Dealing with an engine with oil blow-by - hoping for some thoughts and coaching on options |
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Dealing with an engine with oil blow-by - hoping for some thoughts and coaching on options |
Tdskip |
Jun 25 2019, 01:13 PM
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#21
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Advanced Member Group: Members Posts: 3,686 Joined: 1-December 17 From: soCal Member No.: 21,666 Region Association: None |
OK - so here is the scoop on the '74 AZ car that has me about to learn new things.
This is the car that has the 2.0l case with 1.8 heads. Runs strong, good pulling power, no bad noises, and has good oil pressure. Came to me with a recently put together engine with no guarantees but believed to be redone heads and fresh bottom end. Price was right on everything so I bought it, no regrets. The issue I am seeing is that the engine has too much blow-by. After a short time (under 30 miles) it started smoking very noticeably from the breather and blew out the oil seal on the breather tower. Since then I've changed the oil and done more heat cycling and it's smoking significantly less (barely noticable now) but I still have too much blow-by. I don't think I have much to loose by driving it some more and seeing if the rings seat better but I am working on the expectation that isn't going to work. Assuming the most likely case, which is that the rings don't seat any better, I believe I would need to pull the heads and pistons off and start again. Yes/no? Should I be thinking of just replacing the jugs and pistons with a new set from AA or do these clean up (in general). I believe replacement is the usual approach these days. I think I would plan to send the heads out for servicing as a precaution so I know I have good ones with good oil control going back on. Assembly from this point should be pretty straight forward I'd think? Thanks, appreciate the continuing education here. |
JamesM |
May 5 2020, 12:47 AM
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#22
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Senior Member Group: Members Posts: 1,916 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
I think you need to back up and look at the external bits before you dig into the engine itself. A few things you mentioned stand out to me.
1. You mentioned you are running 1.8 heads. You didn't specify but I assume given your situation that they don't have the head vent port by the left side intake manifold stud? 2. You appear to have an earlier 1.7/2.0 oil tower and PCV valve that is vented to atmospheric pressure (air cleaner) The crankcase vent system changed somewhat significantly between the early and late cars, and it sounds like your whole crankcase venting system is mismatched in addition to having a PCV valve that requires manifold vacuum and head vents to operate properly. So it sounds like you essentially have very minimal crank case venting capacity, which is most likely why the engine keeps venting itself by way of the oil tower seal. Ill give a little more background info to illustrate what i am talking about 1.7, and pre 75 2.0s use an oil tower with a small port (13mm hose) with a PCV valve (whose internal passage is closer to 8mm + restrictions from the square valve) that connects to manifold vacuum. These cars ALSO have 13mm vents in both heads that route to the flashback valve and into the air cleaner. You can read about the PCV operation here https://members.rennlist.com/pbanders/PCV.htm but the main take away of consequence here is that under high load the crankcase pressure exceeds the capacity of the PCV with the excess pressure venting via the heads (which i am assuming dont exist on your motor). The 1.8 engines eliminated the head vents, and use a different oil tower with NO PCV valve and a MUCH larger ~22mm vent hose that routes to the air cleaner with all crankcase pressure venting unregulated through the MUCH larger oil tower vent. So I may be wrong, but I suspect your issue is probably related to the inability to vent what pressure you do have more so than something mechanical causing to much pressure to be generated. Swap out the oil tower for one from a 1.8 or 75+ 2.0 and see what happens. |
JamesM |
May 5 2020, 01:22 AM
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#23
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Senior Member Group: Members Posts: 1,916 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
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