface, so uoi don't run the hone into the crank or main webs, and hone away.

 

And it doesn't have to be a perfect hone job. The bores in my engine now had rust in 2 cylinders from sitting with coolant in it, and I didn't even know it until compression, and oil consumption forced me to finally take a look.

Honed until one just had a shadow in the bore, and the other was at about 95%, with some pits still showing, and it runs fine for a street engine.

Are you saying pull the pistons and leave the crank in there so I don't have to rotate it and reset the timing chain tensioner? 

[G-Duax]

You can rotate the crank if you are very careful.

Sometimes it requires a helping hand.

Just hold the chain up tight as you rotate it, then re-secure it.

But if all cylinders are at TDC or BDC now, you won't have to rotate it at all, or maybe just once, 180 degrees.

 

Wish Nissan had put the limiter strap on all their tensioners, like they sell through Nismo as an aftermarket piece.

I put one of these on every L-series I build these days.

Don't know if they fit laterZ engines.

 

 

Edited August 12, 2019 by G-Duax

[datzenmike]

Honing is going to be hard to do with the head off and nothing to keep the tensioner in when you turn it. Never heard of honing on old worn and seated rings. 

 

Honing leads to the pistons being taken out, and if they're out might as well put new rings in and if going that far might as well replace the rod bearings and no sense going half way, change the main bearings too. I though I saw the word BUGDET????

 

Clean what you can and new oil seals because the heads off anyway and slap it together. Drive her and see how well it runs, do a compression check, keep track of how much oil it burns, then set up a proper re-build.. 

 

.

[TimmyG]

8 hours ago, datzenmike said:

Honing is going to be hard to do with the head off and nothing to keep the tensioner in when you turn it. Never heard of honing on old worn and seated rings. 

 

Honing leads to the pistons being taken out, and if they're out might as well put new rings in and if going that far might as well replace the rod bearings and no sense going half way, change the main bearings too. I though I saw the word BUGDET????

 

Clean what you can and new oil seals because the heads off anyway and slap it together. Drive her and see how well it runs, do a compression check, keep track of how much oil it burns, then set up a proper re-build.. 

 

.

Those were my thoughts exactly. I wanted to hear out everyone's ideas regardless. 

 

This is gonna sound crazy, but I found a rust free body yesterday for cheap... I plan to swap it onto my 2wd truck frame. So now I'll probably pull the whole block and trans. I think budget goes out the window at this point. Might as well go through the whole motor if I pull the block. Now I plan to keep this long term with a rust free body in sight. 

[Stoffregen Motorsports]

20 hours ago, TimmyG said:

I was thinking today I really should drop the oil pan... it's not that I'm too cheap to buy the gasket. I just know I might get carried away and not planning on keeping the truck long at this point. I will definitely drop the oil pan after talking with y'all and thinking about it more. 

 

When I check the bearings, should I just remove the rod bearing caps one by one to visually inspect...and the same with the crank main bearing caps? 

 

I definitely don't disagree with the advice you gave, so hope I haven't come off the wrong way. However, if I can't turn the bottom end after removing the head with timing chain wedged then I can't hone all 4 cylinders. I'd have to strip the whole block, remove the timing cover and reset the tensioner, etc

No, you can move the crank with the head off, but do it carefully so you don't lose the tensioner.

 

I completely understand your desire to keep it simple, but you also have to understand the risk vs reward. Dropping a pan to inspect a bearing or two will take an hour, and then re-sealing it with the right stuff will guarantee it will never leak. Two hours tops.

 

Note - some people recommend using a pan gasket, and that is how they came from the factory, but since I found the right stuff RTV, I have stopped using the gaskets altogether. It really is that good.

[Stoffregen Motorsports]

Just read through all the posts.

 

No, you don't have to remove the pistons to remove most of the crap from the cylinders with a ball hone. Sure, removing them is better, but in the spirit of keeping it simple, it can be done without removing the rods/pistons.

 

What's that saying about perfection? - "Perfect is the enemy of good." Strive for perfection, but also understand the rewards of cutting a few corners. In this case, you probably wouldn't have honed the cylinders at all, so honing them most of the way is better than not doing them at all.

 

Mike - it does help, even if only a bit. I've said it here before - some of the best engines I ever built had only a new head gasket. As long as you know the tricks, you can get away with cutting lots of corners. We are giving him the tricks and warning him of the pitfalls, so any benefit will be a win.

[TimmyG]

Thanks y'all. I think my project just went to a whole new level with the addition of a rust free cab swap. I must be crazy. Anyway, whole block and trans is coming out now. Might as well put new bearings in the bottom end, new rings, have the block cleaned and decked, cylinders honed, new freeze plugs, timing chain kit, new front/rear main seals. What did I forget? New clutch. I must be getting carried away. 😂

Edited August 13, 2019 by TimmyG