Blue Smoke While Under Compression - Defender Source
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  #1  
Old March 30th, 2010, 03:17 PM
outfield
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Steve
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Blue Smoke While Under Compression

Hi Guys,

My 3.9 is smoking more and more while under compression. I rebuilt the top end the fall of 2007, heads were redone, new cam, lifters etc. I don't notice the blue smoke on the road, only while under compression on the trail, usually in low range. I'm at about 175k total on the engine now, about 20k after the top end was done.

Does anyone have any ideas on what could be causing this?

Thanks for any suggestions.

Steve
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  #2  
Old March 30th, 2010, 03:31 PM
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Chris Davis
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Sounds like oil getting past the rings/worn rings under load.
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  #3  
Old March 30th, 2010, 03:40 PM
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evilfij
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Bad valve seals? Did you use the black disc type or the newer blue type?
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  #4  
Old March 30th, 2010, 07:37 PM
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Andrew J. Hutton
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Valve seals is the most likely but do a compression check to see if there is a bad/burned valve/seat. Do a dry check, then a wet check and that will eliminate the rings as the problem.
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  #5  
Old March 31st, 2010, 02:30 PM
outfield
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Steve
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Thanks Guys, I'll do the cimopression check and see what the results are.
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  #6  
Old March 31st, 2010, 02:51 PM
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Robert Klima
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Quote:
Originally Posted by evilfij View Post
Bad valve seals?
Bad valve seals normally make the engine smoke while coasting and not under compression. Doing a compression test won't be the worst thing but I think you will not see much. Is the engine blowing by (gets pressure in the crankcase)?
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Old April 1st, 2010, 02:55 PM
outfield
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Steve
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Hi Robert,

I don't see any obvious signs of blow by, do you have any suggestions on what to look for? Is the blow by caused by worn rings?
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Old April 3rd, 2010, 03:13 AM
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Robert Klima
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Yes, blow by is caused by worn rings. At the moment I really have no better idea what else could cause blue smoke under compression. What's the oil pressure when the engine is warm and idling? Have you done the compression test? I think there were no bad results and all cylinders are on the same level. As you say the top end was done 20k earlier and you've already got 175k on the bottom end I'd say the problem is there. There is one thing you can check. Remove the spark plugs on all 8 cyl, remove the valve covers and then test the rings by blowing in compressed air. I made the tool myself, just used an old spark plug and drilled and taped a hole. Then put in a fitting, fit a gauge and valve to it. You have to make sure the tool has no leaks.
Then you can test each cylinder: put the piston in the cylinder you want to test to TDC (both valves fully closed), put in first gear and handbrake on. Then put compressed air in and close the valve on your tool. If the rings are worn you will loose pressure fairly quickly.
I don't have a photo of this tool here on my laptop put will post one when I'm on my other laptop.
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