Hi everyone, My chevy 250 engine is finally tore down. I decided to pull it out of my Camaro and freshen it up because it had sit for 20 plus years and looked pretty dirty inside. The engine did run pretty good and didn't miss.
After pulling the head I didn't expect what I seen. At first glance I though something had fell in down in the cylinder and was being smacked by the piston. However I didn't find anything and the pistons show no damage at all. I'm guessing detonation done this? It's two cylinders side by side and the fifth cylinder is just starting to show signs. The damage doesn't extend up to the head gasket.
I'm assuming this head is junk. I've heard of people grinding away the jagged edges to not cause hot spots. I would have several to grind away here. I'm surprised I never had any signs the head looked like this.
Hm. That's weird. I don't think I've ever seen anything like that before.. you said there was no visible damage to the pistons at all? How'd the plugs look when you pulled them? Maybe this could be a byproduct of ignition timing being way off and left alone for too long?
Not detonation that will take the aluminum pistons long before doing damage to the cast iron head.
The damage looks a lot like impact, but if the pistons don't show corresponding damage, I'd have to say that at some point it ate a hard part and while the head wasn't replaced the pistons were.
Actually the head isn't the original one for the engine. I'm assuming the previous owner installed this head for some reason. The pistons are in great shape.
IF the head isn't cracked.. Get it milled .010" have a valve job done and use it.. The peening on the surface will not hurt anything. After all it has run that way for a while in the past..
The engine is out of my 68 Camaro. However the 250 has a 69 date code, so it's not original to the car. My Dad said the head is newer than a 69 because it has the small 5/8 spark plugs. I'm not sure when Chevy changed to the smaller plugs.
I may see if it will clean up, as you guys said, it was already running and there was no problems.
When I changed the plugs, the old ones looked fine. I did have to replace the vacuum advance because the old one didn't work at all. It could have been run like that for a long time.
I bought this Camaro in June, so I know very little about its history. I do know it had sit in a garage for 20 years before I bought it.
I built a 250 up once upon a time. Used a 194 six head I had milled .060 to get roughly 10:1 CR on the 250 (the particular head I used had the smallest chamber size of the later model sixes to start with). That was in 75 however, and the gas has gotten even worse than what it was back then. You should be able to clean it up with milling. I think it was from something prior to finding it's way onto your engine, but who knows; it's odd that the chamber does't seem to be involved (?). If it ran fine this way, don't worry too much about it. JMO. Butch/junior stocker.
I thought originally detonation damage. However from what I've researched, the pistons would have melted before this would have happened. The pistons look great with no damage. From the picture you see two of the combustion chambers, two of the other other cylinders have 4 or 5 marks on them as well. The two middle cylinders are fine.
I know the head didn't come on this engine. The damage had to take place before it was installed on my engine. Cylinder walls, pistons, and spark
I use to see this quite a bit on the 230's & 250's w/ 1 bbl Rochester.Tho not this bad.The mounting bracket for the air cleaner was fastened to the carb with 2 very small screws on ea side.If the wingnut for the air cleaner was overtightened,1 or both screw heads would break off & go down the carb.Most likely,whatever caused this damage,wrecked the pistons as well,so,the short block has been replaced,or,rebuilt using the same head.
I detonated my 8-71 blower motor on the strip a couple years ago, so bad I destroyed pistons and couldn't remove the rings with vise grips from 5 pistons, there was no damage to my aluminum heads.
I agree the damage done prior to putting them on this motor, maybe for a fast fix??
Thanks Joker, after pulling the valves out I could see nicks in the valve face and feat. Good proof of whatever came through made contact. I have enough 250 head that I'll use instead of this one.
I also agree with what most have said. That is prior damage. Something bad happened in the engine that head was on and the engine was either repaired or replaced and the head reused. If that happened on the current engine you would be missing the tops of the pistons. I cant imagine why someone would put a head that looks like that on a rebuilt engine but people never cease to amaze.
Im surprised I didn't have any signs the head was in this condition. However I never drove the car further than a mile or two. If I drove it on a long trip or in hot weather I could have had issues.
The biggest issue I would worry about is it is probably more prone to cracking now that the metal had been hammered and has gouges in it. I don't think you would have noticed any driveabliity issues to be honest.
well, here's a comparison image for you.. I believe this head ate some valves at some point in a previous life.. and this picture from my engine that dropped the #2 valve will explain why
and this is the matching piston.. that was shattered, and cocked sidways in the bore..
"" the really sucky part, was it was my own fault for not making sure I had the keepers installed properly ""
you dont set the valves with a rubber/nylon mallet?
you got that right.. this is a mistake I won't be making again.. in fact when I built my new motor, I had the machine shop install the new valves, springs, etc.. glad I did.. the valves needed a lot of shimming to get the install height right.
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