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Kit - Splayed Main Cap Set 6.5L
Kit - Splayed Main Cap Set 6.5L

Kit - Splayed Main Cap Set 6.5L

Your Price: $629.53
In Stock.
  • Condition:New
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Replacement Splayed Main caps produced exclusively for the 6.5L Diesel engine.

The 6.5L Diesel engine is a compact and relatively light-weight engine produced to deliver improved fuel economy in GM product lines as well as improve upon the available low-end torque and towing performance compared to gas engines in the 1990's in particular. Some of the compact and weight saving design of this engine yield to less than ideal block strength in some critical areas. The 6.5L block is a 4-bolt main, which is typically a performance type block item in the gas world, on this diesel it was the minimum requirement, bare minimum. This shallow-skirted block takes material out of the bottom of each main bearing web for piston skirt clearance with this long-stroked engine. This missing material allows the bearing web to move. The rotating forces against the outside bolt holes on the 4-bolt main take a lot of load and were there for a reason. This load forms cracks along the side of the main web starting at a bolt hole. This crack then starts down a path towards the already flexing main missing material.

End result is a cracked block. Not all blocks do it all the time, there were many changes to the engine throughout it's evolution, but this problem seems to have remained in all versions, some better than others.

Fortunately, for many standard performance engines these cracks are only found during rebuild, and are not reasonable to repair, safer and cheaper to source another block, or complete new longblock (we sell those too).

For those asking more performance from their 6.5L Diesel engine, the added stresses from more combustion pressure to make power adds to the likelihood of the cracks forming, and with the additional performance the added risk of the block failing and causing catastrophic failure in this area increase greatly. Then take into account the 1997 and later blocks missing more material in the webs for piston oil spray cooling, these jets crack from the flexing too, leading to coolant in the oil, which is game over.



Splayed main caps are certainly the answer to adding strength to the bottom end of the engine. A lot of strength.

This process is not easy. What is being offered here for sale is a bare set of 3 center caps which are the caps in need of help on the bottom end of the engine. This set includes the 6 bolts you'll need to install into the angled holes you'll have bored into the block. Optionally you can opt for a complete set of fasteners for the bottom end that would include studs for all mains, and the 6 bolts for the splayed holes, all ARP performance fasteners.

Cap Install Requires:

Machining block register (lip that holds cap on block) wider to accept wider cap.
Boring 6 new angled holes into the block to be the new outside bolt holes
Performing an Align-bore on the caps to bore the ID of the main cap matching front and rear
Performing an Align-hone to finish size the ID bore of the new main caps.

Requires an experienced machinist who has done this for other performance items and is extremely meticulous, and they exist.

We are providing the caps, some specific yet general 6.5 information needed for install and the fasteners needed, that's really it.

If you want to have these installed on your block. Unique Diesel has the experience to perform this task on used verified good blocks and complete new engines.

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