5.9 mag tear down with pics...no tensioner?

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mbaird

mbaird

mbaird
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I tore down the bottom end of a 5.9 magnum I have had for a while. There was an old style cam plate instead of a tensioner... I thought magnums had tensioners ?
It is supposed to be a low mile 98 motor. The bores look like a low mile motor . Not sure about bearings though... give me your thoughts.
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Well, you were due for bearings for sure! No tensioner, no problem. Buy one or a new chain or both. I bet your crank is perfect.
 
I already have a new tensioner . I was just surprised to find it didn't have one. If it was a 88 block it would be different.
 
They didn't come with a tensioner. I would only consider one on a stock type timing chain and I never use them on any build.
 
Which motors did come with tensioners ?
I understood they came from the factory on magnums.
 
They were installed in dealerships on the 3.9 and others to keep the chains from cutting the timing cover to pieces.
 
Having a tensioner is free horsepower... keeps the timing accurate.

Smokey made a plexiglass timing cover for a sbc then took a slow motion film of the timing chain...it looked like a snake trying to escape at 6k.
 
The plastic in the oil pan up is a looser every time. I have run them and gave up,everyone can believe what they want about some magic HP they might gain. lol
 
Krooser said:
Having a tensioner is free horsepower... keeps the timing accurate.

Smokey made a plexiglass timing cover for a sbc then took a slow motion film of the timing chain...it looked like a snake trying to escape at 6k.
Click to expand...
That would be something to watch:)
 
I’ve had 3 5.9s apart. Never a tensioner. Never replaced with gear with one.
I’d like to see that too...but I’m not crazy about snakes.
 
mbaird said:
Good info....
Can you tell me what year this block is ?
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The year will be cast into the block. Look for more numbers. I think it was on the passenger side, if I remember correctly.
How much ridge is at the top of the bores; does it catch your fingernail pretty good, or not much at all? Your block should be useable no problem. Most of them are.
Also, could you post a photo of the valley area, and one of the deck surface where the head bolts on?
It looks like this one did not have very well maintained oil changes, and I often find the camshaft bearings falling apart on a Magnum block with poor oil changes. I would suggest removing the cam and checking. If they are in tact not showing excessive wear, leave them alone.
 
I've read that only the 3.9 V6 magnum engines had the tensioners. I looked at a few in the salvage yards and it seems to be true. I put one in my 5.9 with a mopar performance double roller timing chain. I doubt it was necessary but I'll tear it down next winter and see how it all looks.
 
No ridge in bore at all... still has nice hatch marks . Valley is really clean as is most of the block exterior.

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Mopar Tech said:
The plastic in the oil pan up is a looser every time. I have run them and gave up,everyone can believe what they want about some magic HP they might gain. lol
Click to expand...

Yep, the tensioner wears and the bits go into the oil and through the engine worst case but more so partially block the smaller round pick up.
 
I paid 100$ .. the guy wanted 650 on CL but I told him I would pass because it was a pig in a poke and gave him my number.
He called me 6 months later .

As for the guide wearing. Wouldn't any shavings be picked up by the oil filter ?
And if it takes as little as 20k miles to eat it away the particles would have to be very minute I would think.
 
They were for the 3.9L originally but you may find them on any Magnum that had a timing chain done. I use tensioners on all the small block I build. Never had an issue with them coming apart, but admittedly most of the engines I've built have not reached 30-40K miles since the rebuild. I do have some over 20K but no reports of issues.
 
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