This March I plan on doing lifters and the timing chain on my 603.

[Hatterasguy]

I am not sure when spring break falls this year but I think it is either the last week or second to last in March. This would be a good time for me to do some internal work that I have been wanting to do.
I plan on doing:
All 12 lifters
Timing chain
Upper guide

Now I was thinking about pulling the head and replacing the head gasket. It has an annoying oil leak by the belt tensioner. How much more work would it be to pull the head?
What else should I replace while I am in their? I was thinking about doing cam bearings and the timing chain tensioner. Also what about valve seals? How hard are those to do? I don't plan on touching the head or sending it out, it is a 14 head but I have no problems so far. If it cracks it cracks but a new head gasket would be nice. The car runs fine so I am not going to touch the valves.

[Brian Carlton]

You have not exhausted your possibilites for quieting the lifters.

AFAIK, you have not measured the chain stretch to determine if you must replace the chain.

You certainly know that digging into these engines is not without an element of risk.

There is a very good statement from a very knowledgeable and dear member of this forum, which I'm sure you have heard before, but, I repeat it:

If it ain't broke, don't fix it.

[Hatterasguy]

Well I am pretty sure my timing chain is pretty stretched out. 244k without any oil change history? It is simple to do anyway. As to the lifters well I am tired of them, I will try a little MM before I drop the current change but I don't think that will matter. I am tired of hearing the lifters and feeling the engine vibrate when they act up.

I am just not sure whether it is worth doing the head gasket or not. That is a can of worms on a 603.

[Jim H]

OK, now I'm curious.

How far can a timing chain wear before the power loss and smoke insist that I finally replace the chain?

Will it wear to the point that it breaks, or jumps a tooth with equally disastrous results?

252k+, original chain. Runs good, lifters don't make noise, starts without using the block heater down to single-digit temps.

Best Regards,
Jim

[Brian Carlton]

Originally Posted by Jim H

How far can a timing chain wear before the power loss and smoke insist that I finally replace the chain?

Will it wear to the point that it breaks, or jumps a tooth with equally disastrous results?

There are differences of opinion on this with regard to the 603. IIRC you can run the engine just fine with 5-6 degrees of stretch based upon results from Dave.

However, my indy strongly discourages any use of a chain that has stretched more than 2 degrees due to risk of failure.

I think we need more data to show if a stretched chain is more prone to failure or not.

The chain will not jump any teeth when it "stretches" because the tensioner keeps the chain taut.