Timing chain slack range by using timing marks and distributor?

[rjrobin2002]

I decided to test my timing chain slack due to some mild engine running symptoms and less power than I thought was normal. So i rotated the engine to the 0* timing mark, pulled the distributor cap and turned the crank back and forth and could move the engine from 0*to 10* before the distributor rotor started moving. I feel sure that it is a severely worn timing chain, just wanted to know what a normal degree of movement is?

 

[.94 OR]

Ford mechanic told me to swap it when it reaches 7° of play. I think at 10° you can remove the chain first, then the gears.

 

[DirtDonk]

I have always used that same range. We used to discuss it quite a bit here, but haven't seen that come up in a long time.
There are some here that have run them at the high end of that and said it was fine, and some that said there new chains had that much. Can't say for sure as I don't remember checking a new chain on any of my engines. But it seems a bit loose to me, so that's when I go in to change one.

Or when doing any other work that needs the front cover taken off. Or, even just the water pump if an engine has more than 50k miles on it. Yeah, I know these chains can last 200k miles when treated right, but if I don't know the history of an engine, I'm changing it when I'm in there even if it's just down at the low end of the scale.

Assuming you do change yours out, maybe you can re-check the numbers with the new setup? That would be great.

Hope it goes well and does not turn into a typical Bronco-snowball!

Paul

 

[DirtDonk]

By the way... How many miles on this engine, and have you had it a long time?

Paul

 

[rjrobin2002]

Unknown engine mileage 1970 bronco 302. I will recheck when done.

 

[dave67fd]

Not sure if 70 or 71 was the year of the Nylon gear.. Chewed mine up years ago but as mentioned you have the cover off change it regardless.. Go with a quality double roller chain/gears as well. It's cheap money spent and quick and easy install.

 

[.94 OR]

I had an '86 F150 with 5.0 EFI that the nylon timing gear went good-bye and I blew the motor up. Surprising how much detonation had eroded the piston edges as well. Chains are cheap.

 

[DirtDonk]

Brother's '66 Corvette was had the nylon teeth (well, there weren't any by the time he got it) and when I pulled the cover during the rebuild, I was able to literally pull the chain forward without any effort at all, right off the gears and into the garbage.
I was shocked the thing had driven all the way from Wyoming and not spit it out at the worst possible moment.

Nylon teeth are great for lo-po engines that get regular maintenance and don't overheat, but otherwise suck!
Most/All the Police car engines and sometimes truck engines and sometimes hi-po engines (like in 'Vettes and hipo Mustangs) got steel gears as a general practice by the big factories. For a good reason I'm thinking.

Paul

 

[rjrobin2002]

Looks like 25% of the plastic teeth cover was gone causing the timing gear to not be round, found the chunks in the oil pan. Had about 10* timing slack and 7/8" lateral chain slack. New gears and chain on its way.

 

[barronj]

When I bought my bronco, the 289 was already gone and a 302 in its place. When I pulled the timing chain cover, there was so much slack in the chain that it had eaten 1/2 the oiling fin on the inside of the cover, from slapping against it for so long.

 

[rjrobin2002]

10-12 degree slack before, 1-2 degree slack going off timing mark movement before distributor rotor moved. Just a FYI for yall.

 

[rjrobin2002]

1-2 degree slack after replacement

 

[DirtDonk]

Great! Thanks for the follow up on this. Shows just what you were dealing with before. As if you didn't know after taking the cover off!

Good info. I'm sure you'll see it increase over time, and probably a measurable amount in just 10 or 20 thousand miles even, but not to the extent you had. Probably just a couple of degrees extra over that time.
And now you know for sure when you see an engine with 7 degrees of play it's time to start planning the next replacement.

Sounds like that engine was somewhat tired, or at least had plenty of miles on it. A little peace of mind knowing the new chain and gears are in there.

Paul