Posted by Bulldozer on January 30, 2013 at 08:54:51 from (24.165.92.6):
In Reply to: Re: head bolt question posted by John Smith8N on January 28, 2013 at 18:12:28:
Also agree with ZANE that surfacing the flat head cylinder cover is not required, even if there is evidence of warp using a machined straight edge.
However, do believe that surfacing is required if the cover has been subjected to overheating of the engine causing a leak between the cylinder and the coolant jacket.
Believe overheating of this engine is quite unlikely since the maximum rated rpm is 2000 and the compression ratio is only 6.7:1, unless the engine is run when low on coolant or no coolant.
Consider when the cover is manufactured as a sand casting, it cools non uniformly, creating temperature gradients in the cooling process. These thermal gradients result in a residual stress state in the cover. Now, the cover is machined flat and installed on the engine. The engine is run at normal temperatures. The cover is not at a uniform temperature and temperature gradients are developed. There is stress developed in the cover from the thermal gradients. When the engine cools to ambient temperature a portion of the stress developed at normal operating temperature still remains as residual stress in the cover. When the cover is removed the residual stress developed at normal operating temperatures causes the cover to warp. If the warped cover is reinstalled from warp to flat condition additional stress are added to the residual stress so the cover is back to the original stress state before it was removed The the cover is now bolted down flat on the flat deck and seals at the fire ring and coolant jacket openings with no problems. The cover was sealing all right before it was removed.
Another condition The engine is overheated and causes a leak between the cylinder and coolant jacket opening from warping between the bolt holes. The leak can easily be detected by removing the radiator cap when the engine is first started before it is hot. Small gas bubles can be seen rising to the top of the coolant surface. The gas source is from the combustion chamber. This type of warp between the holes is permanent. Removing the cover and re installing it will not seal the passage between the cylinder and the coolant opening. A re surfaced cover or new cover is then required.
Note: In addition, when the gas is present in the coolant jacket ,the gas bubbles decrease the film coefficient between the coolant and the radiator surface reducing the heat transfer and resulting in an even hotter running engine creating more permanent warp.
If the cover is removed for general engine overhaul like rings and valves and the engine was not overheated, believe the cover can be reinstalled, even if it shows warp with a straight edge off the engine. The cover will again bolt down flat against the block deck and seal. Believe this to be 99% of the cases for removing the cover.
Again, if the engine was overheated and gas bubles showing up with the radiator cap removed the cover must be surfaced or replaced with a new one. Believe the probability of overheating on this engine to be remote, as evidenced by a 3 psig radiator cap.
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