CO2 test to check valve guides on a 3.2?

[notfarnow]

I am arranging for a PPI on a low-mile (64k) 86 Carrera cab for my father. The owner, who seems like a very forthcoming and straightforward fellah, says there is no smoke at startup or otherwise. He hasn't put enough miles on it (3-4K in 2 yrs) to notice any oil consumption.

Just the same, I'd like to be cautious. I've read up a fair bit, and according to some of Wayne's and John Walker's replies in other threads, compression or leakdown tests won't show valve guide wear unless they are really far gone... to the point where the valves aren't seating.

The other method mentioned was checking the valves for play with the springs compressed. Again, one would think there would be noticeable smoke before the play was significant.

On another forum, someone mentioned checking the CO2 at the tailpipe:

"Another way to check for bad guides is to test the CO2 at tailpipe. The meter doesnt lie and can detect smoke that's hard to see."

Thoughts?

[john walker's workshop]

at 64K, it's probably ok. i've done a couple cars over the years that did have worn guides at low mileage, but it's the exception. no smoke at startup? must not be a 911. a CO test won't tell you anything except rich or lean. hydrocarbons are more of an indicator of something wrong, but many things cause incomplete burning. if the leakdown is good and the HC is low, it's probably fine. worn guides cause the valve to wobble around and beat up the seat. that usually will show up as higher than normal leakdown.

[notfarnow]

Well, I can't do much better than having JW reply to my post!

I guess that's the potential downside of a low-mile car. It's not a problem NOW, but it's hard to just "keep your fingers crossed". Sometimes it's easier to have confidence in a higher mile car with no issues, than a low-mile car just getting to the point where these issues can surface.