When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So I am about to put the engine back together today but I wanted to do Tim's oiling mod to the #1 Main Bearing on the old 351M. The problem is online it says to drill the hole out to 7/16" and tap 1/4 NPT and insert a 1/4" plug. Here is the problem, you cant drill something that is 1/2" with a 7/16" drill bit AND the 1/4" tap I have barely made marks when I did try to tap it. What am I missing? Can this only be done to Cleveland engines, all the stuff I have read shows that Cleveland Oil passage diagram but everyone seems to be talking about 351 Modified engines.
I haven’t been down the road yet, but this is the diagram I have. A 1/2 hole is a bit big for a 1/4(.540) plug, you’ll have to decide if it’s good enough. The other passage shows 5/16 on here.
1/4" NPT tap takes a 0.422" drill to start a new one, and a 1/4" Pipe is 0.54" OD, but the smaller end of the tapered threaded portion is 0.439" and grows from there as the tap goes in ... so while the beginning of the tap is a loose fit, the major or larger threaded section at 0.540" and growing is cutting threads in a 0.500" hole. Unlike bolt threads that enjoy no taper, pipe threads taper at a rate of 3/4" per foot. It's a plug right?
Your tap you have I think is 1/4" thread size not 1/4 npt. I did the mod during my build.....ill attach a picture if I can find it
Heres a 1/4 tap vs 1/4 npt tap
Have you drilled the holes out yet?
Also a picture after I tapped mine. I used a steel flat Allen pkug. The brass was all i had to check the threads.
I dont think id install anything until you drill them out and clean the oil passages with all plugs removed. Alot of debris will get into there drilling and tapping. I believe the center hole you drill out slightly is a straight shot to the front cam bearing. All the cuttings will get in there and destroy all your hard work.
Mine for sure is NPT, its says 1/4" NPT or Pipe on there. As for drilling how can I drill out a 1/2" hole with a 7/16" drill bit. My bit fits loosely inside the oil passage. I had my tap over half way and stopped because it wasn't doing much. I used a mic and the passage is 1/2"
Mine for sure is NPT, its says 1/4" NPT or Pipe on there. As for drilling how can I drill out a 1/2" hole with a 7/16" drill bit. My bit fits loosely inside the oil passage. I had my tap over half way and stopped because it wasn't doing much. I used a mic and the passage is 1/2"
The specification for a 7/16" hole is the minimum needed for starting the 1/4-NPT tap in a place where there was no hole or no hole big enough to get the tap's small end started. At 1/2", you already have a hole big enough to start the 1/4-NPT tap. Notice the taper of the tap, it get's bigger the whole way. That is not an illusion. When you were "not doing much", the taper of the tap was just starting to bite.
Good wrote up about it, I agree with above comment. Keep going with the tap. Just make sure not deep enough the plug will block the flow to right side lifters
Well if the hole is too big for the 1/4" NPT it would appear that you will need to go bigger. How about tapping for a 9/16-18 set screw? Drill size would be .5156", 33/64". If you can go this route I would use red locktite when installing the set screw.
How much oil pressure gain will I have Hot if I do this?
Also I have a separate issue but its small enough I'm not sure if I should start a new thread. My New Engitech #3 Thrust Bearing has a gap on the thrust surface and the original they are flush, is this ok?
Bearing clearance will have alot to do with oil pressure
Before my rebuild I was all the way to the low side of guage when warmed up at idle and would pickup slightly with little throttle startup was middle of guage( factory dash guage)
after rebuild the with a new guage startup is around 80 cruise with any sort rpm 1000 rpm or above 70+
Idle fully warmed up 32-35.
10-30 stock non high output pump
In teardown bearing were shot in sure causing some of my issues so I cant say how much of effect it will have on your situation. I think the mod made alot of sense to me so I did it. I think with correct bearing clearance it should be good pressure with or without the mod
In teardown bearing were shot in sure causing some of my issues so I cant say how much of effect it will have on your situation. I think the mod made alot of sense to me so I did it. I think with correct bearing clearance it should be good pressure with or without the mod
In '92 my 351m lost about all it's oil pressure on a trip, I thought was a bad gauge as it didn't knock or quit. I finished my trip, another 700 miles easily, tried several senders, got home and tried a real gauge with tube, was but 4 psi. Pulled pan, swapped in a set of main and rod shells in place of copper colored ones, rubbed finger nail on crank with no catching, new high volume pump, it still carries 60 psi on the highway. I did not know of this mod in 1992.
Funny now ... I never noticed an oil pressure drop until I jumped into passing gear north of Chatsworth, Ga. and I heard a "looseness", not a bearing knock. Sounded miore like lifter noise, sounded like several of them collapsed for a few seconds. It stopped as soon as I let up on it and the C-6 shifted back into 3rd. Was November '92, I drove on to BIL's house at Carrolton, then the race on Sunday at Hampton, back to Carrolton, loaded up and back to Lexington, Va. area by way of detour through the Smokies on Monday.
I ended up doing the mod, had to tap way down but everything checks out and the plug didn't go to far. Blew the passages out with air and break clean twice with some more air on on top haha, I didn't remove any of the passage plugs, don't want to replace and they are real tight. Loctite and drilled the other hole to 5/16, should be good to go hopefully.
