Compression Test Results

[crownvic97]

Finally got around to doing a compression test on my new Marauder. It’s been having a cylinder 8 misfire unchanged by plug or cop change. I pretty much knew what the test was going to say, but here are the results to back it up...

Cyl 1: 210
Cyl 2: 210
Cyl 3: 210
Cyl 4: 210
Cyl 5: 210
Cyl 6: 210
Cyl 7: 190
Cyl 8: 85

I put a little oil in 8 and retested, it was roughly the same, maybe reached 90 but that could just be gauge inconsistency.

So, correct me if I’m wrong, I have a valve/valve seat issue on 8 and the head needs to come off.

Question for all:

Do I just pull the D/S Head have it gone through and slap it back on? Do both heads? Pull the engine and do an entire rebuild?

I plan on checking/replacing the timing chain guides and tensioners when I pull the head. But at 166k miles, am I stupid to put all this work in to the top end and leave the bottom end alone?

Any advice is much appreciated.

[Logizyme]

Well you should probably finish your diagnosis by determining the actual failure.


A leak down test would help indicate where your compression is going - into the intake could indicate something wrong with the seat, or possibly the lifters/followers or spring.


Depends how much you want to spend, you could do as little as replace a seat and headgasket to replacing the engine.

[RubberCtyRauder]

Send a pm to A_D_A_M here..he had pretty much same issue a couple years ago on number 8 and just did the head..He can prolly tell you some info.

[crownvic97]

Well you should probably finish your diagnosis by determining the actual failure.


A leak down test would help indicate where your compression is going - into the intake could indicate something wrong with the seat, or possibly the lifters/followers or spring.


Depends how much you want to spend, you could do as little as replace a seat and headgasket to replacing the engine.

I’m not disagreeing, but given the numbers and that adding oil had no measurable change in the number, it is pretty likely the issue lies in the head and not the the bottom end/piston. That, and the history of the cylinder heads with #8 issues.

[crownvic97]

Send a pm to A_D_A_M here..he had pretty much same issue a couple years ago on number 8 and just did the head..He can prolly tell you some info.

Yes, that is a good idea, I did see his write up.

[Zack]

I would do both heads

[justbob]

I would do both heads

100% agree.

The fact that you are only 10 bolts and 8 exhaust studs away from doing it anyhow only makes sense. Sure it's another $225 or so in rebuild labor, but if you wait till next year or whenever it goes bad you'll certainly kick you own ass for having to dismantle the top and front of the engine again! If your on a tight budget though I totally understand that..

Here is a good price on a gasket and bolt kit.

https://fordracingpartsbydonwood.com...SABEgJWjfD_BwE

Might want to consider a rear cooling mod on the re assembly as well..




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[crownvic97]

I would do both heads

100% agree.

The fact that you are only 10 bolts and 8 exhaust studs away from doing it anyhow only makes sense. Sure it's another $225 or so in rebuild labor, but if you wait till next year or whenever it goes bad you'll certainly kick you own ass for having to dismantle the top and front of the engine again! If your on a tight budget though I totally understand that..

Here is a good price on a gasket and bolt kit.

https://fordracingpartsbydonwood.com...SABEgJWjfD_BwE

Might want to consider a rear cooling mod on the re assembly as well..




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That’s what I was thinking, it would be kind of crazy not to do both cylinder heads once it’s torn down. Thank you!

Budget isn’t tight really, I’ll spend what I need to get it done right, just wasn’t expecting to be doing major repair so soon.

Thank you for the link to that, and I will definitely be doing the rear cooling mod when I put it all back together.

If I can find some 96-98 Cobra intake cams I may try to swap and degree the cams. I hate to tear something apart without upgrading anything.

[a_d_a_m]

I only did the driver's side head, but I also only had 100k on my car and the inside looked fairly clean, plus I was pretty cash-strapped that year.

If you can swing it, yeah, doing both sounds like the better option.

[crownvic97]

I only did the driver's side head, but I also only had 100k on my car and the inside looked fairly clean, plus I was pretty cash-strapped that year.

If you can swing it, yeah, doing both sounds like the better option.

If I only had around 100k I probably wouldn’t do both, but at 166k it seems like the right thing to do.

[crownvic97]

Last question before tear down...should I do this with the engine in the car or pull it?

[BLACKMARAUDER04]

What is the approximate cost to fix this?
I have same problem in cylinder #7 on my new Marauder.
It has a miss at low speeds causing the engine light on.

[crownvic97]

I’m up over $5k in parts, but that’s because I went way over the top and am rebuilding the whole top end and adding a bunch of mods while it’s all apart. I suspect you could do the whole job for around $700 if you only do one head and put everything back together as is.

[FordNut]

Or just drive it.

[crownvic97]

Or just drive it.

Wouldn’t that cause further damage? I was wondering about that actually.