Blown head gasket

[Maclab58]

Well my wife and I were out driving our 31 Cabriolet last nite looking at the Christmas lights when the car started running kinda rough. We headed home and put it away for the night with plans to look at it this morning. This morning there was some antifreeze on the floor so I backed it out of the garage. It started fine but when I popped the hood there was antifreeze on the top of the head and what appears to be bubbles coming around the #2 plug. Previously there had been some dampness around a couple of head studs but no obvious fluid so I retorqued the head to specs but didn't notice any change. Of note, I have only had this car for a couple of months, it has a balanced babbit engine with low miles and runs and idles very nicely but I can't seem to get it over about 45 mph. I plan to drain the oil and coolant tomorrow and pull the head to replace the head gasket. Any suggestions?

[1931 flamingo]

Try to clean as many cooling passages as you can with the head off, ck the head and block for flatness. Maybe shave the head a bit just to be sure.
Is it a copper or silicone gasket??
Paul in CT MERRY CHRISTMAS

[BRENT in 10-uh-C]

I suggest performing a "leak-down test" by injecting air into each cylinder while the piston is at TDC. I would not change the oil or anything until this is done.

[Maclab58]

Brent, can you explain how to do the leak down test ?

[Bob C]

Here is a how to on you tube https://www.youtube.com/watch?v=ofSiTGeLXvc

Bob

[BRENT in 10-uh-C]

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Overall that is the foundation for a leakdown test however I think that guy's gauge is malfunctioning as it needs to be set with 100 psi (--or at least mine does) to get an accurate reading. The biggest thing, however, that you are searching for is to find where the compression is leaking BEFORE you disturb anything. For example, if you inject air into #3 cylinder and you see bubbles in the coolant, then you can search for gasket issues or cracks in the #3 area however if you should hear air escaping out of an adjacent spark plug hole, you can pinpoint where the gasket damage is. It also is a great way to check ring wear or non-seating valves.

[Logan]

Get the head milled flat while you have it off

[larrys40]

Maclab,
I would definitely do as Brent described. Do a leakdown before the head is removed and disturbed. Look/listen for leaks in the intake, exhaust, and cooling system. An yes, as suggested I would surface the head to ensure that it is flat. You can put a straight edge on it if you have one and with a feeler gauge see if it is out anywhere.

If you can't get over 45 mph it could be a number of things. First I would test to make sure you're getting full throttle. Have someone press on the accelerator and make sure the throttle is going to the stop on the carb. IF not you have an issue there... and may need to fix/tweak the throttle assembly and or rods to correct the issue. Timing, other carb issues, etc can also be attributed, but I can say that at least 25% of the "A"'s I've worked on don't have full throttle or have issues with the linkage. It is very common.

I like the old Sun Test Equipment slogan. " Test, don't Guess".... so do your compression test and leakdown and see what you have before you pull the head. You won't be sorry. Go ahead and then pull the head. Examine bock and head and valves for proper seating. If any valve service is required now is the time. Also.. proper clearances can be checked and corrected if need be.
Best of luck!

BTW.. I have a 68C to restore... so looking at your's when you posted the photos definitely makes me envious.
Larry Shepard
St. Charles, MO

[Mitch//pa]

agree with brent and larry do the diagnosing now "a leak down" which will lead you to what to ck for once its apart. i have used a hollowed out spark plug base and then welded an airline nipple onto it and used an inline air regulator to do leakdowns. the only thing missing was a gauge showing leak percentages but youll be able to mainly accomplish the same thing without buying anything....

same goes for drivability issues on some of the other threads, a systematic diagnosis spark//fuel sure beats winging parts on and off. its ashame most just dont listen to the advice given, very frustrating at times

[larrys40]

As Mitch said you can/should do the leak down . You can build you own setup or and I forgot to mention harbor freight has an economy leak down on their website or in their stores. I've used them before. As Mitch said you will probably need a spark plug base modified for the "A" use
Listen to hear if you have any poor seating valves either thought the carb doe intake and tailpipe for exhaust
Keep us posted
Larry

[Maclab58]

Great advice guys! I will make a compression ck gauge and a leak down gauge tomorrow. I agree with the fact that there is a lot of great advice given here that goes unused. The thorough explanation as to why to take all of these steps sure helps us newbies understand the logic behind the testing! Will post my results!

[BRENT in 10-uh-C]

Larry, did you watch the YouTube video posted above? Does your Harbor Freight unit only set to 15 pounds like the one in the video did?

[larrys40]

Brent I don't have a harbor freight unit but have used them No I haven't watch the video yet but I will
Thx
Larry

[larrys40]

Ok I took time to watch the video. It's ok. There is a point where too much pressure will actually turn the engine over which will also happen on a loose engine as well. I will have to look at mine tomorrow to Check the pressure set I think mines a little more than that if you have a poor seating valve or leaking head/water jacket it will probably show up at the lower test pressure of 15-30lbs

I just suggested the hf units as they are inexpensive and readily available and for the most part will get the job done. Being a tool nut and Krw junkie good quality tools are my thing
Would love to read more feedback and experience on this
I've done quite a bit of in the car valve seat grinding with my portable souiX unit it does a great job, replace valves when needed , lightly grind seats and lap and test for contact will improve many an engine
Larry

[tbirdtbird]

15# ?? gotta be 100#

yes a lot of readers just guess or randomly replace stuff instead of listening to the step-by-step diagnostic stuff tossed out here by the pros.....

When reading problems here the most obvious thing missing is any attempt at diagnostics.
what we get is, 'it won't start'

what we need is,
-it won't crank
-it cranks but won't fire
-it cranks but won't fire and there is a nice blue spark from the wire to the plug

etc etc

it won't spin the engine if it is in gear and the ebrake is on.....

[Mitch//pa]

here is a pic of the tools i made for conventional engines from hollowed out spark plugs. the same can be done from a model A spark plug or even a 3x by unscrewing the electrode.....

[James Rogers]

I always use my thumb. I just remove all the plugs and put my thumb over each plug hole and spin the engine with the starter.When I find one with no compression,I know what the problem is. If this test is inconclusive,I use a compression tester.

[81deeds]

Great youtube video...thanks for sharing