OT. 67 mustand engine

JL Ray · Jul 1, 2015

I have a 67 mustang with a 200 inline six. The engine was rebuild two yrs ago and has ran fine. 9000 miles now. last week it started to miss real bad so I started checking things out and find I have cylinder 4 and 5 with 30 psi compression. The rest at 140 to 150. My guess is right now I have a blown head gasket. No oil in the water yet. No water in the oil yet. Does this sound right? Just guessing is this all I'll find wrong? I would think it to be smart to have the head check for flatness when out. Working on this old car is like working on my Super 55 or my IH 350 tractor, easy to get to.

Thanks in advance.
JL Ray

ohiojim · Jul 1, 2015

did you check it wet ?? likely tell if it's rings...JIM

Russ from MN · Jul 1, 2015

Sounds like a head gasket just starting to go, we had the same thing on a 300, those cylinder were awful close together. the head was warped, got it machined, a new gasket and all was well! Maybe your head was not torqued thoroughly.

jimg.allentown · Jul 1, 2015

Definitely head gasket. It is failed between the two cylinders. Since there is not a lot of coolant flow through the head in that area, you probably will not get oil in water or water in oil.

To answer a couple of the other posts.....

There would be no point to doing a wet/dry compression test on something this obvious. The likelihood of two adjacent cylinders BOTH having ring problems is simply nonexistent. Why? Rings do NOT fail all at once. They fail GRADUALLY over long periods of time. And, two right next to each other while the other cylinders are ok??? Come on!!!

As to the head gasket "starting" to go.......
There is NO "starting" about it. It is GONE. You simply cannot run a 6 cylinder engine on 4 cylinders for any length of time - too rough running, to much loss of power, and too likely to stall in traffic.

merlynr · Jul 1, 2015

We had one in a 66 Mustang that ran sweet for about 40k miles and it got low pressure in one cylinder and it was the valve seat. Had the head redone with hardened valve seats and all was ok. Tough little 6 with 7 main bearings.
I'm guessing you have blown gasket because of adjacent cylinders.

David G · Jul 1, 2015

The probability of a blown head gasket is so high, I would just pull the head without any additional checks.

M-MAN · Jul 1, 2015

It would be a good idea to lay a straight edge on the head and block. It would be a better idea to use a good torque wrench and use the proper sequence this time around. It should not have blown between the cylinders in 9,000 miles. Then again a crack in either one can cause the same symptoms.

ditchwitch · Jul 1, 2015

Buy the combustion test kit from NAPA or any parts store. Its simple easy to use. It will tell you
right off if its a head gasket.

RandyB(MI) · Jul 1, 2015

Will add to "M-man" post, use NEW top quality head bolts and clean thread bolt holes good.

Billy Shafer · Jul 1, 2015

Head gasket most likely problem. Cylinders swapping compression. I have found it on many Onans that used that engine.

kencombs · Jul 1, 2015

That only works if the leak is into the water passage. I'll bet this one is blown cylinder to cylinder with no water passage affected.

Either the head wasn't surfaced or improperly torqued on last rebuild. new bolts are not required on that engine. Later Fords do have the torque to yield bolts but not back then!

Anonymous-0 · Jul 1, 2015

(quoted from post at 12:45:50 07/01/15) Definitely head gasket. It is failed between the two cylinders. Since there is not a lot of coolant flow through the head in that area, you probably will not get oil in water or water in oil.

To answer a couple of the other posts.....

There would be no point to doing a wet/dry compression test on something this obvious. The likelihood of two adjacent cylinders BOTH having ring problems is simply nonexistent. Why? Rings do NOT fail all at once. They fail GRADUALLY over long periods of time. And, two right next to each other while the other cylinders are ok??? Come on!!!

As to the head gasket "starting" to go.......
There is NO "starting" about it. It is GONE. You simply cannot run a 6 cylinder engine on 4 cylinders for any length of time - too rough running, to much loss of power, and too likely to stall in traffic.

Good post. Dead on.

ditchwitch · Jul 2, 2015

We use it here at the shop and its never failed us before. If the head gasket is blown either straight at the water jacket or in between cylinders it dont matter . you can bet some of the combustion is going into the water jacket. That what this stuff does it detects exhaust gasses in the antifreeze.

Brian G. NY · Jul 2, 2015

I'm throwing this out for what it's worth.......burned valves?
These engines, as with other Fords of around that era, had some problems with premature valve guide wear and resultant burned valves.

jimg.allentown · Jul 2, 2015

Just throwing this back...
What do you think the odds are in favor of burning valves in TWO ADJACENT CYLINDERS AT THE SAME EXACT TIME?????????
Come on already. Pull the head and be done with it for crying out loud.

Love this - every answer under the sun except the right one. Anything to avoid doing what it needs. Maybe it needs a can of "mechanic in a can" - that is sure to fix it.....

Anonymous-0 · Jul 2, 2015

(quoted from post at 19:11:45 07/02/15)

Love this - every answer under the sun except the right one.

Pretty common around here.

OT. 67 mustand engine

JL Ray

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ohiojim

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Russ from MN

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jimg.allentown

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merlynr

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David G

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M-MAN

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ditchwitch

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RandyB(MI)

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Billy Shafer

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kencombs

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Anonymous-0

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ditchwitch

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Brian G. NY

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jimg.allentown

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Anonymous-0

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