Originally Posted by eric32
Hello guys I was just curious about if you can convert an early style gm block to an oem roller setup with the spider rack and dogbone type lifter holders? I already have retrofit lifters but if they ever need replaced or if I get a new cam and lifter set some day its over 500 plus for hydraullic retrofit lifter sets now
I am going to build a new engine next year if funds allow but I am going to use a Dart special high performance block from jegs ($1500.00) with 350 main size and 4.030 bore finished and a scat forged balanced rotating assembly for over 1500.00 and I might use my big thumpr cam and lifters but if I ever need to replace them it says it has provisions for oem type roller cams. Are oem type roller lifters the same length as retrofit lifters and compatible with retrofit roller cams ? I know they are the .842 diameter. Can anyone shed any light on the subject. Crap for 230.00 you can have a complete set of hydraullic roller lifters they are not much different then the crane retrofit hydraullic ones I have now. Hope anyone can help with info.
Yes the early blocks can be converted with a minimum effort.
- Lifters, use 16 for a 4.3 block V6, these are shorter than the V8 version, thus alleviating the need for the taller lifter blocks cast into the roller V8s.
- Spider can be secured to the center oil galley. Some guys just drill and tap thru the top of the galley, I'm not too keen on what little support this provides for the spider, so I go crazy and drill the main galley to a half inch dia. Then after locating the spider's mounting position, I drill through the galley top in the valley out the bottom above the cam. I set up the cam, lifters, and retainers in place to get the dimensions for the block, this is a stack of washers to locate the spider above the galley since these blocks don't have the bosses here of the factory roller block. Then I determine the length of the spider mounting bolt and the area of the bolt inside the galley. Then I turn the bolts to remove the threads that would be in the galley and trim the shank diameter in this area to 1/4 inch from the bolt's original 5/16s. The bolt diameter trim and the 1/2 bore of the galley restores the flow area inside the galley to the original size. I use a grade 8 course thread bolt for this purpose. The assembly is tested a few times to determine the total bolt length so it doesn't project into the cam. Final assembly is with a touch of 222 or 242 Loctite to seal the oil in and prevent unintentional loosening of the bolts.
- Pushrod length will vary with the effects of deck and head milling as well as type and ratio of rocker arm, plus selected valve stem length. So get a rod length checker and check springs to test this during the mock up stage so that you end up with the correct length pushrods.
Almost forgot thus this edit, you'll need a conventional cam bumper to stop fore and aft movement of the cam. Also, you need a bushing to fill the area on the nose of the cam occupied by the OEM roller thrust plate. This is usually achieved by taking a thrust plate and timming it so that it acts as a bushing between the back of the timing gear, which needs to be for the cam not block, and the block's thrust face.