| johnpoly | -- 01-27-2010 @ 3:45 PM |
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My '36 Conv Cpe has a 21 stud engine with the heads carrying two different numbers. The left head is marked "68-6050B", and the right head is marked "68-6049B". There is a difference between them in that the four spark plug wells on one head are deeper than the other head. What have I got and what issues are there with having these two different heads, i.e., compression? Replies appreciated. John
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| CharlieStephens | -- 01-27-2010 @ 9:07 PM |
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The number 6050 means it is a left head and 6049 means it is a right head. The "B" is a revision number. The "68" is the prefix for the year the head was first used. Thus the heads should be a pair. My guess would be that the heads started with the same compression but one may have been milled more than the other over the years. If the combustion chamber appears different have your machine shop measure the head combustion chamber volume (this is something I usually do when rebuilding an engine). If the heads have visible different combustion chamber volumes I would look for a new head (or 2) and skip the machine shop. A machine shop can rework the heads a slight amount to make the combustion chambers equal but it will cost. This us usually referred to as "cc"ing the head since the measurement is in cubic centimeters (cc) Charlie Stephens This message was edited by CharlieStephens on 1-27-10 @ 9:10 PM
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| BrianCT | -- 01-28-2010 @ 5:59 AM |
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Are you saying that the depression in the head is deeper on one? Does one head also have a larger diameter depression? I think the smaller diameter depression is usually marked A2 and is a second generation design. I should have asked if these are aluminum.
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| johnpoly | -- 01-28-2010 @ 7:53 AM |
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The heads are cast iron,not aluminum. John
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| supereal | -- 01-28-2010 @ 9:34 AM |
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As a machine shop operator, I agree with Charlie regarding measurement of the combustion chamber. Equally important is to determine, particularly with non matching heads, whether there is adequate clearance for the valve heads. Some replacements for early heads required milling the valve area to prevent interference and the possibility of bent valves. To do this, we "clay" the heads, placing modeling clay into the valve area, bolting the head on, and turning the engine over. When you remove and examine the heads, you will quickly see if there is a problem. If there is a large difference in compression readings in an engine, the valves should be checked to see if the stem is slightly bent from lack of clearence.
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