I have a Gt dyno serial number WYC8I00217 who can help me get the year and model

Question

It's 100% steel serial number is WYC8I00217k

Answer 1

For most bicycles the serial number is not decipherable.

For some very popular bike makers there have been people who did the work of figuring out what the serial number means.

While GT was a very popular maker and several people have posted information attempting to provide guidance. I'm sure they did the best they could with the information they had but the information posted is incomplete at best.

Bottom line -
Looking at the information posted none of the descriptions match the number you have posted well enough to draw a solid conclusion. You would probably do better looking at the distinctive features of your frame and browsing bmxmuseum.com's collection of GT bikes to find a visual match.

Here are a few examples of the serial number information posted for GT:
bmxmuseum.com GT Serial Numbers

Here is an email I got from an actual employee of GT:

If the bike frame was manufactured at the Santa Ana CA facility, the first three or four digits of the serial number should be letters abbreviating the model or size of the frame such as "XL", "XXL", CR24, or something like that.

The next part of the serial number is eight numeric digits. The first four numbers should be a two digit month followed by a two digit year.

The last four digits are the serialization digits 0000 to 9999 depending on what number the frame was of the years production.

If the frame was made overseas in Taiwan, it gets more complicated. If the number starts with a K, the frame was made by Kinesis.

That's the only one I remember off the top of my head.

There were at least four companies in Taiwan that made the GT lines :

Robinson, Dyno, Powerlite and Auburn included)

The first digit would be a letter designating the factory that made the frame. There might also be a second letter digit specifying the factory that assembled the bike, if applicable. The model and year of production was also coded by a letter, so you won't be able to spot a two digit month and two digit year.

There is more - none of it matches your serial number.
Here is another example:

How to read GT serial numbers for mid-school and new-school BMX bikes

For mid-school GT BMX bikes built in Taiwan through most of the 90’s with a serial number that begins with 4 letters before the series of numbers. The 3rd letter corresponds to the year of manufacture.

1991-2000 – 4 letters at beginning, 3rd is year A B C D E F G H I J 91 92 93 94 95 96 97 98 99 00

The 4th letter indicates the Month A B C D E F G H I J K L Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

A few examples are: HFGB00000 – 4 letters, GB are the dates. G is the year (1997), B is the month (Feb) HFBH00000 – 4 letters, BH are the dates. B is the year (1992), H is the month (Aug)

For new-school GT BMX bikes built through most of the 2000’s with a serial number that begins with 5 letters. The 4th letter corresponds to the year of manufacture and follows on from the mid-school serial numbers.

2001-2010 – 5 letters at beginning, 4th is year K L M N O P Q R S T 01 02 03 04 05 06 07 08 09 10

The 5th letter indicates the Month A B C D E F G H I J K L Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

A few examples are: HAMRF00000 – 5 letters, RF are the dates. R is the year (2008), F is the month (Jun) HAMOI00000 – 5 letters, OI are the dates. O is the year (2005), I is the month (Sept)

This information does not address the first two characters in the serial number. If we guess that the "8" in your serial number is really a "B" we could assume that this information tells us the year would be 1992 and the month would be September.

There is a thread at bmxmuseum.com named GT Serial Number Info that goes on for a very long time - 80 pages - discussing GT serial numbers. Some of it repeats the above information and some is different. None of it addresses a serial number that begins with "WYC8"

There isn't enough information available to be useful.

Answer 2

As DavidW indicated in a comment, please read the links for reasons why presenting serial numbers in isolation on an internet forum is often worthless, barring the odd case where someone has managed to decipher the numbers as in David D's answer.

If anybody can help you with this information, GT Bicycles itself would be one party you might contact. However, do note that their corporate history (as detailed on Wikipedia) contains a large number of ownership changes. Past records might or might not have survived. Calling or emailing GT itself shouldn't be less fruitful than asking here, but don't be surprised if they're not able to answer, or if they can't be bothered to answer.

If the motivator is that you want replacement parts, a bike store is likely to be able to identify what is currently commercially available that will work with the bike. If the motivator is some sort of valuation exercise, then do remember that bikes don't hold much value, maybe barring rare exceptions.