Doing the 750 Seca's Forks.. (Rebuild.. now a HOW TO!)

Do we have a parts break down jpg showing location s of parts for assembly??? For I laid them out but things happen!! Hate second-guessing

 

Tim, have you opened up your package? There should be an instructions sheet with parts diagram with the rebuild kit...….

 

Yes thank you sure instructions are great if you can read !and know what part is what lol diograms picture s always help the situationlike when you're in the middle of it and you got to walk away and come back and look at it again and say oh my God what did I do you know what I mean short-term memory getting bad the older I get

 

I linked both the parts fiche (diagram) and the photo thread of the parts layout earlier.

 

That deems to be a very simple overhaul once you dive in , Thanks to all of you 1 note spring goes in loaded side down into the forks I think .?hope I'm right got time before I add oil and seal it all up going to use fork tree to hold it all together whilst I compleat other tasks.

 

Thanks so much for all this info everyone, I'll be tackling both forks and the anti-dive on my 81 750 Seca soon...cheers!

 

So I'm going through this job right now, and I'm having trouble removing the damper rod bolt. My bike is a 1981 SECA 750RH, and my damper rods do NOT have the fluted 3/4in ends that other describe. I am in the same situation as OP, except my bolts did not crack loose. I am also unable to see any point in the lower anti valve hole where an Alan key can fit through both the aluminum valve AS WELL as the actual rod itself.

Any advice? A heat gun will only take me so far. One fork tube I was able to take the bolt right out. The other one is spinning pretty freely

 

You can see here....no fluting...and the hole in the damper rod is way too far away for you to put something through both the valve and the rod. The question becomes...if there is no way to hold the rod how does one tighten to spec?

 

Well...I got it out with the rattle gun. I guess ill have to just get it PFT when I put the tubes back together. Even with the spring and cap back on it wasn't nearly enough to hold the rod still - even when compressed!

 

To follow up on this (Sorry for spamming this thread). I just did a second set of identical forks and it took me all of 15 minutes to break both damper bolts loose. This is the sequence of steps I used to avoid the situation I had last time:

1. Leave the fork fully assembled before attempting to remove the bolt.
2. Turn each fork upside down (so the bolt is pointing towards the sky, and spray the bolt with PB blaster. Let it soak in for a few hours.
3. Give each bolt a few good taps with a hammer to shock the threads.
4. Use a heat gun and heat the bolt for 2-3 minutes.
5. Brace the fork against something and try to break er' loose.

When I did it this way they both broke loose the first try around with very little difficulty. I still have to solve the problem with tightening them up to spec when finished, but I hope this helps someone else.

 

I'm about to do mine on a 81 Seca as well lol so spam away, the more info the better. I've had this bike sitting for almost 4 years now and it's gonna run this year dammit. I got super tied up in life but this bike on the road is all I want right now.

 

I nearly moved your comments to a separate thread, but realized that there is a previoulsy unknown difference between the '81 and the later fork internals.
That's worthy of keeping it in this writeup.

As a general rule the writeups are not the place to go into depth asking questions about a individual motorcyle. Keeping all the work you do to your specific machine in a single thread in Technical Chat is preferred.

 

I just completed my fork rebuild. All I have to do is add oil.

I discovered a trick to get the damper rods tightened to spec. Using a wooden dowel is a fools gambit - it does not put nearly enough pressure on the rod to hold it to allow 14 ft/lbs of torque.

In order to get the damper rod bolt tightened to spec I used a 5/8's spark plug socket and put a 5/8's head Temperature sender adapter screw into the end of it (the one where the thread diameter most closely matched the inside diameter of the top of the damper rod. I then electrical taped the temp sender screw to the socket well enough that I knew they would not separate. I also taped the threads so that they would bite into the inner diameter of the damper rod without actually scratching the metal.

With a bunch of extenders, I lowered the socket into the top of the inner fork tube and held the damper rod bolt from the other end with the torque wrench. I then tightened the socket "tool" until I felt the threads engage the damper rod bolt. At that point, it's just a matter of having an assistant hold the tool in place with a ratchet while you tighten to spec. After you tighten, simple loosen the ratchet attached to the tool and it will pop right out!

Hope this helps! Thanks Chorca for this guide!!

I've attached some pics of the tool I made.

 

Hi all,
After a massive oil seal leak I stripped down the left fork using this incredibly useful thread, only to find that I was missing a washer and a half. The flat and spring washers on the end of the damper rod. I found the half spring washer stuck down the end of the fork leg. (see pic)
I was wondering would these be available. I tried my usual go to parts supplier (cmsnl) but they dont have them in stock.
Also the seal itself was only about half the height of the replacement seal that I got from cmsnl. (genuine yamaha part).
I am now confused. Do I risk damaging the new seal to see if it will fit? Or is the lower height seal the correct one?

 

contact info@xj4ever.com

I do not think your supplier sold you the correct seal, but sold you a seal that Yamaha chose to substitute because of the diameter.

 

Ok, Thanks,
Here's a pic of the seals. original one is on the left. There is a couple of mil difference, I dont think the new one will fit.

 

The one on the right looks like its for something completely different. Yeah, probably not gonna work.

 

I have a spare set of Yamaha fork seals (1KH-23145-00) and they measure 10.7 mm for height.

There is a spacer in there that I always kind of wondered why it was there, perhaps Len can verify that dimension or any changes.

@chacal

 

Yeah the larger one is 10.7mm, the original is 7mm.
I've ordered a new one from Len, just hope it'll fit.

 

You are correct, the current Yamaha (and repro versions of same) are all about 11.0 mm thick. Original seals (no longer available) were probably the 7mm (or so) thickness, although we don't have one around to verify. Sometimes oil seals will have sizing numbers "cast" into the rubber, such as 36-48-7 (ID/OD/thickness). Zeb, you should check that original seal that you have to see what numbers are on it (if any).

Just guessing here, but the XJ750 Seca forks are specified to use 2 different spacer washers with their fork seals; one under it (which is about 3mm thick) and one on top (which is a little bit over 1mm thick). I suppose this was done to "shim up" the 7mm seal to the "proper" 11mm height:

This washer is about 1mm thick:
HCP12948 Aftermarket lower fork tube OIL SEAL SPACER WASHER, fits either left or right tube on the following models: all 1981-83 XJ750 Seca, XJ750 Euro, and 1980-81 XS1100 Special and Midnight Special models. One washer does one tube. This washer goes above the oil seal. Each:
$ 6.95


This washer is about 3mm thick:
HCP3092 OEM lower fork tube OIL SEAL SPACER WASHER, fits either left or right tube on the following models: all 1981-83 XJ750 Seca and XJ750 Euro models. One washer does one tube. This washer goes below the oil seal, and above the metal slider bushing! NOTE: original spacer washers were "cupped" at the outer edges; these replacements are flat, but fit and perform as original. Each:
$ 13.95



The replacement oil seals are indeed 11mm tall, and also feature dual springs (one below and one on the top face of the seal), which supposedly makes them more "leak proof" (this is questionable, IMO, but it's what the marketing hype says.......).

So theoretically, you could dispense of both the lower and the upper oil seal spacer washers (this saves 4mm in height), and just substitute the new/improved 11mm tall seal, and you'd be happy. @Rooster53 or @StarGeneral, is this what you did when rebuilding your 750 Seca forks, or ?????


We do have some 36 x 48 x 8mm tall seals (HCP1814, for XJ550 Maxim, XJ650 Maxim, and a host of others), so theoretically you could use this 8mm tall seal, continued to use the lower (3mm thick) washer, ditch the upper (1mm) washer, and this set-up would also get you to 11mm in height.

Of course, all of this assumes that the original seals WERE only 7mm in height.........

 

There are two spacers. the lower one is kinda curved inward. I was unsure whether I could leave these out, but you have eased my mind. Thank you.

 

I think that was a way of making a 1mm thick piece of metal displace 3mm of vertical space, by "cupping" the outer edges so it "stands up" an extra 2mm in height..........

 

I can't recall exactly what I did as it was 8 years or so ago that I did the fork seals. I may have had the original seal at the time, although one thing I do remember is it seemed like it was taking a bit more force to get that seal to clear for the snap ring. It's a bit odd that it hasn't come up before at least to my memory.

 

That's the understatement of the year (the decade? millenium?). No one has ever asked me about it either, and we've sold lots of them.........we all owe a round of thanks for asking the question and bringing this issue to everyone's attention!

 

@chacal Nope, I assumed the new seal was designed to use the original washers. I smashed the hell out it until the snap ring fit in there

 

Yikes! Send me a note, we'll see what we can do to solve this problem!

 

Alright, I went the "keep the brake lines sealed" route for this operation and it dawned on me that I don't know how to fill the forks while they're installed (or half installed) because there's not enough brake line to allow the fork back into the triple tree with the antidive attached. Does anyone have any advice? I'd rather not bleed the brakes, but if that's the way it is, that's the way it is.

 

You can fill the forks while the fork caps are off and installed into the triple tree. Just don't tighten the upper pinch bolts until after the fork caps have been reinstalled.

So, with the handlebars removed:
1: collapse the fork legs as needed for slack in the brake line.
2. Install the fork legs into the triple tree.
3. snug the lower triple tree clamps just enough to hold the upper fork legs.
4. Install the fender and wheel (leaving the axle nut and pinch bolt loose).
5. Fill the fork legs with oil.
6. Install the springs and fork caps.
7. Give the front end a few good bounces to settle everything into place.
8. Check for gaps at the axle spacers.
9. Tighten the axle nut, followed by the axle pinch bolt and triple tree clamps.

 

Got it. Each system (fork oil and brake fluid) has a sealed piston as shown in this video: , so you can break the antidive units at the 4mm allen bolts without compromising the systems. Thanks for getting back to me, k-moe!

 

Hi guys,

Is the damper rod supposed to stick out from the bottom of the chrome tube? My rod doesn’t. That means that I can’t reach the threads with the bottom (locking) bolt.
Anyone know what the problem could be?

 

It should stick out a good bit. Did you get all of the washers out of the bottom? Mine were covered in old, sticky oil and were a pain to get out. There's a picture in the OP that shows they stick out a lot.

 

I probably didn’t get everything out then‍.
Do you know (prefer pics) what should follow the rod out?
Tips of how to get it out?

750 seca -83

 

Look through the second post for pics. There should be two thin washers (one with a bend in it), a chamfered ring, a spring, and a valve body with a plastic ring. I put a carpet on my concrete garage floor and gave it a few taps. I blew the whole thing clean with brake cleaner, so that might loosen stuff up, too.