74-78 CR125 520 conversion front sprocket? Lightweight project.

newmann
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newmann
Edited Date/Time 5/9/2015 3:39pm
11 or 12? What do you guys run?
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tydog
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tydog 4/14/2015 9:00am
4/14/2015 9:00am Edited Date/Time 4/14/2015 9:02am
Both, at the same time. It does require a really long and assed
up looking axle push bolt though.
You really should have known.
newmann
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newmann 4/14/2015 9:30am
4/14/2015 9:30am
tydog wrote:
Both, at the same time. It does require a really long and assed
up looking axle push bolt though.
You really should have known.
Uncle Rondo?Laughing
newmann
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newmann 4/14/2015 9:34am
4/14/2015 9:34am
tydog
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tydog 4/14/2015 9:34am
4/14/2015 9:34am
Yupp.

The Shop

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Lonestar_399 4/15/2015 6:19pm
4/15/2015 6:19pm Edited Date/Time 4/15/2015 8:49pm
The 78 CR125 you rode once (2012?) at 3 Palms that I have runs a 12/48 520 setup. It feels pretty good and no I have no idea who made the sprockets for this thing...no marking except "HO" . I guess that means it came from the North Pole.

newmann
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newmann 4/16/2015 7:07am
4/16/2015 7:07am
12/48 sounds right(4.00) but still quite a bit larger in diameter than the 13/52 which has always been my "go to" gearing with the 428 chains and sprockets. I have a NOS set of FMF (CT Alloy) boxed away somewhere and can't remember what they were, maybe 12/47??? Trying to figure out something for this lightweight project I keep coming back to. 11/44 in the 520 is still a little larger in diameter but I don't think a 10 tooth up front is possible or even available. Sure would be a lot less chain links involved Anyway, some really neat info available here with their sprocket diameter calculators.

http://www.rbracing-rsr.com/calcsprocketdiam.html

Chain link calculator.

http://www.rbracing-rsr.com/chainlength.html

Tire diameter if you are considering a 19 inch rear on a vintage bike.

http://www.rbracing-rsr.com/tirediamcalc.html
newmann
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newmann 4/16/2015 7:14am
4/16/2015 7:14am
Did I mention lightweight? Pure tastiness that I was able to finish up the details of on the Smithy, cutting , chamfering and dishing the heads of some 7075 pinch bolts. Ti swing arm pivot and some aluminum swinger and axle nuts. Swing arm spacer cups cut from aluminum with ti thrust washers. Good stuff!









newmann
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newmann 4/16/2015 7:58am
4/16/2015 7:58am
With a different set of axle blocks you can run the shorter 15mm diameter 79-80 CR125 swingarm pivot bolt as a rear axle. It's shorter, hollow, lighter. Combine it with some hard anodized wheel and bearing spacers to replace all the heavy steel and cast iron Honda parts to lighten things up even more.



newmann
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newmann 4/16/2015 8:10am
4/16/2015 8:10am
Needle bearings and a lightweight spacer in the pivot area instead of the chunk of steel Honda uses knock a chunk of weight off the swingarm assembly as well. Dumped the useless steel Honda chain guide for a small KTM plastic one on an adjustable aluminum mount. The all aluminum (shafts too)CH Omega air shocks weigh next to nothing compared to the steel bodied spring shocks Honda used in 76. We shall see if they are worth using. Don't even mention the pressed steel swingarm, one of Honda's greater ideas. Probably knocked 12 pounds off just in the rear swinger and suspension.



tydog
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tydog 4/16/2015 3:42pm
4/16/2015 3:42pm
Rear axle adj bolts needed sir?
tydog
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tydog 4/16/2015 3:59pm
4/16/2015 3:59pm Edited Date/Time 4/16/2015 4:00pm
I cannot believe that with the recent onslaught of 74-78 cr125 experts around here that no one
can provide more data on the 11 or 12 question. Unbelievable!
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Mike P. 4/16/2015 4:07pm
4/16/2015 4:07pm
13/53 Sprocket Specialist alloy sprockets (however, i do plan to play with the gearing a bit as I feel the motor out). I think this is going to be a really really fast Elsinore once I'm done (we'll that;s the hope after the small fortune i've sunk into it).



yzvet426
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yzvet426 4/17/2015 7:43am
4/17/2015 7:43am
I'm trying to figure out what to do about the chain not clearing the swingarm pivot. The only thing I can think of is a bigger sprocket. Any ideas? It's stamped 53 teeth.






newmann
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newmann 4/17/2015 10:13am
4/17/2015 10:13am Edited Date/Time 4/17/2015 10:14am
How much travel are you getting out of the rear of that beast Jeff? Go to that sprocket calculator I linked up above and plug in the number of teeth and chain pitch and it gives you the diameters. Going to 520 will definitely up the diameters without going to some oddball 15/60 gearing with a 428. Some of the old aftermarket swing arms for the CR125's had a roller bracket welded in front of the pivot tube to help get the chain up and over to the countershaft. Which bike is that on? I see traces of some Muganisms .....
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Mike P. 4/17/2015 12:06pm
4/17/2015 12:06pm
That's why I added the skateboard wheel tensioner (to clear the pivot). You could also take a block of ABS plastic and mount it on the frame (the tube that the rear lower motor mounts connects to). I had did this at first and then made the skateboard wheel chain tensioner. I took a skateboard wheel and cut it in half and mounted to the frame and it seemed to work, but I had not tested it on the track. I do the skateboard wheel tensioners work so that's why I went with it. Mike
newmann
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newmann 4/17/2015 12:12pm
4/17/2015 12:12pm
Mike P. wrote:
That's why I added the skateboard wheel tensioner (to clear the pivot). You could also take a block of ABS plastic and mount it on the...
That's why I added the skateboard wheel tensioner (to clear the pivot). You could also take a block of ABS plastic and mount it on the frame (the tube that the rear lower motor mounts connects to). I had did this at first and then made the skateboard wheel chain tensioner. I took a skateboard wheel and cut it in half and mounted to the frame and it seemed to work, but I had not tested it on the track. I do the skateboard wheel tensioners work so that's why I went with it. Mike
I think Jeff is more concerned with how hard the chain is dragging over the top of the swingarm.
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yzvet426 4/17/2015 12:18pm
4/17/2015 12:18pm
Hey Joe, Been waiting for you. Yeah it's my Mugan. Your correct If I'm on the bike the sag makes it work but obviously once the rear end unloads it's going to eat away pretty quick.
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Frankie 4/17/2015 5:52pm
4/17/2015 5:52pm
I need to spend more time here... Smile

Pit Row

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StevieD113 4/18/2015 12:28pm
4/18/2015 12:28pm
Newman, I sent 3 sets of titanium axles for these 125's out to Holly in japan last month. (looking forward to seeing what he does with them!) Drop me a line if you need any Ti for this little beasty!

Stevie



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Mike P. 4/18/2015 2:32pm
4/18/2015 2:32pm
I ran into the same problem with the swingarm on my 78 CR250 (the top chain buffer was aluminum). So what did was go down to Home Depot and found these large rubber hose connectors (they connect with large hose clamps). I cut one up and wrapped it around my swingarm (bolted down) and I ran it for 2 seasons with no problems at all. Below is a photo of the one I made for my 78 CR250 swingarm, which was aftermarket (JD Engineering) so the stock buffer would not work. I also made one for my 76 CR125 for the X-Cross UP swingarm (although I could have shaved it a bit more on 76 to make it look prettier, but I know it does work in competition). Mike







newmann
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newmann 4/19/2015 5:13pm
4/19/2015 5:13pm
StevieD113 wrote:
Newman, I sent 3 sets of titanium axles for these 125's out to Holly in japan last month. (looking forward to seeing what he does with...
Newman, I sent 3 sets of titanium axles for these 125's out to Holly in japan last month. (looking forward to seeing what he does with them!) Drop me a line if you need any Ti for this little beasty!

Stevie



Good stuff you have going on there Stevie. Much appreciation for you dedicating the effort to build stuff for the old Hondas! I'll be putting together a list for the whole bike soon, engine included for aluminum and ti hardware. Looks like a lot of it is just pretty standard 6 and 8mm hardware. Do you stock any of that or is it all custom made to order?
StevieD113 4/20/2015 3:11am
4/20/2015 3:11am
It depends what you need or want Newmann. We can supply the "stock" type where the M6's have 8mm hex, dished heads, and stock M8's have 10mm hex, dished heads. If you wanted more period correct 10mm hex fir the m6's and 12mm for the M8's or a different style of head (shallow dish, no dishing, counter bore, etc) then we'd make those to order, no real difference in price as we try to stay as competitive as possible with the "stock" stuff we buy in. The larger M10's we always make. We can get them exactly right then!
Stevie
newmann
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newmann 4/28/2015 5:54am
4/28/2015 5:54am Edited Date/Time 4/28/2015 6:06am
Been having a bit of fun on the Smithy whittling away at things. Need more tooling...lol.
newmann
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newmann 4/28/2015 6:09am
4/28/2015 6:09am Edited Date/Time 4/28/2015 6:11am
Drilled out the shift shaft. Whole ounce of weight savings. Now back to my breakfast burrito...



newmann
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newmann 4/28/2015 6:15am
4/28/2015 6:15am Edited Date/Time 4/28/2015 6:22am
How many destroyed left side engine cases do you have laying around for your old CR125's that tossed chains? Don't toss them out, just finish cutting off all that useless aluminum and make a set of semi RC replica cases. Find someone who can weld magnesium and trick out an old broken ignition cover while you are at it.

What to do with that brand new NOS ignition cover besides using it for weight comparisons? I remember seeing them fetch over $500.00 on eBay on many occasions.






newmann
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newmann 4/28/2015 6:24am
4/28/2015 6:24am Edited Date/Time 4/28/2015 6:27am
Buzzed a set of forged 35mm Marzocchi triple clamps down to the size of a stock set of CR clamps. Got some work left to do sanding and polishing. Bushed them up to fit a stock 74-75 steering stem.



sjsingle1
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sjsingle1 4/28/2015 11:42am
4/28/2015 11:42am
newmann wrote:
[img]http://cdn3.bigcommerce.com/s-95aji/product_images/uploaded_images/mr_know_it_all-1.jpg[/img]
what ever happened to Krause racing? he had tons of stuff for all kinds of bikes
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Hasletjoe 4/28/2015 7:47pm
4/28/2015 7:47pm
Newman, just reading through, looks like you are building a 76-78 model. What is your target weight?

Did you remove any weight off the shift drum? I have not measured, but the early motors (74-78) had solid rods for the shift forks. The 79 came with hollow ones. Or just grab some PVC!

What about the clutch? Any way to lighten the drive gear?

I am curious about ceramic bearings. Never experimented with them.

I need you to work through all the details so I can copy them.

joe

newmann
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newmann 4/30/2015 11:16am
4/30/2015 11:16am Edited Date/Time 4/30/2015 11:24am
Junior high shop class continued as I work to mount the Marzocchi triples to the early Pro-Fab Elsinore frame. Bushed up a stock 74-75 steering stem in the lower clamp and went to work on the upper. Took an old rusted bearing cup and cut it down in diameter and thickness and bored the triple to fit. Recut the spanner grooves. Now, if it was only done in Ti. Should be good for a chuckle from the in house machinists here. Bearings and seals just arrived a couple minutes ago so I'll be fitting them tonight to determine if I need to trim down the stem.








VintageRacer 4/30/2015 12:59pm
4/30/2015 12:59pm
Good stuff you guys.

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