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Just finished reassembling the heads on my 327 l79. I noticed that some of the valve stems protruding above the spring caps are higher than other cylinders. I measured this difference and it seems to be in the area of 1/10 inch. I also noticed after I had assembled everything that there are two different types of spring caps in use. Apparently the result of an engine rebuild in the early 90s. So my question is how much variation can be tolerated, or do I have to have the high stems ground down?
I removed the springs from an intake and exhaust pair and I see that the distance above the keeper groove is about 30 thousandths more in the valve on the right as shown in the picture below. The locks were properly seated. That would make a difference in installed spring height and I will recheck that .
The real question is in differences in installed stem height. A valve job was done in the rebuild, so seat height could be different. How much difference can be tolerated?
I like to keep them within .030". The flat retainers are early the tapered are later model. There may be a small difference in installed height but it won't be significant. The heads will vary more from valve jobs over the years.
Its as though the intakes tip height were cut .030 to offset the exhaust valve being ordred to short because the head height (exhaust being thicker than an intake) wasnt taken in account? Or the intake seats were cut .030 over the exhaust seats.
From: Las Vegas - Just stop perpetuating myths please.
Originally Posted by After38Years
I removed the springs from an intake and exhaust pair and I see that the distance above the keeper groove is about 30 thousandths more in the valve on the right as shown in the picture below. The locks were properly seated. That would make a difference in installed spring height and I will recheck that .
The real question is in differences in installed stem height. A valve job was done in the rebuild, so seat height could be different. How much difference can be tolerated?
Well the shop that rebuilt the heads should have mentioned if the installed height were different. But an extra 0.030" at the valve tip would only affect the rocker geometry not the installed height as that is a result of the location of the valve lock groove location, the spring pocket, the shims used and the retainer used. There maybe a reason why they used different retainers as you can see a shim under one spring and not under the other. My guess is the installed height are corrected by the different parts used. As for how much tolerance can be tolerated that would be a function of the smallest size shim you have to use - can't install a shim thinner than what you have.
Yes verify your installed height and move on.
The difference in the tip heights is not really a concern. It's just a variable in aftermarket parts. Make certain the distance from the second groove to the seal is at least the amount of lift you have at the valve. You don't want that groove working in and out of the seal. The seal that I can't help but notice is NOT a Viton seal it's just a black rubber seal which will harden with age. You'll be the first to know when this happens, or maybe the guy driving behind you.
Im not sure about your valves but valve keepers can bought in an offset to correct spring install height. Poor valve train geometry as we know causes issues with premature valve guide wear and if one runs high rpm occasionally valve springs can break.
Thanks GordonR, I've been able to get the installed height correct for the springs. It's just the difference in overall stem height that was my concern. I'm going to re measure this morning but I think it's going to be okay as it is.
Ralph
Your spring installed height is way more important, the overall height is no big deal unless you are building a race motor and it doesn't sound like it. The seals will be good for a few years.
All the springs have been tested for pressure at max lift and have been shimmed for proper installed height.
the valve seals are black vs the usual blue of many viton seals. Trick Flow does show them as black on their website.
I can be led to water but I prefer beer.
....Make certain the distance from the second groove to the seal is at least the amount of lift you have at the valve. You don't want that groove working in and out of the seal.....
Good point, I'll check to be sure there is enough clearance.
Ralph
All the springs have been tested for pressure at max lift and have been shimmed for proper installed height.
the valve seals are black vs the usual blue of many viton seals. Trick Flow does show them as black on their website.
I can be led to water but I prefer beer.
Ralph
Well butter my butt and call me a biscuit. I hope they are vitons. Never seen black ones but I haven't seen everything.
Robert61 - Measured between top of seals and two random valve stem lower grooves, shows right at 0.5 inches, so with clone cam and factory rockers I should have about 0.050 clearance at max lift. Will verify cam lobes just to be on the safe side.
Thanks,
Ralph
Installed valve stem height difference - problem?
