The International Cessna^® 170 Association

Where can a guy get information about 0-300D valve springs?
My engine has had an AD on the cylinders and I suspect the springs are not installed to the correct installed height and the pressure is down.
I've bought an 0-300 engine CD & a manual, but they don't cover that info on the valve springs. All I've been able to get is the free length.
All that will tell a guy is when the spring is old and fatigued (settled)
It is the actual pressure installed and at full lift that will keep the valve gear stable and keep the engine making power at higher revs.
Any info sources?
Thanks.
Adger Smith

The continental overhaul manual has all that you need to know to test your springs.

The free length of the springs is unimportant. The installed length is determined by the valve seat depth and valve stem length.
Compress the springs to the specified length and measure their force (just don't try to get me to tell you a dirt-simple method to do that.)

If I was going to measure the compressed length and force required for a valve spring, I would put a nut and fender washer on an eye bolt and slip the bolt thru the spring with the spring resting on a vice with the jaws open just enough to clear the eye bolt shank. Then I would hook an accurate spring scale to the eye bolt and pull down until the desired compression is obtained and read off the load applied from the scale. Or conversely, pull a desired load and measure the compression.

No problem to test. I have the proper equipment at my shop. I even have on engine spring removal& spring height tools. I have my business where I machine and build race engines. I just needed the correct specs. The manual I bought was very incomplete. It was copies of an original manual. Lots of pages missing. So much for cheap e-bay purchase.
I hope that is why it is not as crisp at high RPM. I'm also going to check the mags & timing. I've got it down for interior and windows and it is a perfect time to do some checking.
Thanks,
N2582D I appreciate the info, but I still need to find an installed height. Your info will help determine if the springs are actually in spec. or weak. I suspect that the installed height is incorrect making the spring pressure less than spec.
Adger Smith
Adger Smith Performance Engines
2802 W 7 th St
Texarkana, Tx

How would the installed height be wrong unless you had the incorrect valves? There are no shims to adjust installed height.

n2582d wrote:How would the installed height be wrong unless you had the incorrect valves? There are no shims to adjust installed height.

That was my thought also in my previous thread.
It would require the wrong valve, the wrongly installed valve seat, the wrong keepers or spring-seat...or shim/washer beneath the spring... I can't imagine this happening and am also curious.

OK, quick lesson in machine work. When you grind a 45 degree seat angle on the cylinder a normal grind will remove .005 to .010 material unless each seat is worn bad. In that case you will replace the seat and cut/grind it to the correct height. If you do replace the seat & the valve there will be no problem with stem length & installed spring height. Now to the used reconditioned valve. Same thing applies with the 45 degree angle of the valve. It will need .005 to .010 material removed in normal regrinding. When you add .010 to the valve and .010 removed from the seat together it is not .020 because you are using 2 ea 45 degree angles. It will be (Let's say for even numbers) more like .015 downward movement in the stem length. That would loosen the valve spring set/installed height by .015 making the seat pressure and open pressure less. How much less? I don't know on this application because I have no specs on the spring rate & haven't tested a good spring.
To my situation. I have bought a plane that had an AD on cylinders 375 hours before I bought it. We have had one cylinder off and noticed that it all didn't look new. Like they just put on cylinders and old valves and old springs and old pistons.
What I saw makes me question what was really done. I have the log books and the entry is very vague. I do have the yellow tags for all the cylinders, but it doesn't say (in black and white) whether they were reconditioned or new. It also doesn't tell me if it was assemblies or just cylinders. While the plane is down for new interior and windows/windshield I just want to verify a few things. To do this I am looking for some specs. BTY: A quick on line search shows there is a spring shim kit sold by Lycon & no specs listed :~( .... Bummer.
Adger Smith
Adger Smith Performance Engines
2802 W 7th St
Texarkana, TX
903 794 7223 shop
903 824 4924 cell

Adger, I think you are over-thinking this.

While a reground valve/seat will minutely affect installed height, as I mentioned before, unless the valve or seat is ground/installed incorrectly (with excessive material removed) then installed height will not be a problem. IN any case, that is not how the valve springs would be condemned or accepted.

The Ovhl manual provides the information to determine if the springs are serviceable: Compress them to the specified length and measure their strength. IT matters not whether they are installed with a poor valve/valve-seat fitment as to whether the springs are serviceable.

Sixracer wrote: ...It will be (Let's say for even numbers) more like .015 downward movement in the stem length. That would loosen the valve spring set/installed height by .015 making the seat pressure and open pressure less. How much less? I don't know on this application because I have no specs on the spring rate & haven't tested a good spring...

Are these old slow rotating engines that sensitive to spring height?
I think I've had carbon build up close to that much.

I'm not doubting your abilities as a mechanic but things that really matter in a race car engine may not be so much of a factor in a farm tractor engine.

Valve springs can be weak and fail to excersize proper valve action, especially with a cold engine. But the springs are tested independently from the installed condition. (I have a number of springs which have failed the test in a bag with red tags. I also have some used spring which pass the test. I have no idea why I'm keeping the failed springs.)

I have a lot of old and worn-out parts in my hangar on my special "Shelf of Shame". I keep them because each one reminds me of a problem solved and something new and shiny installed.

Regarding valve height, .015 change is insignificant to the spring operation. The valve stem tip sitting higher might cause insufficient dry tappet clearance, in which case you'd have to replace the pushrods with shorter ones. Or slightly grind down the ones you have.

Failed springs make good vibration isolators for generators, etc. You can always find good use for failed parts. A good spring compressor always works to check specs.

John