Yamaha SR250 - A clean standard build

JadusMotorcycleParts said:

Thanks for the ideas on the brake xb. Do you have any literature/links about that offset cam for the drum brake? And have you seen anyone do the double cam adaptation? I would be very interested to see any solutions there and would def try something myself if it looked doable for me.

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no i dont but it was in the ad literature that yamaha put in the magazines
specifically it was the 1980 yz250 i am almost certain now because i was racing at that time on a canam mx6-250
i broke one of the fork legs in half while competeing in the viginia city grand prix
i was never happy wiith the marzocchis anyway this was in 1983 so i went to the breakers and found the complete forks and wheel afrom the yamaha yz250 i think it was just the cam was either offse or one side a littkle longer
anyway the idea is to get more actual movement in the trailing shoe the trailing shoe is weaker the only way to make it stronger is move it more than the leading shoe
you asked about adopting a 2ls,i was going to do it with honda bike and parts but i went another course a disc
all you need to do is find an older yamha sreet bike or honda with the same diameter brake drum adopting the twin cam brake panel over will be simple some basic mahine work

here is the 1980 yz250 offset brake cam used only 1 year then they kept the same wheel and put on a twin cam brake like everybody else ,then in 84 or 85 disc brakes for the yz's
http://www.cmsnl.com/yamaha-yz250-g-competion-19801981_model8776/camshaft_24x2515100/#.VjjF7rczYlw
and the 1978 same wheel ,same brake plate, no offset cam and a different part #
http://www.cmsnl.com/yamaha-yz250-g-competion-19801981_model8776/camshaft_24x2515100/#.VjjF7rczYlw

i

datadavid said:

Are you doing the xs headers for a guy in Linköping?
If thats the case he asked me too, but i havent had a spare minute for the last year.

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Na its a dude from Stockholm. They're a bit of a nightmare to try and fix and it's not the most professional job out there but it'll hold for a good while anyways. Its those damn flanges that rust out and there doesn't seem to be any weld in repair parts available

xb33bsa said:

here is the 1980 yz250 offset brake cam used only 1 year then they kept the same wheel and put on a twin cam brake like everybody else ,then in 84 or 85 disc brakes for the yz's
http://www.cmsnl.com/yamaha-yz250-g-competion-19801981_model8776/camshaft_24x2515100/#.VjjF7rczYlw
and the 1978 same wheel ,same brake plate, no offset cam and a different part #
http://www.cmsnl.com/yamaha-yz250-g-competion-19801981_model8776/camshaft_24x2515100/#.VjjF7rczYlw

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Damn so cool! I was wondering of something could be done with the cam to boost the mechanical action without too much more strain at the hand. I'm gonna try this! Thanks!

On the topic of improving the braking performance, I studied this guys work pretty hard and would like to try some of the ideas for the next build I do. Its great that racing always improves the breed and that this guy has taken the time to document everything. Looks like the reason he stuck with the single sided, single cam drum and improved it was regulations in the racing class.

I am so keen on a Bighorn now! 2-stroke single power! Makes me miss my DT400.

http://www.klemmvintage.com/bighorntech.htm

I'd pay for a shock tube and a front wheel that has the caliper option. Newer SR250 stuff is so rare online.

JadusMotorcycleParts said:

Damn so cool! I was wondering of something could be done with the cam to boost the mechanical action without too much more strain at the hand. I'm gonna try this! Thanks!

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glad you like that !
i actually did some testing wayback and recently to try to understanf some of the dynamics
all that is required is 2 dial indicators
secure the brake on a table thru the axle hole so that you can easily pull the cam lever in the correct direction as on the bike just some spacers on a long bolt so the brake is up off the table
then put the indicators on the shoes at 9 oclock and 3 oclock.the cam at 12, position them evenly form the cam with accuracy !
then you can test away( good idea to get a spare cam) with a spare cam different offsets and even changing the contact radius of the cam will have an effect you can use welding or brazing to build up material
one thing to remember is that the leading shoe does most of the work probably 75% that shoe needs no help so i believe that the actual plan is to either reduce its acual movement slightly OR increase the movement of the trailing shoe
be carefull to do accurate filing so the contact of the cam is not out of paralell

I'll keep all that in mind when I am testing. Cheers!

When a finally do blast the engine (hoping next week) I will be using one of these bolt kits I have prepared. It has everything, down to the oil check bolt (a nice button head screw) and the clutch bracket even! The only bolts it doesn't have are the 4 head bolts and the barrel bolts. I will post up some pictures when I have mounted everything.

I am thinking about making a separate kit for the carb too... Depends of there is a need/interest for it.

http://www.ebay.co.uk/itm/Jadus-Yamaha-SR250-Engine-Bolt-Kit-Black-Allen-Head-Bolts-/262127572748?hash=item3d0805570c:g:YaAAAOSw5VFWOgTD

Get those in stainless or titanium and you'll have buyers.

cosworth said:

Get those in stainless or titanium and you'll have buyers.

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I will look into titanium, I can imagine its insane expensive though.

Never say never, but I don't think I will offer a Stainless kit - I really dont like what it does when combined with aluminum - being susceptible to galvanic corrosion and all. I have personally messed up some good casings with stainless fasteners even with taking the precaution of adding anti-seize paste. Not worth it in my opinion. I know there will be some arguments for using SS, but there is a lot of information out there that says the two metals corrode and bind together - then you end up with stripped casings like I did. Each to his own of coarse! If you're not going to ride in the wet, then you're not adding the electrolyte and nothing should corrode (in a perfect world), so then using SS would be fine! But I wouldn't want to sell a product that could be responsible for ruining someones engine...

I have a UK sourced stainless bolt kit on my SR250.

Zero corrosion. The bolts are in dry. Zero issues. And I live in a wet climate. If I had a titanium bolt kit like I had on my gixxer, I'd heat them up to make the purply. Yum.

There is a large a variety of alloys in both aluminum and stainless, and this has a significant effect on galvanic corrosion. High corrosion resistance stainless alloys are usually expensive and not what you find in a hardware store. if I was gonna have custom bolts made I would go for 316, 15-5, 17-4, or nitronic 50. The precipitation hardened stainless alloys are very similar to the proprietary alloy ARP uses in its high strength stainless bolts. A plated finish would be a good option too. IMHO black oxide shouldn't be used on anything that isn't regularly coated in oil, or where surface rust isn't an issue. BO will often rust just sitting on the shelf in a humid environment.

cosworth said:

I have a UK sourced stainless bolt kit on my SR250.

Zero corrosion. The bolts are in dry. Zero issues. And I live in a wet climate. If I had a titanium bolt kit like I had on my gixxer, I'd heat them up to make the purply. Yum.

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Thats sweet. I guess if they are the correct grade stainless (which a lot of cheaper fastenings are not) they would hold out and be slower to galvanize.

You mean that purply sorta colour that titanium exhausts go? I love that!

doc_rot said:

There is a large a variety of alloys in both aluminum and stainless, and this has a significant effect on galvanic corrosion. High corrosion resistance stainless alloys are usually expensive and not what you find in a hardware store. if I was gonna have custom bolts made I would go for 316, 15-5, 17-4, or nitronic 50. The precipitation hardened stainless alloys are very similar to the proprietary alloy ARP uses in its high strength stainless bolts. A plated finish would be a good option too. IMHO black oxide shouldn't be used on anything that isn't regularly coated in oil, or where surface rust isn't an issue. BO will often rust just sitting on the shelf in a humid environment.

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that is some great information doc i dont understand as much as i think i know about metals and there makeup mechanical properties etc
maybe you could answer what kind of stainless steel can be hardened.the reason i ask is the old original works performance and curnutt shocks use a stainless rod 1/2" round and it is almost too hard to comfortably machine ,it holds up just fine to the harsh conditions,but if the rod gets minor pitts they can be blened smooth unlioke chromed shaft

doc_rot said:

There is a large a variety of alloys in both aluminum and stainless, and this has a significant effect on galvanic corrosion. High corrosion resistance stainless alloys are usually expensive and not what you find in a hardware store. if I was gonna have custom bolts made I would go for 316, 15-5, 17-4, or nitronic 50. The precipitation hardened stainless alloys are very similar to the proprietary alloy ARP uses in its high strength stainless bolts. A plated finish would be a good option too. IMHO black oxide shouldn't be used on anything that isn't regularly coated in oil, or where surface rust isn't an issue. BO will often rust just sitting on the shelf in a humid environment.

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Thanks doc, that's really good info. Yes, 316 is a grade that is often only used for higher end stuff because of its cost compared to 304. And I didn't know about the nitronic 50 - it's always good to look towards marine stuff for quality! Harshest environment possible! The OEM bolts are steel - zinc plated, so of coarse this is the best/preferred method of coating/material for a cost-performance balance (otherwise the clever Japanese engineers wouldn't specify it right?). I just really dont like the look of zinc plating, I personally think it looks tacky - like an off chrome if you know what I mean?

I really like the black oxide finish - it is very similar to gun blueing and parkerizing (used extensively by Harley in the past) and has a very high aesthetic finish which I love, but as you say, requires a bit of care - an oil/grease coating from the beginning and a rub down every now and then (like gun maintenance). But the big plus is dimensional stability with the coating process, and the fact that it is a non-sacrificial coating means there is little dimensional build up when they do corrode - means no stripped threads (hopefully)! I always put a bit of gun oil or similar on these kind of fastenings when installing them, and I specify that with the kit. I guess as long as people are aware, it will be down to personal preference. Hope people would still be interested in the kit!

xb33bsa said:

that is some great information doc i dont understand as much as i think i know about metals and there makeup mechanical properties etc
maybe you could answer what kind of stainless steel can be hardened.the reason i ask is the old original works performance and curnutt shocks use a stainless rod 1/2" round and it is almost too hard to comfortably machine ,it holds up just fine to the harsh conditions,but if the rod gets minor pitts they can be blened smooth unlioke chromed shaft

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Its quite possible they are work hardened 304 that is super tough stuff. the only two heat treated alloys I know of are 17-4 and 15-5, i'm sure there are many others, lots of proprietary alloys.
Sorry to thread jack.
you are doing nice work. I recently have gotten access to some 3D printers to mess around on, so I am quite interested in the work you are doing. what software are you using?

doc_rot said:

Its quite possible they are work hardened 304 that is super tough stuff. the only two heat treated alloys I know of are 17-4 and 15-5, i'm sure there are many others, lots of proprietary alloys.
Sorry to thread jack.
you are doing nice work. I recently have gotten access to some 3D printers to mess around on, so I am quite interested in the work you are doing. what software are you using?

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No worries, its great info!

I am using Cura at the moment. I downloaded that because it was recommended for Printrbot and it had pretty good support/forum info. It has decent customization but i think the slicer was better with Makerbots software Makerware. I tried to get one of my mates to look into writing a script to convert the exported g-code from Makerware to a format the Printrbot can read, but it never happened.

What printer to you have access to?

i have access to Objet printers (Eden, Prime, Objet30) and a ZCORP 310. I have only used the Objet30 so far. cool stuff.

doc_rot said:

i have access to Objet printers (Eden, Prime, Objet30) and a ZCORP 310. I have only used the Objet30 so far. cool stuff.

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Wow cool. They are more industrial printers right? Using the SLS process? I had access to an Objet at my job in Australia and it was awesome. We ordered it because of its dimensional accuracy. We just used the proprietary software that came with the printer and it was very user friendly and seemed to produce good prints. I have a feeling that most of the free downloadable softwares out there are for the FDM process though...

We also had a big water blaster enclosure to clean away the gel like support material. Do you have something similar for that?