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Rebuilding a 400. This is our first time. Installed many new parts, new cam included.
Our question is in regard to the valve springs. In our ford book, Tom Monroe, he says to shim them to a specific height. The strange thing is that the intake and exhaust heights are completely different. Also, the valve spring retainers are noticeably different. Is this normal?
Where should we go from here?
Previous owner did not have any shims. The truck ran, but with no oil pressure, which is why we are rebuilding.
Should we leave them as is? Let me know any insight on this. I couldn’t find much on it.
Here is a couple photos of our set up. In the photo you if you look, you can see the one set of retainers is thick, while the other is thin. You can also see the valve posts go from long to short in a repeated fashion.
Valve spring shimming is used to ensure that the required spring pressure is obtained at a specific height.
The camshaft supplier should specify the specs.
The OE valve lift, spring pressures, and compression were all pretty low, so assuming your cam lift exceeds OE, then yes new springs, of the appropriate strength, would be required.
And new lifters too !?
And new retainers too !?
There is a specific tool available to measure spring pressures at a given height if you want to do them yourself.
Read all instructions.
Valve spring break in differs to cam break in.
Are you rebuilding the bottom end too ?
Did you measure the engine specs to ensure the correct choice of cam ?
Unless you're wanting to do this yourself, let the machine shop set it up.
Valve springs have an "installed height". The length or height of the spring itself when installed in the valve assembly has to fall within a specific dimension. That way it will be within specification in terms of spring force, measured in pounds, when open or closed and everything in between.
The trick way is to measure the length of each valve assembly minus the spring with a valve micrometer or snap gauge, and find the narrowest one. This measurement becomes the spring height for all of them, each valve gets shimmed as required to get them to the same height +/- .020". If you're really picky, the spring force too is measured for each spring at the installed height, and any spring that doesn't meet spec is discarded. There are special tools for this (kind of spendy) but a lot of guys just use a drill press and a bathroom scale with good result.
You don't have to necessarily want to do all this yourself but it is important to understand what the objective is, because it also isn't necessarily the case that whomever is setting up the heads knows what the hell they are doing. Trust, but verify. New valve springs are inexpensive, and generally often overlooked. They are one of the most stressed components inside any engine.
There is a break-in or a kind of heat treating procedure recommended for brand new valve springs. Read and follow spring manufacturer instructions.
Are the valve springs supposed to be different lengths? My exhaust and intake springs are different lengths, and different retainers. Most of the springs I've looked at for purchase have been in sets of 16 of the same size. So for the 400 we need to buy two separate sets? That seems the truth, just looking for confirmation. Thoughts?
That weird looking retainer on the exhaust valve is a rotator and it's good for nothing, throw it in the junk and use the same retainers on both valves. New springs will all be the same height. They do make shims for your heads but it's limited how much you can put under the spring because the more shim, the less register the spring will have to stay seated in the head. If it's necessary to shim beyond that then you can also get special retainers to close the distance. The reason you run into shimming is the seats / valves have been sunk too much through wear and grinding. If it's real bad then it might be time to consider putting seats in. It is also very important that whoever does your heads keeps the valve tip heights all the same exact height. If not you would need a different length push rods to get the lifter preload set.
As said the exhaust retainer to the rotating type normally used in heavy duty truck engines.
Since your getting a new cam get the kit that has matching springs and purchase a new set of retainers, they will all match, then take everything to a machine shop for proper valve job and matching connotes to spec.
