Hey everyone,
I'm switching out my stock valve springs to single hi revs for a turbo application. I ordered a kit of valve spring shims which came with 2-3 different sizes. The motor is a 1500 dual port and has the stock cam in it, which spring shims should I use? .030 or .020 ? It may also have .010's in the kit as well.
Thanks in advance!
Which valve spring shims?
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Marc
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- Joined: Thu May 23, 2002 12:01 am
Re: Which valve spring shims?
IMO you should always use a steel shim under each valve spring, they keep the springs from burrowing into the heads as they rotate - and any metal particles generated are magnetic, making them easy to catch before they go into the oil pump.
Without a means to check the spring pressures (both on the seat and at max lift) the pragmatic approach is to trust that the springs are all the same and different shim thicknesses are only needed to compensate for any variation in the installed heights of the valves. Specialized tools are available to make that job easy too, but not worth purchasing for one-time use. If you have a depth mike you can use it in conjunction with a deep socket that fits into the spring pocket to make a poor-man's installed-height gauge. With a helper to provide a third (and perhaps fourth) hand you can use the deep socket and the tail of a set of calipers to take this measurement too. You don't get the actual installed height this way, just the difference between the lengths of the valve & the socket, but a relative measurement is good enough for our purposes.
Typically on a head that's had the valves/seats reground the intakes will be sunk a little deeper than the exhausts, so they'll have a taller installed height. To set the overall height even so that rockerarm geometry's the same for all valves, the ends of the intake stems may have been ground off a little - but that doesn't change where the keeper grooves are, and they determine the installed heights which are of concern for the valve springs.
So, cheap-and-dirty pragmatic approach is to measure the distance from top keeper groove to tip of each valve, and if you find any significant (>.005" or so) difference jot them down.
Then with all valves in the head and pressed against the seats, find their relative installed heights. The socket & mike/caliper method is best but if you lack those just place a long straightedge across the top of all four and look for any difference in total installed height. Again it's more typical for the intake seats to have needed more work than the exhausts so usually you'll find that one or both intakes sit taller. There'll be some guesstimation involved in judging when the straightedge is exactly level, but you can sight across the gasket rail to see when it's parallel - just take your best shot.
Select the shim thicknesses which'll compensate for the difference in height, PLUS the amount that's been trimmed off the stem (if any), and the springs should have roughly the same pressure - that's about all you can do with shadetree tools, perhaps not perfect but at least you made the effort to get them close. Using the straightedge technique the best you can accomplish is to make all four on each head about the same, but even just that is better than not checking at all.
More often you find the provided shims to be .015", .030", and .060" (.020" are fairly common too) but I'll take you at your word that you have 10/20/30s to work with.
In the unlikely event that you can't find any significant difference in installed height at the keeper grooves, just throw eight of the same at it (say, .015" or .020") and if you only have four of each use thicker ones on the intake than on the exhaust - the rationale being that the intake valves weigh more
...it's not worth buying more shims when using this crude technique.
Without a means to check the spring pressures (both on the seat and at max lift) the pragmatic approach is to trust that the springs are all the same and different shim thicknesses are only needed to compensate for any variation in the installed heights of the valves. Specialized tools are available to make that job easy too, but not worth purchasing for one-time use. If you have a depth mike you can use it in conjunction with a deep socket that fits into the spring pocket to make a poor-man's installed-height gauge. With a helper to provide a third (and perhaps fourth) hand you can use the deep socket and the tail of a set of calipers to take this measurement too. You don't get the actual installed height this way, just the difference between the lengths of the valve & the socket, but a relative measurement is good enough for our purposes.
Typically on a head that's had the valves/seats reground the intakes will be sunk a little deeper than the exhausts, so they'll have a taller installed height. To set the overall height even so that rockerarm geometry's the same for all valves, the ends of the intake stems may have been ground off a little - but that doesn't change where the keeper grooves are, and they determine the installed heights which are of concern for the valve springs.
So, cheap-and-dirty pragmatic approach is to measure the distance from top keeper groove to tip of each valve, and if you find any significant (>.005" or so) difference jot them down.
Then with all valves in the head and pressed against the seats, find their relative installed heights. The socket & mike/caliper method is best but if you lack those just place a long straightedge across the top of all four and look for any difference in total installed height. Again it's more typical for the intake seats to have needed more work than the exhausts so usually you'll find that one or both intakes sit taller. There'll be some guesstimation involved in judging when the straightedge is exactly level, but you can sight across the gasket rail to see when it's parallel - just take your best shot.
Select the shim thicknesses which'll compensate for the difference in height, PLUS the amount that's been trimmed off the stem (if any), and the springs should have roughly the same pressure - that's about all you can do with shadetree tools, perhaps not perfect but at least you made the effort to get them close. Using the straightedge technique the best you can accomplish is to make all four on each head about the same, but even just that is better than not checking at all.
More often you find the provided shims to be .015", .030", and .060" (.020" are fairly common too) but I'll take you at your word that you have 10/20/30s to work with.
In the unlikely event that you can't find any significant difference in installed height at the keeper grooves, just throw eight of the same at it (say, .015" or .020") and if you only have four of each use thicker ones on the intake than on the exhaust - the rationale being that the intake valves weigh more
...it's not worth buying more shims when using this crude technique.-
66NCVW
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- Joined: Wed Dec 30, 2015 11:47 am
Re: Which valve spring shims?
Marc, you are 100% correct. I looked at the shims this morning and I have the following. 8 .015's 8 .030's and 4 .060's. So I'm guessing the quick and easy approach since this motor is more of a test mule with a stock cam and low boost settings would be 4 .015's on exhaust and 4 .030's on intake? Then straight edge check them?
Thanks again for the advice!
Thanks again for the advice!