Z24 Timing Chain Questions

[sTanTruck]

Hello all, 

I have a 1986 720 Z24 with 118K on it. I am thinking that a timing chain is in my near future unfortunately. It is of unknown origin and I don't want to let the valves and pistons get to know each other. I have been driving this truck fairly regularly since buying it about a month ago and it is an absolute TURD (living at 5k elevation and driving up into the mountains regularly) . I plan to swap a 32/36 weber on it and do the timing chain but I have a question. 

 

Can I estimate the wear on the chain (lengthening) by looking at how much timing is on the engine currently? I have read that this engine was stock with 3-4 degrees of advance in the timing. If the chain has truly stretched the timing should have retarded slightly. If I were to use a timing light to check what it is currently at would that tell me if I am ok to keep driving it? Does anyone know of a way to check the condition of the timing chain through the valve cover? I want to pull the valve cover off, check the valve lash, retorque head bolts and evaluate the timing chain. 

 

 

Thank you in advance, 

Dylan

 

[bottomwatcher]

Chains last a long time. Why do you suspect the chain. Noisy?

[ElliotV]

51 minutes ago, sTanTruck said:

Hello all, 

I have a 1986 720 Z24 with 118K on it. I am thinking that a timing chain is in my near future unfortunately. It is of unknown origin and I don't want to let the valves and pistons get to know each other. I have been driving this truck fairly regularly since buying it about a month ago and it is an absolute TURD (living at 5k elevation and driving up into the mountains regularly) . I plan to swap a 32/36 weber on it and do the timing chain but I have a question. 

 

Can I estimate the wear on the chain (lengthening) by looking at how much timing is on the engine currently? I have read that this engine was stock with 3-4 degrees of advance in the timing. If the chain has truly stretched the timing should have retarded slightly. If I were to use a timing light to check what it is currently at would that tell me if I am ok to keep driving it? Does anyone know of a way to check the condition of the timing chain through the valve cover? I want to pull the valve cover off, check the valve lash, retorque head bolts and evaluate the timing chain. 

 

 

Thank you in advance, 

Dylan

 

I would pull the valve cover and take a look at it. You should be able to tell if it is tight and take a look at the guides. Also I believe these trucks were a single chain from the factory(not 100% sure) so if it is a double roller it could be fairly recent. I have seen people on here claiming 400k miles with original chains. I think what fails first is the guide which you would possibly hear some chain slap if that was the case.

[bottomwatcher]

They came as double rollers and unless extreme lack of oil changes I am not surprised to see them going at 400k. These engines are overbuilt for their anemic horsepower so unless abused, extremely overheated or blown headgaskets the long block rolls on a long time.

[ElliotV]

2 hours ago, bottomwatcher said:

They came as double rollers and unless extreme lack of oil changes I am not surprised to see them going at 400k. These engines are overbuilt for their anemic horsepower so unless abused, extremely overheated or blown headgaskets the long block rolls on a long time.

These are pretty much tractor motors with the way they are designed being very low horsepower but everything is pretty beefy for the power they make and they sound like it too which is nice cause I hate fart can 4 cylinders. 

[banzai510(hainz)]

I went over Bluett Pass here in Washington. The higher I got the less power I had!!!!!!!!!!!

 

Unlesst thee timing chain was installed by a previous owner wrong I would not tear into it if you dont know what you doing.

[datzenmike]

I have never heard of an L or Z series engine break a timing chain, it's .... impossible. In fact the next generation KA series reduced the chain to a single row from dual.

 

The timing chain has absolutely nothing, no connection to the distributor ignition timing. At 100k it's too new for something to be wrong with it.

 

 

TIPS

The Z24 is known for blowing head gaskets every 100k. Yours is close to over due. The preventative for this is to re-torque the head bolts once a year. Engine must be cold from sitting over night. Loosen only ONE bolt at a time and immediately tighten to 60 ft. lbs. Only then move to the next bolt. You can do in any order you like.

 

Start it and warm thoroughly 20 min at least. Set the valve lash to 0.014" while hot. Miss adjusted valve lash will reduce power.

 

Altitude reduces air pressure. Less air into the engine less power out, this is normal. AS you go higher the air fuel mixture becomes richer so you economy will be lesser. If you get a Weber you can replace the jet for a smaller one.

 

Set the ignition to 3⁰ Before Top Dead Center on number one compression stroke. Once set the ignition timing is unlikely to change but a previous owner may have messed with it.

 

The engine is now pretty much tuned up as much as it can be. The Z24 is not a power house but it makes really good torque and it's extremely reliable.

 

 

Engine oil...

When this engine was designed in the late '70s oil contained over 1,000 PPM ZDDP, an anti scuff additive package. Starting in the early '90s oil makers have slowly been reducing the ZDDP levels to almost half that because newer engines don't need it and it poisons the new catalytic converters. To keep using the same oil the Z24 was made for I switched to Shell Rotella T4 a 'light' diesel oil with 1,200 PPM ZDDP. It comes in 10w30 and 15w40. I avoid synthetic oils, they offer protection that the Z24 will never need and way too expensive. One time I added one quart to top off and the front seal started to leak.

 

Always change the oil filter. NEVER use fram. WIX is still good.

 

Check the spark plugs. Only use NGK BPR5ES on the exhaust side and BPR6ES on the intake. Check the ignition wires for damage and the distributor cap and rotor for cracks. If anything looks odd or bad then it is.

[NC85ST]

Yeah, here’s the tensioner from my 400,000 mile engine.

[banzai510(hainz)]

yes a weak spot could be the tensioner wearing

[datzenmike]

Change it when it starts making noise. It's got a long way to go yet.

 

The L series have a provision for checking cam timing. You can even make an adjustment to correct it. Funny but the Z series do not have this. Probably because chains don't stretch enough to matter.

[sTanTruck]

Thank you all for the responses. This makes me feel a lot better about driving this thing. I will switch to the Rotella T4. As for the weight oil, living in SLC Utah, should I run a little heavier weight oil in the summer? 

 

I will inspect the timing belt and tensioners when I pull the valve cover off. And I will post a video and link it so you can see what I am looking at. 

 

Thanks everyone for chiming in!

[sTanTruck]

On 5/3/2024 at 9:37 AM, datzenmike said:

I have never heard of an L or Z series engine break a timing chain, it's .... impossible. In fact the next generation KA series reduced the chain to a single row from dual.

 

The timing chain has absolutely nothing, no connection to the distributor ignition timing. At 100k it's too new for something to be wrong with it.

 

 

TIPS

The Z24 is known for blowing head gaskets every 100k. Yours is close to over due. The preventative for this is to re-torque the head bolts once a year. Engine must be cold from sitting over night. Loosen only ONE bolt at a time and immediately tighten to 60 ft. lbs. Only then move to the next bolt. You can do in any order you like.

 

Start it and warm thoroughly 20 min at least. Set the valve lash to 0.014" while hot. Miss adjusted valve lash will reduce power.

 

Altitude reduces air pressure. Less air into the engine less power out, this is normal. AS you go higher the air fuel mixture becomes richer so you economy will be lesser. If you get a Weber you can replace the jet for a smaller one.

 

Set the ignition to 3⁰ Before Top Dead Center on number one compression stroke. Once set the ignition timing is unlikely to change but a previous owner may have messed with it.

 

The engine is now pretty much tuned up as much as it can be. The Z24 is not a power house but it makes really good torque and it's extremely reliable.

 

 

Engine oil...

When this engine was designed in the late '70s oil contained over 1,000 PPM ZDDP, an anti scuff additive package. Starting in the early '90s oil makers have slowly been reducing the ZDDP levels to almost half that because newer engines don't need it and it poisons the new catalytic converters. To keep using the same oil the Z24 was made for I switched to Shell Rotella T4 a 'light' diesel oil with 1,200 PPM ZDDP. It comes in 10w30 and 15w40. I avoid synthetic oils, they offer protection that the Z24 will never need and way too expensive. One time I added one quart to top off and the front seal started to leak.

 

Always change the oil filter. NEVER use fram. WIX is still good.

 

Check the spark plugs. Only use NGK BPR5ES on the exhaust side and BPR6ES on the intake. Check the ignition wires for damage and the distributor cap and rotor for cracks. If anything looks odd or bad then it is.

Do mean  3 degrees of idle ignition timing (advanced of TDC)? I am a total novice to setting timing on a gasoline engine and I have never used a timing light before. 

 

Also, any tips for setting my idle mixture screw? I have to pass emissions this month and I failed last time for running too rich. I have heard that you can tell if its lean or rich by how it reacts after blipping the throttle. 

 

Thank you for your tips!

[datzenmike]

It's 3⁰ + or - 2⁰ before top dead center on the number one cylinder. If it was set correctly it just needs checking, probably hasn't moved.

 

The idle mixture screw is sealed at the factory. Too rich? where at idle?

 

The oil viscosity is determined by how cold you expect it to get before the next oil change. It for making it easier for the starter to spin the engine when cold. The colder, the lower the number you want. 10w30 is good to 0 F. 20w40 is good down to 20 F. Once the oil heats up to engine temperature they are all almost the same viscosity. An engine at 185F when it's 20F out is the same as 185F when it's 100F out.

[sTanTruck]

Can tensioners for the timing chain be changed without removing the chain? It would be handy to be able to change tensioners and save chain for the future. 

[Logical1]

If you are changing the tensioner, taking the chain of is a non-issue. Scribe the sprocket and the chain on both ends. remove, re-install anytime.

[Logical1]

I have a 85 4x4 king cab in AZ @ 7k' elevation. I know the head is tired, I know the rings are tired. with a weber on it and a little bit of love she drives great! 

[datzenmike]

10 hours ago, sTanTruck said:

Can tensioners for the timing chain be changed without removing the chain? It would be handy to be able to change tensioners and save chain for the future. 

 

You can but the timing chain cover must come off. You have barely 100K on the engine it's far too early to be worrying about the timing chain components. First order is re-torquing the head bolts. Now THAT is something that is due.

[sTanTruck]

I will get on that this week! Thanks @datzenmike