rebuilt heads
Posting Guru
Joined: Sep 1999
Posts: 2,297
Likes: 1
From: Indiana
Originally Posted by red75
Is there any truth in the saying if you rebuild your heads that you will probley blow out blow out the bottom end on an older motor, say 76-77
You get the valves sealed up good and tight again where you are not losing any compression around them and it puts more pressure against the already and still, worn piston rings.
Elder User
Joined: Sep 2003
Posts: 908
Likes: 4
I've heard that all my life. I'd have to say it would depend on how good the rings are.
One thing that does happen with a high mileage engine is that when you torque the heads on assembly, it may pull the cylinders into a slightly different shape than they were. Worn rings would then not reseat correctly, and the engine becomes an oil burner.
I can't say that I've ever seen this happen in real life. I've changed head gaskets on fairly high mileage engines, and the engine would smoke for a little after but then seal up again.
One thing that does happen with a high mileage engine is that when you torque the heads on assembly, it may pull the cylinders into a slightly different shape than they were. Worn rings would then not reseat correctly, and the engine becomes an oil burner.
I can't say that I've ever seen this happen in real life. I've changed head gaskets on fairly high mileage engines, and the engine would smoke for a little after but then seal up again.
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
It makes sense though, that a valve job will increase working pressures and, therefore, increase demands on the rings, so I think Scroob has a good assesment. I was taught the same thing, more or less, don't do a top-end without doing the bottom. Same theory.
Anyway, unless outside factors demand it, I hate to rebuild part of anything. It kinda of smaks of fencing 3 sides of the pasture... the cows will find the easy way out sooner or later.
Anyway, unless outside factors demand it, I hate to rebuild part of anything. It kinda of smaks of fencing 3 sides of the pasture... the cows will find the easy way out sooner or later.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
I don't think that rebuilding the heads will 'blow out' an older motor, but if it is an older motor chances are that the clearances are worn in the rest of the motor as well as the heads and when you fix the heads the parts that you didn't fix will break down soon. This is mostly because they were going to break anyway.
It is probably cheaper in the long run to redo the whole motor at one time, but if you just rebuild the heads they will still be good when something else fails. It is just a matter of inconvenience and some additional labor.
It is probably cheaper in the long run to redo the whole motor at one time, but if you just rebuild the heads they will still be good when something else fails. It is just a matter of inconvenience and some additional labor.
