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By jamit793 - 4 Years Ago
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OK, I lost oil pressure to the right head valve adjusters after a complete rebuild and about 500 miles of run in. Resulting in a complete teardown to find the issue. The recommendations are that the cam bearing was too soft due to the manufactures recent material changes resulting on the bearing closing (mushrooming) in on the small slot in the bearing that allowed the oil to flow. The exerts recommend that I use the cam bearings from SCHUMANNS SALES AND SERVICE with an external groove around the exterior of the cam bearing. This will eliminate the need for the oil to penetrate the small slot in the bearing travel around the smaller slot in the cam and exit to the again small slot in the cam earing to either the right or left head passages which allow the oil to lubricate the valve adjuster assemblies. Solving my issue.
My first question is what will happen if I simply replace the existing cam bearings with cam bearings from Schumann's sales and service and their external groove around the exterior of the cam bearing, or run a drill down the 1/4 " hole in the block to the cam bearings and opening up that small slot in the cam bearings? Or take the cam groove on the existing cam journal and open it up with (forgive me) a chain saw file to 0.60 deep? Yes it fits. Or what if I do all three. purchase the SCHMANNS Sales and Service cam bearings with the external groove, drill the 1/4 " opening in the cam bearings existing small slot and file the existing small groove on the current cams? Am I playing with fire? I simply don't want to rip the engine out after another 500 miles and rebuild it for the 3rd time????????
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By jamit793 - 4 Years Ago
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were the cam bearings on a new 312 engine in 1957 from FORD made from sintered Iron or Sintered bronze?
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By Ted - 4 Years Ago
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My preferred fix is to machine a groove in the #3 cam bearing hole behind the cam bearing to provide an alternate oil path to the top end of the engine. The Schumann bearing with the groove on the outside of the bearing is a suitable alternative to this but be careful in installing the bearing as it can crush easily at the grooved center of the bearing if hammering that bearing in place. Using a puller or draw bar to install ‘outer grooved’ bearings is recommended. There are some aftermarket blocks out there that use ‘outer grooved’ cam bearings and care must be taken when installing those to prevent deformation of the bearings when installing them.
For the Y, machining or cutting the groove deeper in the #3 cam journal also solves the issue of the soft babbit of the bearing pressing into the shallow groove of the cam journal.
Doing all the aforementioned modifications to get more oil past that center cam bearing can have too much oil going to the top end of the engine. That’s easily solved by just installing restrictors on the #2 and #7 rocker arm support stands. A restrictor hole size of 0.078” is sufficient in most cases.
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By jamit793 - 4 Years Ago
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Where can I purchase the restrictors for #2 & #7 rocker arm support stands?
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By 2721955meteor - 4 Years Ago
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I enlarged the groove in the cam(re hints on the site) I also ran a long drill down the lube holes to be sure their was not restricted. my engine has now got7000 miles no issues,tho there is plenty of oil to the rockers. as I have blocked the tubes. running the engine with covers off a lot of oil goes down the spinning push rods, also good valve cover gaskets and seals for the retaining studs. ihav a un restricted breather hose to air cleaner from the valley cover dit end. no excessive oil use, never had to adjust the valves.
would be easy to make restrictor plugs for the rocker stands on both sides. I don't bother to restrict, oil pressure 18 to 20 psi hot at idle
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By PF Arcand - 4 Years Ago
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Apparently, John at Mummert Machine, says part of the problem is that the oil groove in all the replacement Cam blanks is not to original standards. His shop machines the groove deeper on all the cams they sell. However, I don't know how much deeper that is?. You could link to his sight here & contact him possibly. It might be a good idea to try to avoid those particular soft cam bearings if possible. I believe that he lists a hardened center bearing or it may be available elsewhere...
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By Florida_Phil - 4 Years Ago
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Two years ago, I installed a new Isky cam in my TBird engine. We measured the cam oil grove before installation and found it to be .018" deep. We cut the oil groove to .030". This increases the oil to the heads substantially. Our oil tubes at the rockers were not closed and are in the stock location. We did not have to restrict the oil to the heads. So far, I have about 3,000 street miles on this engine with everything running as it should.
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By darrell - 4 Years Ago
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john mummert was selling a hard centre bearing.how did that turn out.
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By Ted - 4 Years Ago
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jamit793 (5/25/2021)
Where can I purchase the restrictors for #2 & #7 rocker arm support stands?
In those cases where I need top end oiling restrictors, they are made using 5/16-18 set screws. Just drill them to the orifice size you need.
Using a 5/16-18 tap, tap the appropriate rocker stands (#2 & #7) at their bottom holes and then install the drilled restrictors in those holes. The stands do need to be removed from the shafts to do this to eliminate the possibility of any machining chips making their way into the shaft. It also helps to not fully tap the holes all the way to the shaft and use short or shallow restrictors that can be tightened without going into the rocker shaft holes.
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