273 Commando - Coolant leak - Cometic MLS Head Gasket

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robodhran

robodhran

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Hi - just finished my 273 cui 1966 commando engine outside the car and started it on an extra-made test-stand (wish I could show you the movie - it's cool)

It started properly but developped small drops on the driver's side head gasket (see blue arrow).

I am using cometic MLS .51" head gaskets, that need a Rough Average of 50 (RA). Let's suppose there is no crack in the head and block, because it has been pressured.

I am rather supposing, the block and head surface has not been smoothed fine enough, so water has found its way across those small grooves still existing. Altough Cometic Gaskets provide a small coating of sealant, it might not have been enough.

Since I am an engine-"rookie" I am also wondering about those missing water channels in the heads (red circles) - head # 2658920 / the block has its openings... ? I do have two identical blocks and four heads, they all are the same.

My idea is to smoothen the surface with an oil-stone first.

Any ideas about the gasket? Is there any other manufacturer, who provides at least .51"-thickness gaskets with the bore size 3.700"? Gaskets, that have a softer surface to completely seal up the heads?

Any suggestions?

Thanks - Robert
 

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Thanks - Great! By the way: no water in the cylinder! It's completely tight!
 
I wonder if the head gasket just wasn't sealing the water hole in the block since there's no corresponding hole in the head? Perhaps some kind of plug for the hole in the block?
 
Those extra block deck holes are there for the casting process for the block. Being blocked by the head gasket is normal. The coolant flows front-to-rear through the block, enters the heads near the back, and then flows back-to-front through the heads.

I think I'd just put a light spray coat of CopperKoat on the head gasket, just to help fill out the surface roughness. It's standard procedure for reusing Cometics for when the coating gets worn off anyway. I can't see where it will hurt as it ought to bond to the block and head surfaces, and help fill in the surface roughness. And it is SOP for shim metal head gaskets.
 
The direction from Cometic is a minimum of 50 on the Ra. It's myexperience that you really need closer to 30 for them to seal immediatey. Looking at your pictures - those are too rough. It is very common for them to leak a little if the surface or surfaces are too rough. They tend to stop after a couple heating cycles. If you don't want to do that, they can be pulled, cleaned, and copper coated before reinstallation.
 
In this instance it's basically the surface finish of a machined part. What we see is a metal surface cut or ground to a certain finish. but the act of cutting or grinding tears away material, leaving high and low spots on the surface. The Ra value is a number that represents how smooth the machined surface really is. The smaller the number, the smoother the machined surface is. Normal stock type gaskets seal from 40-100 but too smooth and they can't grip the surafces and can move around. MLS need smoother surfaces because they don't really bite They're made to move a little but if the surface is rough, the fuilds can seap past it. Sometimes it goes away. Sometimes it doesn't.
 
Ford takes like a 20 RA on some of its motors, thats like a mirror! MLS are designed to slip and slide with AL heads on iron blocks with different heating coefficiants. A touch up with some 220 on a long sanding block wouldnt hurt. And a touch of spray paint sealer.
 
Those scallops are for the steering gear on the first gen chassis as they were so narrow.
 
Moper got it rite on the head! My 273 did the same thing shortly after getting it running. The key is very smooth finish! Its wild mine dribbled from the same area ever so slightly. Never made it to ground just noticed paint discoloration when I change oil after break in. BTW what pistons do you have in there? They look sweet!?
 
The pistons are from RaceTec, Huntington Beach, Ca. They are sweet but pretty expensive. Unfortunately they missed to widen the Pin Boss, so the original rods did not have enough space. Decided to machine them here in Switzerland, instead of shipping back to U.S. (freight cost vs. machine costs). I ordered many engine parts at FBO in Oregon. Don does a good job!

So I guess we circle the problem. I have a nice New Mexican Oil-Stone and will smoothen the surface of the head and block and put a little spray on, although Cometic does not recommend that. I don't mind. Asked them, but they do not provide thicker sealant-coating. Maybe I'll check the bolts (stretching issue) as well. Found some new bolts at ARP.

Any other gasket manufacturer known, that provides thicker gaskets with f.e. compound material?

Engine wants to go back into the car finally...and I promised my mother-in-law a ride with the fish long time ago. :)

Thanks for your helpful comments so far!
Robert
 
...and I will definitely have to continue my thread in "members restoration"....just did not find time and muse... but do have wife, kids and job...haha
 
robodhran said:
...and I will definitely have to continue my thread in "members restoration"....just did not find time and muse... but do have wife, kids and job...haha
Click to expand...

Lol! I have a wife, no kids or grandkids at home and now I'm just a retired bum with not a lot of money lol! Good thing I tried to buy everything I thought I would need or though I needed before retiring for good. When we decide to come back to Europe (and we will) gotta save long time for it!
 
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