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Rebuilding an engine.

Fix A Connecting Rod Knock - GM 4.3 V6:

Rebuilding An Engine (Part 0)
Deciding What To Repair

A Partial Rebuild Fixed The Knocking Sound, At A Decent Price

 
In This Article:
A discussion of repair options when a car has a serious engine problem, and the cost of this engine rebuild.
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By Bruce W. Maki, Editor
By HammerZone.com Staff
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Serious Engine Problems:
Replace, Rebuild, Or Junk The Vehicle?

When a car or truck develops a serious engine problem, such as a loud knocking sound, the first step, besides getting the vehicle out of traffic, is to diagnose the problem.

The repair options depend on the diagnosis. A connecting rod knock is a serious engine problem, but it's not the worst thing that can happen. Problems such as overheating and seizing, or "throwing a rod", can render an engine unfit for rebuilding.

Other reasons to rebuild an engine:

  • It burns a lot of oil.
  • Low compression caused by worn piston rings. When a vehicle gets old and lacks power, a compression test can reveal the degree of wear inside the engine. Then, a "cylinder leak-down" test can pinpoint the exact locations of wear or leakage in each cylinder.

 

Repair Decisions:

Before my 99 Jimmy developed a rod knock, the engine ran just fine. It had plenty of power and it didn't burn oil. That meant the piston rings weren't worn out, the valves sealed up properly, and the valve guides (and seals) weren't worn badly.

When the engine started knocking, the only problem that needed to be fixed was the source of the knock... the worn-out bearings between one (or more) connecting rods and the crankshaft.

After I towed the car home, I proceeded to call local auto parts stores to inquire about the various options I could pursue. I also looked at the Kelly Blue Book website (kbb.com) to get an idea of the car's value. I discovered that this well-equipped Jimmy could be worth as much as $3,750 on a dealer's lot, if it was in excellent condition. I figured the car was worth maybe $3,000 to me. Knowing the vehicle's value is helpful because it can guide your repair choices. If I paid a mechanic's shop to replace the engine, it would surely cost more than the value of the car, and that never makes sense.

I've always figured that it doesn't make sense to pay more than half of the car's value to get it back on the road.

After calling around, the best price I found on a remanufactured "long-block" engine was $1,850, with rebuildable trade-in. Personally, I would consider that option if a vehicle was worth at least $4,000 and I wanted to keep it for a long time. A "short-block" engine (no cylinder heads) was a little cheaper, but I don't remember the amount. I've always figured a short block isn't worth the savings.

I've known people who have bought engines from junkyards (er, I mean... salvage yards) for $600 to $800. Buying a used engine is a reasonable approach, if you know its history. I didn't like the idea of paying that much for a used engine that might be a few thousand mile from developing its own rod knock, or some other problem.

Here's another point: Engines (and cars in general) often have their weak areas. If you looked at a thousand vehicles of the same make, model, and year, you might see a pattern of failures. Certain parts or systems are prone to breakage or early wear. I've talked to several owners of late 90's Chevy Blazers and GMC Jimmys who had the same rod knock problem after 100,000 to 150,000 miles. I have a friend who had a Blazer that started knocking right after he stomped on the gas pedal to go from a standstill to highway speed.

I doubt all that bearing wear happened in one incident of full-throttle acceleration, but stories like that make me wonder if a salvage yard engine might already have a badly-worn bearing. Replacing an engine is a lot of work, and having the new(er) engine fail within a few months was not a risk I wanted to take.

One local parts store (Thirlby Automotive in Traverse City, Michigan) sold a "remanufactured crankshaft kit" for $230. A crank kit is a re-ground crankshaft sold with all the necessary bearings, which are oversized to fit the smaller journal diameters. That option would require buying an engine stand (which I could get for $90) and removing the cylinder heads, all the pistons, and a few other things. I would need to buy a lot of gaskets and some special tools. Initially, I figured I could fix the Jimmy for $500 and a bit of my time. I was wrong about that... twice. It cost quite a bit more than $500 and took a LOT of my time. But it was worth it, because I gained a lot of valuable experience.

Before I even removed the engine, a friend recommended replacing the piston rings, since it would be easy to do with the engine torn apart. A set of rings only cost $37, but I also had to buy a Flex-Hone (ball hone) to create the proper scratch pattern on the cylinder walls. So I figured that option made sense. New rings and bearings.

There was no reason to remove the camshaft, since it had no visible wear or damage. I also did not remove the hydraulic valve lifters, which rid against the cams and push on the pushrods to open the valves.

I did nothing to the cylinder heads except clean the mating surfaces and remove some of the carbon buildup on the bottom of the valves. I inquired at my local parts store about buying a valve spring compressor to remove the valves and replace the valve seals, because those do wear out and let oil into the engine. The parts guy talked me out of it. His point was "if the engine didn't burn oil before the rod knock, and the car isn't worth all that much, it's a waste of money to buy a tool to replace the valve seals". Besides, I've seen mechanics replace GM valve seals while the engine is in the car... it's a bit of work not a huge job.

 

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The Cost Breakdown For My Engine Rebuild:

 

Bare Minimum - New Crank and Necessary Gaskets:

Crankshaft Kit: $230 (Reground crankshaft and all bearings)

Upper Gasket Set: $70 (Includes gaskets for the cylinder heads, intake manifold, water pump, upper intake manifold, and a bunch more.)

Lower Gasket Set: $46 (Includes gaskets for the oil pan, oil filter adapter, rear seal block, oil drain plug, and a bunch of O-rings.)

Head Bolts: $24
The old bolts cannot be reused on this engine.

Machine Shop Work: $65 (Included checking the diameter of all 6 connecting rods, and machining one stretched rod cap back to the proper size.)

Timing Chain Cover: $29 The old timing chain cover is not supposed to be reused. This cover is plastic with a built-in gasket (a bead of silicone) that gets squashed over time. In a pinch, I suppose this cover could be reused if RTV silicone was applied carefully.

Assembly Lube: $6

Plastigauge: $3
Needed to check bearing clearances when installing the crankshaft and connecting rods.

Engine Hoist Rental: $46 for two separate days.

Sub-Total: $519 (plus sales tax).

It turned out that my seat-of-the-pants initial estimate wasn't far off... but there were some tools that I needed to buy. Of course, if you can borrow these items, all the better.

 

Tools Purchase For This Job -
(The Bare Minimum):

Engine Stand: $90
This could be sold to recover part of the cost.

Harmonic Balancer Installer / Remover Tool: $75
There are cheaper pullers available.

3-Jaw Gear Puller: $100 at Sears. Again, there are much cheaper gear pullers, but I needed a good 3-jaw puller anyway.

Piston Ring Compressor: $8

Angle Torque Gauge: $31
It's possible to get by without this tool, but not easily.

Oil Pump Priming Tool: $30
This could be made from an old GM distributor shaft.

3M Roloc Bristle Discs (2) $13

Sub-Total: $347 (plus sales tax).


Additional Parts That I Bought:

Piston Ring Set: $37

Oil Pump and Pickup Tube: $60

Timing Chain and Sprockets: $65

Engine Mounts (2): $34
One mount was broken. It's a good idea to replace these because they eventually wear out, and they're easy to replace.

Oxygen Sensors (2): $102
I replaced both "upstream" oxygen sensors, because they wear out, and they were easy to replace when the exhaust pipe was out.

Sub-Total: $298 (plus sales tax).

 

Additional Tools:

Flex Hone: $48

Piston Ring Pliers: $8

Oxygen Sensor Socket: $27

Sub-Total: $83 (plus sales tax)

 

Fluids and Supplies:

Oil and Filters: $40-$50
The engine needs new oil and a filter, and then the oil needs to be changed after the "break-in" period of 500 miles.

Miscellaneous Chemicals: $25 to $50
This stuff nickels-and-dimes you to death... Antifreeze, brake cleaner, carb cleaner, solvents, hand cleaner, thread locker, thread sealant, anti-seize, dielectric grease... it adds up fast. TIP: Look for these things at Wal-Mart. I love my local auto parts stores, but they charge a lot more for these minor items... and I gotta keep my cost down.

 

Total Cost: $1347 (including an estimated $100 for fluids and supplies)
Some of the $430 spent on tools could be recovered if the tools were sold.

The cost for parts and tools appears to rival the cost of a remanufactured engine, until a proper comparison is done. Read more about this at the end of the page.


Still More Tools I Bought:

Rigid Hone: $36
I bought this to remove some rust patches in two cylinders, because some water got into the engine while it sat in my garage.

Metric Tap and Die Set: $100 at Sears
Actually this wasn't that useful on this job, because most of the engine threads are conventional inch-sizes. But some taps are needed.

Oxygen/MAPP Gas Mini Torch: $60 at Menard's
This little torch gets almost as hot as an oxy-acetylene torch, for a fraction of the price. It was essential to remove some of the fasteners for the exhaust Y-pipe, and helpful for removing the oxygen sensors. This torch uses MAPP gas and oxygen "cylinders" that are the same size as a 1 pound propane bottle. The MAPP gas lasts a long time, but the $8 oxygen bottle (which contains about one ounce) lasts about 10-15 minutes of total run time. And this torch is a bitch to light.

 

Still More Parts I Bought:

Battery: $60
It was due for a new battery.

Starter: $140
I broke off a terminal while trying to clean up the corrosion. Oh well...

Catalytic Converter and Gaskets: $182
This was bad long before the engine developed the rod knock.

Idler Pulley: $25
These wear out anyway.

Oil Pressure Sender: $30
I broke this sensor when removing the engine.

I mention all these parts because when you are doing major engine repairs it's likely that you will either break something, or discover other worn-out parts.

 

 
 
 
 
 
 
 
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Rebuilding vs. Remanufactured Engine:

The cost for parts and tools appears to rival the cost of a remanufactured engine. But for a true "apples-to-apples" comparison, it's important to realize that a remanufactured engine will (or might) still require:

  • Engine hoist rental (2 days)
  • Motor oil and filters for 2 oil changes
  • Some of the miscellaneous chemicals (e.g. antifreeze)
  • Gaskets for the intake manifold, exhaust manifold, valve covers, water pump, etc.
  • Timing chain cover
  • Harmonic balancer remover / installer tool
  • Oil pump priming tool
  • Engine mounts
  • Oxygen sensors
  • Oxygen sensor socket

These items add up to $393, not including the gaskets and miscellaneous chemicals. Just the gaskets for the intake manifold cost almost $50 when I replaced those 3 years ago. You may be able to find a gasket set with everything needed for a remanufactured engine. I'd figure at least 50 bucks for that, and maybe $20 for chemicals, bringing the "overlapping" costs to about $463.

A remanufactured engine may have other costs. During remanufacturing, the cylinder heads and engine "deck" may be machined, which reduces the overall height of the heads by perhaps .020" or more. With an inline 4 or 6 cylinder engine, this is no problem. For a V6 or V8 engine, the intake manifold bolt holes might not line up with the holes in the cylinder heads. Sometimes the bottom of the intake manifold needs to be machined so the bottom doesn't hit the block. Maybe there is some special extra-thick intake gasket available to restore the proper head-to-intake geometry. If you pursue a remanufactured engine, you need to inquire about this issue.

Here's another issue with a reman engine: Handling. How do get the engine from the parts store to your garage? Presumably an engine would be sitting on a shipping pallet that the store can load onto the back of your pickup truck (with no topper) or utility trailer. Then you can use an engine hoist to lift the engine off your truck and install it in the engine bay. Then you need to load your old engine onto the pallet and take it to the store.

So the better comparison is $1347 for my repair versus $1,850 + $463 = $2,313 for a remanufactured long-block engine. That's a difference of almost a thousand dollars. Very reasonable for a newer, more valuable car, but not for a '99 Jimmy worth $3,000 or so.

One major benefit of a remanufactured engine is the warranty. I've seen reman engines with warranties up to 3 years and 36,000 miles. But the warranty won't cover the time and expense of removing and replacing the engine. My new crankshaft came with a warranty too. Big deal... the cost to get the crank out and replaced is kinda high.

 

 

Next Page: Part 1 - Removing The Cylinder Heads

 

More Info:
Tools Used:
  • Extensive sets of sockets, metric and inch, shallow and deep, 1/4", 3/8" 1/2" drive.
  • Assorted ratchets, large 1/2" breaker bar.
  • Combination wrenches, metric and inch.
  • Screwdrivers, pliers, punches, etc.
  • Hammers
  • Prybars, various sizes
  • Air compressor
  • Impact wrench
  • Impact sockets, deep well.
  • Electric drill
  • Bench grinder with wire wheel
  • Right-angle die grinder
  • Floor jack and jack stands
  • Set of taps and dies.
  • See Cost Breakdown in article above for special tools purchased for this job.
  • Other tools mentioned in Parts 1 through 12
Materials Used:
 
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