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Should I change my timing chain?

S

SuperRA

NAXJA Forum User
Location
Santa Clara, CA
How likely is it to stretch in 180k miles? I'm already down there, so to change it wouldn't mean much work, but if it should be fine, then I won't bother. Is it a waste of $13 to change it?
Thanks
 
Im around 180 myself and not worried about it, but if I had the cover off for some reason I'd change it. You should usually replace the gears as well with a new chain.
 
Worn Sprockets will wear the new chain, I'd replace the timing chain SET, not sure if your talking just the chain or the set.

Is the motor an interference fit? i.e. if the chain breaks will pistons contacts valves or not?

I know a guy who had a 5.2L V8 have the timing chain break at 230k miles. It was not an interference fit motor, so it just left him stranded, but the cost of a tow is more than a timing chain set.

If they stretch, the valve timing can be off, not enough to create problems, but maybe enough to loose a couple of HP, as well, make the pollution check a little harder to pass. If you've got it open, I'd spend the couple of bucks for a set and change it out.
 
Its not an interference motor, thankfully most American and pushrod motors aren't. What a brilliant idea that is, to not engineer enough piston to valve clearance on timing belt motors. I agree, unless you are taking the timing chain cover off, no real need. If you give the motor a complete overhaul, then I would also change the set.
 
Thanks for the replys. Well, since it is recomended to change them as a set, it will cost alot more than $13. So.. I'll check it for stretch first when I'm in there. I read also that some Renix's came with roller type chains, I'll cross my fingers, hope to have one!
 
bajacalal said:
Its not an interference motor, thankfully most American and pushrod motors aren't. What a brilliant idea that is, to not engineer enough piston to valve clearance on timing belt motors.
Click to expand...
I "THINK" the Chrysler 3.3L and 3.8L V6's are Interference Fit, not sure though.

Its a case of making compromises to meet the higher demands, want more power and efficiency out of a smaller motor, we'll need more compression and higher valve lift, you'll have to compromise on piston-valve clearance to get it. So if your timing belt snaps, the valves and pistons will contact.

You can make the same argument about using Aluminum Heads on Iron Blocks, the headgasket always eventually fails on that configuration; BUT, if you want a lighter weight motor that makes more power on low octane pump gas, an aluminum head gives you a real advantage.

Do any of the 4.0L I6 Motors have aluminum heads?
 
Well, thats one thing the AMC motors have going for them, Iron Heads, they must have a much better headgasket record than most other vehicles.

I'm a little surprised how much power the AMC motors make when I look at the specs and they do it without Aluminum Heads.
 
bajacalal said:
Its not an interference motor, thankfully most American and pushrod motors aren't.
Click to expand...

Carefull about that generalization - a lot of chevy 'v' engines are interference.
Its not a bad design with a Chain -- till some dumb-ss decides to spec plastic gears!
 
I had a 360 with double roller timing chain and gears. It didn't stretch so much as the rollers eventually wore down into the gears. The timing got sloppy enough at 250,000 to require a new set. When I overhauled the motor ar 350,000 the new set was good enough to keep. Last I heard it was still running at ~400,000.

Actually, I changed the water pump on the XJ soon after I got it, but I don't know if the cam drive is link or roller. With our experience of plastic gears in MOPARS, my Dad wanted to change the cam drive on the XJ at 130,000 when I bought it but was told it would never fail and not to bother. I'm waiting to see if that statement is true. Now at 218,000. That said: If I have reason to open the front of the motor I would replace the set. It's relatively cheap peace of mind.

Didn't Ford have a motor where the crank throws would interfer with the cam lobes if the timing was out? Seems I remember hearing that somewhere.
 
SuperRA said:
How likely is it to stretch in 180k miles? I'm already down there, so to change it wouldn't mean much work, but if it should be fine, then I won't bother. Is it a waste of $13 to change it?
Thanks
Click to expand...

I suggest you change the whole timing set since you're already there. The teeth on the sprockets slowly wear out so even if the chain isn't stretched beyond the recommended maximum 1/2" deflection, it's a good idea to replace the whole caboodle anyway. The Cloyes dual roller timing set costs only $110 so it's a worthwhile investment. I also strongly recommend that you also replace the crank pulley with a new unit. If you don't do that, you may regret it later.
Timing chains rarely snap (it's almost unheard of) but an overstretched chain can skip a few teeth on the sprockets (or come off altogether) and the result could be pistons hitting the valves. It's not a good idea to wait until that happens.
 
bajacalal said:
Its not an interference motor, thankfully most American and pushrod motors aren't.
Click to expand...
Cherokeelaredo said:
So if I snap the timing chain, there will not be any damage to the internals of the engine? Am I reading this right?
Click to expand...
According to Bajacalal it is NOT an interference fit motor. If the timing chain snaps, the motor will die, but the cam and piston turning independent of each other will NOT result in the pistons hitting the valves. I.E. with the valve at full extension and the piston at TDC they do not touch.

Not sure if Dr. Dyno is saying the motor is interference fit or not, I'd find out for sure, either thru a search or FSM, etc. Sorry, wish I knew for sure. www.allpar.com has a section for motors, including the AMC motors, since they are taken over by Mopar, so perhaps they have some info on it.
 
OK, I just checked it, and my chain ( a single roller type) has about 1/2" of deflection. Does that sound within spec? Or would you change it out? Also, is it wise to get a new harmonic balancer too?
Thanks
 
bajacalal said:
Its not an interference motor, thankfully most American and pushrod motors aren't. What a brilliant idea that is, to not engineer enough piston to valve clearance on timing belt motors.....
Click to expand...

*cough* Honda! *cough*
 
SuperRA said:
OK, I just checked it, and my chain ( a single roller type) has about 1/2" of deflection. Does that sound within spec? Or would you change it out? Also, is it wise to get a new harmonic balancer too?
Thanks
Click to expand...

A 1/2" of deflection is right at the limit. Get a completely new timing set AND harmonic balancer as I advised in my last post.
I'm not sure if the 4.0 is an interference motor or not but it's better to play safe and assume that it is.
 
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