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Old 03-08-2010, 03:01 PM   #1
Bartacus
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Found out 3 spark plugs are cross-threaded: what would YOU do?

So I found out Friday that 3 of my spark plugs are cross-threaded. I'm not sure when or how this happened, only that the last people to change my spark plugs never said a damn word to me. So I don't know if THEY did it, or if they had a hard time taking the plugs out and failed to tell me. I was getting a compression test done, and surprise surprise I get bad compression on those 3 cylinders. The guy that did the compression test was confident that even with the threading issue, his compression tester made a good seal, so according to him I'd have low compression on 3/6 cylinders no matter what.

Question 1: what would YOU do here? Go after the previous mechanic, with whom I had a good relationship until this? Or just suck it up and buy a new engine? I suspect my cylinder head is cracked anyways, as I'm having pressure problems in my cooling system.

I have a line on an engine from a 1999 323i (2.5L with 150,000KMs on it), which is slightly more powerful than my little 2.2L which has 261,000KMs. I might be able to get that engine for $1000, and get it installed for another $1000-$1200. So for $2200, I get a better engine with less mileage, plus the cost of a new rear diff to match the new engine (no price on that yet). Plus I can get that engine chipped to be more powerful than a stock 325i engine (or so I'm told, since the 2.5L in the 323 is a de-tuned version of the same engine in the 325i), thus the next question.

Question 2: what are the differences between the 2.5L engine used in the 99 323i, and a 325i in the same date range? I know they're both 2.5L, but how is the 323 engine de-tuned? Different hardware? Software downgrade?

Before anyone starts recommending S54 swaps, I'm poor and this is my only car. I can't afford to dump 10 grand on this. I WISH I could afford an M3 engine + hardware!!
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Old 03-08-2010, 03:03 PM   #2
mvrk10256
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so the 323 and the preface 325 engines are the same at the wheels. the facelift 325 makes a few more horses due to electronics.
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Old 03-08-2010, 03:32 PM   #3
Minnoe07
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You can try and clean the threads up by using a thread restorer kit. You can buy one at sears for less than $50.

or

You can thread sert or heli-coil the sparkplugs. That way you only pay for a few hours of labor instead of a new engine.

Now if your problem runs deeper than that and you are just kidding yourself, then you probably need to figure out what is happening. Honestly crossthreading the sparkplugs isn't a BIG deal. I would be pissed too but if you can't hold any shop responsible, it shouldn't be more than a few hundred bucks to helicoil the threads.
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Old 03-08-2010, 03:47 PM   #4
rowdy lee
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Half-full...

Look on the sunny side...

Your mechanic did a super OK job on 50% of them...

Doesn't help much...
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Old 03-08-2010, 04:00 PM   #5
xi_ter
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Consider the Sears kit as a fix.
http://www.sears.com/shc/s/p_10153_12605_00942275000P
Can restore the thread while removing the min of the factory thread. Some of the comments confirm good results. Guess you'll need to use anti-seize to beef up the seal.
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Old 03-08-2010, 04:42 PM   #6
Kubica
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Why would you not bring it back to the mech who changed them the first time?

Seems like he's on the hook if you have a receipt . . .
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Old 03-08-2010, 04:45 PM   #7
Bartacus
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Quote:
Originally Posted by mvrk10256 View Post
so the 323 and the preface 325 engines are the same at the wheels. the facelift 325 makes a few more horses due to electronics.
Interesting. I'd love to get more details on this. Sounds like this new mechanic is telling the truth, and I could easily be around 195HP on this engine. That would do me fine until I can go turbo and get a 6 speed stick.
Quote:
Originally Posted by Minnoe07 View Post
You can try and clean the threads up by using a thread restorer kit. You can buy one at sears for less than $50.

or

You can thread sert or heli-coil the sparkplugs. That way you only pay for a few hours of labor instead of a new engine.

Now if your problem runs deeper than that and you are just kidding yourself, then you probably need to figure out what is happening. Honestly crossthreading the sparkplugs isn't a BIG deal. I would be pissed too but if you can't hold any shop responsible, it shouldn't be more than a few hundred bucks to helicoil the threads.
Yeah I was told about those helicoils today too, but I *think* my problem is deeper than this. Problem is, the only way to really confirm a hairline crack in the cylinder head is to pull the head. This being my only car, that's a pain unless I rent a car for a few days, and that would cost even more. I need a second car in the worst way! If I can save up enough coin, I'm getting an E36 next year as a winter beater / 2nd ride!
Quote:
Originally Posted by rowdy lee View Post
Look on the sunny side...

Your mechanic did a super OK job on 50% of them...

Doesn't help much...
I LOLed.
Quote:
Originally Posted by xi_ter View Post
Consider the Sears kit as a fix.
http://www.sears.com/shc/s/p_10153_12605_00942275000P
Can restore the thread while removing the min of the factory thread. Some of the comments confirm good results. Guess you'll need to use anti-seize to beef up the seal.
Question about these helicoil things: is there any chance metal shavings could get dropped into the engine when doing work like this? Noob question, but I'm mechanically retarded and know nothing.
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Old 03-08-2010, 04:50 PM   #8
Bartacus
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Quote:
Originally Posted by Kubica View Post
Why would you not bring it back to the mech who changed them the first time?

Seems like he's on the hook if you have a receipt . . .
Oh I'll be talking to them, but I doubt they will do anything. They could just claim ignorance, claim that they were stiff coming out but they forgot to tell me, etc etc. Knowing these guys, I'd have to threaten a lawsuit to get them to fix me up. But we'll see. I'm going to calm down a bit first before making the call. Anger will solve nothing, so I'm going to be cool and polite, and see what they say.

Thanks for the input so far guys.
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Old 03-08-2010, 04:58 PM   #9
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Try this tool, it starts restoring the thread from the bottom of the sparkplug hole, to prevent filings from dropping into the cylinder. If the BMW sparkplug is not 14mm, I would think that Snap-On would have a tool in the proper size.

http://www.snapon.com/International/...iles/sphr1.pdf
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Old 03-08-2010, 05:05 PM   #10
Bartacus
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Quote:
Originally Posted by tac911tc View Post
Try this tool, it starts restoring the thread from the bottom of the sparkplug hole, to prevent filings from dropping into the cylinder. If the BMW sparkplug is not 14mm, I would think that Snap-On would have a tool in the proper size.

http://www.snapon.com/International/...iles/sphr1.pdf
Awesome, thanks for the tip!
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Old 03-08-2010, 07:40 PM   #11
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What are the chances that you have a crack in the cylinder head? What happened to your car to where you would suspect a crack in the head? I think a thread restorer will do the trick and will get you back up and running with as little money as possible. That snap on tool looks really really cool.
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Old 03-08-2010, 07:59 PM   #12
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Low compression in the 3 cylinders that just happen to be associated with the cross-threaded spark plugs? Compression testers are threaded. If there is a problem with the threads, then the compression test will not be accurate. I would first try the heli-coil route and test compression after. If still low in those cylinders, then consider replacing the engine.
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Old 03-08-2010, 08:13 PM   #13
toddkageals
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The strange thing is that it's VERY difficult to cross-thread the spark plugs on these cars. I've done 3 sets and have had "0" problems, not even had to start/remove start over. The chances of 3 being cross-threaded on the same car??????? Beats me.
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Old 03-08-2010, 09:23 PM   #14
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First...confirm the cross thread issue. If cross threaded, then re-thread or helicoil. This is no brainer stuff, people have to do it all the time. An experienced mechanic can do this stuff in their sleep.
Now address your cooling system issues. What maintinence/service has been done on the cooling system since you have owned the car? We all know the weak spots in this system and there is TONS info and DIY's on it.
Next, stop planning on pulling engines and replacing with used engines, turbo charging, etc etc. Do you really realize how much of a headache, time, expense and risks are involved in all of this??? Spend what little money you have and fix the darn simple problem first. Also, buy and read a Bently manual, you might be surprised by how easy it is learn something.
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Old 03-08-2010, 11:32 PM   #15
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Yeah, he's right, swapping engines and all things that go along with it is an expensive and frustrating adventure.

There is something wrong with a compression test performed with stripped threads as IXTOXI points out. Should the tester not seat due to cross threading (rotating freely at the seat point), most mechanics would agree the compression results are useless. Have someone verify the thread condition before a plug blows out like a missile.
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Old 03-09-2010, 09:07 AM   #16
Bartacus
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Quote:
Originally Posted by Minnoe07 View Post
What are the chances that you have a crack in the cylinder head? What happened to your car to where you would suspect a crack in the head? I think a thread restorer will do the trick and will get you back up and running with as little money as possible. That snap on tool looks really really cool.
Hairline crack is suspected because I have excess pressure in the cooling system, and over the past year, EVERY SINGLE PIECE of that cooling system has been replaced with NEW parts, water pump / rad / all hoses / both thermostats / several expansion tanks / tank cap / etc etc. After every decent drive (say over 60KMs), I've been popping the cap on the expansion tank to relieve the pressure. As long as I do that, there are no leaks and everything is fine. If I DON'T relieve that pressure, I get issues with funky temp gauges, and small leaks near the expansion tank cap.
Quote:
Originally Posted by ixtoxi View Post
Low compression in the 3 cylinders that just happen to be associated with the cross-threaded spark plugs? Compression testers are threaded. If there is a problem with the threads, then the compression test will not be accurate. I would first try the heli-coil route and test compression after. If still low in those cylinders, then consider replacing the engine.
I'm leaning towards this. If this wasn't my only car, I'd get a proper diagnosis by getting the head pulled and X-rayed.
Quote:
Originally Posted by toddkageals View Post
The strange thing is that it's VERY difficult to cross-thread the spark plugs on these cars. I've done 3 sets and have had "0" problems, not even had to start/remove start over. The chances of 3 being cross-threaded on the same car??????? Beats me.
That's my luck. I must have been one HELL of an a$$hole in a previous life, because I have the worst karma ever!
Quote:
Originally Posted by dwebb99 View Post
First...confirm the cross thread issue. If cross threaded, then re-thread or helicoil. This is no brainer stuff, people have to do it all the time. An experienced mechanic can do this stuff in their sleep.
Now address your cooling system issues. What maintinence/service has been done on the cooling system since you have owned the car? We all know the weak spots in this system and there is TONS info and DIY's on it.
Next, stop planning on pulling engines and replacing with used engines, turbo charging, etc etc. Do you really realize how much of a headache, time, expense and risks are involved in all of this??? Spend what little money you have and fix the darn simple problem first. Also, buy and read a Bently manual, you might be surprised by how easy it is learn something.
See above, entire cooling system has been replaced over the past year. And yes I know how much headache/time/$$$ is involved with custom turbos. But FI has always been a distant dream of mine, especially a turbo with a 6 speed stick. But you are correct, I should just calm down and get this issue properly diagnosed and fixed before thinking about that.
Quote:
Originally Posted by White_Knuckles View Post
Yeah, he's right, swapping engines and all things that go along with it is an expensive and frustrating adventure.

There is something wrong with a compression test performed with stripped threads as IXTOXI points out. Should the tester not seat due to cross threading (rotating freely at the seat point), most mechanics would agree the compression results are useless. Have someone verify the thread condition before a plug blows out like a missile.
For some reason, the guy that did the test thinks he got a good seal on the holes, and the test is valid. But who knows, he could just be trying to sell me on a very expensive fix. I only met this guy once, and I don't know him at all, except by reputation and he does have a good rep.
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