390 timing chains...when to replace...how to check

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Jul 10, 1999 | 11:59 AM

steveh

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390 timing chains...when to replace...how to check

Folks

I have a 70 f350, 390 2 barrel motor home with about 70K miles on it (all highway). I will be replacing the water pump shortly and got thinking what about replacing the timing chain at the same time. So typically when do the chains need replacing? Can it be checked without removing the cover by turning the crank back and forth a measuring the free play by watching the distributor? How may degrees of crank turn is ok? If I have to remove the cover to check the chain I might as well go a head and just replace it, but why replace it if it's not needed.

Thanks in advance
Steve

Jul 10, 1999 | 03:38 PM

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390 timing chains...when to replace...how to check

One method I know of is this.
Put a timing light on it, if the mark seems to be moving around quite a bit at a constant idle the chain and gears probably need to be replaced.

Jul 10, 1999 | 09:57 PM

Mulletwagon

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390 timing chains...when to replace...how to check

Timing chain and gears on v-8s should always be changed by 100,000 miles. Dropping one while on the road is really ugly - bent valves; pull heads; big $$$$. If you are changing the water pump anyway, all the a/c, power stearing pump, alternator stuff is pulled anyway. Definitly the best time to go the whole route. Also change the fuel pump since the old one will be off anyway. Chains are pretty well stretched by 50,000 anyway and result in delayed valve timing. When I change chains now I get the double rollers with changeable timing. I use the 4 degrees advanced setting on the crank gear. That is supposed to give a little more bottom end. I can't tell the difference but it does compensate for eventual wear. If you don't change the chain now it WILL haunt you until you do. It's dark, raining, 100 miles from civilization .........

Jul 11, 1999 | 07:14 AM

jowilker

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390 timing chains...when to replace...how to check

Steve, look at it this way, the engine is nearly 30 years old, and only has 70k miles. Thats a little over 2k per year, it's all highway, and pre smog control. I think I'd just put the pump on and take a trip. If you start worring tooooo much you could get run over going to the mail box.

By the time you get a 100k on it you might be ready for one of those $250,000.00 rides.

Have a nice vacation,

John

Jul 11, 1999 | 01:07 PM

Like M. Fords

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From: LAT 46.55501° & LON -122

390 timing chains...when to replace...how to check

I would change it. A good roller timing chain set will only cost about $40-$70 depending on brand; and just about anything is better than the factory nylon top sprocket used on the cam. The factory one in my '76 Bronco 302 went out at about 150,000 miles. Most of the nylon teeth were stripped off the top sprocket. Luckily the chain skipped just as I was leaving the driveway. I threw in a used set I had lying around and I was back in business. This one used a similar chain, but had a cast iron top sprocket. Supposedly not as quiet as the nylon, but I could not tell the difference.

Change the front seal while you are at it and put a dab of silicone at the joints where the old section of oil pan gasket meets the new section on the front cover. When you put your front cover back on, make sure that it is perfectly centered with the crank, otherwise your new seal will leak. You can get a special tool for this, however most people just center it up with their harmonic balancer.

Jul 12, 1999 | 09:14 AM

Jeff

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390 timing chains...when to replace...how to check

Steve,
Until two months ago I would've always suggested that you leave the chain alone. I'll share a recent experience with you and let you decide.

I'm an autobody guy and recently bought a really nice, garaged 1970 Galaxie which had been sideswiped. It was a S. California car with all records and 101K miles. It ran beautifully.

Two weeks after buying it the timing chain "Slipped" a few teeth. It seems the nylon covering over the metal gears had disintegrated over the years. I found pieces inside the chain cover. The chain was still intact but had stretched enough to finally slip while only gently cruising down a back road. After replacing and a few more disassemblies to make sure everything was set properly I discovered I have no compression in three cylinders. Now I have to remove the heads and have them repaired. At least the engine compartment will look as new as the outside since I'm refinishing every piece removed in the process.

If you have nylon type gears, I would go a step further and replace the chain while all of the accessories are off.

Jul 12, 1999 | 11:12 AM

Carl..cheap cheap insurance...

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390 timing chains...when to replace...how to check

Yeah, I would change the chain..peace of mind and cheap insurance to know that it won'tskip or fail on the road. A quick test is to rotate engine to # 1 tdc, then very slowly, rock the crank pully by hand and view the rotor after removing the distributor cap.
Youshould be able to see the slop and play in TC by the rotor moving when the crank pully is moved back and forth...
My advice, change it and have peace of mind!!!!

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Jul 13, 1999 | 03:13 PM

greg_2

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390 timing chains...when to replace...how to check

I just change one last weekend. 1979 351 with 103,000 mi. I,m origional owner. Thought I better check it and glad I did. It was very loose and close to jumping.

Jul 14, 1999 | 07:32 AM

#10

Steve Heidt

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390 timing chains...when to replace...how to check

Thanks for all the comments on whether to change the timing chain or not.

The verdict is in. I changed the timing chain and gears when I did the water pump and was glad that I did so. The timing chain was worn past it’s recommend limits. The top gear was fiber and had about 8 cracks in it (although non of the pieces were missing). I replaced both gears (now steel) and the chain

When I had everything back together I set the timing back to 6 degrees. It started out at 24 degrees which gives you an idea of how worn the chain was.

I have not noticed a change in performance yet, but hope I will.

Thanks again
Steve

Jul 14, 1999 | 11:53 AM

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390 timing chains...when to replace...how to check

Jul 28, 2004 | 06:26 PM

#12

baitmaster

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From: nevada

I always err on the side of caution, when replacing worn parts. Especially when they are labor intensive and you've already done half the work when changing some other worn part. Like if you have a blown rad hose: while you have the fluid drained, change both hoses, and the heater hoses. If one blew, the others aren't far behind.