I’m tearing down a 235 engine and I’ve observed the following: Why do the piston heads have a “dimple” in the center?
Why are there two holes in the head cooling jacket and in the corresponding matching block surface there none? The reference area are between cylinder 1 & 2, and cylinders 5 & 6
See attached photos.
Last edited by TexasA&M48Truck; 06/13/20267:54 PM. Reason: Added ref affect areas
That "dimple" is a tapered center hole, used to steady the piston in a cam grinding machine while it was being manufactured. It serves no purpose once the engine is assembled. Those open holes in the gasket don't correspond to cooling passages in all blocks, so that gasket id made to fit more than one application. As long as the other head/block passages aren't blocked, just ignore the big holes. The gasket will seal properly without them. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Jerry, just for my peace of mind I’ve attached photos of the head and block. The arrows point to port alignment. The head has ports but the block doesn’t have matching ports for coolant flow.
I fully understand your point related to the gasket design.
The same thing exists on a 216. Not sure why the block didn't have holes there to allow coolant to circulate, but maybe they wanted to force flow thru the ports in the head that have nozzles on them. I believe those are there to jet coolant toward the exhaust valve seats.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
Take a look at the big holes on the other side of the head- - - -the ones right under the exhaust ports. It seems that they wanted to direct most of the coolant flow leaving the block to the hottest part of the head. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Not necessarily, especially if they're not standard bore size (3.5"). I believe all 216s and early 235s had cast iron pistons. If they're aluminum, they're definitely aftermarket. Common oversizes are .020, .030, and .040" overbore, possibly even .060 or ,080. and they can be cast iron or aluminum. Measure the cylinders (not the pistons) for tapered wear, and if the taper is much more than .005" from top to bottom of the cylinder, you'll need to rebore the cylinders and install oversize pistons and rings. At 2000 RPM, rings in a taper-worn cylinder have to flex to maintain contact with the cylinder walls 60 times per second, resulting in very short ring life and really bad compression sealing and excessive oil consumption.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Cleaned the top of the pistons and they are all stamped 0.030. So engine had been worked on sometime in earlier life. That’s not bad, if need be I can hone the to .040 or .060.
