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post #1 of (permalink) Old 01-11-2005, 07:06 PM Thread Starter
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Engine blow-by and possible remedy

I've been searching this subject the past couple of days on this forum and others and have come across a wealth of info. Although my main question isn't about the blow-by please feel free to throw ideas out at me about it. I have an '88 YJ with the 4.2 and am getting about a quarter of an inch of oil in the air filter element, as well as some in the engine compartment. I have replaced the PCV valve twice, however, I have not done a compression test (yet). I am still running the stock setup (as far as I know, I just bought the Jeep in May of last year). Most of my research showed that this was related to either a clogged PCV system (or elsewhere) or piston rings that had failed.
My main question is this: I was thinking about taking the engine and boring it 0.030" over then fitting it with new pistons and rings. I found a few folks that had done this but was wondering what the benefits were? Did this fix the blow-by? I was planning on doing the Motorcraft 2100 switch and either the TFI/HEI upgrade at some point, would they still work well with this setup? Or is it smarter to just replace the rings, if the compression test shows that they are faulty?
I know this is a lot to ask but I'm trying to plan this all out and want to do it right.
Also, I'm new to all of this information so please bear with me. If I missed a thread on this exact subject in my search just let me know. Thank you in advance
Seth
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post #2 of (permalink) Old 01-11-2005, 07:18 PM
 
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Re: Engine blow-by and possible remedy

Having your Cylinders bored 30 over and installing new pistons and rings will solve your blow by issues. If you are going to have you whole engine apart you might want to think about getting the crank turned and putting in new rod and main bearings, along with anything else you might need, you will end up with an engine that is tighter, runs better, consumes less oil, and will last much longer.
Carbuerator, and ignition upgrades will work fine with an overbored engine. My 258 is .040 over. I put new pistons, rings, and bearings in it, along w/ a head job (and a lot of other parts) and it excelent great now and has very minimal blow by ( a very small amount can be expected even w/ a rebuilt motor).
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post #3 of (permalink) Old 01-11-2005, 07:45 PM
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Re: Engine blow-by and possible remedy

If your milage on the 258 is normal (16 yrs x 12k miles/yr = 192k miles) then some to a lot of blow by should be expected...Rebuilding or buying a rebuilt is good. Or, upgrading may be smart...When I melted down my 258 I went out and had a rebuilt put in, it's a good motor, but for what I spent...I could have had a V-8...It's not an easy swap...but it can be done. Just gotta find a motor that is newer than 88, going FI is good...I've seen a couple of YJ's with Grand Cherokee V-8's...makes for a complicated swap but can be done...

As for the mc2100/TFI it'll be the best upgrade to the 258 you can do (especially for the price)...but, you'll need to know your inspector...Wake County is known for calling people on the "non-original equipment" thing...With our 88's we still have 2 or so years of inspections till they quit (if they ever really do) sniff testing and motor equipment check...Most of the inspectors wont catch it if you can make all the plumbing (smog pipes) and vacuume hoses look original.
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post #4 of (permalink) Old 01-11-2005, 08:13 PM Thread Starter
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Re: Engine blow-by and possible remedy

I figured that Wake County would try and give me trouble (possibly) regarding the mc2100//TFI upgrade. I've been taking my truck to the same place for 10 years so I feel pretty comfortable that it will pass the visual with minimal problems. Plus, like you said, I plan on trying to leave things looking as close to original as possible.
I know that some blow-by is to be expected with any engine, new or old. Its just the amount of it that bothers me, and I've only got 136k on this engine. I had thought about the V8 route but figured that the cost would be far more than taking the old 258 and rebuilding it. I may be way off base on that one however.
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post #5 of (permalink) Old 01-12-2005, 01:15 AM
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Re: Engine blow-by and possible remedy

Nice to see another Raleigh Jeep person around.

Boring out to .030 will mean that you are pretty much rebuilding your entire engine. That is a lot of work if you've never done it before.

As far as inspections go, I've gotten many Jeeps passed. As long as your tailpipe emissions are within the limits, then I think you are OK. In the past I have put some emmissions stuff 'around' my engine to make it look like they are hooked up.

I would rebuild your 258 or get a 4.0L to swap in. Either one will be a lot of work if you are new to this stuff. I like 6 cylinders.
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