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mc79
11-16-2007, 02:47 PM
I have a 79 MC with 302 Pleasurecraft; The Holley 4 barrel carb is sucking oil through the Oil cap on the valve cover up into the spark arrester. It puddles up in the spark arrester and runs down the back of the engine into the bilge. I suspect it is pulling oil through the PVC valve (located on the right side valve cover) into the carb as well. I mop up about 1/4 cup per day of operation. Dirty spark arrester (insufficient air flow) or oil circulation problems? Suggestions for resolving this are greatly appreciated.

TMCNo1
11-16-2007, 04:33 PM
Could be blow by from the rings if the engine has a lot of hours and the crankcase is getting pressureized and the carb vacuum in the flame arrester is sucking fumes from the crankcase as it is suppose to, but it's drawing up some oil too! Just my opinion.

Hunterb
11-16-2007, 05:12 PM
How does oil get from the oil cap to the carburator? I'm not sure where the PCV hose enters the carb on a PCM motor but it's usually below the throttle plates so I'm also not sure how oil could get from there up to the spark arrestor. It would be going against the vacuum. Does your PCV hose connect to the spark arrestor?

This seems unusual. Hopefully someone with more motor smarts than me comes along.

Good luck

Bruce

TMCNo1
11-16-2007, 05:23 PM
If the PCV Valve is not working and or is clogged, then the fumes and gasses have to escape somehow and the vent line from the oil filler neck to the flame arrester is then the only path for the gases and fumes because the carb is drawing the pressurized gasses out and into the engine to consume.

Hunterb
11-16-2007, 09:30 PM
Aha, I see. I don't have any kind of vent hose coming from my filler cap. Should I?

Bruce

TMCNo1
11-16-2007, 10:34 PM
Now I see, 302 PCM! Indmar has a vent line from the filler cap tube on the port valve cover to the flame arrester on the front of the flame arrester, then a PCV Valve from the starboard valve cover to the spacer plate under the carb. at the rear of the carb. Does the PCM have a seperate PCV Valve line and a vent line.
On the Indmar the big vent tube on the front draws fresh clean air from inside the flame arrester into the engine, because the PCV Valve is in the valve cover with the line that is used to vacuum the gasses into the base of the carb. on the other side from the vacuum created by the engine running, creating a cycle that ventilates the crankcase and valve covers.

Hunterb
11-17-2007, 03:53 PM
It's becoming clearer, however, I still don't have any kind of vent hose on the filler cap. My engine came with a chrome, dome shaped, cap that has a wire mesh type filter in it ( I think). I thought what was happening was that the air was drawn in through the cap then it circulated through the crank-case, up through the PCV valve and into the engine via the hose to the carb base plate. I assume that's what's happening anyway. The difference is that the air drawn into the cap is not filtered by the spark arrestor, but then it's not really filtered as it passes through there anyway. Given that, I will not start searching for the missing vent hose.

Always good to figure these things out.

Bruce

TMCNo1
11-17-2007, 04:01 PM
It's becoming clearer, however, I still don't have any kind of vent hose on the filler cap. My engine came with a chrome, dome shaped, cap that has a wire mesh type filter in it ( I think). I thought what was happening was that the air was drawn in through the cap then it circulated through the crank-case, up through the PCV valve and into the engine via the hose to the carb base plate. I assume that's what's happening anyway. The difference is that the air drawn into the cap is not filtered by the spark arrestor, but then it's not really filtered as it passes through there anyway. Given that, I will not start searching for the missing vent hose.

Always good to figure these things out.

Bruce


Yea, the vacuum from the carb thru the PCV valve is drawing outside air into the filtered cap and throughout the valve covers, crankcase, oil passages, etc into the carb to be burned by the engine, including the generated gasses. The Indmar vent line from the flame arrester is just using filtered air(?) from inside the flame arrester and into the engine thru the oil filler stack under the filler cap. The PCM air is probably filetred better, but who knows but PCM and Indmar.

mc79
11-21-2007, 09:31 AM
Thanks for the explanations. I'll check these areas over the weekend, but let's see if I have this straight. No clear air passes through the sides of the flame arrester, even though it looks perforated. Instead, it is pulled primarily through the the 1 1/2 hose that connects the flame arrester to the Oil Cap on the port valve cover. The oil cap has vents around its base where the clear air enters.

If those vents do not have good airflow, the vacuum from the carb could pull excess air from the secondary air supply. The secondary supplies are the engine gases from the valve covers. On the port side, these gases pass through the oil cap into the primary air supply. On the starboard side, the gases pass through the PCV into the base of the carb. Excess air flow from the valve covers would pick up oil, bringing it into the spark arrester.

Is it possible that the problem is caused by excess pressure within the valve cover? I guess this could be caused by worn rings or poorly seated valves, maybe? Is there an easy check for this?

TMCNo1
11-21-2007, 12:27 PM
Thanks for the explanations. I'll check these areas over the weekend, but let's see if I have this straight. No clear air passes through the sides of the flame arrester, even though it looks perforated. Instead, it is pulled primarily through the the 1 1/2 hose that connects the flame arrester to the Oil Cap on the port valve cover. The oil cap has vents around its base where the clear air enters.

If those vents do not have good airflow, the vacuum from the carb could pull excess air from the secondary air supply. The secondary supplies are the engine gases from the valve covers. On the port side, these gases pass through the oil cap into the primary air supply. On the starboard side, the gases pass through the PCV into the base of the carb. Excess air flow from the valve covers would pick up oil, bringing it into the spark arrester.

Is it possible that the problem is caused by excess pressure within the valve cover? I guess this could be caused by worn rings or poorly seated valves, maybe? Is there an easy check for this?

Primary test would be a compression test on all 8 cylinders! It could indicate poor valve seating, blown/leaking head gasket, failed piston rings, causing pressurization of the crankcase, valve covers, oil passages from the seeping compression, IIRC.

You may want to discuss this with JimN and or Enginenut here on TT, by post here, pm or email.

Hunterb
11-21-2007, 07:11 PM
One way of checking for excessive blow-by is to take the oil filler cap off with the engine running, or better yet, take it off before you start it and then watch the hole during start-up. A little 'smoke' coming out of the hole is normal. If there's a lot then you most likely have worn rings. Air should be flowing in through the filler cap and then out through the PCV valve. The air should be being 'pulled' through the PCV valve by the engine vacuum, which is why the PCV hose goes into the base of the carburator where there is constant vacuum. It may be possible, if you have a lot of blow-by, for the crankcase pressure to be high enough to cause air, and oil vapor, to be blown out the filler cap and subsequently up the hose and into the spark arrestor. I'm not sure about that though. It strikes me that it would take a lot of blow-by to have the system 'back up'. Have you made sure that your PCV valve is working properly?

Good luck with this. Hopefully it's not serious.

Bruce

mc79
12-02-2007, 11:07 PM
Compression test performed twice to verify results. The PSI readings are:
Port side, front to back, 122, 120,120, 120
Starbord, front to back, 122, 122, 120, 124

Now the problem is, I don't know what that means. Any idea what the compression should be on an 79 PCM 302, 4 barrel. I checked the net and all I could find was for an 1968 which indicated that the acceptable range is 130-170 psi.

Jesus_Freak
12-02-2007, 11:35 PM
Compression test performed twice to verify results. The PSI readings are:
Port side, front to back, 122, 120,120, 120
Starbord, front to back, 122, 122, 120, 124

Now the problem is, I don't know what that means. Any idea what the compression should be on an 79 PCM 302, 4 barrel. I checked the net and all I could find was for an 1968 which indicated that the acceptable range is 130-170 psi.

My input is likely worth less than $0.02, but I am going to vote that these values are fine since the cylinder-to-cylinder deviation is low. It is not likely that components of all 8 cylinders (or the entire head gasket) are failing at once. If these are indeed lower than the target (whatever that may be), one could question the gauge or testing method.

KHall
12-03-2007, 05:01 PM
The compression looks good!

mc79
12-03-2007, 10:16 PM
Thanks. Thats a relief. I've had the boat for a year and had to fix numerous things. It was "totaly rebuilt" but sat for 8 years without being properly prepared for a long lay up. Shows subtle evidence of both freezing and overheating at some point.

88 PS190
12-03-2007, 10:42 PM
all within 4 psi is exceptional.

does it have any problem with leakdown?

Hunterb
12-04-2007, 10:16 PM
it's good that the numbers are all about the same, but they are on the low side of acceptable. In a perfect world they would be around 150. If the engine was warm when it was done (which it should be) then I would say your rings are worn or the valves are leaking. Did you have all the plugs out and the throttle blocked wide open? Did the pressure build gradually to those numbers or did it jump quickly and then increase a small amount on the last couple of compressions?

Those numbers aren't terrible but they might explain your blow-by problem.

Engine Nut of JimN would likely have some good suggestions.

Good luck.

Bruce

mc79
12-05-2007, 12:04 AM
This was my first compression test so it was a good excuse to buy a new tool (it doesn't take much of an excuse). I got one of Autozone's higher end compression testers and ran the test by the book. Warmed the engine for 15 minutes, removed all spark plugs and wired open the throttle plates. I turned the motor over for 10 compression strokes. That seemed to be where the pressure stabilized.

I get a bit of smoke but it isn't blue. Smells more like it's running rich than burning oil. I only added 1/2 quart over the summer. The plugs were black with carbon instead of that nice white powdery look. I get some carbon blown through the exhaust ports. I have to wipe soot off of the back of the boat after a day on the lake. Hope these are indications of valves rather than rings.

TRBenj
12-05-2007, 11:53 AM
it's good that the numbers are all about the same, but they are on the low side of acceptable. In a perfect world they would be around 150. If the engine was warm when it was done (which it should be) then I would say your rings are worn or the valves are leaking.
I disagree. The chances that all cylinders/valves are evenly worn is very low. Having all the cylinders with nearly the same pressure is very good. Results will vary depending on exact engine temp, the exact gauge used, etc. The numbers seem to be perfectly in line, especially for a Ford- which has a relatively low CR at ~8.5:1.

I agree that by your description the boat is running a bit rich. If its not putting out blue smoke, Id say the rings are fine- especially with those compression test numbers.

mc79
12-05-2007, 10:43 PM
Found a Holley manual online. I'll check the mixture settings next time I get in the dog house on a warm day.

cartoon head
12-06-2007, 08:57 AM
I agree with TMC01, I think you could have worn piston rings, an easy way to check is to take the oil cap off from one of the rocker covers with the engine running and see how much the engine is breathing.
If the engine is good there should be no fumes or smoke, if the engine is worn then fumes/exhuast will puff out.

JimN
12-06-2007, 10:25 AM
mc79- If the motor wasn't laid up properly, there was undoubtedly some moisture in the cylinders and that means there was some rust on the walls/rings. Not a good thing. Test the compression again and if possible, have it tested for cylinder leak-down and do a vacuum check.

If the smoke is there at start up only, it could be valve seals but age is more likely to kill those, although overheating isn't good for it, either.

TMCNo1
12-06-2007, 10:37 AM
Thanks. Thats a relief. I've had the boat for a year and had to fix numerous things. It was "totaly rebuilt" but sat for 8 years without being properly prepared for a long lay up. Shows subtle evidence of both freezing and overheating at some point.


I agree with JimN on this one, but disclosure of freezing and overheating early on in the thread would have been helpful.

JLeuck64
12-06-2007, 01:42 PM
To recap:
Engine was never winterized and then stored for many years.
You purchased the boat and ran it this summer, during which you only had to add 1/2 quart of oil.

I think that half quart of oil you lost was probably blow-by past the rings. This was when the oil was getting up to the flame arrestor. After you ran the engine for a while the rings finished scraping the rust off the cylinder walls and started to seal again. I would suggest cleaning all traces of oil from the pcv system then monitor the flame arrestor periodically next summer.

Oh, and of course winterize the engine this year ( =