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post #1 of (permalink) Old 03-02-2003, 10:27 AM Thread Starter
 
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Jeep I-6 engines have a blow-by problem!

Has anyone figured out why so many 4.2 and 4.0L engines have so much trouble with blow-by. I have a newly rebuilt engine that was bored .060 over with new pistons and rings. The compression is good and the engine has great power. However, if you remove the oil filler cap and rev the engine two or three times you will witness the gases being forced out in puffs. This is diffently blow-by and it causes the oil to be comtaminated much quicker by the carbon contained in the fuel hence the oil turns color much quicker than it should. I think that Total Seal piston rings may be the only answer. Has anyone on the board used these rings sold by HESCO?

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Fran
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post #2 of (permalink) Old 03-02-2003, 10:36 AM
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Re: Jeep I-6 engines have a blow-by problem!

I have not used them but it makes perfect sense to me maybe the engine builder did not offset the ring gaps properly
post #3 of (permalink) Old 03-02-2003, 03:30 PM
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Re: Jeep I-6 engines have a blow-by problem!

someting doesnt sound right... the rings I used were for the newer 4.0 pistons...I cant recall the manufactuer, but I remember thay were $100. they are some strange metris size too. I have no blowby even with [img]images/graemlins/tongue.gif[/img]9.6/1 compression
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post #4 of (permalink) Old 03-02-2003, 03:39 PM
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Re: Jeep I-6 engines have a blow-by problem!

ive seen what appears to be blowby when you take the oil filler cap off, doesnt mean it is though, remember it probly idles at 40 psi and if you are getting blowby it means your rings are seating...a little blowby in a new engine is common
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post #5 of (permalink) Old 03-02-2003, 07:42 PM
 
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Re: Jeep I-6 engines have a blow-by problem!

This is common with the inline 6, there are two lines coming off the Valve cover, the one in the front allows air to flow into the valve cover and is about a 1/2 in hose the second is a small vacume line on top towards the back of the valve cover and is a vacume line, if it is clogged or the little baffle built into the valve cover below is clogged then you will eventully will notice oil on you air filter. Check the small one first.
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post #6 of (permalink) Old 03-02-2003, 08:28 PM
 
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Re: Jeep I-6 engines have a blow-by problem!

Unless you have oil blowing into your air filter box ...you may just have normal crank case pressure....don't forget when you have your oil filler cap off you can see the rockers as the oil gets atomized in the crank case it will flow out the path of least resistance = the big hole created when you take the oil filler cap off.
The PCV valve is a metered valve that is actuated off manifold vacume,and draws the crankcase gasses out.when the vacume gets too high it closes the PCV valve also when it gets too low it closes it off...while fresh air is circulated into the crankcase via the hose going to the airfilter box.
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post #7 of (permalink) Old 03-02-2003, 08:29 PM
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Re: Jeep I-6 engines have a blow-by problem!

Total Seal is a great idea ...two thinner rings in the top groove ..appropriately gapped and 180 out ... allegedly more easy to fit than "no gap" single rings. My engine builder pal uses them on the stock car engines that he builds.

Even with those you will be some cylinder leakage ...although it's very low. The race engine gurus have even designed some pistons that will allow the passage of metered blow-by gasses to the second ring area. I can't speak inteligently on it to length ..but what I grabbed out of it was that they allow enough combustion flow to pass to pressurize the ring outward ..but can not too much that can't be evacuated in the intake cycle. Most advance builders have abandoned the drilling of the top of the piston to pressurize the top ring outward. There are also special techniques to the fittment of Total Seal rings. That is, you don't just fit the two rings identically.

Given your year ...you should have a regular PCV valve ..as opposed to us injected types that have gone to the inferior CCV due to our idle management system (or so I reason). Your's can handle a lot more volume than ours before it migrates to the "above the throttle plate" area. We don't have an air cleaner to foul since we vent into the intake flow behind the element..

I think your problem is one of perception. You're revving it up and seeing a puff or two. But I'll venture to say that if you sustain the high idle ...you don't see anything. You're just cycling beween high production of normal blow-by ..and inadaquate evacuation capacity.

As to the reason that the 4.2 and 4.0???? I think it is because they are such torque monsters at low rpm. If I'm anywhere near 1800 rpm all I have to do is give it the gas and I can overcome most grades (or whatever). Owners take advantage of this ability to be under heavy load without shifting gears ...putting more stress on the rings ...........add 100,000 miles ...blow-by. This is naturally just an opinion ...but I can't see anything being inherently wrong with the material or the design (this isn't some engine that Detroit just $hit out yesterday) ...hence I tend to look at the characteristics of its use.
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