What makes a 1979 RD400 Daytona Special

[IR8D8R]

 Get the adjustable preload caps from Economy Cycle. It makes setting the preload 10x easier. While you have it apart you should consider the Gold Valve conversion and new springs. There are cheaper knockoffs online (Mikes XS) but I used the originals. https://www.mikesxs.net/yamaha-xs650-damper-valve-pr-front-forks-77-84-oem-1t3-23170-00-00.html
 The Race-tech kits come with some pieces of 1/2" PVC pipe to use as preload spacers. You can use that instead of the stock spacers. If I recall correctly the stock spacers are around 3-1/2" long? They are just rolled sheet metal like a big single-slot roll pin. The length is spring dependent so you really need to set the preload instead of just using the stock spacer. Stock springs are probably going to be shorter than they were in 1979.
 The Race-tech spring kits come with a handful of fender washers to use for shims on top of the PVC if you need to add more preload. Basically you measure the fork cap threads and subtract that from the amount the spring and cap stick up above the top of the fork. If you have at least 5mm of preload to start you can set it with the adjustable cap.

The "too much preload" photo shows how to measure preload. It's a bad example because it's way too much preload.
I copied the text from the RaceTech instructions:

11 - Setting the fork spring preload is done by making the correct length preload spacers.
Find the recommended preload in Product Search or on your DVS Setup Sheet. [I don't have that info but  correct preload is somewhere between 15 and 35 mm or 15% of sag (% of the suspension depression from the bike's weight)]
 
1. If your forks have Preload Adjusters set them to minimum.
2. If you have a fork with an Emulator. Drop the Emulator down the tube. Install the Emulator Adapter first if required. It sits on top of the damping rod with the Emulator Valve Spring facing up and is held in place with the main fork spring. Visually check to make sure the Emulator is sitting squarely on top of the damping rod or the Adapter.
3. Extend the fork tube all the way.
4. Insert the fork springs into the fork tube on top of the Emulator (No emulator, no problem).
5. Install a steel fork spring washer
6. Install the fork spring spacer tube (1/2" PVC or any size that will fit inside the fork tube). Any length that goes above the top of the fork tube is ok for now.
7. Install another steel fork spring washer (washer-spacer-washer)
10. Adjust the spring spacer tube length (or PVC) to achieve the proper preload.
In this example using the image:
If you are looking for 15mm preload you would shorten the spacer by 46 - 15 = 31mm length of spacer (I guess the 15 mm is the desired preload? Doesn't matter as much if you have adjustable preload. You can start with 5mm and increase by 10 easily).
NOTE: You must have steel washers on both ends of the spacer. The spacer must not rest directly on the spring or the cap.
12 - If there is very little preload the thread on the cap will hit the thread in the fork tube before touching the washer.
Measure from the top of the fork tube to the Steel Spring Washer.
13 -  Measure the Fork Cap Height In this case 18mm.
Calculate the Preload
(Fork Cap Height) - (Top to Washer) = Preload
18 - 11 = 7mm Preload (the 18 is the distance the threads will close when you screw the cap down).
Adjust the Spacer Length or add washers to get the recommended Preload.

The adjustable caps have a self-centering spring washer included. Any washers used as shims go under it.

Hope this helps
IR8D8R

[Andrew S]

Thanks, that does help.  I'll start with a 3.5" spacer and work from there.  If I can outride the stock forks, then I'll pursue some of the emulators.  I've often thought about trying emulators on other bikes, but have been happy in the past with some tuning of fork oil and preload.

[Andrew S]

I realized today that the passenger peg brackets have been cut off, as well as the loop on the left side.  Any chance I can talk somebody into tracing their brackets and loop so I can re-create them here?  Or even better a bent Daytona frame and I can buy the sections I need.  (yeah, right.)

[Andrew S]

Thanks to the generosity of others in the RD world, I was able to buy a donor frame section with the muffler/passenger peg loops.  Unfortunately, the donor also was missing the mounting tabs.  A local Daytona owner let me disassemble part of his bike to trace out the missing tabs and take measurements, (thanks Troy!) and I had sheet metal laser cut at SendCutSend.
3D printed some tooling to make the complex bends, and some locating fixtures to align all the pieces, and welded it all together.







Almost like when it left Japan!  I can share the laser cutting files and 3D tooling if anybody needs to repair their own frame.



Which brings us to today:  I'm hoping a few more weeks and we'll be on the road tuning.

[grcamna3]

I appreciate seeing you posting the history of your Dad and you and the Daytona Special:excellent ! 

[RDryan]

Wow that is quite an update, I do recall your earlier postings finding this family heirloom. Nice job restoring the bike frame. I just can't imagine most people particularly myself gong to the trouble to do what you have accomplished. 

[m in sc]

wow. impressive, extremely impressed.  thats a labor of love for sure

[Andrew S]

Thank you for the compliments.  Dad looked at progress right after welding, and said, "Maybe you should have just gotten another frame?"  I can't argue, that would have been much easier.  It's been a challenging but fun project returning everything to 1979.

[Andrew S]

Nothing special, but first start after 20 years of sitting!  And 45 years since I first heard stock exhaust!

Still have to bleed the brakes and oil pump lines, modify the chain guard to fit with the YSS shocks, sync the slides, and lots of other little things.  Hopefully on the road tuning this weekend.

[RDnuTZ]

nice work there  a real labor of love. I see you swapped out the swingarm and pipes for OEM, but kept the gold heads. Are you going to leave the heads or swap them with stock too? Tuning will probably change if go back to the stock head.

[Andrew S]

Thank you!  All the DG stuff is going to the previous owner for his 77 RD.

I have heard the DG heads are terrible, and that the Daytona head was also terrible.   

How drastic of a tuning change have you seen between the two?  A couple jet sizes?

[SoCal250]

That DG swingarm is a nice one and it's one of the more rare versions with the brake stay tab on top and on the bottom of the arm. Designed to work with all years of the RD400.

The 2V0 head is not a bad head performance-wise, but it's designed to work with a 0.055" head gasket. A standard RD400 gasket is 0.020. Any vintage head will perform better by taking advantage of today's technology advancements with machining to correct squish and optimize for today's fuel. (This is especially true with the DG heads.)
One disadvantage of the 2V0 (and the 3J7, 2R9, 3M4) head is that you have to remove the entire head to work on either side of the engine. For this reason they're sometimes cut in half between the chambers because it makes maintenance and machining easier.

[Andrew S]

Thank you for the details about head gaskets.  I'll measure the one piece head gasket I have here and see how it compares.

I am interested in having the 2V0 head machined to modern specs, but I haven't found anyone with a lathe big enough to swing it in once piece. 

[RDnuTZ]

Thank you for the details about head gaskets.  I'll measure the one piece head gasket I have here and see how it compares.

I am interested in having the 2V0 head machined to modern specs, but I haven't found anyone with a lathe big enough to swing it in once piece. 

from SoCal250 reply to you above: "One disadvantage of the 2V0 (and the 3J7, 2R9, 3M4) head is that you have to remove the entire head to work on either side of the engine.

For this reason they're sometimes cut in half between the chambers because it makes maintenance and machining easier."

[SoCal250]

Thank you for the details about head gaskets.  I'll measure the one piece head gasket I have here and see how it compares.

If you have a US Daytona 1-piece (2V0-11181-00) it should be 0.055"
A Canadian 1-piece for a '79 or '80 model (3J7-11181-01) is 0.020" (Same part used on the 3M4 in Australia)
And for reference, the standard 1A1 RD400 2-piece gaskets (1A1-11181-00) are 0.020"

And a correction to my previous post: The 2R9 is a 2-piece head.