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Sears Super 12 Hydro "Blows Head Gaskets"

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Post  Shelby3601 January 28th 2014, 9:38 pm

Hello Everyone, I have a 1968 Sears Super 12 hydro and have had it over 25 years, I am having trouble with blowing the head gaskets, on the 12 horsepower Tecumseh, with the electronic ignition, It blows at least 2 a mowing season since I have owned it, and one just this week while plowing snow. I have had the head shaved, and even bought a new head at one point, it has the airflow tin on it, to keep it cool, Ive torqued it correctly, 220 Inch lbs. I have done everything I know to fix it and I just keep blowing head gaskets? Any one out there have any Insight? Thanks in advance..

Shelby

21:34:10  2014-01-28
Shelby3601
Shelby3601

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Post  TKW January 30th 2014, 9:32 am

this sure is an odd one , shelby , couple questions : have you ever done a compression check ? you said you had the head shaved . because it was warped ? or ? does the engine seem to be overheating ? lean fuel mixture ? does it blow out in the same section of the gasket each time ? / tim

TKW

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Post  Shelby3601 January 30th 2014, 12:10 pm

I only have done compression checks when it was blowed, 30 on the gauge, but surprisingly it was hard to start, but once it started it ran good even with only 30 lbs compression!! Yes it seems to blow near the same place everytime, looking down at the top of the engine, exhaust muffler side, 2nd bolt back, from the front of engine on the right side. Yes when shaved it was warped a little the dealer told me, dose not seem to be overheating, same thing the dealer asked me, it didn't have the cooling tin on it at first, so I ordered it from the dealer but to no avail, it blew the same month with the tin. It starts and runs good, for a while then bang, one day I will hear the air puffing from the side of the head?
Shelby3601
Shelby3601

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Post  TKW January 31st 2014, 11:41 am

i've been up all night thinking about this , ha! work third shift , got two or twenty more questions or thoughts.
> have you ever had the top of the cylinder checked for warpage ?
> what head is on it now ?
> has the engine been rebuilt if so over bore ? valve job ?
> the section that is blowed out does it look burned ?
> with this happening two times a year have you ever pulled the head between times to see what things look like ?
> have you checked the exhaust valve clearence ? should be set at .020
> is there a bunch of carbon build-up between times ?
> adjusting the carb to a richer mixture ?
thinking outside the box
> ever tried stacking two head gaskets ?

hope these aren't the same questions you've answered a thousand times before. i'm sure i'll think of some more. / tim


TKW

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Post  Shelby3601 January 31st 2014, 11:49 am

Hi, Thanks for thinking about this lol,.

Well here goes.
1 no never had the cylinder checked
2 the head on it now was a new one 5 or 6 years ago
3 engine was never bored its all standard as far as I know, I have owned it over 25 years
4 Yes the section that blows looks burnt out
5 No never pulled it apart to just check it
6 Valves have been set a few years ago.
7 no carbon build up
8 carb adjustment was just the power screw as far as I know
9 thought about 2 gaskets, we might have something here? I was going to try it.
Shelby3601
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Post  TKW January 31st 2014, 12:46 pm

sent you a pm / tim

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Post  spence February 1st 2014, 12:24 pm

Check the top of the cylinder....not the head....for deck warpage. It's kind of hard on a single cylinder, but being as you know where the gasket blows, it may make it easier to lay a straight edge across there to see if you can detect warpage.

Search Youtube for videos for further explanation on the procedure. Most videos will relate to auto applications, but you will get the concept. It can be applied to your engine also.

Tecumseh made a big deal about Belleville washers on their heads back in the day. I don't think I've ever see them on any of my machines, only lock washers. It may be an option to find some of them and use them on your engine.

Are you using quality head gaskets? Putting two head gaskets on will lower compression just a bit. Yes, it will help if there is warpage also. If you do that, make sure you keep a routine check on cylinder head bolt torque.






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Post  bluecometk February 24th 2014, 12:02 am

A couple thoughts on your dilemma
You will have to have both surfaces checked to see if they are true/straight.
Next you need new factory or high-grade bolts and flat washers.
All the boltholes and threads need to be chased and cleaned out.
Check your existing bolt to see if they are all factory length
You will need to measure the bolt hole, Thread, and shoulder depths and verify all bolts have deep enough holes and threaded to the proper depth.
Contrary to common automotive beliefs the mating surfaces of the head and block need to have a smooth polished surface. Not a rough surface. The head has to be able to move around on the block and gasket as it expands and contracts.
When installing the new bolts use thin motor oil on the threads, shoulders, washer (both sides) and the head of the bolt.
Note don’t use so much oil as to cause a hydraulic lock in blind bolt holes.
Torque the head down in small increments.
Let sit and back the head bolts off a ¼ turn and re-torque them to spec.
Lastly run the engine up to temp and let cool repeat the torque procedures above.

When using the engine it is imperative that you build heat in the motor before using it under high rpm and heavy load. This is so it can get thermally relaxed so to speak.

If these recommendations don’t help you can have a copper annealed head gasket made with a stainless fire ring built in custom made for your engine.

Just my two cents on the subject hope this helps.

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