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4.0 SOHC Timing Chains

Jimmy Hoffa

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Is it too late to replace the tensioner?

According to the previous posts once it starts rattling on start up the end is near. 220,000 miles is pretty good but now the motor needs to come out. If the chains and tensioners are replaced you should get quite a few more miles out of it, especially since only Mobil 1 has been used. I would consider a compression test.

IMHO, if the rust is getting bad it may be time for another Explorer. My '98 was super clean and garage kept but needed a trans. I paid a $1,000 for it and the AC is still ice cold!
 


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Dave98XLT

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you should get quite a few more miles out of it, especially since only Mobil 1 has been used. I would consider a compression test.

Jimmy, Agree, the motor is strong as a horse as the Mobile 1 does an exceptional job of keeping the cylinder walls and pistons in shape...

once it starts rattling on start up the end is near.

Can anyone offer a 2nd opinion?
 




BubbaFL

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Can anyone offer a 2nd opinion?

Could fail tomorrow, or could last another 75k.

Take the valve cover off and visually inspect the cassette. If it's missing chunks of plastic or the chain is eating into the mounting post, the engine is close to done.
 




XLTrunner

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You said the noise was coming from the right rear...correct? If it were me, I'd pull the old tensioner out and see if the spring inside seems weak when you push down on the plunger with your thumb. It's easy enough to remove by first pulling the wheel and then accessing it through the wheel opening (behind the rear portion of the dust shield). Need a 27mm socket (upper tensioner needs a 27mm DEEP socket).

I ran down to the local U PUll this afternoon to get a first hand glimpse into how the upper tensioner works. They had just gotten in a '98 SOHC w/223K miles. I pulled the intakes, thermostat housing and LH valve cover to have a look (don't need to remove all this to access the tensioner...I just wanted to have a look at the timing chain/cassettes inside). The tensioner still had plenty of resistance to keep the cassette/guide firmly against the chain. Who knows if it had ever been replaced. As a reference for resistance, I held it in my hand after removal and pushed down on the plunger with my thumb. I can't quite compress it all the way in this manner...and, I'm no 98lb weakling. I don't have a new one to compare, but seems plenty strong to me to hold the plastic cassette in place on cold start.

The conclusion I've reached is that odds are good that failure can be postponed by routinely replacing the tensioners; preferably before the dreaded "rattle" is heard. However, if the plastic cassettes are prone to breaking simply due to becoming brittle with age, the only true solution is to replace the plastic cassettes/guides along with the tensioner. That probably isn't a terribly difficult job to do on the front. But as I understand it, the rear one requires engine removal...and, the expense of paying someone to do that can't be justified for most owners of these aging trucks.
 




Dave98XLT

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Would an automotive stethoscope help to determine the situations severity?
 




Flash

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The conclusion I've reached is that odds are good that failure can be postponed by routinely replacing the tensioners; preferably before the dreaded "rattle" is heard.

Most of the time that would be correct.

Except in my case and a few others, the jack shaft chain tensioner went.
You can't easily replace that that as prophylactic maintenance.
 




Jimmy Hoffa

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Several experts I know have recommended using oil with zinc. One is a Porsche dealership mechanic certified to work on 918's. The other runs a 650 hp big block in his boat.

http://blog.hemmings.com/index.php/2012/10/18/tech-101-zinc-in-oil-and-its-effects-on-older-engines/

Quote," What was discovered through oil testing by several engine component manufacturers is that many where older engines experience a short period of time during engine start-up critical lubrication is insufficient between metal-to-metal lubrication points when using modern oils with reduced amounts of ZDDP/ZDTP."

There are downsides to using zinc, "These same enhancers unfortunately have their downside: The phosphorus in this compound creates carbon buildup in engine bores and valvetrains, and both compounds can also lead to the early demise of catalytic converters."

Still, the benefits seem to outweigh the downsides. Catalytic converters can be replaced or removed. Also, I would prefer to have carbon buildup verses a blown motor.
 




2000StreetRod

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pre-oiler

A pre-oiler avoids dry starts and the wear associated with them. It also pressurizes the cassette tensioners so the chains are taught when the engine starts. However, pre-oiling may not prevent cassette guide failure if it is due to fatigue or brittleness. In my opinion, the only part of the cassettes that should be plastic are the surfaces that contact the chain. Everything else should be metal for strength, rigidity and durability. That's pretty much what Ford did for the modular V8.
TimingChains.jpg

Also, the cassettes should be in the front so the engine doesn't have to be pulled to replace them. Unfortunately, Ford cheaped out on the tensioners in the SOHC V8 and made them out of composite material that fails. They used metal tensioners in the DOHC V8.
 




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