The International Cessna 170 Association

mmcmillan2 wrote:

mschlender wrote:Main spring looks old

How does one determine when it needs to be replaced? My limited spring knowledge is that springs wear from use (flexing back and forth), not so much tied to time. I agree, the paint does look old.

It’s been recommended by consensus that the tailwheel mainspring be replaced every 500 cycles/flights.
An indication the mainspring is due for replacement might be to inspect it at the point of contact between itself and the spring just-above it. The spring just above it has a lower, trailing-edge which “digs” into the mainspring and creates a stress-riser (groove) in the mainspring. The Mainsprings commonly break at that point.

When installing a new mainspring, it is recommended that you use a file and/or emory to remove the sharp lower trailing-edge of the spring-above to reduce the tendency to damage the mainspring.

GAHorn wrote:

mmcmillan2 wrote:

mschlender wrote:Main spring looks old

How does one determine when it needs to be replaced? My limited spring knowledge is that springs wear from use (flexing back and forth), not so much tied to time. I agree, the paint does look old.

It’s been recommended by consensus that the tailwheel mainspring be replaced every 500 cycles/flights.
An indication the mainspring is due for replacement might be to inspect it at the point of contact between itself and the spring just-above it. The spring just above it has a lower, trailing-edge which “digs” into the mainspring and creates a stress-riser (groove) in the mainspring. The Mainsprings commonly break at that point.

When installing a new mainspring, it is recommended that you use a file and/or emory to remove the sharp lower trailing-edge of the spring-above to reduce the tendency to damage the mainspring.

Do you mean here?:

Exactly there.
Two things to consider if your wondering whether your main spring might need replacing. 1) Signs of fretting especially at the contact point you’ve circled between the main spring and the leaf above it. The red “dust” suggests you’ll likely find a gouge at that point on the main spring and suggests the roulette wheel is spinning. Your spring also shows widespread surface corrosion, a varying concern when it comes to spring steel based on the depth of the corrosion. 2) The angle (sag) of your tailwheel in relation to the fuselage.
Tons of info in threads on these issues.

Before buying a new spring set, see if the thickness issue has been resolved.

viewtopic.php?f=24&t=15043

Thanks for the great help! Should these springs be assembled then painted, or painted individually?

I'm painting mine individually and using T-300-1 teflon tape between each leaf. Here's some interesting directions from the L-19 service manual. Sounds like a great way to attract dirt.

n2582d wrote:I'm painting mine individually and using T-300-1 teflon tape between each leaf. Here's some interesting directions from the L-19 service manual. Sounds like a great way to attract dirt.

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With an O-300 in front all of the tailwheel springs will automatically be covered with oil.

They come from Univair with black paint. I painted mine white before assembly AND put a thin layer of wheel bearing grease between the leaves. I then wiped off any grease on the outside that might attract dirt. I do like Gary’s idea of the Teflon tape though.

I tried teflon tape 15 years or so ago between the mainspring and the 3rd spring and it was crushed/squeezed/extruded and pushed out over the next few weeks. If you have a tight fitment on top of all that it’ll only add to the problem and isn’t a durable solution, IMO. That’s when I decided it was better to radius and smooth the lower/aft edge of the 3rd spring.