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Permalink Reply by Ernest Christley on April 7, 2020 at 11:39am

Have you checked compression?  I had a low RPM issue that was cleared up by torquing the heads.

What's your mixture look like?  I've found that the Corvair will run from a low of 11.5 to a high of 19.0 on my mixture meter.  Neither extreme produced much in the way of power.

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Permalink Reply by Dale Walters on April 7, 2020 at 11:47am

Thanks for the reply Ernest.

I haven't checked compression yet (I need to take my compressor down to the hangar, but turning the prop didn't show any soft spots, and the EGT/CHT temps were all in the normal range (all reasonably similar to each other)

I also have a fuel air meter; it's showing between 11.7 and 12.0 (fluctuates a bit).  Think I should try leaning the engine to 13 or so and seeing what power I get? (I was always told that you should run full rich when taking off)

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Permalink Reply by Ernest Christley on April 7, 2020 at 11:57am

I've always seemed to get my best power at around 12.2.  These devices will vary a bit, so take that with a grain of salt.  But, below 12 does seem awful rich.  Have you inspected your plugs?  The top half of the tip should be clean, with a small amount of "smudge" on the lower half.

BTW, if the heads were not torqued to specs, you just might have nothing BUT soft spots.  :-)  My 3100 requires a definite tug at the compression spot on the rotation that it didn't have when the heads were looser.

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Permalink Reply by Dale Walters on April 7, 2020 at 7:34pm

Cylinder #5 has low compression (~ 58/80); the air is coming out of the oil overflow. I pulled the head, it looks like there's a burn mark on the gasket for cylinder #5.  

Unfortunately, Clarks is closed for COVID-19; is California Corvair a good substitute?

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Permalink Reply by Ernest Christley on April 8, 2020 at 8:39am

You said it was a 3300, didn't you?  VW jugs?  If so, you may be able to get the seals locally.

A burned gasket could be an indicator of a defective gasket, but also that the head was not torqued down completely.  Also, I don't understand how the air would be coming out of the oil overflow.  Generally, it would have to be a problem with the rings for that to happen.  You might want to pull that #5 jug and check the rings. 

I'm willing to venture a guess that you had some detonation in that cylinder as the root cause for your problems.  If that is the case, make sure that your head doesn't have any sharp knicks or gouges, and pay special attention to that CHT once you get it back together.

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Permalink Reply by Dale Walters on April 8, 2020 at 9:59am

I mistyped; it's a 3000 (3L), not a 3300.

I see what you mean about the rings.  Looking back thru the pictures I took of my temps (I don't trust my memory), I see the CHT was pretty low for cyl 5, but the EGT was higher.  

If I pull the jug off (easy, now that the head is off), what would be the indication that my rings are bad?

And do you think I can get the rings at Clarks, or is this something I should get from William?

Thanks, I really do appreciate all of the help... I'm fairly good mechanically, but don't have a lot of experience this deep into the engine

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Permalink Reply by Ernest Christley on April 8, 2020 at 11:08am

For me, the indication was when pieces of the rings fell out.  Seriously, if there is a problem, it will be painfully obvious.  I mean, painful to the point of you wanting to cry.  The rings should each be in one piece and "floating" around the piston. 

Whether you can get the rings from Clarks all depends on which pistons you have.  Clarks has all the rings for stock TRW pistons.  However, if you had detonation AND you have TRW pistons, your problems are probably worse.  The oil drain hole in the groove for the scraper ring in the TRW piston is a long slot.  This makes for a week point on the piston, and detonation will cause the piston side to collapse onto the rings and break them.  The piston is scrap at that point.  Replacing the piston requires removing the entire thing from the crank and pressing out the piston rod.  I wish to God that I hadn't learned all this first hand.

If you don't have stock pistons, you're going to have to go back to where you got the engine and ask what to replace them with.  I accidentally set my timing too high, and burned a piston.  It literally melted a channel down the side of the piston.  This was different episode than the one discussed above.  Yeah, I've been hell on some Corvair engines.  I don't think this would be your problem, as then you would have zero compression, but that one required replacement of the piston, rings, and cylinders.

Pull the jug.  That is the only way to know what the real damage is.

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Permalink Reply by Dale Walters on April 8, 2020 at 6:55pm

So I pulled the jug; the piston looks to be in pretty good shape.  Ditto the rings; the oil ring is perfect, the two compression rings are also looking good

The only concern I see is there seems to be quite a bit of buildup between the two rings (hopefully this pic comes through okay)

The jug doesn't have any issues; in fact it looks to have a pretty good cross hatch still.

So I'm thinking if I clean up the carbon buildup, it should be okay.  Thoughts?

(pic showing carbon buildup between rings)

Bottom of piston in question showing part #; I haven't yet found this number online)

(underside of piston... no buildup)

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Permalink Reply by Ernest Christley on April 9, 2020 at 8:09am

I'm not an expert on carbon buildup, just on blowing up perfectly good engines, but this doesn't seem to be much of a buildup at all.  Looks perfect to me.

Still, it leaves the question open as to how the case is getting pressurized.

Permalink Reply by Dale Walters on June 12, 2020 at 6:10pm

Just to close the loop on this thread; the issue turned out to be the distributor.  It was advancing 10 degrees greater than what it was supposed to (30 degrees instead of 20); so the total advance was closer to 38 degrees.  A new distributor fixed the issue

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Permalink Reply by JEFF COCHRAN on June 13, 2020 at 1:00pm

Dale,

I don’t understand.  You said your timing was set to 28 degrees and verified with a timing light?  Wouldn’t a timing light ignore how much advance the distributor has and tell you when actual firing is taking place in reference to TDC.

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Permalink Reply by Vincent Maggiore on June 13, 2020 at 3:11pm

Did you set the timing at full static rpm? See William W MOP manual, if you haven't got it yet it's worth the investment! Timing should be 28 degrees at full static, also check out his YouTube video on setting the Timing. 

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