In the early 1980s I had numerous steel bikes including a Mercian.
I always regretted selling it. At some point migrated to carbon bikes but occasionally would look for a replacement for the Mercian.
But nothing ever came up, they were always the wrong size, wrong price or too beat up.
But a few months ago one came up on ebay and it seemed perfect, the right size in great shape at a reasonable although maybe slightly high price.
I knew this might be my only chance and pulled the trigger. But when I got it there where lingering questions:

Would it really fit me?
Would I like the ride like I remembered it?
Could I fit the parts on it that I wanted.

While I appreciate a vintage bike that is period correct, I am a firm believer that modern components are just better in terms or weight and performance.
I did not want to use down tube shifters and square taper bottom brackets. The first task was getting rear dropouts spread to 130mm which had a local frame shop do for me.
It turned out that the seatpost was extremely hard to get in so I got a flex hone and cleaned out the seat tube and now it is much better.
There was much thought about the crankset and was originally going to use Campy Over Torque, but after getting the BSA bottom bracket discovered it was not going to work,
so I went with Shimano 105 in sliver. Not the best fit visually, but the best I could do for my budget.
Here is what I have on the bike so far:

Innicycle headset
Shimano 105 crankset with Wheels Manufacturing BB
Ritchey Classic seatpost
SRAM Rival shifters
SRAM Force RD
Dia Compe Royal Compe brakes
Ritchey stem with black anodizing stripped and polished.
FSA bars with black anodizing stripped and polished.

I just ordered some Kinlin XR22T polished rims for the wheels.
In making measurements I discovered that the top tube is relatively short at 51cm, most of my bikes run 53 to 53.5cm.
But since my legs are relatively short I normally use a zero offset seatpost. So using a 25mm seatpost on this bike gets the fit close.
I was able to do a short test ride around the neighborhood by borrowing wheels and pedals from my other bike.
So far the I think it rides nice, very quiet and smooth. The SRAM shifting works perfectly.
I was surprised how stiff the frame feels, no noticeable flex, but that might become more apparent on a longer ride with some hills.
The weight is right around 19 lbs which what I had calcualted.
Really looking forward to doing a real ride on this.

Very nice. Does that threadless stem adapter only come in one length like that?

Really nice looking Mercian. I’m slowly assembling an 83 and looking forward to riding it (hopefully by spring?).

About the conversion — the inventor is a BF member and sometimes updates this thread that discusses its development: Threadless Conversion Headset

AFAIK there is only one length. I will be cutting it once I have it dialed in.
it is really nice compared to a separate headset and adapter.

Looks nice even with the greasy finger front derailleur system.

I use a piece of newspaper to shift the front to avoid the grease. 🙂

Great bike! I love the way you built it.
I have a couple 1982 models. They are both built up vintage however.
What size seat post was it. I'm curious?

JJ

seatpost is 27.2. Initially I could not get it in even though the frame looks barely used and no rust.
spent some time cleaning the seat tube with a flex hone, now it is much better but still a little tight.
would love to see some pictures of yours.

Is the model the King of Mercia Touring? I ask because mine is, and it takes a 27.0 seat post. I was having trouble getting my 27.2 seat post to even start, so I tried a 27.0 and it fit like a glove. I wrote to Mercian about the serial and to ask about the 27.0, and sure enough, they said that in the early 80’s, they would have reamed the touring frame out to 27.0. But again, I couldn’t get a 27.2 to budge with a clean seat tube, so it was clearly the wrong size for mine.

Yes I believe it is a King of Mercia. Prior to using the flex hone I measured the seat tube at several places and it measured 27.2mm using digital calipers.
it is possible that a 27.0 mm would have worked but those are hard to find.
According to the seller mine was made in 1985 but I did not verify that.
did you measure the diameter of your seat tube?

You can figure out the date from the serial number. For example, my '82 Mercian Colorado is marked 45882 built by no. 6 (George Bryan, I am told).

Mine is 70185, so indeed it is a 1985.

Hi, Here are some links to videos and some pics!

Beautiful bikes, you are lucky to have them.
I believe the one I owned in the 80's had the same triple crankset and Rally derailleur.
It was white with red panels, I wonder where it is now?

Here it is with the build completed. Just finished building the wheels with BORG22 (Kinlin XR22T) rims and Bitex hubs.
I have done a few 30 to 40 mile rides and really like it. Compared to my Cannondale the wheelbase is 45mm longer.
I like the stability especially when standing. As far as bumps and rough roads so far it seems about the same as my Cannondale.
Makes sense since I am using the same tires. I am seriously thinking about ordering a new Strada Speciale from Mercian.
While I like the longer wheelbase I would like something a bit shorter but longer than my Cannondale and maybe 853 tubing.
Also the top tube on this bike is too short for me so I had push my saddle way back.