Timing chains

[DonTom]

My year 2000 RV has 105,300 miles on it. It has a 7.4L MPFI GM engine. It runs great. A lot of power in that 26 foot RV. Gets almost 10 MPG average, which is really good for a rig this heavy.

I have a few questions about timing chains and would also like some opinions.

1. Is my 7.4 L an interference engine?

2. Should I change the timing chain now just because of the high mileage or should I wait for a water pump failure to make the job easier? Or should I just forget about it?

3. How much hassle is it to change a timing chain after a water pump is removed? How much longer will it take? I have changed timing belts and water pumps many times but not yet replaced a timing chain.

-Don- SF, CA

[MikeHalloran]

1. I don't know.
2. If the engine has always had synthetic oil, probably not. If no or unknown, it may be time. The classical symptom of a stretched timing chain is hard starting, but normal running; but that's with carburetors and distributors. With EFI and computers adjusting the timing dynamically, the engine computer may compensate until it just flat can't.
3. The usual biggest hassle is removing and replacing the harmonic balancer and/or the hub behind it, which are usually a press fit on the crank nose. With the right special tools, it only adds an hour or two to a water pump job.

[Eric]

My year 2000 RV has 105,300 miles on it. It has a 7.4L MPFI GM engine. It runs great. A lot of power in that 26 foot RV. Gets almost 10 MPG average, which is really good for a rig this heavy.

I have a few questions about timing chains and would also like some opinions.

1. Is my 7.4 L an interference engine?

2. Should I change the timing chain now just because of the high mileage or should I wait for a water pump failure to make the job easier? Or should I just forget about it?

3. How much hassle is it to change a timing chain after a water pump is removed? How much longer will it take? I have changed timing belts and water pumps many times but not yet replaced a timing chain.

-Don- SF, CA

Is this a big block Chevy?

If yes, I'd say it's really, really unlikely the chain will break. Stretch (and get a bit loosy-goosy, eventually) maybe. But I have never heard of one actually breaking.

[DonTom]

Is this a big block Chevy?

If yes, I'd say it's really, really unlikely the chain will break. Stretch (and get a bit loosy-goosy, eventually) maybe. But I have never heard of one actually breaking.

Yes, it's a Vortex. Aren't all the 7.4L big block?

They don't use the nylon teeth sprockets in this, do they?

I have had several timing chains either break of fall off and every one of those vehicles were GM, all from either the 1970's or 1980's.

I have also had a timing chain jump a tooth or two, that was also in a GM of the 1970's.

But I have owned more GM's in the past than anything else.

-Don-

[DonTom]

1. I don't know.
The usual biggest hassle is removing and replacing the harmonic balancer and/or the hub behind it, which are usually a press fit on the crank nose. With the right special tools, it only adds an hour or two to a water pump job.

What are the special tools needed and about how much do they cost?

-Don-

[MikeHalloran]

Drag out the shop manual for your engine and see what's required of a harmonic balancer puller. Some of them can be done with simple generic 2 or 3 bolt pulley pullers.

Ford Fe blocks have a pressed bushing behind the balancer, that will yield to a couple of hose clamps around it, connected by a short chain to a bolt in the crank nose. The official tool is a heavy split sleeve sort of thing with pinch bolts and a jackscrew, and costs a lot. The backyard way requires at least two decent hose clamps, and ruins both of them, but they're cheap.

I think a Vortec is a truck motor, different from the porcupine head 396/427/454/502 that we think of as a Chevy big block.

[grouch]

Is this a big block Chevy?

If yes, I'd say it's really, really unlikely the chain will break. Stretch (and get a bit loosy-goosy, eventually) maybe. But I have never heard of one actually breaking.

It's a big block, sort of. It's a redesigned engine from earlier type engines. The 5.7 small block for instance is the same displacement as a 350 but it's heavily modified. Even down to the flow of coolant.

Generally, I've seen engines need a timing chain around 120-140K. You can often hear timing chain slap from the block if you know what to listen for. If it has a distributor, you can check it by eye. Mark a spot on the distributor housing where the rotor is pointing. (Obviously, you need to pull the cap off for this.) Use something besides a pencil (graphite). You want to harmonic balancer timing mark set on TDC. Now move it reverse of engine direction slowly and watch the rotor. Stop when the rotor starts to budge.Anything over 8 to 10 degrees means there is too much slop in the chain.

The problem with later model engines is the amount of stuff that has to be removed to work on them. I've got a slow seep from the bypass hose on my 2001 Ram after a timing chain replacement. It just needs a little tightening but I have to remove the alternator/air conditioning compressor bracket to get to it.

[DonTom]

Drag out the shop manual for your engine and see what's required of a harmonic balancer puller. Some of them can be done with simple generic 2 or 3 bolt pulley pullers.

I will, the next time I am at our Reno home, where my RV shop manual is.

-Don-

[J. ZIMM]

Rule of thumb has been at 100K, most Gears and Chains are replaced. Engines equipped with timing gears and chains, will usually have a Nylon covering on the camshaft gear, which will wear down to the point where the chain could slip a tooth, causing the engine to loose power or stop running. If the engine is an Industrial type, it may have a Roller type of chain which will give it a lot more life. The point is, when the chain wears, the valve assembly will lag behind the crankshaft as far as timing goes. Most people won't notice the power going away since they drive it every day. But they will notice a big change when the timing assembly has been replaced. When replacing, upgrade to a Roller type. It will last a lot longer, and not stretch out like a 'Chain" will. Most Engines with a Roller chain will go 100-150K with no problem. Some have hit the 300K and beyond mark.

[grouch]

Usually, I replace a stock chain with a double roller type. I've never put enough miles on one of those, even under heavy usage, to have it need replacing a second time. If I rebuild an engine or put one in, one goes in. When putting a used engine into a vehicle, anything that's a stinker to work on in the vehicle gets replaced. Timing chain, oil pump, expansion (freeze) plugs and so on. The engine I put in "Betty" had an extra 30K on it when I sold her and it was still running strong.

[DonTom]

Usually, I replace a stock chain with a double roller type. I've never put enough miles on one of those, even under heavy usage, to have it need replacing a second time. If I rebuild an engine or put one in, one goes in. When putting a used engine into a vehicle, anything that's a stinker to work on in the vehicle gets replaced. Timing chain, oil pump, expansion (freeze) plugs and so on. The engine I put in "Betty" had an extra 30K on it when I sold her and it was still running strong.

Does a double roller chain and sprockets always fit in okay? It's wider and does require both sprockets to be replaced, right? Since this all has to be non-stock stuff, where's a good place top buy such stuff?

I certainly will look into that if I ever replace the timing chain.

At just over 100,000 miles, should I just start the job or should I wait until a water pump failure or something like that? Or should I just forget about it for now and take my chances? I wish I knew for sure if the 7.4L is an interference engine. Because if so, then I would start the job now instead of waiting for it to break to see what happens.

My experience with timing chains is that they usually leave you stuck. Either they fall off or break. Only once have I had one slip and still be drivable. The way I discovered that one was when I discovered I had to have the ignition timing off quite a bit for it to run right, which did nothing for the valve timing. But sure ran a lot better. Lasted fine that way until I junked it, many thousands of miles later.

I almost always keep the same car until it's pure junk and not worth fixing. So I have had a few timing chain failures. But the earliest was in my 1988 Biretta at 138,000 miles. I have had other engines (including some GM) last more than 300,000 miles without the timing chain being touched.

BTW, I have only had timing chain failures in GM vehicles. But I have always owned mostly GM, until now. I now have a couple of Fords as well as a Chryslers & Jeep (same 5.2L engine).

But in my RV, I want it to be fairly reliable as it's usually used for very long trips with a couple of doggies, which can make break downs a much bigger hassle to deal with.

-Don-

[grouch]

Does a double roller chain and sprockets always fit in okay? It's wider and does require both sprockets to be replaced, right? Since this all has to be non-stock stuff, where's a good place top buy such stuff?

I certainly will look into that if I ever replace the timing chain.

At just over 100,000 miles, should I just start the job or should I wait until a water pump failure or something like that? Or should I just forget about it for now and take my chances? I wish I knew for sure if the 7.4L is an interference engine. Because if so, then I would start the job now instead of waiting for it to break to see what happens.


BTW, I have only had timing chain failures in GM vehicles. But I have always owned mostly GM, until now. I now have a couple of Fords as well as a Chryslers & Jeep (same 5.2L engine).

But in my RV, I want it to be fairly reliable as it's usually used for very long trips with a couple of doggies, which can make break downs a much bigger hassle to deal with.

-Don-

It probably has some life left in it. I'm not sure how the engine is packaged in your RV. If it's easy to get to the front of the engine, labor cost won't be so high. Personally, I'd check for slop in the chain. Unlike a heavy truck, your engine is working the same most of the time. A heavy truck often runs empty going back for another load.

I often replace timing chains if they make any noise, I did this with the Ram 2500 I recently bought. It didn't really need it but it was worn a bit and at 191K I just wanted to be safe. If you need to do any work on the engine around the front, oil pan repair, water pump replacement, or even a radiator repair, yes, I'd go with a new chain.

I've seen a lot of small Mopar engines (318, the same as a 5.2) quit around 120K when the chain stretches and jumps. If it's the original chain and it had nylon coating to cut down on noise, it probably is cracking. A lot depends on how the engine was maintained when it was newer. I junked a truck once that had been wrecked and I was going to reuse the engine. I had changed the oil every 3000 miles from new. I replaced the timing chain with 112K on the engine and it looked fine. The girl friend whose truck it went into is gone but I see her every now and then and the engine now has 200K+ on it.

Since the RV is for a time when you DON'T want to break down, I'd have a good mechanic check for slop. If he thinks it needs replacement, go for it, maybe replace the oil pump while you're at it. I usually put a high volume oil pump in one, NOT a high pressure pump.

[DonTom]

It probably has some life left in it. I'm not sure how the engine is packaged in your RV. If it's easy to get to the front of the engine, labor cost won't be so high. Personally, I'd check for slop in the chain. Unlike a heavy truck, your engine is working the same most of the time. A heavy truck often runs empty going back for another load.

But why would there be more strain on a timing chain under a heavy load compared to a light load? The chain only moves the cam, distributor rotor and valves, which I would think would be about the same load down hill as going up hill. I would think RPM's would be the only thing that increases the load. Oh, I think I just answered my own question. We're in a lower gear running more RPM's when going uphill.

As far as the labor, it will be the cost of tools, parts and my own time, because I will do the job myself. But it will be the first time I have tried to replace a timing chain. But I will do the job myself even if it costs me more to do the job after paying for the parts & tools. I just paid a few hundred bucks in parts and tools (over engine creeper) to replace by Dodge Ram cap and rotor plus spark plug wires. I just like to fix things myself, when I can. It's not about saving money, in my case.

Yeah, I think I will take my chances for now as I don't like to fix things that are not broken, except for timing belts. But when anything fails in the front of the engine, I will start the timing chain job. Yeah, I think there will be a lot of room in there after I remove the radiator fan shield.

I often replace timing chains if they make any noise, I did this with the Ram 2500 I recently bought. It didn't really need it but it was worn a bit and at 191K I just wanted to be safe. If you need to do any work on the engine around the front, oil pan repair, water pump replacement, or even a radiator repair, yes, I'd go with a new chain.

Yeah, timing chain noise (if I notice it) will make me start such a job sooner.

I've seen a lot of small Mopar engines (318, the same as a 5.2) quit around 120K when the chain stretches and jumps. If it's the original chain and it had nylon coating to cut down on noise, it probably is cracking. A lot depends on how the engine was maintained when it was newer. I junked a truck once that had been wrecked and I was going to reuse the engine. I had changed the oil every 3000 miles from new. I replaced the timing chain with 112K on the engine and it looked fine. The girl friend whose truck it went into is gone but I see her every now and then and the engine now has 200K+ on it.

The 5.2L in my 97 Jeep has just under 200,000 miles. AFAIK, the timing chain has never been replaced, but the Jeep had 150,000 miles on it when I bought it, so I cannot be sure. My 99 Dodge truck (also 5.2L) has about 130,000 miles. Have I been lucky so far, with these timing chains? BTW, do you know if the 5.2L is an interference engine?

Since the RV is for a time when you DON'T want to break down, I'd have a good mechanic check for slop. If he thinks it needs replacement, go for it, maybe replace the oil pump while you're at it. I usually put a high volume oil pump in one, NOT a high pressure pump.

I have NEVER seen a bad oil pump. Isn't that a rare failure?

-Don-