312 coolant leaks

55Brodie

55Brodie

Member
Purchased a freshly built 312 (approx. 100 miles on it) for my '55. Prior to install we pulled the heads and oil pan for a look see and everything checked out fine. We replaced the heads with a set of ECZ-G's I had run on my 272 for about 3 years with no problems. Looking for a little more compression we used steel shim head gaskets. Started the engine today and within minutes we had a pretty good coolant leak coming from both heads near the firewall end of the engine. Definitely not from the intake. The heads were installed per shop manual..gasket was copper coated both sides and heads torqued in 3 steps, 55,65 and 75 ft.lbs. The 2 long bolts each side are in the hollow dowell locations.

Questions:

The block had been drilled for coolant holes between the center cylinders while the heads were not. The steel shin gaskets do not have the corresponding matching holes for this modification. Is there a problem with running non-drilled heads on a drilled block?

I did not use sealant on the head bolt threads (a departure from the shop manual) because it appeared to me all head bolt holes are blind with no passage to the coolant. Did I mess-up here?

Finally, pending any great advice here the plan is to pull the heads and go back with composition head gaskets (which the rebuild 312 had).

Bummer...it sure sounded strong - if only for a little while.

Sorry for being so windy...I appreciate comments in advance.
 
Using the shim gaskets isn't a problem. When I had my last ECZ C heads looked at I had them faced. The machinist also faced my block which was way out. At the very least I would reface the heads.
Regards
 
Was the block decked? After so many years of heating and cooling, a skim off the block would have made a good surface for any gasket you choose. If you have a long straight edge, go over the cleaned block to check it. More than .005 out is a problem. Drill the holes, it can do nothing but help. Let us know how it comes out.
 
Brodie, When I first started my 312" (with steel shim gaskets) I had leak at the back of the head. Couldn't see where it was coming from. Started to pull the head and noticed the center studs for the intake were damp. The studs go into the water jacket on the heads and the water flowed along the valley pan and down the back of the head. Applied sealant to the threads and all was good. Before you pulled the heads check the studs. just a thought.

How you been otherwise, don't see you of the sites too much anymore??
 
I had some holes in the head that if the heads were reversed the hole was used for intake hold downs. WHen reversed the hole was not used, so it needs a bolt in it to plug the hole. I hope that makes sense. Gerry
 
Hi Blockhead - I'm okay, just a little bummed at the moment. I'll check the intake hold down studs before the big yank.

Don - no the block showed no evidence of being decked..the heads were shaved prior to the install on the 272 so warpage is probably a concern. If Blockhead's trick doesn't work out I'm going composite gaskets as thats what was on it.

Gerry..yes I know the bolt hole you're referring to. Not an intake hold down, though.

Thanks all. Follow up report will be forthcoming.
 
The two 3/8 holes rear of where the intake bolts down go right in to the push rod hole. I always use very short bolts with a dab of sealer on them to try and keep water out. A wrong length bolt here can bend a pushrod.
 
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