Frequent re-torquing or coolant leaks on Flat 6 heads?

12905 · January 25, 2007, 12:05:22 AM

The Welch/frost/core plugs are properly named Welch plugs. They are there as a means of removing the sand core after casting the unit. I'm told they got the name 'frost plug' because in the days before ethylene glycol antifreeze, alcohol was often used, or just water that was drained (supposedly) after each use when the cold engine would be subject to freezing temperatures. In additon to that hit and miss system the alcohol used as antifreeze was volatile and boiled out, and was often replaced with water only.? Sometimes the owner got lucky and when the coolant froze the Welch plugs popped out and saved the casting. Hence the development of the term frost plug. However, more often than not the plugs did not pop and the result was a great number of cracked blocks/heads up to post WWII.? In fact, our plant had one specialist on staff whose job it was to repair cracks in heads and blocks and to replace whole chunks of crankcases that were broken out by "thrown rods". A phenomenon known to many earlier models of vehicles produced some of the independents and one of the "Big Three" (not Chrysler Corp).

Just as a matter of interest: Does anyone reading these posts have experience with the system of "stitching" cracks using 1/8" pipe plugs?

TodFitch · January 24, 2007, 10:50:17 AM

My way of removing core/welsh/freeze plugs is to use my electric screwdriver to put a self-drilling, self-tapping sheet metal screw into the center of the old plug. I don't run it all the way down but leave the head up a bit. Then I take a carpenter's hammer and use the claw portion to hook on the screw head and pull the plug out.

As for installing the new one, I have done it exactly the same way as elmo54 describes. On my 1933 PD I was able to get to the plug at the rear of the block by removing the floor boards and accessing the plug from the inside of the car. I suspect that would not work on your car.

elmo · January 24, 2007, 01:50:13 AM

Ryan i dont know what it is called over there ,but that plug in the top of the head on the drivers side is called a frost plug or a welch washer here .it is most likely the cause of the leak, the heater outlet is on the other side. if the frost? plug is leaking it would pay to check the drivers side of the block as there are five more plugs along there ,also there is one on the rear of the block but it is located behind the bell housing . i dont mean to be negative but if the top plug is leaking the chances are the other ones are not far off . they are not to big a deal to replace except the back one. if you have to replace i would suggest that you do with brass plugs . to remove them you simply drive a hole through them and lever them out with a screw driver to fit clean all round the hole wipe on some gasket sealer or liquid solder and hammer the dome of the plug with a ball pene hammer, (engineers )not to much as you can cause it become loose .Iam not to sure on the size of the top plug .i think it is 1 1/16" but i have just replaced the ones on the side and they are 1 5/8"....Rex

50Plymouth · January 24, 2007, 12:21:50 AM

I think there is some kind of plug in that upper corner. Also something coming out of the side if I remember right. I think you guys are right and one of those is the guilty party, probably the plug since the leak evidence is on the top and not side. Since the water guage is on the side it seems unlikely for the coolant to defy gravity.

Not sure from memory if there is one of those vertical heater valves back there going to firewall or not. I've read those leak sometimes.
Would replacing the plug be a big deal at all?

Ryan

TodFitch · January 23, 2007, 11:50:18 PM

On my older head there is a freeze/welch/core plug on the top of the head near the back on the driver side. I am not sure if they continued that on the later engines. But you could have a leak there.

In any case getting a head for a Plymouth L-6 engine, if needed, should not be hard to do. They use that basic engine design for decades.

martyb · January 23, 2007, 11:29:53 PM

The rear driver's side of the head is exactly where the water temp gauge bulb is installed; it could be leaking from there.

Marty

50Plymouth · January 23, 2007, 08:47:02 PM

Thanks. When I get the car into my garage for a closer look I'll check into that. Is there a sending unit or anything around the rear, drivers corner of head that could be leaking on the top? (car is a ways away) I'd heard of over heating, warping cracking issues with other makes L-heads and wondered if it applied to all engines.

My fears are mostly alleviated about head being messed up. I'd hate to have to locate another undamaged used head for it.

Ryan

elmo · January 23, 2007, 07:42:21 PM

Ryan....Some of the Plymouth flat head studs are tapped right through in to the water jacket i think from memory the rear ones are. If that is where the coolant is coming from you may have to remove the stud and clean the threads on the stud and run a tap through the block thread to clean it. when i install the head studs i apply a little sealer to the stud threads, with the exception of the three studs that go into the inlet manifold ports as it is possible it could be sucked up in to the carb. When installing the studs first torque them down to 35lbs then to 65-70lbs .after travelling about 100 miles retorque them again with the engine hot ,after that you should not have to touch them again .....Rex

57plymouth · January 23, 2007, 06:30:47 PM

I retorqued mine, but I'm very paranoid.

50Plymouth · January 19, 2007, 08:35:22 PM

TSM = Technical Service Manual ... oops, maybe thats not the common acronym for Chryco\mopar Shop Manuals?

Go Fleiter · January 19, 2007, 06:33:04 PM

sorry, Ryan, what please is Your "TSM"? Greetings! Go

50Plymouth · January 19, 2007, 03:33:38 PM

Thanks, that answers my question concerning any reputation or common issues at least (totally new to Chryco's let alone old..) As I said, I haven't yet so much as checked the torque so when I get my TSM I'll check.

Ryan

12905 · January 19, 2007, 03:25:01 PM

Ryan:

I have never heard of a head gasket problem with any L-head Chryco sixes, and my experience covers samples of virtually every year they were used. Any time we had a head off, we simply cleaned the gasket surfaces really well, checked the head for warpage (very rare) and used a good quality head gasket to reinstall it. However, we did follow the tightening sequence exactly, and after the head was snugged down we did torque in 3 steps (2 increments and a check after the engine was warmed to operating temperature). I don't recall ever having a come back for a leaking head gasket.

There could be one or more of a number of reasons why you have a leak, including a cracked head, poorly cleaned mating surfaces, a warped head, incorrect torque, incorrect torquing sequence, re-use of an old gasket, putting gasket "goo" of some type on the gasket, poor quality gasket, and probably some more I can't think of.

Brian

50Plymouth · January 18, 2007, 09:40:58 PM

I noticed a small teaspoon amount of coolant on the top rear drivers of my '50 plymouth p20 after running in a circle around the yard a few times recently... I never check head bolt torque before starting up the project. (also am still waiting on TSM)

Do these flat 6's have a reputation concerning the heads at all? Frequent overheating, cracking, or gasket issues if not regularly torqued?

Thanks,
Ryan