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engine woes: need a guru


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Hey guys, getting really frustrated.

The long and short of it is: I pulled my 2.5 last summer and had it rebuilt, got an ax 5 out of a 2000XJ with the external slave. I went to a "reputable" machine shop/engine builder, and broke it in properly. When it continued to use oil well past break in, sometimes a quart every 500-1000 miles depending on load, etc., I called the builder. Now, it was cold weather, and I wasn't going to get to into it, but he assured me it was probably valve seals and he could take care of that easily. Now, he's just a machine shop, and not a garage, so anything more than seals would mean I have to take the head off, or the engine out, and bring it back to him.

 

I have a neighbor, a good guy, who is an ASE mechanic, former Ford dealership pro who's now teaching at a vo-tech. He was more skeptical, and thought maybe it was valve seats, but the builder didn't knurl or re-use them, he put new ones in.

 

Anyways, we thought the first step, before taking anything apart, was to do a leak down test. My friend had a junky Harbor Freight unit lying around, and it didn't work very well, but we noticed that cylinders 2-3, which had fouled Champion plugs, hissed when we applied shop air at TDC, and you could hear the air coming out of the oil filler. He said that I should go to a shop, get a documented leak down test, then go to the builder with the numbers. He was fairly certain that the rings on 2-3 were bad.

 

So, not knowing any mechanics very well, I took it to a place called "Motorworks." They do a lot of Jasper installs there. I dropped the MJ off, and they called back, saying compression was 135-140psi and consistent, and that the leak down test was "normal." When I asked him what normal was, he said "in the green area." I said 'meaning what?' He said "less than 40% in all cylinders." Well, I didn't like that answer, found out that he was a manager and did the test, but did not admit to being a mechanic, which makes me wonder if he did the test correctly.

 

I haven't picked the truck up yet, but I feel like I'm going to spend some money and not get a real answer. When I asked him why I would foul 2-3 and use oil, with good compression and acceptable leakdown, he said "I have no idea." He suggested I get NGK spark plugs ("b/c Champions are crappy") and "run some good gas in it." I mentioned that the vehicle came from the factory with Champions and calibrated to run at 87 octane.

 

I'm picking the truck up tomorrow. Anything else I should ask him? I'm pretty bummed about this whole thing. Engine builder keeps insisting I check the valve seals. Could that do what is happening here??

 

THanks!

 

Tom

 

:wall: :wall: :wall: :wall:

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First, I think you mean valve 'guides' not valve seats. You don't knurl valve seats. Find someone else to do the leak down test. Less than 40% could mean 39%. That is totally unacceptable. Do you see blue smoke on start up, especially after sitting over night? That is a classic valve seal sign. Valve seals won't cause a leakdown problem.

What are you using for oil? Hopefully you did not put in synthetic at first. It has been said that it can keep rings from seating properly.

What type of work was done on the block, and how many miles were on it? Hopefully the shop did bore out-of-round and taper measurements on it. What did they use for rings? Did they do the assembly, or did you? Do the plugs appear to be oil fouled or gas fouled? There are so many variables it could be from a number of things.

 

I guess if the shop is willing to do the valve seals N/C, I would let them do them and go from there. Keep all your documents as it may end up being a legal issue in the end. Also ask them if they have a spec sheet from when they did the work on your engine.

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As noted, you can't knurl valve seats. But I also don't know how you would install new valve guides, since they are an integral part of the head. That notwithstanding, if you were losing compression through the valves you would either have air being blown back through the intake, or out the exhaust. Leakage at the valves would not pressurize the crankcase.

 

It sounds like your rings are not seated. It could be that the rebuilder didn't fit them right, didn't use the correct rings, or didn't hone the cylinder walls correctly. It's also possible that he honed the bores too much, and used the original pistons so that they are now a sloppy fit in the bores. Another possibility is that he used chrome rings, which are very hard, take forever to seat (and never really seat well), and require a different hone pattern. Even then, they often always use more oil than regular rings.

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Right; sorry. I meant valve guides, not seats.

 

He did bore the engine .030 over, and the understanding was that he was going to put in the appropriate pistons for that bore. What kind of rings he used, I do not know. He did all the assembly of the engine, and gave me back the block to bolt the accessories and trans onto. I do see occasional puff of blue smoke on startup, but would valve seals foul plugs (oil fouled) as badly as a poorly seated ring?

 

Thanks guys

Tom

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Right; sorry. I meant valve guides, not seats.

 

He did bore the engine .030 over, and the understanding was that he was going to put in the appropriate pistons for that bore. What kind of rings he used, I do not know. He did all the assembly of the engine, and gave me back the block to bolt the accessories and trans onto. I do see occasional puff of blue smoke on startup, but would valve seals foul plugs (oil fouled) as badly as a poorly seated ring?

 

Thanks guys

Tom

Technically, there ain't no such critter as valve "seals." The valves are fitted with little rubber/plastic unbrellas whose purpose is to direct as much oil as possible dripping off the valve cover away from the valve stems, but the umbrellas go up and down with the valves and don't seal anything. The are more correctly called "deflectors."

 

Fouled plugs are much more likely to be caused by ring problems.

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Eagle, on the 4.0 and 2.5 there are actual valve stem seals. They are pushed on to the valve guide and are stationary. Some of the early motors also used a deflector on the exhaust valve in addition to the seal. A worn guide will allow the seals to leak as excessive side clearance will damage the seal.

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Right; sorry. I meant valve guides, not seats.

 

He did bore the engine .030 over, and the understanding was that he was going to put in the appropriate pistons for that bore. What kind of rings he used, I do not know. He did all the assembly of the engine, and gave me back the block to bolt the accessories and trans onto. I do see occasional puff of blue smoke on startup, but would valve seals foul plugs (oil fouled) as badly as a poorly seated ring?

 

Thanks guys

Tom

 

What was the total for this rebuild? Don't usually hear of .030 bore jobs being done to the lowly 2.5. There is the chance that he needed to custom grind the rings for the .030 pistons to set proper end gap. How does she run other than the oil usage (when the plugs aren't fouling out) ?

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She actually runs really nice and smooth. Fresh rebuild + Yella Terra roller rockers + Clifford header and it has nice pull. No more downshifting on hills on the highway (with 31s).

 

I ran dino oil for the first 3-4K miles, was consuming what I thought was too much oil, and I switched over to full synth, and without any scientific measurement, seems to be using less.

 

There was some early plug fouling on rebuild, but I was having MAP sensor issues, and a friend with the MT2500 helped me get everything in tune. I had no idea that 2+3 were fouled until I took them out to do the leak down test....

 

 

Going to talk to the "mechanic" who did the official leak down test today. Results later...

:ack:

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  • 2 weeks later...

OK,

Here's the update. My mechanic friend brought home a good snap on cylinder leak tester. All my cylinders are <15%! So it's not a compression ring. My friend is still convinced it's something in the head, so we pulled the valve cover off, and all the valve seals looked good - none lifted up. He thinks it's valve guides, and it may well be.

 

I changed out all the Champion truck plugs with NGK one heat range hotter than stock, checked the dist. cap, which is practically brand new, and we'll see. I'm going to take it on some good long highway drives the next couple of weeks and see if I'm using oil/fouling plugs. If I'm fouling plugs, the head is coming off and going back to the builder. I'm relieved it's not bottom end- I 'd really hate pulling the engine again. Now the a/c clutch pulley is getting noisy. Got to love old cars, it's always something!

 

:fs1:

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