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Oil relief valve


Ken/Alabama

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The small brass valve next to the fuel pump push rod bushing is actually a by-pass valve. It's purpose is to supply oil to the hydraulic lifters when the oil supply from the oil filter return line is restricted or on start-up before oil start flowing thru the filter. If it sticks "open" this will allow oil to continuously flow from the main oil line into the lifter feed lines. No harm but the oil pressure might be reduced a bit due to the 20 psi relief valve at the front of the valve chamber. If this by-pass valve sticks "shut" then the valve lifters are completely dependent on oil supply from the oil filter system and could result in noisy lifters. Early '38 engines did not use a by-pass valve, they used, instead, a metering plug which allowed continuous oil flow from the main oil line. The oil filters returned oil directly to the oil pan on this set up.

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The little brass poppet valve in the rear of the v-12 is a volume reducer fed directly off the filter which feeds from main oil pump output galley.

The lifters tend to fog the chamber with oil mist from too much pressure or volume which is reduced by this orfice, which has a check valve built in..

the other end of the feed tube has a ball and spring to regulate pressure in lifters, and provide some lubrication to the cam gear...Remember those awful split valve guides in a high vacuum enviroment sucking oil into the combustion chambers and you will have learned one of the causes of the stinkin lincoln syndrome!!

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Timely thread for us. Our V-12 will have a Melling M 15 pump, a full flow oil filter and solid, adjustable lifters. So with the above advise, I'm thinking I should plug the rear valve, replace with a '36 plug with metering hole, or just find a stronger spring. Sounds like the stock front valve should work OK. Make sense?

Thanks

Abe

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Yes, when using adjustable, non-hydraulic liters its best to replace the by-pass valve with a plug. However you need to do more if you use a plug. In order to maintain oil flow to the timing gear a 1/16" hole needs to be drilled down thru the middle of the 2 slanted valve lifter return lines in the area under the from oil relief ball and spring. This hole should extend down to the oil grove around the front cam bushing. This will allow oil to flow into cavity where the oil relief valve is and when oil pressure goes above 20 psi it will flow past the relief thru an exit passage that sprays oil on the timing gear. The 2 slanted hole from the lifter oil lines need to be plugged using a couple short pieces of 1/8" drill rod; this will keep the oil from returning back into the lifter system.

Drilling the 1/16" hole straight down in the cavity around the cam bushing is difficult. I use a larger drill and then install a plug in the exit oil line that lubes the timing gear. You need a about a .040" to.060" hole in the plug to limit flow. You can install the plug from the front side of the timing gear oil exit hole in the block.

If you choose not to do these mods you might be better off leaving the by-pass in place. You will still of course get some oil flow thru the filter and if you use hollow tappets oil will flow thru them and then into the pressure relief cavity.

Hopefully you have had the cam reground with clearance ramps for the adjustable tappets? If this isn't done it will be almost impossible to attain quiet tappets.

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I was going to do that as well, hot rod and such...but, it is not a rod, it is a luxury car and one of the charms of it is the silent running h-v-12 with the silent hydraulic lifters...I dont think you can eliminate the clatter of solid tappets...not bad, but not silent..I am not sure how many horses you gain from more positve

lift, which I suppose at wide open would be important to reduce valve float at high rpms,

by the way, the valve is not a relief valve, but a metering orfice

Edited by Mssr. Bwatoe (see edit history)
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Dee:

Good advice. I already figured I needed a hole in the plug from the front, I'll see about getting to the front cam bearing and plugging the lifter lines. Now I wish I hadn't already installed the cam. Mine was reground by Oregon Camshaft in Vancouver, WA, hopefully they got the ramps right.

Bwatoe:

I'm calculating that with the cam change, Aluminum heads, better intake, and headers I can get about 30 more hp, should be able to feel in the seat of the pants when there was only 120 hp originally, and mine was down to 50 lbs compression with two burnt valves. If you want more, there is always supercharging, but then I'd worry more about overheating. Ford flatheads with adjustable lifters seem to have low noise when everything is adjusted right. Stock Fords weren't adjustable. We'll see about the Lincoln.

Abe

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After the final valve lash clearance adjustment I put a dab of Loctite on the threads of the adjuster on the lifters. Getting those valves adjusted is a long and tedious operation but if you don't go over them a couple of times, they will be noisy. Drilling a hole in the lifter boss will be a big help in holding the lifter (with an ice pick ) while wrenching the adjustment screw. Unless you're going for high RPM's you might consider using standard Ford valve springs, less friction.

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