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Timing Chain / Casette Question


SolidSnake84

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Hey friends, i apologize in advance if this question has been asked a million times, but Im seeking help about tackling this repair on my wife's 1998 Ford Explorer that has the 4.0 SOHC.

I want the experts' honest opinion here on if replacing the casettes / tensioners, and chains (if necessary), are absolutely necessary, as I was browsing another ford specific forum and one of the members there said that he's been around hundreds of explorers that have the timing chain rattle, and he has yet to see one that has resulted in either the chain breaking, or the engine jumping time. Some of them were even higher mileage, IIRC.

Let me give you a little background on the vehicle. We are the second owners (mother in law bought it brand new in 1999), and the vehicle has been babied and well cared for. All oil changes on time and all required maintenance. I switched to fully synthetic Valvoline at around 153,000 miles which quieted the engine greatly. I first noticed the timing chain rattle at around 160,000 miles. I have isolated the sound to be coming from the Front Chains / cassettes, and not the rear, by using a mechanic's stethoscope as well as hearing the noise much clearer after taking off the oil filler cap.

At first, the noise was very loud on cold startup, but would disappear completely after the engine would warm up. I replaced both tensioners with the revised OEM Ford ones, and the noise was completley gone for about the last 10,000 miles. Now, at around 170K, the noise has returned on startup, disappears when warmed up, but if you rev the engine above 3,000 RPMs, you can hear the noise clearly. My question is, will the engine keep chugging along like this? or am I at the beginning of the end? The motor is stone quiet except for the timing chain noise. It does not knock, or make any kind of strange noises. The engine uses no oil between changes, it doesn't even leak.

My step father who is a diesel truck mechanic has offered to help me do this job to replace the front casettes. We are going to evaluate the condition of the chains, and if they look bad or real sloppy from being stretched, we will rent the tool to lock the cam into place and then do the chain as well. But is this really necessary? Will the engines blow up from this problem or is the worst to happen the rattly chain? Have any of YOU encountered an engine that has jumped time, or god forbid broken the chain? I just want to be sure that what we are going to tie our garage up with over the next month is really 100% necessary. We love the truck and want to keep it!
 


RonD

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Don't bother doing just the front cassettes.
It is an all or nothing thing.

4.0l SOHC is for sure an interference engine, valves and pistons can touch if valve timing changes too much, so that is the down side, replacing the bent valves, pistons and rods would probably be OK but that is a "lets look and see" thing

What happened with the old design and materials is that the tensioners would start to let the chain bang around a bit and that would wear down the guides, eventually breaking them apart.
The cams are not pinned to all the chain gears, i.e. no guide pin or woodruff key to hold gear and cam at the right place, the timing is maintained just by the bolt holding the gear to the cam............
So if a piece of broken guide happens to get in the chain..........

If a Cam slips you would notice a loss of power and if you do a compression test one bank would be around 100psi and the other above 150psi, but no valve damage because it just slipped.
And in general if cam stopped it would usually go to neutral position so no valve would be fully open so you can get lucky.

The newer design and materials has been bullet proof since 2005 model year so once done engine will not have the problem again.

You do need to pull the engine out to do all the work, the rear chain setup must be done.

So you can just leave it alone and run it until you can't, some have said synthetic oil helps.
While you could bend the valves it is not 100% that that would happen in the event of a failure, but it can happen

Or pull the engine and redo all the chains.
 
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