1970 134 Fhead Head Gasket Replacement

guys...help me out here. I'm still not understanding what all went wrong. I had my head gasket replaced about 400 miles ago, by someone, not me.

the water pump overheated. it was a 46 year old water pump. it was time I'm sure. but then I replace it and the head gasket blows.
I had a 13 lb cap on the radiator. fine, I get that. too high a rating. but its a brand new 3 core radiator. shouldn't that prevent it from overheating right there?
if it got too hot at that poundage, by putting the 7lb cap on, isn't it just going to blow that much sooner?

I guess my question is what caused it to overheat so dang much to blow the head gasket or the water pump? if I had a 7lb cap, wouldn't it just have popped the release valve on the cap that much sooner?

I hope I fixed my problem, but understanding the problem is also important to me.

 

Overheating may have been the result, not the cause of your main problem.

If your head gasket (or possibly still a head/block crack) gets even the tiniest leak that can allow compressed gases to escape into your cooling system, it will build more pressure in there than any cap could hold. If that was the case, that excess pressure could have been what blew out the seal in your water pump. As soon as your cooling system is compromised with an air/gaseous pocket where there should be water, that spot will get super-hot due to air being a better insulator than water (water transfers heat away from the metal much more efficiently, and the air pocket isn't circulating). Water will boil at the edges of the air pocket and your engine will show signs of overheating by boiling over, even though the rest of your engine might not even be up to operating temperature yet. Does that make sense?

If this happens again, I'd suspect it is a crack in the head or block, or the head or block is out-of-flat, and it's probably not the head gasket.

Be sure to re-torque the head bolts at the recommended interval.

 

tonight I am going to change my oil before I fire anything up. if the oil is fine, and not mixed with coolant, that's a good thing. if its an oil and collant mix, that's a big problem, most likely more than just my head gasket, correct?

 

I wouldn't panic if you see drops or a pool of clean coolant in your oil, because some may have spilled in when you had the head off. If the oil is milky, that means the water was introduced when the engine was running and it all got stirred together. That might point to a bigger problem like a crack - as long as you're sure it is antifreeze and not just heavy condensation buildup from your engine not getting up to normal operating temp (but I don't remember you having that issue, did you?). Condensation usually shows up as a foam on the upper half of your dipstick.

 

Just for future reference the 13lb cap let your engine run hotter without boiling over. The higher pressure radiator cap doesn't make your engine run cooler.

 

I know it doesn't make my engine any cooler. its a pressure setting, but thank you.

 

I just did this same thing and these steps are absolutely critical:

1)pay attention to the throttle bracket and oil filter bracket (if I remember correctly) that use head bolts to hold them on. It's a bit frustrating having to remove and re-torque because you forgot them.

2)chase EVERY head bolt hole with a tap (7/16 x14 I think) and clean the debris out with a plastic bore brush from a gun store (spin counter-clockwise in a drill so the debris work with the thread pitch to get out.

3)make a tube out of thin cardboard to go around each piston so that no junk gets in the piston/cylinder space when you scrape the head clean... only use a razor to do it, no abrasives.

4)get a straight edge and check the head for any warping... shine a flashlight at the bottom of the straight edge, if you see light it's either warped or you need to do more scraping.

 

This was the explanation I was looking for.

 

On a positive note, there was almost no coolant in my engine oil just now. So hopefully that means it's just a cracked head gasket that went to the exhaust manifold area

 

Way to drop some knowledge on people I like it good explanation.

 

so...talking to the father in law....and before I get too involved, he said I need to change the head bolts every time the head gasket is changed. these are grade 8, and appear fine. maybe on newer engines this would be an issue, but do I need to do it in this application?

 

Agree with Howard you only would replace torque to yield bolts that stretch. On subarus etc.

 

My dad just had his L-head rebuilt by an old-timer who is a bit of a legend when it comes to these old engines, and they had this same conversation.

He said he used to always replace the head bolts, but quality bolts are getting so hard to find, old used bolts are better than new ones. He's been stockpiling used head bolts for spares.

He was having a recurring problem with new bolts punching holes in his garage ceiling on initial warmup! As the engine would warm, parts would expand, and the bolts would break rather than stretch, shooting the bolt up out of the head and into his ceiling.

 

Check the FSM. I'm sure it will not say anything about new head bolts. And when the FSM/TSM was printed, these bolts could have easily been pulled from the dealer's shelves.

 

Correct. No mention of new bolts - and why would there be with a compression ration of 7.4 to 1?

The FSM does however recommend re-checking the "tightness of the head bolts" again after 500 to 600 miles. (Perhaps not necessary with modern gaskets?)

 

I didn't think so, but my father in law was pretty sure. if they were replaced with grade 8 bolts 400 miles ago, I don't see them stretching.
thanks guys!

 

Grade 8 bolts are not the same as head bolts... proper head bolts will have a shoulder below the cap that distributes the torque more evenly instead of directly on the bolt head. On engines like ours, the head bolts are fine to re-use unless there is any defect in the threads.