Narhay

I've got a Mercier 300 with a worn metric threaded Stronglight P3 headset. I measured the head tube and the steerer and came up with 35mm difference. The P3 doesnt have great adjustability as it has knurled edges and the flattened portion of my steerer tube has worn so doesnt hold the lock washer in place as well an.

I am looking at some Shimano 600 or Dura ace 7200 metric headsets which have stack heights listed at 38mm. If I remove the washer between the upper threaded cone and the lock nut it would give me about 36 or 37mm which leaves me 1 to 2mm short. I understand there would be less thread engagement but I'm wondering how much leeway there might be in this respect.

mprince

I'd look for a different headset with a lower stack height that gets you in a usable range. IMO leaving the washer out (it has a purpose, it is not a spacer) and not having sufficient thread engagement on the locknut is not a recipe for success. But, that's me - find the right component for the job, as taking shortcuts to get a different component to work is a compromise I'd rather not take. And, I am confident there are other options out there that would fit.

Edit - while my comments above have not changed, if you are determined to take the approach you outline, I would make sure to apply some loctite/thread locker to the locknut threads to help prevent it from loosening. You can remove the keyed washer, but it does have two practical purposes - to allow the locknut to tighten without imparting rotational force on the headset upper cup, and to help "lock" the locknut to the cup so that neither loses its adjustment.

Narhay

Thanks. I would also rather get a perfectly sized replacement headset but low stack metric headsets are not as easy to source these days. Having a bit of space in terms of stack height opens up more possibilities for sourcing a headset in good condition and one that doesnt cost a fortune.

Andrew R Stewart 

The lock washer can be left out, many have done this, with no issues. If the 1.5mm+ amount of stack change was enough then as long as you counter tighten the threaded race and lock nut all will be well. Few shops have the proper curved jaw headset pliers so slip lock pliers are usually used and can cosmetically mar the knurling. Proper threaded headset tightening requires two wrenches and not relying on a lock washer.

One data point missing is how many threads are engaged in the current lock nut. If the nut is AL you had better aim for closer to full engagement/ If steel a couple threads less can be gotten away with. Also one can always use the old lock nut with the new cups and races. Andy

Crankycrank

Contact Mercian as they may have some headset recommendations. I'm sure they have many buyers that keep their bikes a loooog time and run into this situation.

Narhay

Mercier's name has been bought out by the bikes direct people so the original company is no more.

mprince

Agree, I did some searching and there's not a lot our there in the new market. What you want to do will work, the good news as Andy stated very well is that you could use a different locknut if needed to get better thread engagement. I'd still hit it with some low-strength threadlocker for that last little peace of mind. I re-read my original post, I came across a bit harsh-sounding (in my opinion) on your post and didn't mean for that, so apologies.

Crankycrank

Oh dang it, I read that as MerciAN. Sorry about that.

JohnDThompson 

I wouldn't do it. You need a headset with a shorter stack height. You have limited headset replacement options. Velo-Orange offers a metric thread headset, but it has a 41mm stack height, so that's not an option. Typically, it is just the lower race that wears out on a headset, so you could buy a short stack headset like the Tange "Levin" and just use the lower race parts (crown race and lower pressed cup), while retaining the metric thread upper parts.

Narhay

https://www.bikeforums.net/classic-v...nce-tdf-2.html

You helped me with my last stronglight P3 headset on this Gitane where I used a tange levin lower. I tried replacing the lower cup and crown race with a so-so set I had on hand and it improved but not perfect. I may try again but the upper portion isnt great.

Moe Zhoost

Your P3 stack height is probably spec'd at 34mm since you subtract the 1mm lip on the locknut. Shimano 600 (HP-6400) has a stack height of 33.5 mm. These show up used (sometimes NOS) on ebay occasionally (as do P3s). I am not sure the HP-6400s were available in metric though. The 600EX (HP-6407) headsets were available in metric, but the stack height is ~40mm.

Have you considered replacing the fork? Doing so would give you a lot of options. I plan to replace the fork on my Raleigh Super Course when it's 50 year old headset bites the dust. Try to find a 26tpi threaded headset these days.

Andrew R Stewart 

There's always the dark side to go to. Shave down the head tube. Done this a few times when all else failed. A few years ago I replaced the front portion of a frame I had helped build decades ago to regain full lug bands after it had been cut down for a too short fork. Andy