Project YZ Inspection

1980 Yamaha YZ125G Restoration

Inspection

What do you have to work with?

It is helpful to do a complete visual inspection of your machine before beginning the restoration. This is the stage where we find out what you have and what you will need. While doing the inspection you should have a visual reference, a brochure, a magazine test, some old photos or the owners manual. Using a visual guide will show you if parts are missing, have been replaced with aftermarket parts or if they are parts from another year or model bike.

For the purposes of the inspection I have used a bike that is almost complete. The bike that I am building for myself is being built from the ground up from parts! This is probably the most difficult (and expensive) way possible to build a vintage bike.

The handlebars are tweaked, the throttle assembly is cracked, the levers, perches and cables are rusted and not original.

Here is a close-up of the throttle and front brake lever assembly.

The CDI black box and hardware are missing.

The original front fender is still on the bike, but it has extremely deep gouges and has a “K” shaped crack in the middle front that goes all the way through the plastic.

The fork seals have been leaking for a long time and will need to be replaced. The original fork boots and clamps are still on the bike, but the boots are stiff and brittle. They may not take the stress of removal.

The front rim appears to be round without any cracks or dents. The spokes are badly rusted.

Working our way back to the motor we find.... a mess! First, I admit to a bit of creative licence, I didn't get this bike with the cylinder, head or pipe on it. I put them on to take these before photos. I didn't get a piston, rings or other assorted top end parts with the bike either.

The exhaust pipe is rusted through in areas and has been repaired, including a big patch of JB weld, which I bet doubled the weight of the pipe! This must be replaced. The carburetor and reed block with the original reeds came in a box. Although the rubber intake manifold is dried out and cracked.

The big problem with this motor is that the right main case half is cracked around the stator assembly. It looks like it has been hit with a hammer. This needs to be replaced.

A closer look at the Stator and cracked case and you can see that wires have been cut and spliced, the flywheel has been badly marred and the rest of the assembly is badly rusted.

The left side of the motor is in much better shape. The outer clutch cover is intact and in really good shape. The shift lever is not an original Yamaha part. Strangely the bike has the original kickstand on it. The air box is missing the outer cover and the hardware that hold it on. Of course the air filter is missing!

All the fins on the cylinder and head are intact and straight. An important part of the cylinder on this bike is the tab that holds the clutch cable, in some cases this is broken off.

Notice the original but rusted silencer and the swing arm which is in very good shape. There is a huge amount of side to side play in the swing arm bearings which will need to be replaced.

This end of the mono shock is badly rusted and it looks as though the lower shock pin will be very difficult to remove. There are steel sleeves pressed into the aluminum swing arm at this point and the pin can rust solid to the sleeve and also to the inside collar of the shock.

I would spray these points with liquid wrench or WD40 in an attempt to remove this pin without damaging the shock, pin or swing arm. It would be in your best interest to spray all the rusted bolts, nuts and hardware on your bike. Saturate them, let them sit for a day or two, then reapply as often as you can. Use any resource available to ease the difficult job of disassembling a vintage motorcycle.

The chain is rusted and must be replaced along with both sprockets. The brake stay arm was removed and the brake rod got tangled up and twisted. The rear rim looks very straight and has no dents! The chain adjusters, brake lever and most of the hardware are badly rusted. The plastic chain guide, rub block and chain roller are also worn and must be replaced.

Look at how badly the chain guide block is worn and the frame guide for the brake rod is bent. Of course there is a lot more rust! Luckily it is mostly just surface rust.

The rear fender has deep scratches and the plastic is sun faded, yet there is a very good chance it can be restored. Unfortunately the rear fender and all the rest of the plastic are no longer available from Yamaha.

If you are attempting a perfect restoration, it may take a long time to find the original plastic for your restoration. The side panel number plates are especially rare and NOS ones (if you can find them) go for some very serious money. Don Ruffin (suzukidon@cox.net) has a set of reproduction side panels and original style front fenders available for the 1980 YZ125.

Yamaha does have an updated front fender available but it is not exactly the same style as the original. Maier (www.maier-mfg.com/) also makes replacement fenders, but again they are not exact reproductions.

Some restorers will wait until they locate all the plastic body pieces before they begin a restoration. This is a very good idea.

The frame tabs that hold the coil are bent and the coil is missing. There is a broken bolt in the coil tab and also in the tank mounting tab. These will have to be removed. The frame looks really good, no cracks anywhere, the frame is straight and the underside of the engine cradle tubes are not dented.

When the head was removed I found that there was damage caused by a broken piston and rings. If you look closely on left side of the photo you will see the Yamaha prefix (3R300) cast on the underside of the head.

When I removed the cylinder I found that a professional engine builder had done a really nice port job. That was the good news. The bad news was that the cylinder had been sleeved. This is where a new cast iron sleeve is pressed into the aluminum cylinder. Normally this is not a bad thing, but in this case someone had done a terrible job! The sleeve is off axis and the ports do not line up with the sleeve. This cylinder will need to be re-sleeved by a professional.

Here is a sample of the port work done to the cylinder. If you look close you will see that the sleeve is smaller than the ports. I could not get a good photo of just how bad the alignment was on the exhaust port side. I have not measured it, but I suspect that the ring would get snagged on the port if you attempted to use this cylinder. Maybe that’s why it’s not running.

The connecting rod has been replaced with an updated part. This number is 4V2 which is the Yamaha pre-fix for the 1981 YZ125H. There are a few parts from the 1981 YZ that are interchangeable with the 1980.

The crankcase was filled with water for a long time, there was rust on the lower rod bearing and on the crank halves. The bearing is crunchy, tight and the crank is hard to spin. There is no way this bike could be run in this condition without disastrous results.

A close up of the lower connecting rod end, it is in bad shape.