burning oil and catalytic converter

[themess]

My '95 Mazda turned over a quarter million miles last month. I need to license it in NM, which means that I need to pass an emissions test and replace the catalytic converter, the one that Mazda stuck on it 19 years ago.

When I start it cold, I get a puff of smoke. The puffs are gradually getting larger. I assume that the valve guides are bad and getting worse. No noticeable oil consumption between changes, just the smoke on cold start.

Q1: Will this level of oil burning hurt the new catalytic converter?

Q2: What' invovled in changing valve guide seals?

[Steve]

A1: I would think that if your trips are long enough to get the cat up to full operating temp and keep it there for a while, that little puff of smoke is not going to hurt it (much). What reason has been given for the 'need' to replace the cat now? Just age, or have you had a preliminary test done?

A2: Usually, that involves pulling the head. However, some have had success by stuffing some thin rope into the spark plug hole while the piston is down, then bringing it up slowly to hold the valves in place while you release the keepers on the springs. It works quite well on some engines, not so well on others.

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[themess]

A1: I would think that if your trips are long enough to get the cat up to full operating temp and keep it there for a while, that little puff of smoke is not going to hurt it (much). What reason has been given for the 'need' to replace the cat now? Just age, or have you had a preliminary test done?

A2: Usually, that involves pulling the head. However, some have had success by stuffing some thin rope into the spark plug hole while the piston is down, then bringing it up slowly to hold the valves in place while you release the keepers on the springs. It works quite well on some engines, not so well on others.

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1) The check enginer light has been on for about 20K miles, code is catalytic converter. Exhaust system is beginning to get noisy.

2) Inventive method. I should probably get an estimate on the cost. My fingers are too weak for head removal and reinstallation.

Thanks,

[Steve]

Here are a few examples:

https://www.youtube.com/watch?v=zFmC66YU6zI

https://www.youtube.com/watch?v=fZ5nZhDdAMs

https://www.youtube.com/watch?v=HtC7huYT_H8

Plenty more, but you should get the idea from these.

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[themess]

Neat! My engine is very similar to the Miata engine. I might try it, after I get a few other projects out of the way. Thanks.

[bwringer]

As long as it gets up to temp regularly, the catalytic converter will put up with quite a bit of oil burning -- I've seen as much as a quart every 500 miles with no issues. Eventually, there's a point where it's too much or you get enough buildup to cause issues, of course.

A puff of smoke is nothing much to worry about if oil consumption isn't too high.

Yes, you can replace valve guide seals with the rope trick or an air hold. The rope is probably more reliable if you don't do this often.

[themess]

There is only a puff at start up after sitting overnight. Oil consumption is very low. The drive to work in 9.8 miles, mostly at 45 mph, so there is plenty of time to warm up twice per day. I'm almost convinvced to try the rope method. Access is excellent at the top, and the engine is in several ways identical to early Miata engines.