Written by Jamie Avant Tuesday, 14 October 2008 19:00
|The Best-Ever 6.5 Chevy Diesel Rebuild|
The 6.5 L diesel has always had certain structural weaknesses. Cracking in the main webs of the blocks and in the number seven and eight cylinders, blown head gaskets and broken crankshafts have all been common issues over the years. In choosing which components and processes to use for this build, we sought those that would yield the strongest possible combinations to mitigate or eliminate these known weaknesses. That is, we used parts and procedures with proven track records of reliability in our custom built engines over the years.
The first decision we faced was which block we would use as the foundation of our engine. It may surprise some of you that we decided to use an earlier 6.2L engine block with the casting number 660. In our opinion, these early 6.2L blocks are stronger in many cases than the later 6.5 L diesel blocks. Of course, there are newer, improved original equipment (OE) blocks; but we have seen even these latest blocks exhibit the same cracking as other 6.5 L diesel turbo engines in critical areas. Mostly, I have seen cracks in the main bearing bolt hole areas as shown in the photo below. New aftermarket blocks, produced in China, are also available. For me, these are buyer beware: they are still unproven in long-term, real-world conditions. We have not used any of these imports and we have not been able to find any other engine builders who have used them in any volume. For this project, we chose to use a crack-free and seasoned 1990 6.2L block.
In order to prepare the block, we cleaned, magnetic particle inspected (magnafluxed) for cracks and checked line bore distortion as well as torque plate boring and honing, surfacing the deck to even the deck heights (square decked). We made sure that the deck heights on both sides of the block were as close as possible. Ultimately, the block ended up 0.020 inches over on the bore with 0.004 inches taken off of the deck surface.
A standard bore 6.2L engine is .080 smaller in diameter than a standard bore 6.5 L diesel engine. By starting with a 6.2L block and boring it .020 oversize, we did lose some engine displacement versus a true 6.5 L diesel engine. We figure that Ted’s hybrid engine ended up with approximately a 6.35 liter displacement. In our experience, this slight loss of volume does not sacrifice engine performance. With diesel engines, most of your performance comes from the amount of fuel and air that goes into the engine. As long as the same fuel and turbo systems are used, I would say that the seat-of-your-pants performance of a 6.2L and a 6.5L is identical. We have sold hundreds of these rebuilt 6.2L engines to replace 6.5L and I have never had a customer complain about a loss of performance.
An electromagnet (A) is used in a process called magnafluxing to reveal cracks in the block. Colored iron filings are attracted to the cracks. In this photo, one of the cracks is highlighted and enlarged. There is another crack not quite as visible, can you see it?
When building an engine based on an early 6.2L diesel bottom end (with a two piece rear main seal), there are no crankshaft alternatives other than using a standard or re-ground crankshaft. We chose to use a standard OE crankshaft that had been cleaned, polished, inspected for cracks and measured for straightness.
Throughout the production of the 6.2L and 6.5L, there has been a tendency for cracks to develop at the outer main cap bolt holes on the center three main caps. Sadly, we have made many trips to the local scrap yard with loads of scrap blocks to prove it. When a crack-free block is located, we feel that the best way to combat cracks from developing is to install a stud and girdle kit.
This process uses six ARP studs and a girdle to tie the main caps together. In our application and in general, the use of a stud converts the typical twisting force on the bolt hole to more of a stretching force on the stud itself. Changing this load on the block is, in our opinion, the best and most cost effective way to prevent block cracking at the six locations where the studs are installed.
Next, we installed our own reconditioned connecting rods. Each rod goes through an extensive procedure of:
- Cleaning and relieving stress with a process called metal shot blasting or peening,
- Installing new rod bolts and nuts,
- Re-sizing the big ends,
- Installing a new pin bushing and
- Boring the bushing parallel to the big end.
Perhaps the most critical of these steps is
In this article...
- Airflow Efficiency
- Extrude Hone Process Results
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