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mar2c

Overhaul or rebuild: what's the difference ?

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Before all the flames start coming, let me just start off by saying that I do know what it means to rebuild an engine...

My question is more dealing with an engine overhaul. What is typically done to overhaul an engine ? Where do you draw the line between the overhaul or rebuild decision ?

As best as we can figure, our '78 sat for 5 years before we bought it back on Aug 2001. When you drive it, you can tell that the car isn't giving you all it has.

I plan on replacing the exhaust system soon, but the engine needs some attention as well.

How do you determine what would be best? Beside the difference in cost, is there anything that would make one option more attractive than the other ?

Any advice would be welcomed!

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IMO I have always performed and replaced the following on an overhaul

1. Compression test. This always lets me know whether I need rings or not

2. measure the cylindar bore

3. pressure check the cooling system

4. Inspect all bearings on lower end

5. new gaskets

6. oil pump

7. water pump

8. full valve job

9. timing chain

10. clutch

11. belts

12. hoses

13. clean the carbs if applicable

14. hot tank the block

15. replace all seals

That seems about it.

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A Re-build usually involves machining the block (i.e. Over-boring the cylinders, machining the crankshaft, replacing the rod, and crankshaft bearings to match the machining done in those places replacing the pistons with ones to match the over-bore, ) in addition to all the work described by St. Stephen.

What you end up with is an engine that is as close to new condition as is possible to obtain from the existing engine. All tolerances between the various parts should be within factory specifications for a new engine.

To some people an "overhaul" is called a "refresh". It's kind of a half-way measure to extend the life of an engine that has high miles but is still in reasonable condition, maybe just burning a little oil.

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Rebuilding to me is basically all new parts, overhall would be prefered to me if the bores check out, new rings/bearings/seals yada yada and thats it. Bores should be checked and then cleaned up with a glaze breaker so the rings will seat, its a budget rebuild basically and on most engines should be fine.

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How many miles on the engine? and what is the state of repair. Have a leakdown test done( air pressure is put into the cylinder through the sparkplug hole and then it is measured how it holds th e pressure.) this will tell you what is going on inside the cylinder , weather the rings are worn or valves leaking . If there is need to overhaul the engine , when the cylinders are miked you will see the ammont of wear that has taken place . Many times these engines are so tough that only a hone is used to freshen the chambers and the same pistons can be reused with new rings. The same with the wrist pins and the crank shaft if it is not worn new berrings and your good to go , if the crank shows wear have it ground and then new bearings of the proper size installed and you again are back to new. If all this is going to be done have the block , hot tanked , to clean everything up before reassembly. lf the engine has been cared for properly and has 125k on it , maby it just needs a valve adjustment and a good tune up. Not a lot of information was given here to start with. to answer the question , if you for an example take starter and clean it, replace the brushes , and bushings and reassemble it you have rebuilt the starter. The rest of the starter is untouched but still it can be sold as rebuilt. the same with a transmission intnstall a cluster gear and you have rebuilt the trans . but not overhauled it. I hope this helps gary

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