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Overhaul gone wrong

2K views 16 replies 5 participants last post by  Old Doug 
#1 ·
Has anyone rebuilt a engine and had it to use oil and never fix it or figuered out why. I have rebuilt 2 for my self and they both used oil one i took back apart and had 2 machine shops look at and they couldnt find a problem. Both were Chevys one a 350 the other a 250.
 
#2 ·
Sounds like either a ring gap problem, broken ring caused by installation mishap, or the rings did not seat properly. Just a few guesses. Did you check the ring gaps prior to putting them on the piston? How about after you took the engine back apart?

Also were the heads redone as well? Were the valve seals replaced? Several things could cause an engine to use oil, but from my experience (little as it is) when a new engine uses oil, and it is not leaking any where, it usually resulted in a piston ring problem. I'm sure there are more knowledgable, more experienced people that will give you better responses.

Kelly
 
#3 · (Edited)
If no other problems can be found,broken rings,bad valve seals/guides,leaks,etc,the most likely culprits will be excessive piston to wall clearance,or,an improper hone that prevents proper ring seal.Clearances must be within spec & proper honing w/ the proper crosshatch & finish for the type of rings being used.Just as important are using proper oil & breakin procedures to allow rings to seat.If the problem is in the head,(seals,guides),you will usually see a buildup on the backs of the intake valves.If not,the problem is probably below the head.
 
#6 ·
I worked as a machanic back in the 80s when there were a lot of engines rebuilt and had good luck rebuilding engines. I know i am not the the best there is but out of all the engines i have rebuilt i didnt have one come back because of it useing oil. Both were bored and honed by shops that i had used in the past. I allway used cast rings because of what i had heard about them seating.
 
#5 ·
On the 250 i dont remember checking ring gap the first time i put it together but after i took it apart i did. The head was rebuilt with new hard valve seats and valves. When i had problems i had a second head rebuilt. It just got valves ground. The 350s heads were rebuilt. I check its ring gap when i put it together.
 
#9 ·
Alot of people talk about honeing and now days it is a science. If i was building a engine to get as much out of it as i could i would spend some time to have it right. That being said i have worked on engines that needed to be fixed on the cheap or right now like a truck that burned a piston. One head would be pull and that piston would be replaced. It would never see a hone and not use any oil. I was sent to work on a engine they wanted to put rings in it and rod bearings. We put several sheets of sand paper on a 1/4 rod and honed it out and it never used oil.
 
#10 ·
second time today posting this quote,lol.

Yunick ran "Smokey's Best Damn Garage in Town" on Beach Street in Daytona Beach, Florida from 1947, when he opened the garage repairing trucks, until 1987 when he closed it, claiming that there were no more good mechanics.
 
#12 ·
It is more of a science now along with hands on experience.We have come a long ways in engine tech.That's why you see engines getting 250,000 to over 300,000 miles today.20 yrs ago you were lucky to see over 100,000 miles on an engine.This is because we understand & do things differently now.Not because our Luck was good.
 
#14 ·
I not trying to start argument about if things are better today than yesterday. But when we were Kids it took dad over 10 years to put 100.000 on his pickup that the engine turned around 2800 RPMs. Today it takes less than 2years to put 100.000 on a pickup turning half the RPM. Yes technology has made things last longer engine blocks are harder you dont see the big ridges at the tops of cylinders that you did 20 years ago. Almost all vehicals have overdrive and there isnt gas being poured down the intakes by a carb controled by a foot and a brain.
 
#15 ·
All of those things are contributors to better engines.Agreed.Procedures & techniques have also played just as an important role.The fact that the engine is goin into a gro getter or all out drag car doesn't mean you can get by without doing things the rite way.If you don't get your clearances,honing,or anything done the rite way,you will have issues wether is oil usage,no power,or an engine that doesn't last very long.The use of the motor doesn't allow you skip or get by w/o using proper procedures.True,an all out drag car will have more attention to parts & procedures than a gro getter,but,in the end if it ain't rite,it won't work.At least not for very long.I'm not trying to argue or down your skills.I'm just saying that outside of something being broke or bad parts,your problems can only be in the procedures,or'machine work.Your remarks about the importance of honing & finish says you don't think it's important to a good rebuild,yet,you have 2 engines experiencing the same problem that could very likely be the result of either of these procedures.Again,i'm not trying to criticize your skills or knowledge.I'm just trying to stress that honing & finish is critical to achieving good ring seal.Sry if I offended you.That was not my intent.
 
#17 ·
.Sry if I offended you.That was not my intent.
No offfence take just bounceing ideas around as to why things happen. Yes i do think honeing is important but its hard to explan why a engine that i saved up to rebuild and had bored and honed with new pistons didnt panout. I had both engines bored at a shop i had used in the past and they had pistons and ask what rings. The 250 was in a Jeep and i replaced it with one that i just put in rings. I ran it 2 years and sold the jeep. It was lose and had some piston slap. I had the other engine checked out by 2 shops the last one rehoned it yes it was geting loser and i put it back together with new rings and used it off road for several years adding oil often. The 350 is in my pickup i have lost track of its miles. I never did any thing with it because i needed it and it runs great. I have run it 8 years and the last 2 i have to clean number 8 plug 2 times a year around every 5000 miles.
 
#16 ·
On the engines of today getting high millage it is a lot to do with components NOW to back then 99% of old engines had cast pistons and plane rings today everything is build with forged pistons and moly rings and improved oiling systems I built a few engines in my day using the good parts cleaning and improving oil galleys and would get over 10000 miles easy. and on the engines using it could be valve guides upside down rings anything like that
 
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