boymeetspavement Posted June 25, 2009 Report Share Posted June 25, 2009 So today i spoke to 2 people : 1 a pretty decent mechanic and 2: a guy with some real basic mechanic skills. They both are telling me a new set of heads can possibly kill a bottom end..but how? I cant see a reason why..anyone got any ideas? Quote Link to comment Share on other sites More sharing options...
pitzel Posted June 25, 2009 Report Share Posted June 25, 2009 I guess, if the heads have been shaved to such an extent that the compression ratio is augmented -- you could get knocking, which would hurt the bottom end. But otherwise, ruling out proper installation, etc., I don't see how a new set of heads could hurt the bottom end. Quote Link to comment Share on other sites More sharing options...
xtremerevolution Posted June 25, 2009 Report Share Posted June 25, 2009 take that with a grain of salt. i've got new heads going into my jag, as have plenty of other jag owners. sometimes its the only option as valve work is more expensive. new heads will not hurt your bottom end unless you don't install them properly. Quote Link to comment Share on other sites More sharing options...
Crazy K Posted June 26, 2009 Report Share Posted June 26, 2009 i know it happened to my dad's POS 87 subaru... the head was decked and had the valves lapped, i think, and after the motor was put back together, it started burning oil and made black smoke as it ran. Quote Link to comment Share on other sites More sharing options...
95 vert Posted June 26, 2009 Report Share Posted June 26, 2009 I think what they're getting at is the possibility of you having a weak engine. High mileage, oil changes not done regularly, etc., etc. Working as a service tech, I've seen this plenty. Kinda of works on the "If you need heads, you might as well be doing the whole thing now or over again later" theory. If it needs heads, what kind of condition is the lower end in? Quote Link to comment Share on other sites More sharing options...
BXX Posted June 26, 2009 Report Share Posted June 26, 2009 So today i spoke to 2 people : 1 a pretty decent mechanic and 2: a guy with some real basic mechanic skills. They both are telling me a new set of heads can possibly kill a bottom end..but how? I cant see a reason why..anyone got any ideas? This is typically said with Quad 4 engines and tends to be very true.. The bad heads/headgaskets allow coolant contamination of the oil which accelerates wear on the bearings, and with it leaking you have a compression loss.. Put it back together and with the newfound compression, power is regained and will make quick work of the weak/worn bearings.. So they are both quite correct.. can happen to any engine, but its not a sure thing.. If its high mileage and had coolant contamination of any sorts, then you should get a newer engine or rebuild the one you have.. Otherwise, throw the new heads on and see how it does.. Quote Link to comment Share on other sites More sharing options...
johnnymossville Posted June 26, 2009 Report Share Posted June 26, 2009 The theory behind this is that if you put new heads (or a valve job) on a high mileage engine the engine will start to blow compression by the rings and start using oil. Supposedly this is because of the increase in compression due to no leakage past the valves. Is this true? I don't know but it is possible and many a Quad 4 has lost the bottom end after changing the head. An engine that has been taken care of or has reasonably low mileage could handle a top end swap with no problem as I know many people who have done this. My personal opinion is if you have the skills and tools to swap the top end you should go ahead and put new rings and bearings in it also but hey thats just my opinion and everyone has one. Quote Link to comment Share on other sites More sharing options...
boymeetspavement Posted June 26, 2009 Author Report Share Posted June 26, 2009 Would you consider 100k high? Quote Link to comment Share on other sites More sharing options...
Addicted2bass Posted June 26, 2009 Report Share Posted June 26, 2009 100k is certainly not high on a well maintained motor, any car should last well past that if its kept up properly. However if the oil has never or rarely been changed thats a different story. A kid i went to high school with had a Grand Am (with the Quad 4 ironically). It was a company car for his dads company and i dont think the oil had EVER been changed. The engine went around 100k, not long after he got it. Quote Link to comment Share on other sites More sharing options...
xtremerevolution Posted June 26, 2009 Report Share Posted June 26, 2009 Agreed. 100k is the tip of the iceberg for a well-maintained car. I'd say the number would be closer to 200k, and even on some cars that's barely touching it. Mine is currently at 202k, and the engine feels just as good if not better than it did when I bought it with 61k. Keep in mind I refer to well-maintained as more than just oil changes, and even in regard to those, I'm referring to quality oil filters as well. Quote Link to comment Share on other sites More sharing options...
Lumineer Posted June 26, 2009 Report Share Posted June 26, 2009 Agreed. 100k is the tip of the iceberg for a well-maintained car. I'd say the number would be closer to 200k, and even on some cars that's barely touching it. Mine is currently at 202k, and the engine feels just as good if not better than it did when I bought it with 61k. Keep in mind I refer to well-maintained as more than just oil changes, and even in regard to those, I'm referring to quality oil filters as well. My Bonneville is at 224k and still driving fairly good, though it's show some signs of roughness and minor fuel problems. Quote Link to comment Share on other sites More sharing options...
IRONDOG442 Posted June 26, 2009 Report Share Posted June 26, 2009 So today i spoke to 2 people : 1 a pretty decent mechanic and 2: a guy with some real basic mechanic skills. They both are telling me a new set of heads can possibly kill a bottom end..but how? I cant see a reason why..anyone got any ideas? This is typically said with Quad 4 engines and tends to be very true.. The bad heads/headgaskets allow coolant contamination of the oil which accelerates wear on the bearings, and with it leaking you have a compression loss.. Put it back together and with the newfound compression, power is regained and will make quick work of the weak/worn bearings.. So they are both quite correct.. can happen to any engine, but its not a sure thing.. If its high mileage and had coolant contamination of any sorts, then you should get a newer engine or rebuild the one you have.. Otherwise, throw the new heads on and see how it does.. its more prominent on hisgh mileage 2.2 liter 4 bangers ! Quote Link to comment Share on other sites More sharing options...
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