68 Z/28 Engine Smoking - Any Ideas? - Page 3

**njsteve** · #21 10-23-2009, 05:36 AM

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Brake fluid?

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Forgot about that rare problem: Once in a great while you'll find a master cylinder with a bad rear seal, combined with a vacuum brake booster with an equally bad front seal. The result is the large vacuum hose running from the booster to the intake sucks the brake fluid residue into the intake and burns it. Saw that happen once in 30 years but it was a wild one to diagnose!

**SuperNovaSS** · #22 10-23-2009, 05:50 AM

Come on..........Are you being serious Steve?

JoeG · #23 10-23-2009, 06:12 AM

Global Warming.......

**njsteve** · #24 10-23-2009, 03:58 PM

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Come on..........Are you being serious Steve?

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Absolutely. One of those totally freaky, million-to-one things that will (hopefully) never happen to anyone else in the universe ever again. Discovered it by accident when they pulled the vacuum hose off the engine and noticed the paint curling around the fitting on the intake - you know how brake fluid attacks paint - that was the first clue.

68 RS Z/28 · #25 10-26-2009, 02:45 AM

Thanks to all who have chimed in with an idea either here or via e-mail. I really do appreciate all the suggestions and have been trying to work my way through some of the possibilities. Today I found some time to do a compression test. Cylinders 1-7 pumped up nicely and read between 155 and 160 pounds. When I went to 8 however.....problems. The reading varied between 30 and 90 pounds. I don't have a leak down tester, but I did order one and it will be in on Tues or Wed so I'll see what that tells me, but there is something definately wrong with #8. I'm not sure its related, but for fun I pulled the valve covers and found that the rocker stud on the intake valve had snapped. The rocker was still on what was left of the stud, but the upper portion was just laying there. I was pretty surprised to see this since the studs were replaced when the engine was done. Also, there were NO funny noises - the car sounded good. Just prior to doing the compression test I had noticed that while all the other plugs looked more or less normal, the plug on 8 looked like it had never been fired - which I suppose makes sense if it wasn't getting the fuel/air mix. I did confirm that it has spark. So all in all, I think I've found a major problem, but I don't think its the reason for the low compression - with the valve stud snapped the valve should be closed and compression wouldn't be affected. I also don't see how this would affect the smoking issue. Anyway, it will be Wed at the earliest before I get the leak down results and then obviously the heads come off. Any comments/suggestions would continue to be appreciated.

**SuperNovaSS** · #26 10-26-2009, 02:51 AM

The snapped stud definitely accounts for the low compression.

Jason

Plowman · #27 10-26-2009, 03:13 AM

If number 8 cylinder has a broken intake stud, it would not let any air in to compress so compression should be zero. If it was tapping the valve at times that would tell you why you had what you have. Also, check for a broken valve spring.

68 RS Z/28 · #28 10-29-2009, 06:36 AM

I guess the broken stud does explain the low compression - I hadn't thought of it that way, but of course if nothing is getting in then there is nothing to compress so that does make sense. With the broken stud I didn't want to run the engine again and so wasn't able to warm the engine, but I did do a leak down test anyway this evening before starting to really pull things apart. The results were between 9 and 13% on all cylinders. I'm assuming that on a warm engine these numbers might have been lower. No air was detected leaking out from problem areas like adjacent spark plug hole, bubbles in the coolant, etc. Do these numbers sound okay? I then started to pull stuff off the engine and when removing the right exhaust manifold I found a thin line of oil that had been leaking from the back of the valve cover and it looks like some of it had penetrated into the exhaust manifold near the number 8 cylinder. I think this is the cause of the ocassional smoking given that the leak down results didn't show any big problems. So, I think that once I get the studs replaced and put it all back together the problem should be solved. If anyone has any suggestions on other items to check while its apart, I'd be glad to listen. Thanks for the advice.

**Salvatore** · #29 10-29-2009, 08:06 AM

WOW, I think most of us here figured you got past any oil leaks or broken engine parts. So the rocker arm was laying in the head with a broken stud? Didn't miss a little?

Plowman · #30 10-29-2009, 09:28 AM

30% is bad rings,so you sound good. Paul

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