yz465a

1981 YAMAHA YZ465H

OLD S'CooL Restorations stage-2 project of one of the all time classic's

We wanted this machine to have all its running gear, chassis and cosmetics taken care of for a reliable and good looking bike and be able to be ridden without worry. OLD S'CooL's stage-2 treatment was selected as the best choice for a "Show and GO" bike. As you can see above, it needed a lot of attention! Enjoy the pics and technical info...

CHASSIS:

PLASTICS and BODY parts:

MOTOR:

FINISHED:

This frame and chassis was in pretty good shape because the previous owner had already painted the frame after being stripped and rust removed. After looking it over closely and passing our inspection for any bent or dented frame tubes and cracks, we decided to clean it up, remove the rusted steer bearing races and set aside. All the hardware items were replaced with new grade 5 and 8 fasteners throughout the build. Key originals were inspected and used.

I was told by the seller of this bike that the crank spun freely, that the engine was torn down because they seized the motor. The reason it seized i found out was they forgot to add oil to the fuel and after installing a new piston the thing ran 15 minutes and froze up! Turns out upon inspection the piston was incorrectly fitted being too large for the bore with minimal clearance. Lots of errors here! When we got the motor on the bench checking everything, the crank was in great shape with no signs of abnormal wear in the connecting rod. So we just had the crank seals replaced and the ignition coil fields tested for proper ohmege. Transmission shifted well on the bench, so it was decided to leave the lower engine alone. Just a good flushing of the trans with mineral spirits, an inspection of the clutch plates and springs took place finding no issues. This was a very clean and unabused motor.

Restoring old dried out and scratched plastic parts is at best a very tiring process. We at OLD S'CooL only restore them the old fashioned way. Wipe on and Wipe off, by hand! We dont use any chemicals or so called magic surfacing solutions that put a layer of material that will eventually peel off or bubble up as time goes by. Without letting out too many trade secrets, i will say we use a scraping, sanding and hand polishing process to get these pieces to original condition that will last a long time with periodic plastic cleaner and polish such as GEL GLOSS. You will never obtain a factory showroom gloss but it will come pretty close and be worthy of contest grade bikes.

After 4 months of research, obtaining parts, performing many hand quality services, she's finally done. We hope you like the results. Please feel free to contact us with any questions on the build and how he might help you along with your own project. Remember, Its a passion, not a burden! The time and effort we spend on these and other fine MX machines has a great payoff of pride and craftsmanship that can only be experienced through the process.

The steer bearings and races were in bad shape needing replacement. We went with NOS Yamaha part numbered pieces ordered through the local Yamaha shop. Stock Yamaha brake pads front and rear were chosen. Hubs were sanded with 400grit wetsand to retain as much of the original baked finish for good adhesion of the new polyurethane semi-gloss black paint. Brake actuator levers and spindles were hand cleaned and lubricated with waterproof Mobil red synthetic grease. This i have found to be the best lubricant for offroad vehicles.

Swingarm was glass bead-blasted, primered with metal etching primer then topcoated with 3 coats of Plasti-Kote silver then finished off with a clear coat (see pic below). All chain wear plastics were replaced with NOS Yamaha nylon pieces as well as the needle bearings. Note the Mobil red grease, its great stuff!

Before

After

Forks were completely disassembled, flushed out with Mineral Spirits for its low toxicity and good cleaning qualities. Seals were replaced with NOS Yamaha parts from the same local shop. New progressive wound springs replaced the old soft springs. As you can see the fork sliders were badly cancerous and needed to be restored. The original clearcoat was removed with aerosol paint remover. Then the sanding process began with 320grit wetsand and here's the secret. I used 2-stroke fuel mix for the wet solution. I have found this to be the best cutting solution for aluminum finishing. All done by hand and the final radial grain you see is hand sanded with 600grit! Sliders were then cleaned and clearcoated with Plasti-Kote.

Hubs, spokes and rims were actually in very nice shape. Apparently the bike had never seen the track and was only rode on the weekends. Sat in storage since 1995 in the condition as you see at the beginning of this page. Rims were very straight with no missing or broken spokes. Most of the spoke finish was still entact, so we decided for a rider we would clean everything up, inspect the spokes closely and replace the wheel bearings. Rear chain wheel was in excellent original shape so we kept that piece on the bike. We replaced the countershaft sprocket with a 14T unit for motocross use. Sprockets were fitted with a fresh new D.I.D gold ERT2 chain. New chain rollers were installed.

Rear shock was in pretty good shape, not perfect but it still had some damping adjustment left. It received a good clean up job and since there were no external oil leaks, we just had the bladder re-charged with nitrogen to 220psi. Fortunately when we recharged it there was still 155psi charge on it which means its still holding well after all those years! We went with a IRC rear tire, im not sure why, i think we wanted to keep it original as possible, but then we decided on a Dunlop 756 for the front tire. I think because I wanted the better tire up front for cornering and the rear we didnt care too much as it was going to get chewed up right away anyway. The original fork boots were in excellent condition only needing a cleaning as well as re-painting the boot clamps a gun metal gray.

ONEAL handlebars and NOS hand levers were chosen for the build with using the stock perches and throttle twister. NOS Yamaha cables were purchased through the Yamaha dealer for a modest $20 each. These cables are a very high quality product that really sets these bikes off in the finishing department.

If you look closely at the seized piston, you can tell its a cold seize with virtually no previous wear on the skirt. This is a brand new piston that never had a chance! When setting up new rings, 0.012-18" ring end gap is the max you want to allow. All that was needed on this bore was a re-hone and NOS Yamaha piston and rings fitted. Skirt clearance should be measured at the bottom of stroke looking for 0.00275 - .00295" for a new set-up.

A word about those failed kickstarter shafts. This has been the number 1 question i get asked since this website was first published. Its a common failure that was designed to break! Look at the above photo of a failed shaft assembly. Do you see the crack? Early YZ465's had this inferior 2 piece unit that when whacked enough would finally give out and show the symptom of the kicker not returning or the motor not spinning. What happens when the pressed on cog cracks, the inner shaft just freely spins not moving the gear to start the motor through the primary. This should be the very first thing you check when you get your 465 at home. The 1982-84 kick shaft assembly is the one you want as its a billet construction that will never fail. To answer this problem in a little more detail, the kickstarter gear ratio was designed to help the rider to more easily turn over the big bore thus not allowing the motor to spin fast enough to suck in the air fuel mixture this big boy requires. So one is often seen kicking and kicking and kicking some more until the shaft cog cracks. Thats it in a nutshell. Get that shaft changed out ASAP or you'll be stranded without a hill in sight!

Reed cage was fine but the reed pedals were badly bent not allowing a good seal when relaxed. Reed pedals must have a good neutral seal in order to keep the air-fuel mixture in the porting system and to prevent backfire. We installed Boyesen fiberglass pedals which requires the carburetor be leaned out on the mainjet by one full size. Glass pedals make for a crisper throttle response at low RPM which is where this motor likes to live. I decided to do a "works" looking cylinder by cleaning up the fin edges. This was done by pre-filing the edges clean, then once the cylinder is painted, take a small cloth dampened with laquer thinner and remove the fresh paint from the fin edges and let dry. Engine cases were thoroughly cleaned with laquer thinner and repainted with 500 degree gloss black engine paint. Expansion chamber was repainted after the dents were removed by my friend Steve at Welding Works with 1200 degree black header paint. All these paints i've mentioned are easily found at Peb Boys.

When this bike was built we didnt have access to good quality pre-printed plate and swingarm decals. So we drew them up and printed our own. I've provided them here for you to print if you wish. There is a full selection of Yamaha graphics at YZ Decals.com or Speed and Sport Yamaha on the east coast now. All the numberplate rounds were cut from raw material stock of which we chose gloss black. The seat needed a new seat cover which really improved the functionality and appearance of the bike. Foam was still fine and not crumbling away, so we stuck with the original piece. Some good 3M Super 77 contact cement and a industrial grade staple gun takes care of this task.

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