a certain self proclaimed 351C enthusiast & forum owner that once decried the use of lifter bore bushings has changed his tune for 'his own personal build' but Yep the block is bushed
FWIW your machinist / builder is not aware of the issue, is complacent & confident that every lifter that fits in a 351C lifter hole performs as expected under any & all circumstances. as George has pointed out in another old thread i just read here on this forum, this doesn't make the man a bad guy or incompetent, maybe he just doesn't live & breathe 351C 24-7-365.25
restricting oil to hydraulic lifters is always controversial but seriously, they need enough to function properly & no more. the lifter oil galleys in the 351C block are ridiculous, what about 1/2" diameter? this large window allows the lifters to churn & cavitate the galley (that's bad) further reducing the ability of the main & rod bearings to get proper oil supply. bush the lifter bores and the large window no longer exists, the block becomes Priority Main Oiling (that's good) and the bottom end has an crazy better oil supply from a standard volume pump. the engine will make & hold excellent bottom end oil pressure with no lifters installed!
https://www.youtube.com/watch?v=fI_SanxhGXw this vid shows a .020" orifice bushing under hand crank power, when i did this same priming technique on an unbushed block the valley flooded over with oil in seconds. i'd use a larger orifice for your hydro rollers but it'll still have a dramatic effect
then there's the issue of exposing the lifter oil band out of the lifter bore ...
it's just so easy to avoid all the drama
here's an oldie http://www.network54.com/Forum.../Oil+restrictors...-
quote:Originally posted by George Pence
Lifter to lifter bore clearance, August 7 2011, 8:26 PM
If a 351C is metering oil flow to the valve train with the proper lifters, if it has restrictions in the oil passages supplying the cam bearings, AND if it has no excessive clearance issues between the lifters and lifter bores it is good to about 7000 rpm, but above that the lubrication system will still underfeed the reciprocating assembly. This is what guys were discovering circa 1971 or 1972. Keep in mind they were using factory fresh blocks, not used blocks. The first fix was the high pressure spring, but that didn't resolve the problem. Boosting the pressure wasn't the answer. Several other tricks were tried by Don Nicholson and others, the patch that eventually fixed the problem was the lifter bore bushings. Whatever the dynamics are going on inside the right had oil galley I can't explain, but the only thing that guarantees adequate oil supply to the reciprocating assembly above 7000 rpm is to isolate the oil galley from the lifters. A short time later Ford began selling a lifter bore installation kit similar to Denny's.
Don Nicholson began using the bushings circa 1973, unfortunately the OHO Newsletter was cancelled in the spring of 1973. Had the Newsletter remained in publication I'm sure the availability of the bushing kit would have been announced in its pages. Instead it's existence was hidden in Ford's parts inventory along with all the other semi-secret racing parts.
With used blocks lubrication problems can and do crop up at engine speeds below 7000 rpm. Combine that with the lifter compatibility problems people encounter, and this is why I've adopted the recommendation I have.
There are several ways to misdirect where the oil flows in a 351C; too much oil can flow to the valve train, too much oil can flow to the camshaft bearings, and too much oil can flow in the clearances between the lifters and the lifter bores. In each situation oil is being robbed from the crankshaft, because the crankshaft doesn't have first priority to the flow of oil as it does in the Fairlane/Windsor V8 or the 427 FE "side-oiler" V8.
Lets focus on the lifter to lifter bore clearance issue.
The production specification for lifter OD is 0.8740 to 0.8745. The production tolerance for the lifter bore ID is 0.8752 to 0.8767. If a lifter with the minimum OD (0.8740) is installed in a lifter bore with the largest allowable production ID (0.8767) the clearance is 0.0027 which is greater than the clearance between the crankshaft bearing journals and the bearings! More oil would flow to this leak than would flow to the bearing journals! FYI: the factory tolerance for lifter to lifter bore clearance is 0.0007 to 0.0027", the nominal clearance therefore is 0.0017". According to Fordmech " Lifter to bore clearances exceeding .0015 are surely going to be pretty big leakers as multiplied by 16". Yet the nominal factory clearance is 0.0017" ... and even 0.0027" is within spec! If a block has worn or egg shaped lifter bores the nominal clearances will be greater yet. Lifter bore bushings may be required for a high mileage block simply to achieve enough oil pressure even if the motor is only planned to be used to propel a grocery getter.