Is Your Local Machinist Your BFF? If He Saves Your Cracked Block, He Better Be On Your Christmas Card List! Engines endure much abuse. Sometimes this torture results in damage to either the block or the heads--or both. The block can be very rare, such as a matching-number block for an LS6 Chevelle or the original casting for a Z/28 or an unusual 409 engine. In our case, the block is not necessarily rare, but it certainly is valuable. While assembling a brand-new Dart Little M block, the unexpected happened, and assembly oil found its way into the bottom of one of the blind cylinder-head boltholes. Production small-block Chevy head boltholes are open at the bottom of the water jacket, which often allows coolant to seep up the threads unless thread sealant is used. The Dart team that designed the Little M block eliminated this hassle by ensuring these head boltholes were sealed. This requires the engine assembler to be careful not to allow any liquid to find its way into the holes. If that happens, the liquid in the bolthole can create a hydraulic-lock situation when the assembler torques the head bolts, which is what occurred during this engine's final assembly. Accidents happen, but this one was catastrophic. One of the cylinder head bolts hydraulic-locked, cracking the deck surface. But its close proximity to the two center cylinders allowed the crack to migrate in both directions into the cylinder walls. As you can imagine, this created quite a problem. Not only did the one head bolthole require repair, but now two cylinder sleeves were also needed. We called our friend Don Barrington at Barrington Engines in Van Nuys, California, to get an idea of what would be required to put our block back into service. Barrington said the block could be repaired, and we thought it would be a good idea to chronicle the process so you can see how a qualified machinist resurrects a major fissure. Here are the major steps involved with sleeving a pair of cracked cylinders. The Cost Of Repair DESCRIPTIONPRICE New sleeves$300.00 Cut sleeves to length 40.00 Install sleeves (2) 360.00 Deck block 190.00 Torque-plate-hone 190.00 Install cam bearings 60.00 Total$1,140.00 Here’s what the crack looked like after that dreaded “pulled-thread” feeling in the torque wrench told us something was wrong. The damage extended into both adjacent cylinders. The crack also bowed the top of the bolthole by more than 0.015 inch.Here’s what the crack looked like after that dreaded “pulled-thread” feeling in the torque The next step was to order a pair of 4.125-inch-id, cast-iron sleeves from L.A. Sleeve. These inserts are intentionally built long to allow Barrington to cut them to the exact length he needs after boring the block. The sleeve on the left has already been cut to length.The next step was to order a pair of 4.125-inch-id, cast-iron sleeves from L.A. Sleeve. Th Barrington’s first task was to repair the origin of the damage. He prefers to use a thread repair called Big Sert from Time-Sert. You can usually find this product at a local Fastenal store. The insert requires first drilling the hole larger, then threading the hole with the special tap, and finally threading the entire 7⁄16-inch NC insert into the hole. Barrington prefers Big Sert because its large flange at the top of the insert replaces a large portion of the heaviest damage. He feels this creates a much stronger thread repair compared with a coil of wire.Barrington’s first task was to repair the origin of the damage. He prefers to use a thread Adding the wall thickness to the bore diameter, Barrington had to bore the Dart block to 4.314 inches, which is only slightly less than the 4.400-inch small-block Chevy bore-spacing spec. Barrington bores the block to create an insert interference of 0.00025 to 0.0005 inch. Note that Barrington counterbores a step in the deck and a step at the bottom of the bore. The wall thickness was so good that even at that large bore diameter, Barrington didn’t hit water. Note the first sleeve (to the right) has already been installed.Adding the wall thickness to the bore diameter, Barrington had to bore the Dart block to 4 Once the bores are enlarged, Barrington adds a counterbore at the top that will precisely locate the sleeves. After all this machining is accomplished, he measures the height of the entire sleeve package and cuts the sleeves to that dimension. This is a critical process that requires precision measurement.Once the bores are enlarged, Barrington adds a counterbore at the top that will precisely Barrington uses Loctite’s green sleeve retainer between the sleeve and the block. While the sleeve installation required very precise measurement and machining, driving the sleeves into place was a simple process of pounding it into place with a big hammer and a drive adapter Barrington made from a Ford axle flange, which really rings when whacked with a large hammer.While the sleeve installation required very precise measurement and machining, driving the The sleeve flange dimension measures 4.440 inches, which is 0.040 inch larger than the bore spacing. That means the second sleeve (left) overlaps the first, which actually improves stability. At this point, the tops of the sleeves extend above the factory deck surface and will require surfacing.The sleeve flange dimension measures 4.440 inches, which is 0.040 inch larger than the bor Don Barrington Jr. used the surfacing machine to make minimal cuts to approach the original deck surface. Barrington removed 0.015 inch at this point, and you can see how the original damage raised the deck surface around the head bolthole. You can see that while the material has been removed, the original deck surface has yet to be touched. To clean the deck surface, Barrington only had to remove 0.003 inch from the original block to re-establish a perfectly level deck.Don Barrington Jr. used the surfacing machine to make minimal cuts to approach the origina Because the sleeves will distort the adjacent cylinders, Barrington torque plate–honed all four cylinders on the sleeved bank. This photo depicts honing a different block, but the procedure is exactly the same.Because the sleeves will distort the adjacent cylinders, Barrington torque plate–honed all Blind head boltholes are not limited to the Dart aftermarket small-block. All LS engines are also built with the same concept. Aluminum blocks are especially vulnerable to hydraulic lock, so be careful and be sure to use compressed air to clean blind head boltholes.Blind head boltholes are not limited to the Dart aftermarket small-block. All LS engines a After a good sonic cleaning and installing new Federal-Mogul Dart block cam bearings (with grooves cut on the outside diameter), the block is ready for assembly.After a good sonic cleaning and installing new Federal-Mogul Dart block cam bearings (with By Jeff Smith Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
