Most dedicated race blocks for Sprint Cup racing, Formula 1 and other high end applications are equipped with piston dome/pin oilers. Pin oilers provide direct full time lubrication to the wrist pins to supplement the minimal amount of oil fed to the wrist pin bosses via passages leading from the oil rings. This is particularly important in dry sump applications where splash oiling of the cylinder walls is minimal due to reduced crankcase windage and the remote oil supply. Tough as they are, wrist pins can bend along the longitudinal axis and they can temporarily egg shape within the pin bore at very high engines speeds. Pin deformation and bending under severe loading underscores the need for full time lubrication of the wrist pins. Pin oilers provide this essential lubrication and the oil serves a further purpose by carrying heat away from the piston crowns. You should consider adding pin oilers to your racing engine if you run very high engine speeds, severe loading and/or high thermal loading such as found in high output supercharged or nitrous assisted applications. Race block manufacturers offer the service of adding pin oilers to your block or you can do it yourself using this handy Mike Laws Research pin oiler kit available from CV Products, www.cvproducts.com. These kits are available for big and small block Chevys and small block Fords as detailed in the accompanying chart.
- MLR400-010 Piston Dome Oiler Kit /SB GM 350 Mains
- MLR400-100 Piston Dome Oiler Kit/BB GM 454 Mains
- MLR400-000 Piston Dome Oiler Kit /SB GM 283 Mains
- MLR400-210 Piston Dome Oiler Kit /SB Ford 351 Mains
- MLR400-200 Piston Dome Oiler Kit /SB Ford 302 Mains
- MLR311-000 Rear 4-port Fitting for Spring Oilers
Each reusable kit includes the following components:
- Main bore housing drill fixtures (aluminum)
- Eight metering jets for one engine (extra jets also available separately)
- 1 drill tap with 8-32 thread
- 1 tap 8-32 thread
- 1 6-inch #28 drill
Threaded pin oiling jets are screwed into tapped holes in the main housing bore to provide the correctly sized feed orifice for oiling the piston pins and crowns.
MLR kits allows you to drill and tap your block’s main bore housings for screw-in pin oiler jets. Each main bearing will feed two opposite cylinders with pin oiler metering jets. To install the pin oilers the following installation sequence is recommended. Note: (This sample installation is being performed on a Dart Big M Chevy cylinder block)
CV Products MLR Performance pin oiler kits use drill bushing guides that bolt into the main bearing housing bores to correctly position the drill for a direct shot at the piston pin.
Each kit contains two aluminum drill fixtures that install in the appropriate main housing bores to provide a drill bushing guide. Position the cylinder block on an engine stand with the main bore saddles facing up. Remove the main caps and set them aside. Install the appropriate aluminum drilling fixture into the main bore housing with the fixture pilot hole facing the appropriate cylinder. Because there are so many variations in main bolt and stud locations, a compromise has been added to the fixtures in the form of elongated and enlarged mounting holes. This enables you to position each drill fixture so that you achieve the best alignment of the drill pilot hole and the desired point of impact for the oil jet. In some cases you may wish to further elongate the mounting holes to gain more freedom for properly positioning the fixture. The drilling fixture must always align parallel to the main webs. MLR recommends positioning each fixture so that the drilled hole will be as close to the centerline of the housing bore as the mounting holes will allow. Verify the cylinder number of the fixture and then bolt it securely in place using bolts or studs with spacers if necessary. Install the 6-inch #28 drill bit into your drill and insert it into the drill bushing in the alignment fixture. Carefully and slowly drill through the main webbing until the drill bit penetrates through to the base of the cylinder. Do not rush this step. MLR advises that it is critical to remove the drill bit often to clean the flutes during this operation. Failure to do so may result in a stuck or broken drill bit accompanied by appropriate swearing. Do not use cutting fluid on cast iron blocks as it will tend to clog the flutes with metal. After drilling the hole in the main webbing, remove the drilling fixture, turn it around and re-install it so you can drill another hole in the opposite direction to feed another cylinder. Remember that each main bore saddle feeds two separate cylinders. When all the holes are drilled in the main bores, use a sharp X-Acto type blade or similar tool to lightly deburr the newly drilled holes.
Now you are ready to tap the drilled holes to accept the threaded metering jets. Begin the threading process with the 8-32 drill-tap (right). This is a combination drill bit and tap called a “drap.” The drill bit portion is used to align the tool in each hole so you can tap the hole to a depth of three or four revolutions. It is important that you do not tap any further with this tool as it is easily broken. Once you have established several threads in each hole remove the tool and switch to the regular 8-32 tap (left).
A magnetic pick works great for cleaning shavings out of the hole. The bit is small and clogs quickly. Patience and care are required to drill a clean hole without breaking the bit.
The supplied 8-32 tap is used to finish threading each hole. Great care is required here. The metering jet depth is set by how far the threads extend into the drilled hole. MLR advises that 6 or 7 revolutions is usually sufficient for proper positioning of the metering jets. This also depends on the type of block you are working with and the proximity of rotating components. Some trial and error is often required to accommodate specific block configurations. The thread depth should be set so that each jet protrudes slightly into the cylinder area. This is typically not possible on cylinders 1 and 8 due to the amount of available material in the main webbing area. Do not tap the threads all the way through into the cylinder area as this may allow the metering jets to eventually rotate further into the cylinder area. Setting the thread depth as described here is essential for proper operation.
The drill bit must penetrate all the way through from the main saddle to the bottom of the cylinder as guided by the bushing in the drilling fixture. It will emerge from the main web as shown here.
On some engines it may be necessary to slightly relieve the base of the cylinder to give the oil jet a clean shot at the piston pin. Prior to installing each metering jet, insert a 3/32-inch length of welding rod into each hole t determine where the oil stream will contact the piston/pin/rod assembly. This will also allow you to discover and correct any obstructions that may interfere with the oil stream.
The kit's drill tap (DRAP) is inserted into the new hole to provide a guide for the starting tap. After 3 or 4 revolutions remove the drill tap and switch to the standard tap to finish tapping the hole.
After you have set all the metering jet depths correctly, temporarily remove them so you can cut the feed passage from the man oil feed in each main bore saddle. Use a black ink marker to draw a line between the main bearing feed-hole and the new metering jet holes you just drilled in the main bore saddles. Then use a small diameter circular “cut-off” wheel (.040-.060-inch wide) in a small die grinder to cut a feed channel into the housing bore using the marked line as your guide. The object here is to connect each main feed hole to the metering jet holes with a small channel so pressurized oil can feed the jets via the channels underneath the main bearings. The recommended channel depth for proper oil volume is .040-inch.
The pin oiler jet accepts a small Allen wrench to screw it into the freshly tapped hole as shown here.
After cleaning the engine block and flushing all the feed holes thoroughly the first step in your engine assembly process is installing the metering jets. A small dab of blue Loc-Tite may be used if desired, but it isn’t really necessary since each metering jet is fully captured by the end of the threading on one end and the bearing insert covering it on the other end.
Work patiently and deliberately. You will need a new set of metering jets for each engine you modify. Replace the drill bit and the tap frequently for best results and to reduce the possibility of breakage. The aluminum fixture guides will pretty much last forever if you take care of them. MLR advises that their long term customers typically replace the drill bit for each new engine and the taps after every second engine. CV Products carries all of the required replacement tools and metering jet kits.
The pin oiler jet must screw in below the bearing saddle surface so as not to affect the bearing contact surface.
MLR advises that a 45 degree relief on the inner edge of the piston pin boss often helps the oil stream to maintain longer contact with the piston crown during each engine revolution. If you chose to do so remember that removing material from the piston will cause a balance issue unless the piston weight is corrected after the material is removed. Not a problem when mocking up a new engine, but problematic on existing engines.
Dart block prepped with CV Products pin oiler kit shows the threaded hole for the pin oiler insert. A small rotary grinder is used to cut the feeder channels into the housing bore to direct pressurized oil to both pin oilers fed by this main bearing.
Some B/B engine blocks running wet sump systems have an oil pump drive shaft interference problem which can be remedied with MLR’s 3/8-inch long metering jet for the number 8 cylinder. Check for proper clearance during final assembly.
When properly installed the pin oil will barely protrude into the cylinder if at all. If you accidentally tap too deep the jet can be carefully shortened in a lathe. If this is required, be sure to deburr the new end an insert the appropriate size drill bit to ensure that the jet opening is unobstructed.
Once the metering jets are properly installed they will provide trouble free service with clean filtered oil. Remember that the piston and pin are moving in and out of the oil stream during every stroke so there is ample opportunity to not only lube the pins, but to also extract heat from the piston top via the oil.
The Dart Big M block requires moving the drill bushing forward to the front edge of the housing bore to properly position the pin oiling jet. A C-clamp (not shown) is used to secure it for drilling.
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