Z24 engine best way to disable the fuel for compression test??

[richURVAN]

Hey folks,

Need to run a compression test on my Z24 engine, first time doing a compression test and first time working with a carburettor. Assuming it's a mechanical fuel pump so no good looking for a fuse to take out.

Is pulling the fuel line off the carb going to be the easiest way and redirecting it into a container? If so which hose is the fuel feed?

Appreciate any help.

Ta,
Rich

[datzenmike]

You can do a compression test with the fuel pump active. The carburetor will not allow too much fuel into the carburetor.

 

 

Check and set your valve lash before doing a compression test. An overly tight valve will alter the results.

 

Pull both high tension wires from the coils off the distributor cap so the engine will not fire up and a brick on the gas pedal to hold the throttle full open. The exhaust side would seem easier to get at than the intake side, so take them all out so the engine spins faster and perform your compression test on a thoroughly warmed up engine.

 

Wright the numbers down. Then add a few squirts of oil to each cylinder and repeat the tests and write these new 'wet' numbers down and compare. Wet numbers will be higher a few pounds but a big difference of over 5% indicates the rings are not sealing as well as they could. Highest and lowest numbers should be within 10% of each other. A low cylinder that does not improve with oil may indicate a worn and poor sealing valve. Numbers of 170 and up would be excellent, 150 still ok, 130 showing some wear. Compression of 120 is getting rather low but if all readings are even it will run smoothly and if not burning excessive oil, is fine but a rebuild is in the future.

[richURVAN]

9 hours ago, datzenmike said:

You can do a compression test with the fuel pump active. The carburetor will not allow too much fuel into the carburetor.

 

 

Check and set your valve lash before doing a compression test. An overly tight valve will alter the results.

 

Pull both high tension wires from the coils off the distributor cap so the engine will not fire up and a brick on the gas pedal to hold the throttle full open. The exhaust side would seem easier to get at than the intake side, so take them all out so the engine spins faster and perform your compression test on a thoroughly warmed up engine.

 

Wright the numbers down. Then add a few squirts of oil to each cylinder and repeat the tests and write these new 'wet' numbers down and compare. Wet numbers will be higher a few pounds but a big difference of over 5% indicates the rings are not sealing as well as they could. Highest and lowest numbers should be within 10% of each other. A low cylinder that does not improve with oil may indicate a worn and poor sealing valve. Numbers of 170 and up would be excellent, 150 still ok, 130 showing some wear. Compression of 120 is getting rather low but if all readings are even it will run smoothly and if not burning excessive oil, is fine but a rebuild is in the future.

 

Ok sweet re the fuel pump I'll leave as is.

 

I'll warm the engine up to operating temp. I was going to pull the centre cable off the distributor would that be right? And this Z24 only has 4 spark plugs on the intake side so I'll remove all those and start by screwing the compression gauge into cylinder 1.

 

Will do the oil trick as well thanks Mike, what's a squirt of oil, about a tablespoon? 

 

Ta,

Rich 

[datzenmike]

Ah, yes single plugs.

 

Couple of tablespoons. The piston is hot and it should spread around and seal the rings.

[richURVAN]

On 1/25/2022 at 1:34 AM, datzenmike said:

You can do a compression test with the fuel pump active. The carburetor will not allow too much fuel into the carburetor.

 

 

Check and set your valve lash before doing a compression test. An overly tight valve will alter the results.

 

Pull both high tension wires from the coils off the distributor cap so the engine will not fire up and a brick on the gas pedal to hold the throttle full open. The exhaust side would seem easier to get at than the intake side, so take them all out so the engine spins faster and perform your compression test on a thoroughly warmed up engine.

 

Wright the numbers down. Then add a few squirts of oil to each cylinder and repeat the tests and write these new 'wet' numbers down and compare. Wet numbers will be higher a few pounds but a big difference of over 5% indicates the rings are not sealing as well as they could. Highest and lowest numbers should be within 10% of each other. A low cylinder that does not improve with oil may indicate a worn and poor sealing valve. Numbers of 170 and up would be excellent, 150 still ok, 130 showing some wear. Compression of 120 is getting rather low but if all readings are even it will run smoothly and if not burning excessive oil, is fine but a rebuild is in the future.

 

how to check and set valve lash buddy? 

 

[richURVAN]

google helped me out on this one.

 

valve clearances 0.014 inches for z24 while engine is hot . . . 

 

will need to go buy a feeler gauge. 

 

 

 

[datzenmike]

Hmm my '84 factory service manual (FSM) says 0.012" for the Z24. If you trust the on line information and it's for your year go with it.

 

Warm engine fully first, remove the timing cover. Take the distributor cap off so it will not start. The cam lobe must point down on the valve you want to check. The rocker should wiggle slightly as there should be clearance.

 

The HOT setting is 0.012"* so a feeler gauge of that size should just barely slip between the rocker end and the top of the valve. To adjust, hold the adjuster still with a screwdriver and loosen the lock nut under it. Adjust the adjuster up or down, tighten lock nut and check the 0.012"* didn't change.

 

* or 0.014"

 

 

[richURVAN]

[richURVAN]

I was not expecting that from an old van with over 300k's on the clock! Looks like a replacement engine though to be fair (sprayed a blue colour) . . . 

 

This is not indicative the head gasket is intact though?

 

I don't have a cylinder leak down tester just a chemical combustion leak tester which you screw onto the rad since I suspected combustion gases were getting into the coolant. Although I'm leaning more towards the rad being stuffed inside now. 

 

 

[datzenmike]

The wet number one reading is bad, it will not be less that the dry test. 160 is fine.

 

I would say the head gasket is fine.

 

What water do you top up the rad with? If tap water it's probably hard or contains dissolved minerals. Water goes in and only steam get out leaving the minerals to concentrate. The result is kettle scale. If so, the good news is you can remove the rad leave the cap on and lay face down. Fill with CLR and let sit over night.  I did this to my radiator and couldn't get back to it for 3 days. It won't harm anything.

 

 

https://en.wikipedia.org/wiki/Calcium_Lime_Rust 

[richURVAN]

Cool bro I'll see if i can get hold of some.

 

So here's an update, I put everything back together today including a new fan clutch with spacer so the fan sits within the shroud. Started the engine and it sounded rough to start but (has been sitting for a while) then began idling well and sounded great plus the new fan clutch/spacer combo seemed to be keeping the engine cooler, but whilst i was waiting for the temp gauge to find it's mark it started to run rough and emit a small amount of black smoke from the exhaust so I shut it off.

 

The only thing I didn't re-connect was the whole intake piping and crankcase breather hose, I just had the box on top of the carb and 90 hose bend with a rag stuffed in the end.

 

Could adjusting the valve clearances have messed with the timing? So I removed the rocker cover again and checked the clearances all good. 

 

I took all plugs out and inspected them and the plug in cylinder 1 had a fair bit of crap on it compared to when I put it in a few days ago.

 

The only other thing I did was remove the manifold heatshield and noticed that there is a crack in the header which is leaking a bit of smoke. 

 

Think I'll clean that plug re-fit everything and check the plug wires before giving it another go.

 

 

 

 

 

 

[richURVAN]

Ok put EVERYTHING back together this time cleaned off that spark plug and it ran good up to operating temp no smoke PHEW!

 

Although it's still overheating, all sorts of strange noises coming from the rad yet the heater core hoses still cold and most of the rad fins. Definitely a blockage in the rad / coolant system somewhere. 

 

Going to take the rad off tomorrow. 

[datzenmike]

Once you get this sorted buy some distilled water and mix with a quality brand of antifreeze. Only top up with distilled or rain water.

 

The heater hoses will only get hot if the heater controls are set to hot or on, and there is flow through the core. While the rad is out and the system drained you could connect a garden hose to the heater hoses (in the ON position) and flush the core. Go back and forth to reverse the flow till it runs clear.

 

 

Spark plugs are self cleaning but the engine must get up to running temperature and the choke off. They will get hot enough to clean themselves.

[richURVAN]

13 hours ago, datzenmike said:

Once you get this sorted buy some distilled water and mix with a quality brand of antifreeze. Only top up with distilled or rain water.

 

The heater hoses will only get hot if the heater controls are set to hot or on, and there is flow through the core. While the rad is out and the system drained you could connect a garden hose to the heater hoses (in the ON position) and flush the core. Go back and forth to reverse the flow till it runs clear.

 

 

Spark plugs are self cleaning but the engine must get up to running temperature and the choke off. They will get hot enough to clean themselves.

 

Thanks Mike.

 

I already flushed the heater core (forward and reverse) and I've had the heater switched on/to hot the whole time, still no heat in those hoses. Which leads me to think a blockage in the rad or somewhere. The core of the radiator is also not getting that hot compared to the tanks . . . 

 

Will drain the coolant and take the rad out this arvo. I hope I don't have to take the heater core out as i assume it's take the whole dashboard out. 

[datzenmike]

The heater water comes out the side of the block above the starter. It goes back to the lower rad hose so the rad has nothing to do with it. Unless the heater hoses are not connected right.

[richURVAN]

An update on this buddy . . . 

 

Had the Rad cleaned and refurbished at the local shop and put it back in today and flushed the system one more time via the block drain plug.

 

So up to now I had flushed the system multiple times every which way / replaced the thermostat and rad cap and had the radiator reconditioned.

 

Unfortunately it's still running hot . . . 

 

It seems as though there is still air locks, but when I try and bleed the system (with the rad cap off / idling) the water level in the rad fluctuates up and down and eventually keeps overflowing before it's even at operating temp. 

 

So I drained some water and tried the combustion gas leak chemical test but the water in the rad just boils and overflows.

 

Maybe I'll grab a cylinder leak down kit and give that a rumble  🤷‍♂️

 

[jagman]

My experience was the same as yours with the overheating problem. I flushed and replaced everything I could think of except the water pump and fan clutch which looked good on visual inspection.  After I replaced them the engine runs on the cool side all the time now.

[datzenmike]

Impossible to have trapped air pockets. Air rises and with the water pump pushing water out of the block from behind, air would exit at the thermostat the highest point in the system and collect in the top of the rad.

 

 

4 hours ago, richURVAN said:

 but when I try and bleed the system (with the rad cap off / idling) the water level in the rad fluctuates up and down and eventually keeps overflowing before it's even at operating temp. 

 

 

 

I've had this in a different engine before. It's a bad head gasket. Compression pushes into the cooling system displacing water which exits the open rad cap often pushing water with it. Air escapes, level goes down and it repeats.

 

New radiator and clutch fan so not those. Can only go where the clues you report take us. You said the radiator was cold while the engine was hot so it was not in good shape anyway. Not much left but the head gasket. Maybe time for one of those test kits that detect gas in the coolant to confirm.

 

Compression test is not conclusive for blown HG. It's only 4-5 turns of the engine with pressures of 150 PSI where a running engine produces pressures of over 2,000 psi for an instant but 600 times a minute at idle.

 

Just in case you do not know. If removing the head, the timing chain tensioner needs to be secured so it does not fall out when the timing chain is loosened to remove the cam sprocket. If it falls out add 4-6 hours of extra work. So find out how to do this.

[Stoffregen Motorsports]

No, it's not necessarily a bad head gasket. Coolant expands as it heats up which may account for the rise, and there are also the air pockets in the system that can show rising and falling coolant levels. Then there's the cavitation caused by the spinning water pump that creates bubbles.

 

Essentially, you need to make sure that the radiator fill neck is the highest spot in the system. If you have a heater hose that rises above the level of the radiator cap, you will always have an air pocket there. You can disconnect that hose and bleed the air out of it while filling the system with coolant, but then every time you remove the radiator cap, you need to do this again. Another way to get rid of an air pocket is to install a schrader valve or some other type of bleeder (https://www.speedwaymotors.com/Cooling-System-Bleeder-Drain-Valve-1-4-Inch-NPT,9243.html?NoRedirect=true&OriginalQuery=91720405) at the high point in the system.

 

There are a couple other tricks. When filling the system, have the vehicle pointed slightly uphill. This obviously allows the air to escape much easier than on flat ground. The second way is to use a no-spill radiator funnel when adding coolant (https://www.amazon.com/Lisle-24680-Spill-Free-Funnel/dp/B00A6AS6LY) The funnel will (ideally) be the highest point in the system and will allow you to run the vehicle without the radiator cap on until all the air is out of the system. I usually run three or four cycles of the thermostat and then let the vehicle cool completely before removing the funnel and installing the radiator cap. Lastly, you can also simply pump the radiator hose by hand to help the air bubbles move along.

 

In all, rising and falling coolant levels is a sign, to me at least, that all the air is not out of the system.

[datzenmike]

Still think HG.

 

9 hours ago, richURVAN said:

 when I try and bleed the system (with the rad cap off / idling) the water level in the rad fluctuates¹ up and down and eventually keeps overflowing before it's even at operating temp.²

 

 

 

¹Two gallons of water will expand 9 cu in or a 2.3" cube when heated from room temperature to boiling. It might swell slightly but it wouldn't fluctuate back and forth. I used to leave 1/2" below the rad cap to allow for this but now have a coolant recovery system so any coolant expelled returns when the system cools down.

 

Cavitation wouldn't happen at idle. Besides, cavitation bubbles are basically low temperature steam caused by a vacuum behind any sufficiently fast spinning propeller and immediately collapse when pressure is restored.

 

Air in a heater hose is subject to being pushed through the core and back into the engine where it gets to exit the highest point, the thermostat. I'll accept that idle water pump volume and pressure may be low enough to not work but out on the highway or simply revving it up would. A bubble in a heater hose would not cause over heating.

 

² Compression pushing into the coolant system will do this.

[Stoffregen Motorsports]

I'm speaking from experience. Bleed it with the funnel before you go tearing the cylinder head off.

 

If you're that worried about the head gasket, try a quick re-torque and keep an eye on it.

[richURVAN]

Thanks for the input folks . . . 

 

So I ran another test with a makeshift no-spill funnel and bypassed the heater core. Repeated the usual steps to bleed air, car elevated on jack stands and periodically squeezing the rad hoses.

 

As it started to warm up the water level was fluctuating massively like nearly reaching the top of the 1L funnel then would drop right down.

 

Then once the temp gauge started climbing above half tons of bubbles started coming up along with puffs of smoke, plus I also noticed the other day water dripping from the exhaust.

 

Sounds pretty conclusive now right. Anyone know of a guide for changing the headgasket on a Z24?

[datzenmike]

Disconnect at least one of the battery cables.

Drain and remove radiator

Remove distributor cap and wires, cover distributor with large baggie.

Remove exhaust manifold from head and hang out of the way.

Disconnect anything connecting the head to the block or to the vehicle such as the throttle cable, fuel lines, heater hose, temp sender, EGR tube, hose to PCV valve, electrical plug on carburetor, vacuum advance hose, canister purge line,  and others.

 

If standard take out of gear, set emergency brake

Remove valve cover and loosen the cam sprocket bolt DON'T REMOVE.

Mark the sprocket and chain relationship so it goes back this way.

Set engine to TDC compression stroke on #1 cylinder

Block timing chain tensioner from falling out. Number one priority!!!!!!!!!!

 

NOW remove cam retaining bolt and cam let chain rest down between the chain guides.

From here on crankshaft MUST NOT BE TURNED

Loosen and remove head bolts starting in the middle working alternately to the front and rear.

 

Get help and lift the head and intake away as a unit. No need to remove the intake but a hell of a lot easier to remove/install out of the vehicle.

DO NOT set the head down on flat surface, could bend a valve. Set on wood blocks.

There are two alignment dowels located at the front and rear on the exhaust side. May be stuck in bead or block. They look like short 1/2" pipe lengths with a slit down the side.

 

Fill center cylinders with rags. Clean top of block so you could eat off of it. Clean the threaded HB holes. Can't be too clean.

Tilt head up so surface can be cleaned, or remove intake now if easier to work on.

Head surface is soft aluminum and will gouge if wire wheel used aggressively on it.

Must be spotlessly clean, can't be too clean'

 

Might be a good time to check that the head is flat by using a straight edge. Lengthwise through the center and a X pattern. If you can fit a 0.004" feeler gauge under it. Better get it milled down.

Also a good time to replace the valve seals now. Easy to get at now and cheap... just an option.

If so wire wheel the valves clean of deposits, stay away from the valve face. Valves MUST go back into same position.

Lightly wire wheel the combustion chambers clean. Stay away from valve seats.

 

That should do it, assembly is reverse of taking apart.

Make sure alignment dowels are in block they will properly align the head gasket.

Head bolts are totally reusable if undamaged. Just wire wheel them clean and wipe with oily rag.

 

R  A  D

8......7

4.....3

2......1

6.....5

10...9

 

Use a torque wrench and tighten in the above sequence to 20 ft. lbs. Repeat in same sequence to 40 ft. lbs. Finally same sequence to 60 ft. lbs. Does not need a re-torque after running but if you are so inclined do on a dead cold engine loosening only one bolt and tightening fully to 60 ft. lbs. Never loosen more than one bolt at any time, do in any order you like. Once a year do this re-torque of the head bolts.

 

Probably forgot something. 

 

Oh yeah, cam sprocket retaining bolt torque is 90-115 ft lbs.

 

[Stoffregen Motorsports]

I know this sounds lazy, but if you have a cherry picker, use that to remove and reinstall the head. This way you can leave the manifolds on and the weight of it won't cause you to mis-step when guiding it back onto the motor.

 

Or, pull the motor and do it on an engine stand. That's my MO, but I do this shit for a living, and I like to make things easy...

[datzenmike]

It is a mid engine van....