MERPerformance
07-21-2009, 11:01 PM
Just finished up 2 604CID N/A, with RM BUILDER cams, excellent results for what we had to work with 4.750 stroke, 4.500 bore, cnc 335 dart heads, Dart 4500 intake and Holley 1050. We did some testing with the HI rev hydraulic lifters that others have had some issues with, this was the first design that was made to use 20w50 oil with tight internal clearances, not the modified designed with larger clearances. RL932 is the part #. I was able to prime these lifters with a cordless drill within a few minutes on all16 rockers both engines no problems. The facts on these lifters are as follows: They require .001-.0015 clearance between the lifter and the bore, is is noted on the spec. sheet included with the lifters. A Dart block is .0012, little tight for marine use, Merlin .0022, to large, GM .0022-.0025, still to large. I had 1 new Merlin and 1 of the orginal blocks the other had a crack that someone repaired and I didn't trust it. both blocks had .0022 clearance. The way to correct this is to lfter true the block and install bronze bushings and finish hone them to size. After all you just spent $700.00 on lifters. Then before honing the lifter bushing after you install them you have to drill the out with a 18-25" drill bit, this is done by drilling the oil galley that feeds the lifters, this will also insure that there is no casting defect in the galley, final cleaning is very critical after this. All blocks should be cleaned properly with long brushes through all the oil galleys. We tested to see if there was any problems with the priming of the lifters and was found to be untrue. I myself or RM BUILDER, will not use the 2nd design lifter, the first design was tested and proven with the clearances that were built into it. Our results went back to the manufacturer, what they will do about the 2nd design I don't know. I do know if there is to much clearance the oil will be lost at the lifter bore and never have enough to make it through the lifter up to to rockers. The Merlin block still has the short lifter bosses and also a under-cut radius on the top, with a change in base circle or more lift the lifter oil hole can either come close to the bottom or the top, close to the radius, with a bushing this will extend the boss and fill the radius that was cut out for the bushing in maching. The same 8620 solid roller lifter has the same clearance, excessive lifter clearance will result in wheel tracking on the cam and side loading the wheel on the lifter body which could result in a failure of the lifter. This is also true to the end play you have on the cam. I would recommend that you measure the lifter to bore clearance on engine builds, if your not measuring maybe you shouldn't be building it. After some hard testing the lifter bodies had no scratches as you would find from cast iron, if it's an alum. block you should do the same. Maybe RM BUILDER, can give some tips on valve train installations.