The Beginning
My Build started in May 2014 when friends suggested that it would be a good idea to get into some VMX. Two of the boys elected to find some 78-79 Honda CR250R's while i decided to go back to my roots and find a 1983 YZ125K which i loved and raced back in the day. After an extensive search in Australia, i realized that they are as rare as hens teeth. It seems relatively easy to pick up an old G, H or J and there are some examples of L's and N's around but those models had a really bad rap and i was only interested in one year. The K propelled me into the A grade in Western Australia but i guess my only claim to fame is getting in Steven Gall's way (sorry Steve) at the King of the Cross as the Australian champ came around to lap me on his mighty YZ490. Regardless, i loved that bike and decided that i wanted to restore and ride one again.
I talked to Jason Weaver at East Coast Vintage MX in Carolina USA and he said he could help me get one to Australia if one came up. I searched all of Ebay and Craigslist and found one in New Jersey that looked OK and was cheap. I like the yellow scheme of the US model, previously owning the white Euro version. Jason called the guy in NJ and organized the purchase and transport of the bike down to Carolina. Below is the bike on Craigslist.
I talked to Jason Weaver at East Coast Vintage MX in Carolina USA and he said he could help me get one to Australia if one came up. I searched all of Ebay and Craigslist and found one in New Jersey that looked OK and was cheap. I like the yellow scheme of the US model, previously owning the white Euro version. Jason called the guy in NJ and organized the purchase and transport of the bike down to Carolina. Below is the bike on Craigslist.
When East Coast Vintage MX received the bike, they scrubbed it up, started it , run a compression check and gave me a rundown on the bike. We decided that they would put some decals on, a new seat cover, some grips and other stuff and then crate it up for a boat trip to Australia. Below are some pics of the bike ready for crating but still in need of a full restore.
While waiting for the bike to arrive from America, i started putting together a plan for the rebuild. A bike is a series of systems so i decided to tackle the project as a series of interconnecting systems that need to work in synergy. Ive broken down the K into 7 separate systems which are:
1. Engine and Transmission
2. Fuel and Air
3. Suspension
4. Body
5. Electrical
6. Drive, controls and brakes
7. Cooling
As of 2014, the K is 31 years old so all of these systems will be worn, fatigued, burnt out, loose and just generally in need of attention. Also, there is no use in ignoring or doing a half arsed attempt at restoring any one of the systems as a failure in one will ruin the day. They all need detailed attention.
So lets tackle the systems one by one.
1. Engine and transmission - Well, i haven't got the bike yet but i could at least tackle the obvious. I used the parts number list that is on this website and built up a parts list of all the seals in the engine. I researched a heap of websites that deal in Yamaha parts and decided upon partzilla.com for their ease of use, discounts, and transparent international shipping. Note: I did want to use an Australian company but could not find anything that had the diagrams, part numbers and ease of use like Partzilla. I ordered all the seals i could find along with a new con rod and bearings, clutch springs and plates, full gasket set and anything else i could find for this bike on their website. I went to the allballsracing.com website and ordered the main bearings and seals along with a heap of other bearings.
The transmission has a bunch of bearings in it and obviously gears etc.. A test ride of the bike will have to be done and hopefully there will be no problems. I will identify and replace all the transmission bearings while the engine is apart. Also, this will be a good time to examine the gearbox more closely for worn items.
The exhaust looks a little dinged and has repair welds on it. Its the original so will be the worse for wear. I thought about a DG pipe but the reviews were not that great so i sniffed around and ending up contacting Jon Easton at Jemco. He builds cone pipes and they have the reputation and look that i was after. I put an order in with Jon an at the moment, turn around times are 8 weeks so that will be fine as the bike won't be here for a long time. Go to www.jemcoexhaust.com to check them out.
1. Engine and Transmission
2. Fuel and Air
3. Suspension
4. Body
5. Electrical
6. Drive, controls and brakes
7. Cooling
As of 2014, the K is 31 years old so all of these systems will be worn, fatigued, burnt out, loose and just generally in need of attention. Also, there is no use in ignoring or doing a half arsed attempt at restoring any one of the systems as a failure in one will ruin the day. They all need detailed attention.
So lets tackle the systems one by one.
1. Engine and transmission - Well, i haven't got the bike yet but i could at least tackle the obvious. I used the parts number list that is on this website and built up a parts list of all the seals in the engine. I researched a heap of websites that deal in Yamaha parts and decided upon partzilla.com for their ease of use, discounts, and transparent international shipping. Note: I did want to use an Australian company but could not find anything that had the diagrams, part numbers and ease of use like Partzilla. I ordered all the seals i could find along with a new con rod and bearings, clutch springs and plates, full gasket set and anything else i could find for this bike on their website. I went to the allballsracing.com website and ordered the main bearings and seals along with a heap of other bearings.
The transmission has a bunch of bearings in it and obviously gears etc.. A test ride of the bike will have to be done and hopefully there will be no problems. I will identify and replace all the transmission bearings while the engine is apart. Also, this will be a good time to examine the gearbox more closely for worn items.
The exhaust looks a little dinged and has repair welds on it. Its the original so will be the worse for wear. I thought about a DG pipe but the reviews were not that great so i sniffed around and ending up contacting Jon Easton at Jemco. He builds cone pipes and they have the reputation and look that i was after. I put an order in with Jon an at the moment, turn around times are 8 weeks so that will be fine as the bike won't be here for a long time. Go to www.jemcoexhaust.com to check them out.
2. Fuel and Air - The bike probably has an ok filter but ive ordered a new Uni Filter anyway. The carb is bound to be worn at this stage and i have the option of a new 34mm Mikuni like the original or the Tech Report suggests an upgraded 36mm from an IT 250J. It even gives all the jetting specs. Well, Mikuni still makes the VM carbs and they are very cheap to buy new. I will be upgrading to a new 36mm VM with the recommended jetting specs. I have ordered new reeds so hopefully that should take care of that.
3. Suspension - After various reviews on the web about suspension upgrades for the K, i have decided to go with Race Tech. I talked to Matt Wiley at Race Tech and he pulled the settings from another happy YZ125K customer. He recommended emulators and heavier springs up front and a heavier spring in the rear withe gold valves etc.. He gave my details to Terry Hayes at Shock Treatment in Australia and Terry has suggested i send the stuff to him when i am ready.
4. Body - Not just cosmetics but were talking bearing and seals for the swingarm, steering stem, linkages, shock mounts and wheels. The bike has newish Renthal bars and levers but i have ordered a new shifter. The pegs look worn out and ive read that KTM SX pegs fit right on. Ive also ordered things like fuel cap gaskets and a 250 piece Specbolt fastener kit for Yamaha vintage bikes. The frame will be checked for cracks and then blasted and painted.
5. Electrical - This is one area that can really let you down. I can only assume that the system is old, corroded and worn. It may be OK but could break down under load or heat or just die when you least expect it. I have done some research and come across the PVL Racing Digital Ignition System. Its not cheap but its custom made for the YZ125K and is a complete system upgrade.
6. Drive, controls and brakes - The K isn't going anywhere without decent gear to drive it. I ordered a set of JT sprockets but went from the standard 48/12 to 50/12. This is recommended in the Tech Report. I'll give it a try. I also went with a new Regina gold chain non o ring type. O'ring chains tend to rob the 125's of power so this should be a nice set up. The tyres on the bike are new and are intermediates which should be OK for general VMX. As mentioned , controls look good but i will check all the cables when the bike arrives. The brakes on the K are drum type and shoes are readily available and cheap. They have probably been changed out a few times so these will be checked when the bike is stripped down.
7. Cooling - After 31 years, the radiators are going to be a little on the worn side. You can't buy OEM, and original ones on EBay look terrible. I did some research and decided upon some GPI radiators. Yes, they are made in China but so are some BMW's. They are made specifically for the YZ125K and are polished aluminum that's all TIG welded. You can get them directly from http://www.gpimotocross.com/. They are also a great bargain. In 2014 they are only $140 delivered for both! That's a bargain and i have read some good reports about them. The rest of the cooling system has to be assessed when she arrives.
Late in 2014, the bike arrived from the USA. The photos were an illusion as the bike was a pile of junk. I don't think there was a part that was not bent, warped, twisted, rusted, broken, missing or wrong. This K was going to need some serious work so read on.....
For now that's about it. Further updates will be under the specific system headings.
Below is the bike arriving home.....
3. Suspension - After various reviews on the web about suspension upgrades for the K, i have decided to go with Race Tech. I talked to Matt Wiley at Race Tech and he pulled the settings from another happy YZ125K customer. He recommended emulators and heavier springs up front and a heavier spring in the rear withe gold valves etc.. He gave my details to Terry Hayes at Shock Treatment in Australia and Terry has suggested i send the stuff to him when i am ready.
4. Body - Not just cosmetics but were talking bearing and seals for the swingarm, steering stem, linkages, shock mounts and wheels. The bike has newish Renthal bars and levers but i have ordered a new shifter. The pegs look worn out and ive read that KTM SX pegs fit right on. Ive also ordered things like fuel cap gaskets and a 250 piece Specbolt fastener kit for Yamaha vintage bikes. The frame will be checked for cracks and then blasted and painted.
5. Electrical - This is one area that can really let you down. I can only assume that the system is old, corroded and worn. It may be OK but could break down under load or heat or just die when you least expect it. I have done some research and come across the PVL Racing Digital Ignition System. Its not cheap but its custom made for the YZ125K and is a complete system upgrade.
6. Drive, controls and brakes - The K isn't going anywhere without decent gear to drive it. I ordered a set of JT sprockets but went from the standard 48/12 to 50/12. This is recommended in the Tech Report. I'll give it a try. I also went with a new Regina gold chain non o ring type. O'ring chains tend to rob the 125's of power so this should be a nice set up. The tyres on the bike are new and are intermediates which should be OK for general VMX. As mentioned , controls look good but i will check all the cables when the bike arrives. The brakes on the K are drum type and shoes are readily available and cheap. They have probably been changed out a few times so these will be checked when the bike is stripped down.
7. Cooling - After 31 years, the radiators are going to be a little on the worn side. You can't buy OEM, and original ones on EBay look terrible. I did some research and decided upon some GPI radiators. Yes, they are made in China but so are some BMW's. They are made specifically for the YZ125K and are polished aluminum that's all TIG welded. You can get them directly from http://www.gpimotocross.com/. They are also a great bargain. In 2014 they are only $140 delivered for both! That's a bargain and i have read some good reports about them. The rest of the cooling system has to be assessed when she arrives.
Late in 2014, the bike arrived from the USA. The photos were an illusion as the bike was a pile of junk. I don't think there was a part that was not bent, warped, twisted, rusted, broken, missing or wrong. This K was going to need some serious work so read on.....
For now that's about it. Further updates will be under the specific system headings.
Below is the bike arriving home.....