87 dune rocket sled project

[sdnative]

So, a month ago I was doing some horse trading with a customer and picked up a old beat to hell 87 CR500. For a while there I wasn't sure why I was even entertaining the idea of such a bike. I've had a few dirt bikes over the years; modern bikes just plain hands down rip in comparison to older models ...so why mess with an 87 I asked myself? But, the more I poked around the web, and the more I talked to other riders I began to realize their is some legend around the 500. It's a beast that commands a certain amount of lure and respect from all, both past and present. 500 fricken 2 stroke cc's!! (ok, so 491) One reviewer even wrote that it's un-rideable due to the power... HA! I was intrigued... maybe I could find a place for it in my bike lineup after all.

As I tore it down for a preliminary look-over, I began to take notice. It was really an advanced bike for the time. R/C adjustable suspension. Cartridge fork (albeit non-inverted). Front and rear disks. Multi-link mono w/piggy back on a tube frame that weighed in low enough to rival my modern KTM's. My 500 looked like crap, junk in fact, but I came to the conclusion that at the core this was a bike worthy of my wrench and TLC.

So I have a project in mind. I want an animal of a bike for the dunes. Something that brings me back to my first days on a fast bike, when I thought my arms would get ripped off ...love that.

As things unfold I hope all you 500 experts out there can weight in with ideas and much needed expertise. Your comments and enthusiasm will help keep me working away at it, so please, comments encouraged!

Rough project plan / ideas (not in order):

*Fat paddle conversion - custom front rim build using 2nd set of gold rims (front rim already cracked, with a shitty (and again cracked) weld fix)
*Subframe mod - it's bent currently, and is some aluminum custom?? Want to mod for different plastics, or go 'naked'.
*Seat shave - supermoto style shelf for locking in during hair-pin peak cut back roosts
*Dual shorty exhaust - looks badass if I go 'naked', and helps silence/deepen the tone.
*Nickel plated Pipe - hope to convert to low style - 89+ etc
*Rebuild engine
*Dez tank conversion - need something 3+ gallons, different style, my KTM 530 3.5 acerbis fits it oddly enough (except the high pipe issue).
*Dual core aluminum Rads
*Stator rewind / replacement - At least 30 watts of eye bleed LED
*Redo paint - frame and polish or sandblast then clear coat alum bits
*Plastic adaption - sorry guys, not an 80's style guy, but, really like the pictured CR below, so maaybe keep it original-ish.
*Lots of other minor things to fix.

More to follow! Thanks, Chris

Humble beginnings...............................................



Rough in the looks department..............................



Custom Alum subframe, pretty bent sadly...............



Beautiful Classic looking colors, maybe can work with this look. 88 fighting red



Fat Paddle type bike, floats on dune sand................

[sdnative]

First question for the experienced / experts:

Dug through a ton of posts, can't find the exact y/n answer.

Is it possible to use an 89+ low routed pipe, to get that thing off my leg and knee? The kickstand seems to look different, and I'll need to fab/weld a hanger on the frame ..etc, and the brake reservoir looks in the way ... but does the frame clear? Looks to be tight fit. Thanks!

Pipe wrap, or a fab'd cover / shield my savior otherwise...

[james1985]

Ive seen it done but have no idea what is involved as i have a newer bike

[jr475]

The 89 and up pipe will hit the rear hose going to the back of the cylinder on pre 88 bikes. You may be able to change the cylinder and cooling hoses to make it work. Never looked into it to closely as I prefer the old pipe.

[sdnative]

The 89 and up pipe will hit the rear hose going to the back of the cylinder on pre 88 bikes. You may be able to change the cylinder and cooling hoses to make it work. Never looked into it to closely as I prefer the old pipe.

I see what you mean about the coolant line, tight, if not totally in the way. I've been looking into it more, i think the frame design changed in 89, widened to pass the pipe... So that is also a major issue. thanks for the inputs.

Do you even have issues with that pipe burning you knee?

[Kuma]

The Fat paddle is different, Never tried it, but if it were me I'd just use the money into some nice rims, the bike floats fine in the sand with a few exceptions, some of the slip face sand near gordons has put me on the sand looking back to see my bike standing axle deep

[sdnative]

The Fat paddle is different, Never tried it, but if it were me I'd just use the money into some nice rims, the bike floats fine in the sand with a few exceptions, some of the slip face sand near gordons has put me on the sand looking back to see my bike standing axle deep

Ya, different is good IMO. Everything I've read on the fat tire setup in the dunes isawesome. It makes logical sense, spread the load out, and added ability to air down. I'm tired of digging my bike out or flying off when the dune powder hits the e-brake HA. Will see i guess...

[sdnative]

Started to tare it down this weekend, now glad I didn't try to start it up. What the hell is this stuff? Anyone conclusively know or seen this firsthand. No coolant what-so-ever, and a hard sludge that feels like a mixture of white bar soap and salt. Totally corroded the two in/out pump pipes. Thought for sure the motor was toast, but guess this happened while sitting in the garage for 10+ years, as the bore looks ok. 100% needs a new top end though, piston visually moves side-to-side ... what a mess!





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[sdnative]

Tore the engine mostly apart this weekend. AND ...mystery solved. Lots of green rad fluid in the transmission case. Sooo a blown pump seal. He was making oily soap goo in the coolant system, and corrosion came along for the party. Mud in the trans, but no rust. Soon I will see on actual wear as i plan to parade rest it and check out everything before re-assembly. Fingers crossed...

[james1985]

Your gonna find that that old case is wrotten aswell

[Tharrell]

Wow
Looks like I got off real easy on my '85 waterpump.
Good luck to you.

[sdnative]

New parts!

Found an 89 CR 500 roller up in LA for a price I couldn't pass up, so, grabbed it along with a viable pink slip.

Gets me several significant things.

1) Low pass exhaust pipe setup (I'll post 87 vs 89 frame comparison photos later)
2) Inverted fork
3) Better piggy back shock
4) Newer rear swingarm design, and pivots that are in OK condition (my 87 was absolutely 100% shot).
5) A subframe that is not bent.
6) Another front wheel / hub with good disk on it (the two 87's I had seen lots of water and mud and were grooved badly)

Hopefully a step in the right direction for this dune project...

[sdnative]

Your gonna find that that old case is rotten as well

Ya, not too bad thus far ... which is amazing. May be able to salvage it with some cleanup and added coolant tube inserts. Goal of this project for me is low buck, so, throwing $ at a new case out of the question. BIGGER concern is how shot is the tranny from running with coolant in the oil!

[Tharrell]

With that much corrosion, I'd bet there is some in your rads too.
I used some vinegar to flush my rads, heard that was the thing to use.

[sdnative]

With that much corrosion, I'd bet there is some in your rads too.
I used some vinegar to flush my rads, heard that was the thing to use.

Yep, when i popped the rad cap that was my first thing i noticed, salts and goo. not plugged, but knew right away i had a potential issue to check out. rads need replacing anyway, they are beat up and one is semi crushed. you can get dbl core aluminum ones from china for pretty cheap.

[sdnative]

Progress this weekend. Engine guts are spread. Next comes pushing out the bearing/seals, sandblasting, and some new powder coat.

I was worried about the gears, so after clean-up with kerosene I gave them all a thorough check out. Despite how worn my high power LED flash light makes the teeth surfaces appear in the photo, they are actually not bad. Only 1 set of mating gears appears to have picked up some crap and galled slightly, no other teeth face catches a dental pick point even slightly, and no other wear is apparent on the thru shafts etc (bearings are def shot though). So, once together it might not be the quietest gear box on the hill, but no broken teeth or other issues. Sigh of relief....

[sdnative]

So, another quick update. I started looking more closely at the 87 and 89 frame as I will need to get my head around swapping all the components over to the newer frame.

The 89 clearly is a very different frame. (1) It is much more compact, more like a modern mx frame than the taller 87. The old engine bracket that mounts to the cylinder top is way to long, as pictured, and the spark plug is closer to the upper frame. Clearly the 87 frame is a couple inches taller than the 89 design. BUT, thankfully the 87 engine fits perfect into the 89 chassis otherwise. (2) The rear triangle is symmetrical on the 89, so that it allows the low exhaust pipe to pass. You can see the 87 setup simply doesn't accommodate the low pass as the frame tube is tucked inward on the right side essentially blocking any try at passing a low pipe. (3) The CDI / spark coil layout is different, due to the stronger looking front triangle for those inverted forks etc. (4) Swing arm has totally different design, and the subframe is different dimensions as well. So, not much is similar between the 87 and 89, but at least the engine bolts in!!

...... 1987 CR 500 engine in an 89 frame .........


....... rear triangle comparison..........


.......... 1987 CR 500 Frame ....................


.......... 1989 CR 500 Frame ....................

[sdnative]

So, been working away on the project. Got the engine paint stripped, then sand blasted, and some powder down a couple weekends ago with the assistance of a friend and his DIY setup in his garage. Needs a clear coat still as it didn't turn out with enough protection from mud, grease, etc, but so far so good. Yep, dropped the 80's 'black' in favor of something a little more bling. Will post more pics post assy...

[sdnative]

So, I never knew piston shopping could be such a pain in the ass. I learned a few things surfing the web, opened up some old engineering books and taught myself a few other things, and then finally ended up buying some parts after giving up on weighing in all the factors and succumbing to the stress headache ha. Along the way I also rebuilt my 250SX KTM engine, so I have some added info as a result of that concurrent 'adventure'. For those of you interested in reading, I'd highly recommend "Two Stroke Performance Tuning by Graham Bell" (google it) it's one of the many I've flipped through over the years, but it's a standout for good readability and the author's ability to boil down the tech jargon to real world usable bits of tech wisdom.

So, the cast vs. forged debate. My vote, a quality cast piston. With a cast you end up with a more ideal piston design. Overall it's a better engineered product, which makes me smile. The whys: 1) Light weight: Thin where it can be, thicker where it needs strength, radius transitions between sections for cracking resistance (sharp edges create stress concentrations = cracks). Less piston weight also means overall decreased reciprocating loads (longer engine life), and snappier revvs to boot. 2) Heat distribution: Due to close control over the cross section they can design in better thermal pathways to limit piston distortion at running temperatures and to carry the heat away from the dome. This equates to a longer living piston and more uniform wear.

Forging is great for adding fatigue resistance to a design, but, it's best for steels where work hardening is significant in developing grain structures that resist fatigue cracks. A forged piston only gets you some protection from cracking, but cast aluminum can be alloyed as well as age hardened through thermal/chemical processes to achieve similar results, so...in the end forging for this strength comes at too high a cost for the same end ...loss of the above mentioned items 1) and 2). When done wrong, forged parts can also have cracking and distortion issues of their own. But I digress...

I really wanted a cast Vertex!! It's what my KTM has (OEM supplier) and I read nothing but good things about Vertex. But, I was limited due to my 500 being at 0.25 oversize with a nice sleeve still, so couldn't get a vertex unless I bored it oversize more. I'll get a Vertex on my next rebuild. So, Pro-x gets some serious bashing, and I was extremely hesitant to go with them. I was however relieved to see that the final product is visually near identical to the OEM honda part. Pro-X makes a nice part... with a caveat on the skirt edge, and more importantly the exhaust port as explained more a few posts down from this one. If you're reading this, understand that the Pro-x may or may not work with your CR500, the why is explained later.

Exact Sku pro-x piston kit I bought on eBay from Lionparts ...


Honda OEM left, Pro-x Right. Note the skirt coating and nice smooth blending around the wrist pin. Pro-x retaining clip is 'wingless' so there are no clip 'tabs/legs' to break off and fall into the engine, a problem with OEM honda (tabs not pictured).


Note the transitions to thick-thin on the skirt underside and inner piston core. Shaves weight, and not possible on forged w/o expensive post CNC machining. Made in Japan. Also note cross rib for added dome rigidly.


Compared to Vertex below ...these are my KTM 250 piston parts

Pretty similar negative reliefs to reduce wall thickness. As with the Vertex I must chamfer/buff out the training skirt edge on the Pro-X because it is a razor sharp edge ...which tends to scrap oil off the sleeve wall as the piston goes up-down preventing this oil from reaching the upper skirt or piston rings. Always remove this sharp 'oil squeegee' edge from the skirt!


A 500 dwarfs the 250 piston ...wow this thing is going to be a rocket no doubt

[abrracing]

I don' know why some still think cast pistons are better than forged.. bottom line is cast pistons are not as durable..

good luck with your build though, im sure the bike is going to be nice.

[sdnative]

I don' know why some still think cast pistons are better than forged.. bottom line is cast pistons are not as durable..

good luck with your build though, im sure the bike is going to be nice.

Cause... ahh.... I've used my brain to decide they are. Old school cast pistons sucked, I would agree there, this because of poor alloys, bad casting techniques ...all correctable through mfg advances.

I knew that would ruffle some feathers, ha, so all those haters out there explain why is that the "bottom line". Or link to someone who has made a logical case for forged.

A case like, 1) 83% of OEM's use forged because they are proven through testing to be better (I made this up, I don't think the do actually, they go cast). ...or.... 2) I run 20-1 compression and need a forged one to keep the detonation I run with from cracking the piston crown; I need all that extra thickness in there! 3) Unkle JeD uses forged in his V8 flat bottom jet boat, he said they are the best, he is my idol...

And ...just trying to have some fun here ... don't be insulted

And, thanks, has been quite a good project thus far. Always liked rebuilding stuff...

[Roostius_Maximus]

Should have done more reading.
The prox isn't worth installing. In any bore size the pin area cavitates to the exhaust mid stroke.
Should have bought a vertex if you wanted cast.

[abrracing]

I don' know why some still think cast pistons are better than forged.. bottom line is cast pistons are not as durable..

good luck with your build though, im sure the bike is going to be nice.

Cause... ahh.... I've used my brain to decide they are. Old school cast pistons sucked, I would agree there, this because of poor alloys, bad casting techniques ...all correctable through mfg advances.

I knew that would ruffle some feathers, ha, so all those haters out there explain why is that the "bottom line". Or link to someone who has made a logical case for forged.

A case like, 1) 83% of OEM's use forged because they are proven through testing to be better (I made this up, I don't think the do actually, they go cast). ...or.... 2) I run 20-1 compression and need a forged one to keep the detonation I run with from cracking the piston crown; I need all that extra thickness in there! 3) Unkle JeD uses forged in his V8 flat bottom jet boat, he said they are the best, he is my idol...

And ...just trying to have some fun here ... don't be insulted

And, thanks, has been quite a good project thus far. Always liked rebuilding stuff...

I am not interested in starting a big cast vs forged war..
Instead of getting into a long heated battle about forged vs cast I'll tell you what I know from first hand experience from being in drag racing and motorcycles for the majority of my life.. I worked in speed shops where we built race engines for drag and circle track applications..

Cast pistons would last depending on brand and power level of the engine.. Cast were used in lower class engines like street stock that were basically very mild small block chevies.. You would never see a modified dirt engine with cast pistons lol it wouldn't survive one night of racing turning at 7000+ rpm and 600hp+



Forged pistons would easily last the WHOLE season then alot of the circle track guys would sell their set of JE pistons to some street/strip guys for a fraction of the cost and they would run them for a long time.

The reason factory uses cast pistons is because a factory engine has tight tolerances.. they would be risking it using forged pistons because of this.. the average person purchasing a dirtbike doesn't understand to properly warm up the engine before taking off like a bat out of hell.. if the machine work is correct and the clearances are right and the engine is tuned and running correctly ( no detonation) cast pistons will work just fine, of course depending on power level.. But if the cylinder is a little on the loose side it's a risk running cast because they DO NOT like piston slap.. cast will shatter from this.. forged pistons won't, not to mention the strength in forged pistons is greater.. they can handle heat, vibration and rpm and detonation more than than cast.. You will get more hours on a forged piston than you will on a cast.. forged pistons are more reliable to the least experienced tuner, they're more forgiving..

If i missed on something I apologize, im running late for work, i have to get to our shop and finish a customers MX with a brand new wiseco Pro Lite

[sdnative]

Off topic...

Anybody know if an 89+ 2 piece clutch/pump cover can be installed on my 87 engine. My 87 cover is pretty beat, and i want the coolant up pipe in any case. This 'up' ward pointing inlet is needed to re-route a coolant tube around the low exhaust pipe setup. The 88 prior had this angled rearward, this doesn't work so well with a low pipe.

It seems 90-01 may be a new gen of engine?

Thxs. spend hours looking, not stumbed on a concrete y/n

[sdnative]

Should have done more reading.
The prox isn't worth installing. In any bore size the pin area cavitates to the exhaust mid stroke.
Should have bought a vertex if you wanted cast.

In all honestly, I spent over a week digging posts up after work prior to buying the pro-x, so my lack of research/reading was not the issue at all. The wealth of knuckleheads spewing opinionated statements w/o any support or explanation is. You however have managed to type an intelligent statement after your opinion, and it probably only took you 30 additional seconds to do so, sincerely I thank you.

Have already decided Vertex for my next rebuild, when I need to go to 0.5 oversize. Bore was still good at 0.25 over on mine...

So, I am kinda even more frustrated than previously with this topic, because all someone had to post in any of the other Prox piston threads was exactly what you've said. Thank you, sadly too late for me!!

Yes, after measuring my 2 pistons in the exhaust port area, and then slipping them into the cylinder to examine the port overlap... you are 100% correct. Fuuuck me!!! Prox design simply will not work in my CR500 engine, the skirt on the exhaust side of the piston is too narrow, resulting in venting around the wrist pin area.

I will lay this all down 101 style so at least someone else out there can benefit from my fail.

The What, and the Whys.

What: Pro-x P/N 01.1408.025 Honda CR500 89.25mm cast piston (and probably the other 01.1408.### models) Now at least google will hit an intelligent post with a definitive answer.

Why: Picture of the CR500 tear drop shaped exhaust ports below. The piston must seal this entire exhaust port off during the entire combustion cycle. Design wise the rule of thumb is 2+ mm of piston skirt overlap on either side of the port edge will provide an adequate seal against exhaust pressures, which go up and down as the expansion pipe tuning comes into play.



Now a shot of the OEM next to the ProX. The ProX is too narrow, there is not an overlap area of piston skirt with the cylinder bore, there is a tiny sliver of a open gap actually, so there is no seal created and exhaust gases will vent into the area around the piston wrist pin. This creates all kinds of problems for a two stroke engine. As a result the ProX will not work with the tear drop shaped ports.