Posts
81
Joined
11/24/2016
Location
NL
NiekL
11/27/2017 11:13pm
11/27/2017 11:13pm
Edited Date/Time
8/22/2021 6:47am
Hi Guys, i thought it was time to share my project bike, a Honda CR125 from 1992 build in the 1991 colorways.
I'm a bike mechanic for a living for over 13 years , 29 years old from Holland.I always had the idea to build myself a nice vintage bike. Here in Holland we mainly have deeper sand compared to the tracks all over the rest off the world, so finding a good base bike is a little more difficult!
The main reason i chose a Honda is because i really like the quality of the CR twostrokes from the 90's. When working on modern bike engines, i see less and less material being used for making engine cases and bike frames. When wrenching on the 'older' Honda engines i always thought there is a reason why the 90's cr models are still riding around this much.
The main target i had was build a nice vintage racebike, it had to look like new, at the same time it still needed to stay a under 4k all in budget bike
Found this bike as a good base:
So i started stripping the bike
Had to cut out the swingarm axle after trying every trick i had.
The previous owner rode with a swingarm nut that was nog tightened, so the swingarm axle hole was beatened! I decided to search for a frame that was all healthy, found one from Dirk Timmer. After that i got the frame checked by a good welder and a guy who knows where these frames have there weak spots.
Thanks for the interest, updates coming shortly!
I'm a bike mechanic for a living for over 13 years , 29 years old from Holland.I always had the idea to build myself a nice vintage bike. Here in Holland we mainly have deeper sand compared to the tracks all over the rest off the world, so finding a good base bike is a little more difficult!
The main reason i chose a Honda is because i really like the quality of the CR twostrokes from the 90's. When working on modern bike engines, i see less and less material being used for making engine cases and bike frames. When wrenching on the 'older' Honda engines i always thought there is a reason why the 90's cr models are still riding around this much.
The main target i had was build a nice vintage racebike, it had to look like new, at the same time it still needed to stay a under 4k all in budget bike
Found this bike as a good base:
So i started stripping the bike
Had to cut out the swingarm axle after trying every trick i had.
The previous owner rode with a swingarm nut that was nog tightened, so the swingarm axle hole was beatened! I decided to search for a frame that was all healthy, found one from Dirk Timmer. After that i got the frame checked by a good welder and a guy who knows where these frames have there weak spots.
Thanks for the interest, updates coming shortly!
Frame blasted,welded, and updated at the footpeg assembly points so the new footpeg pins and footpegs fit like a new bike.
Back from the powdercoater.
Meanwhile i got some nice titanium parts for building up the frame: Pro circuit YZ125 footpegs, rear brake pedal bolt, footpeg pins, raptor shift and brake pedal tip andchain adjuster bolts
The Shop
Got all the bolts,nuts,axles and hardware plated and sorted out for the frame and engine. It took me some hours to sort it all out on size ( this was for more then one bike).
Found a CR125 1991 fuel tank wich was in a good enough state for me!
Some bikes i build:
Honda cr two stroke engine cases often tend to have a little damage near the front sprocket side. This one was all ok! I didn't want to save money on the engine, it just needed to be real good! When i picked this bike up i thought the engine sounded fresh. With tearing it down i wasn't unhappy at all by the overal condition of the parts.
I could see and feel the clutch was used, but all like normal wear. But you can tell it when a 25yrs old bike is mainted or not, this one was. The clutch felt good for keeping it spare for the races. But i decided to go for a complete new clutch. Nino Fenaroli got me into plating my new aluminum clutch package: the weight is a lot less compared to the steel versions wich will give a nice throttle response, and by plating them the wear should be minimal.
Engine all stripped. The gearbox had some wear on the dogs, usable for another 30-40 hours running time. Use or dont use: no, i will get that gearbox complete later on for spare. I found a gearbox that had roughly 15 hours riding time on, perfect!
I discussed with some college mechanics about the crankshaft, i know the older type crankshaft CAN break, i don't mean they always do but i had some examples seen before. The steel stuffing can give problems when replacing the connection rod isn't done the right way somewhere in the life of the crank. I decided to go with the CR125 2005-2007 crank with solid crank webs. This is a plug and play update. With these modifications i had a solid lower engine.
New clutch housing
The stock cases:
Yamah YZ125 cases:
Honda HRC CR125 cases:
The rear transfer port from the YZ125 and the HRC CR125 have a cut out in the lower part after the reed to get the rear transfer port feeded. This can be seen at the right side red marked circle.
The v-force reed i was going to use had a restricted part at the upper part of the reed because of the narrow inlet window:
With that in mind i went to work. Starting with the basic refining of the cases by removing rough edges and materials that came with the engine after the production proces of the cases. This wil improve gasflow for sure.
After that i did the 'hrc' mod.
I finished the cases off with some bead blasting, yes this doesnt look better, but the main reason is that want the oil/fuelmix to create a oil film on the surface of the cases to increase airflow.
Cases ready after painting them together with all the crankcase covers:
I really like that Raptor titanium gear shift tip, didn't know they made them. Does it fit right on?
What head and piston combo you are going to use? 90-91 domed, 92 flat or 93 and up flat top ?
I used a brake tip and a gear shift tip from a Beta. So KTM would be about the same i think?
It needs some work, you need to grind down the size of the gear shift lever head.
I have a dyno availible at my work.
I'm using the flat top cylinder 90-91 with a flat type piston and a milled/cut head. Got a new cylinder also from a later year 93-99 so i will try that also.
The ones people sometimes forget are the clutchcable lifter/lever bearing, the powervalve govener bearing and clutch housing needle bearing on the primary shaft. (Just a little reminder)
Some glass beaded engine parts. They look nice and clean again after 25 years of use.
The bearing inside the powervalve governer is a little more difficult to service, use heat carefully together with the right bearing tool (thanks for the tip Nino). I modified one govener with spacers at the end of the spring, this to add load on the spring. Creating a retarded exhaust valve opening rpm, just to test it. In combination with a Honda CR250 air boot and a 38mm carb instead of the stock 36mm this might mod might work.
The engine is getting more and more complete. Using oem Honda gaskets, i like the quality from these gaskets!
At the time i was working on the engine i saw a ad that i couldn't resist to go to and check it out. New oem Honda CR125 hpp pistons are NLA over this side of the ocean. The guy selling them had 13 pieces for sale together with a new 93-99 cylinder. This was a all or nothing deal so i went for it
So if annyone needs a oem Honda piston
With the lower engine being assembled i started piston height mesurement. Together with the info from the head volume i could do some calculating. The stock Honda head is quite small in total volume. I think this was the way to go in the 90's when leaded fuel and compression ratios could be higher?
6.3 cc head volume in a stock cylinder head.
1.37 cc deck volume with piston in tdc
0.80cchead gasket volume (thickness)
8.47 total combution chamer volume
I ended up calculating 15.47:1 static compression ratio (uncorrected ratio)
Pit Row
I found some 98-99 type powervalve guides and valves, these seal a lot better than pre 98/99 type. They also have a more stable construction.
I took some time to get to know how the hpp valve system operates and how to give it a good spring tension with left and right powervalve working exact at the same time. Got that ready, assembled the cylinder head and that got me a ready to fit engine
Happy with the result!
My experience in adding preload to governor is that 3mm is too much on stock cyl. Btw theres three different wire thicnesses on governors so they are not all the same.
Interesting to see dyno charts since you can test what difference every chance makes.
One thing you should test is what difference digital ignition makes compared to stock analog one.
Endless list to test, reeds, carb, exhaust, etc etc
Good build to follow
Here is a ‘91 I restored a few years ago:
Yes i knew that there are 3 different springs wire used. A friend of mine was also changing his bearings from the powervalve govener and noticed different wire thickness. The list of testing material is indeed endless!
First thing i did after the frame got back from the powdercoater was suspension service.
This was a really necassary thing
I don't want to have the suspension revalved before i even tried it stock wise. Got some ideas already, but first i wanted to stay close to the main setting Honda designed it. But i did found out something cool, a titanium shock spring from a Yamaha YZ fits perfect on the stock shock.
Rebuilded the wheels with OEM Honda spokes (a lot lighter than aftermarket spokes), rear wheel went to 19 inch rim size. Hub/bearing fitment was all good, had some luck with that. Searched a while for a hub paint that didn't got me a to shiney finish. I ended up choosing gold rims, just something i always likes. 87-91 colors with gold rims
Stock color
Wheel with new rim and rebuild hub.
Post a reply to: Honda CR125 1991(dyno video + charts) + CR125 1992 + YZ125 1996