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Old 12-03-2007, 10:19 PM   #1
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Default New compression numbers... Motor or HG?

All right, went for a short drive to get everything hot... and then pulled all the plugs and cranked it with the gas pedal down.

Compression:
#1: 191
#2: 189
#3: 130
#4: 125

Those are significantly better than the old numbers with a cold engine, plugs in, and no throttle: 151 136 108 92.

The smoke coming from the tailpipe did not look blue at all. It didn't smell like what I thought burning coolant would smell like, but it was clearly white'ish.

So, whaddya think? Do I have a HG leak between the #3 and #4 cylinders? What is the next step to try and confirm it? I would think I need to drail the oil and check for coolant in it?

So, back to what to do? Since I'm gonna do a new clutch disc, it makes sense to pull the engine no matter what if I've gotta do the HG. I've been looking all over the internet, and Planet Miata has 1.6longblocks for $450. That honestly looks like the best deal for me if they've got something with "low" mileage.

However, I was reading in the Haynes about replacing a head gasket and the directions suck. I suppose it involves removing the timing belt, intake and exaust manifolds, fuel rail, and unbolting the head??? Then replace gasket and re-install??? I know there's probably a little more to it, but it would seem fairly easy???

All right, let me know what you think!
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Old 12-03-2007, 10:30 PM   #2
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I scanned the procedure out of the FSM for you. It doesn't look that grueling.
The intake manifold and fuel rail can stay in place, just disconnect the hoses and wires.

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Old 12-03-2007, 10:31 PM   #3
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My money would be on some sort of leak btw 3 and 4
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Old 12-03-2007, 10:35 PM   #4
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a leak down test would probably tell you..

pushing that air into 4, you should be able to feel it coming out of 3..
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Old 12-03-2007, 10:36 PM   #5
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I just read through the Hakuna page and it looks like I don't have to take the intake manifold or fuel stuff off... might not be worth it to take the engine out if it's as easy as it looks based on the diagram above.

I hear y'all on the leakdown test. I'm headed to Texas Wed morning, so it might have to wait a week.
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Old 12-03-2007, 10:38 PM   #6
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And the torque specs for the head:

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Old 12-03-2007, 10:43 PM   #7
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One of these will test will tell you
1. Leakdown test
2. Leakdown test
3. A leakdown test

One of those should work to find the cause fo the leak. If it's whitesmoking, the exhaust smells like honey, the sparkplugs on 3&4 are much cleaner than 1&2, and it's using a little coolant, it's 'probably' the headgasket. However, a leakdown test will tell you a hell of a lot more than someone on the internet. I would be hoping it's the HG as it's a lot easier, quicker, and cheaper to repair than the bottom end.
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Old 12-03-2007, 10:46 PM   #8
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Option number 4 that he forgot was:

4) leakdown test


As far as that hg that I offered before, incase you didnt see my fs thread I need it now for my backup motor. Sorryz
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Old 12-03-2007, 10:48 PM   #9
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Quote:
Originally Posted by Joe Perez View Post
And the torque specs for the head:

I cannot for the life of me undersatnd why they would want you to loosen them slowly.....in order.

I just crack them all and spin them out in the order that I can reach them with a Blue Point.
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Old 12-03-2007, 10:50 PM   #10
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typically if it were the rings it would be #2 and #4...it's just how they seem to blow (TDC the same). the low numbers on 3&4 probably says theres a leak in between.

if anything, its about an hour to remove the head. but the leakdown test will absolutely pinpoint it.

do you have lower vacuum at idle than normal? what does the MS say in kPa? coolant look good? oil look good?



and fwiw, the entire manual is here: http://www.boostedmiata.com/pdfs/servicemanual.pdf

Last edited by Braineack; 12-04-2007 at 12:42 PM.
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Old 12-03-2007, 11:00 PM   #11
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Quote:
Originally Posted by neogenesis2004 View Post
Option number 4 that he forgot was:

4) leakdown test
Damn, I knew I forgot one. Indeed, if test 1-3 don't get it, 4 will certainly pinpoint the leak.
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Old 12-03-2007, 11:11 PM   #12
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Quote:
Originally Posted by olderguy View Post
I cannot for the life of me undersatnd why they would want you to loosen them slowly.....in order.

I just crack them all and spin them out in the order that I can reach them with a Blue Point.
Only reason I could think is it may help to keep them from stretching. If you removed all but one bolt and that one is still at full torque, it's probably doing a hell of a lot of work, more than it's supposed to. I could be way off but that's my reasoning, and I always remove headbolts in steps just incase.
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Old 12-04-2007, 01:26 AM   #13
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So, I'd like a show of hands... who thinks I should do a leakdown test?
Nobody... really, not a single person... OK, I guess I'll just have to buy that built motor in the classifieds.
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Old 12-04-2007, 01:36 AM   #14
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I think that built motor is getting installed.
To bad for you.
Do a leakdown.
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Old 12-04-2007, 01:36 AM   #15
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Quote:
Originally Posted by samnavy View Post
So, I'd like a show of hands... who thinks I should do a leakdown test?
Nobody... really, not a single person... OK, I guess I'll just have to buy that built motor in the classifieds.
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Old 12-04-2007, 12:34 PM   #16
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Quote:
Originally Posted by olderguy View Post
I cannot for the life of me undersatnd why they would want you to loosen them slowly.....in order.

I just crack them all and spin them out in the order that I can reach them with a Blue Point.
Bruce....it nearly eliminates any chance of warping the head. warping the head would defeat the purpose of any head gasket work.
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Old 12-04-2007, 12:49 PM   #17
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so how about at LEAST a wet compression test? that'll rule out rings.
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Old 12-04-2007, 01:08 PM   #18
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Quote:
Originally Posted by budget racer View Post
Bruce....it nearly eliminates any chance of warping the head. warping the head would defeat the purpose of any head gasket work.
If you run the chance of warping the head by releasing the torque fully on each bolt, not in the pattern shown, it must be made of butter. Granted, that the workshop manual says to do it this way, but it seems like a little overkill.
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Old 12-04-2007, 01:19 PM   #19
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Quote:
Originally Posted by olderguy View Post
Granted, that the workshop manual says to do it this way, but it seems like a little overkill.
I agree.......but it's a good habit to get into.
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