Lots o' blow-by

[ghaegele]

2 years after a rebuild I finally rechecked the valve clearances this Spring because I had noticed a bit of blow-by developing at the end of last season. They were all at spec. Commissioned the boat today and took her around to our harbor--a 1 hour trip, and there was a ton of blow-by. A quick search of past forums suggests two causes--stuck rings and poor timing. Since the rings were replaced 2 years ago it's unlikely stuck but could be a broken ring. But, considering that I had the distributor shaft out this spring to fix a striped distributor cap thread in the housing I'm going to put my money on that. But look at how much blow-by there is. Can this really be from poor timing? The engine started right up and seemed to run fine. In retrospect, possibly not going to full RMP, but I wasn't pushing it. [YOUTUBE]http://youtu.be/qr6cvkgQvic[/YOUTUBE]

[Marian Claire]

All I can say is that when I had a broken ring the blow-by was much less than the video shows. Did you hear any strange/crunching/metal to metal noises? Dan S/V Marian Claire

[ndutton]

Time for a compression test I think . . .

Who did the rebuild?

[Sony2000]

I timed my engine using the separation of the points method, as well as a strobe light. But when I used the dwell angle meter it requested .010" more in opening. It runs better.

[Mo]

There's an active thread "first 25 hours". Dave Neptune put a post in that one that might help you out considerably. (I'd really love how to link those posts but I could spend an hour on it and get nowhere).

[ghaegele]

No crunching noises, pops, hiccups or coughs. After removing and replacing the distributor housing, it started while the boat was still on land fine (after a bit of typical cranking after replacing the fuel filter). It started yesterday just fine and ran fine. As I said, perhaps, with hindsight, I wasn't getting much over 2,000 RPM, but I wasn't trying. After about 15-20 minutes I noticed wisps of smoke catching the sun as it emerged from the cabin, and went down to investigate.

Toward the end of last year there was definitely some smoke in the cabin from time to time leading me to run the blower. (And mind you, I already have the Indigo PCV installation.) That is what prodded me to recheck the valve clearances. (I don't think there is any possible relationship between the two. It was just a miserable job I had been avoiding and I wanted to take it out of the calculations.)

Compression: When checking the valves I did a finger test and all 4 cylinders had good compression. I'm going to try to get a gauge on it today and I will certainly report back. I was hoping to get some reassuring words like "oh, when my timing was off I had at least as much smoke." Truth is, it seems like a lot of smoke even for a broken ring!

[Marian Claire]

"Truth is, it seems like a lot of smoke even for a broken ring!"
Could not agree more. Just for comparison. When I got back to NC and did a compression check #4 cylinder read about 45 psi. #4 is where I found the broken rings. FWIW. http://www.moyermarine.com//forums/s...ead.php?t=2238 Dan S/V Marian Claire

[ghaegele]

Can anybody explain how the timing being off can translate into a lot of blow-by? I'm having trouble conceptualizing the relationship.

[edwardc]

When the timing is excessively advanced, the fuel-air mixture in the cylinder is ignited while the piston is still on its way up (hence "before top-dead-center"). The combination of the rapidly expanding combustion gasses and the continuing compression by the rising piston causes the pressures in the cylinder to rise to much higher levels than normal. This puts extra strain on the bearings, and causes any leaky rings (stuck or broken) to pass even more blow-by gases into the crankcase.

[Dave Neptune]

ghaegel, take a good look at the oil!!! If you do not hear grinding metal on metal type noise, run her for a few minutes and every few seconds pull the dip stick and wipe off the oil with a clean magnet. Do this a few times and check the magnet for bits of metal that stay stirred up in the oil. If you find metal flakes chips or "fine filings" something broke. STOP
If you don't find metal on the magnet the rings are probably stuck, NOT UNCOMMON to happen after a lay up It does not take much moisture to stick rings if they are a bit snug like fresh ones. These can be shook loose often with a bit of "top oil" in the fuel and some soaking in oil.
I would also knock the timing back a tic. What gap do the points require for the proper dwell, sounds like your cam may be worn out, a common issue in these beasties.

Dave Neptune

[ndutton]

Until this issue is resolved expect your PCV valve to be sludged up to the point of not functioning properly. You might want to carry some spares and change them frequently to get the maximum intended benefit.

In fact, that may be the case now. Watching the video there's an awful lot of positive pressure in the crankcase to push out that volume of smoke. If the PCV valve is open at the same time imparting manifold vacuum to the crankcase it's an alarming amount of residual positive pressure.

[Mo]

Dave,....not bad. When I was young I hung around a garage...and saw that trick....with all due respect, you are not the dullest knife in the drawer.

Edit: re: magnetizing the dip stick....last saw that done in the mid 70,s

[ghaegele]

We're okay. It does seem that all of that blow-by was caused by the timing. I'm amazed, but when Ed explained the pre-TDC detonation it made a lot of sense. The piston still compressing while the gas mixture is igniting must create a tremendous amount of pressure that has to go somewhere. The weakest link is the rings, equaling blow-by.

Anyway, first thing I did was a compression test. 94, 82, 85 and 85. Then started the engine and warmed her up, dropped from the mooring and took a run at 2000 RPM. Then, loosened the hold down on the distributor and turned it. First turn was counter-clockwise which almost stalled the engine. I then turned it the other way and heard the RPMs immediately increase. Though the engine wasn't yet fully warm, it was obvious it needed the spark advanced.

Since we were headed toward the dock, an interesting thing occurred when we got to the dock--the engine kept stalling at low RMPs after adjusting the timing. Looks like the timing was so retarded the idle mixture needed to be very rich to burn. I then had to turn the idle mix way lean to get it to run. And then needed to lower the idle screw too. It will take a bit of running to know for sure, but I'm confident that the timing caused all of that blow-by.

Thanks to the entire knowledge-base on this forum. Without it I couldn't have learned why that smoke was there and would have been convinced it was a major problem. You folks are all great!