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S2K Trans Rebuild

Synchrotech gets us back in gear

Dec 18, 2013

Technical Guidance and Captions by James Ornelas

In the previous installment of Project AP1, Golden Eagle was taking care of the F20C bottom end, prepping it for InlinePRO's F24 stroker kit. The chassis, after having spent a few days at the facility, was shipped to ASC Speed-Metal for some fab work before it eventually receives a fresh coat of paint under the hood in the near future. That left the transmission to collect dust and I figured it would be a great time to freshen it up.

I contacted James Ornelas of Synchrotech who suggested I bring the transmission to their facility to disassemble, inspect and clean up the inner workings. If you're not familiar with the name, Synchrotech has been in business since 2008. CEO and president, David Henson was previously employed by a company that had decided to discontinue their performance division. Seizing the opportunity to set out on his own, Henson purchased what was left of the companies inventory and opened the doors to Synchrotech Transmissions Inc. Henson and his team went on to research and develop carbon-lined synchros, a lengthy process that took well over a year to perfect. Well known for their ability to withstand high RPM and high horsepower abuse, the synchros became a hit with D-, B-, and H-series transmission users. Just a few years later that same technology was put into K-series transmission synchros, and more recently, Synchrotech introduced their own hardened steel sleeves, hubs, and carburized synchro springs to compliment their carbon synchro sets.

Beyond the performance realm, Synchrotech has a steady stream of your average, street-driven Honda transmissions to inspect and repair as well. And trust me when I say, this workshop runs like a well-oiled machine and is in constant motion. The years of experience and parts development assured me Synchrotech would have no problem making quick work of my S2K's tranny. Upon inspection, Ornelas states, "The transmission was in impeccable shape. We noticed minimal damage with the secondary drive gear and bearing assembly, as well as the reverse sleeve center hub. The gear had some contact pattern wear and the bearing was getting a little on the noisy side. The reverse hub had some base wear as well as the distance collar, so we replaced those. The rest of the transmission was in really good shape!"

I followed along to snap a few pics as technician Steve Vasquez reassembled the trans:

S2K trans rebuild AP1 transmission internals 01 Photo 1/21   |  
1. The AP1 transmission internals are prepped and laid out on the bench for final inspection before assembly will begin.
S2K trans rebuild synchrotech deburring process 02 Photo 2/21   |  
2. Synchrotech incorporates a deburring process in all of their builds. Using a custom selected ceramic-based media; parts are placed in vibratory machines creating a polishing/cleaning effect. This helps reduce friction and encourages intersecting parts to work in conjunction effortlessly.
S2K trans rebuild gear 03 Photo 3/21   |  
3. Every gear will have the synchro clearances checked prior to assembly.
S2K trans rebuild needle bearings and distance collar oiling 04 Photo 4/21   |   4. Needle bearings and distance collars are well oiled during assembly using Honda MTF. This is a crucial step to avoid a dry start up
S2K trans rebuild 1 2 gear sleeve assembly 05 Photo 5/21   |  
5. The 1-2 sleeve assembly is being placed over Second gear on the countershaft. Most of the sleeve sets available from Honda now come with carbon synchros. Keep that in mind when requesting them from your local synchro supplier ;)
S2K trans rebuild reverse gear sleeve assembly 06 Photo 6/21   |  
6. After First gear is placed over the 1-2 Sleeve assembly, next will come the reverse gear and reverse sleeve assembly. Topping that off will be the bearing, which will need to be pressed or driven onto the shaft.
S2K trans rebuild countershaft top nut install 07 Photo 7/21   |  
7. Next a new countershaft top nut is installed and torqued to spec. Be sure to stake the nut using a chisel or punch to lock it in place.
S2K trans rebuild mainshaft and countershaft assemblies 08 Photo 8/21   |  
8.The mainshaft (front) and countershaft assemblies are complete and ready to be installed along with the forks.
S2K trans rebuild clutch housing case 09 Photo 9/21   |  
9.Steve carefully drops the completed shaft and fork assemblies into the clutch housing case.
S2K trans rebuild countershaft lower bearing clip locking 10 Photo 10/21   |   S2K Trans Rebuild
S2K trans rebuild countershaft lower bearing clip locking 11 Photo 11/21   |  
10-11. Not all transmissions are created equal. Locking in the countershaft lower bearing clip can prove to be a difficult task at times and may require an extra hand. Here Ornelas gives the assist.
S2K trans rebuild countershaft clutch housing with fork set 12 Photo 12/21   |  
12. Here is the clutch housing with a partially assembled fork set.
S2K trans rebuild shift rod install 13 Photo 13/21   |  
13. Next the shift rod is installed into the interlock and shift arm assembly. Be sure to use a new spring pin.
S2K trans rebuild shift rod install 14 Photo 14/21   |  
14. Countershaft access bolt is then installed.
S2K trans rebuild clutch housing sealing surface 15 Photo 15/21   |  
15. Put a nice bead of Hondabond onto the clutch housing case sealing surface and allow it to tack up for a few minutes before installing the main case. These 8mm bolts will be torqued to 20 ft-lb.
S2K trans rebuild clutch secondary drive gear install 16 Photo 16/21   |  
16. Install the secondary drive gear and bearing using a driver, then torque to 127 ft-lb. You will need a mainshaft holder for the portion to keep the shafts from spinning when torqueing the nut. This nut will also need to be staked to keep from backing out.
S2K trans rebuild companion flange install 17 Photo 17/21   |  
17.After installing the end bearing and seal, next you will drive on the companion flange onto the secondary shaft. Once that is complete a new O-ring and nut will need to be installed and torqued to 119 ft-lb. This nut will also need to be staked in place to prevent it from backing out.
S2K trans rebuild bearing lubricant 18 Photo 18/21   |  
18.Be sure to apply a grease lubricant on the bearings to prevent a dry startup.
S2K trans rebuild main case honda bonding 19 Photo 19/21   |  
19. Apply a layer of Hondabond on the main case and allow it to tack up before installing the tail shaft assembly. These 8mm bolts will also be torqued to 20 lbf-ft. And that’s all she wrote. The transmission has been freshened up and is ready for duty.
S2K trans rebuild synchrotech brass synchros 20 Photo 20/21   |  
Synchrotech now offers its own line of brass synchros with an improved lock angle and updated tooth pattern. For those craving more performance, they offer their Pro Series line of Carbon Composite-lined synchros that feature an improved lock angle, tooth pattern, strengthened brass body and bonding process to handle more HP and aid in high RPM shifts.
S2K trans rebuild synchrotech hardened sleeves and center hubs 21 Photo 21/21   |  
Synchrotech also added its own line of hardened sleeves and center hubs for most Honda performance applications. The hardening process is done during manufacturing to help strengthen the sleeves and hubs to offer longer life and improved performance. This is a great alternative to OEM sleeves that are costly and require you to buy the complete sleeve set.


Synchrotech Transmissions
San Dimas, CA 91773
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