87 dune rocket sled project

Recount your rebuilds here!
sdnative
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Post by sdnative »

abrracing wrote: 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 :D
I can respect an opinion that has statements like yours behind it. Nothing to disagree with stated up there. In the V8 world, big cranks, big rods, lots of heft cycling around inside those engines also though, a heavier piston is no biggie I'd think. Anything to reduce the vibration of my CR, like a lower weight piston, I'm all for. I'm not gonna race my CR either.

Anybody seen actual weights posted for CR500 pistons? Curious how much heavier a wiseco would be then say a vertex or OEM etc.

And thanks for adding in some convo on the thread ...
abrracing
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Joined: August 18th, 2013, 5:19 am

Post by abrracing »

just make sure you relieve the exhaust ports before you assemble the top end.. Even though you're using a cast piston you could still drill the oiling holes on the exhaust side..
Once you get it up and running, don't go overboard with jetting.. keep it on the rich side.
sdnative
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Post by sdnative »

abrracing wrote:just make sure you relieve the exhaust ports before you assemble the top end.. Even though you're using a cast piston you could still drill the oiling holes on the exhaust side..
Once you get it up and running, don't go overboard with jetting.. keep it on the rich side.
Comments for the bridge correct? Ya, after honing on the sunnen machine I made sure to re-check it for set-back etc. I've read over the wiseco drilling for the bridge... this really needed though if the bridge is dimensionally relieved enough?

Side note: I may be machining this to 0.5mm oversize, as finding an OEM 0.25 is proving to be a chore. THEN I can get my vertex also... TBD...

Thanks
sdnative
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CR 500 engine powdercoat

Post by sdnative »

So, just some photos. Over the last month I stripped the paint, sand blasted and powder coated the engine with 400 deg Eastwood powder. Garage low-buck setup ...but it works! Time will tell if the powder lasts... betting the head paint won't. Next is a total replacement of all bearing and gaskets during re-assembly.

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Before
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After
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Blasted Aluminum Eastwood powder with full gloss clear Gloss top coat over it. Has a shimmer in daylight. Photo just can't capture that deep gloss clear...
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Also, one of the hubs I did in Metallic Blue. Photo doesn't come close to doing it any justice. It's a beautiful semi-translucent deep blue with silver metallic flakes... my new favorite powder coat color.
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Last edited by sdnative on November 15th, 2013, 8:40 am, edited 3 times in total.
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Kuma
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Post by Kuma »

I would think the powder should hold up, you bake at 400 and a water cooled head should not get there.
Gen 2 AF, yes it's a SH, so I can call it an AF Damm it!
sdnative
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Post by sdnative »

Kuma wrote:I would think the powder should hold up, you bake at 400 and a water cooled head should not get there.
Ya, would agree, specs support that
abrracing
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Post by abrracing »

sdnative, yes my previous comments are meant for the exhaust brigde.. .
blownbillybob
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Location: FRISCO

Post by blownbillybob »

I've detonated/ beat the crap out of my pro-X piston stock exh port and it still runs no problems !!!

The exh side is the only down fall ?? Which I didn't notice any difference in power what so ever!!

I wouldn't have a problem running that pro-x ,you allready have it!!

What finish did you use on the sunnen and stones ?? Yon must be careful with automotive stones they fall into the huge intake port and then jump out makes a mess??????
00'cr500 trailclimber
93'cr500 beater
92'cr500 hillclimber
08,KTM SR500r hillclimber (conv)
89'cr 500 bent frame
04'crf230(wifeys)
02' cr125(sons)
02,pro jr 50 open exh. hill climber(sons)
02'sx65(sons)
03'xr50(sons)
sdnative
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Post by sdnative »

blownbillybob wrote:I've detonated/ beat the crap out of my pro-X piston stock exh port and it still runs no problems !!!

The exh side is the only down fall ?? Which I didn't notice any difference in power what so ever!!

I wouldn't have a problem running that pro-x ,you allready have it!!

What finish did you use on the sunnen and stones ?? Yon must be careful with automotive stones they fall into the huge intake port and then jump out makes a mess??????
Yep, design wise the pro x is flawed on the exhaust side. As back pressure builds at the exhaust port (a great thing to have on two strokes) which forces back in previously vented air/fuel, some of that flow will vent back to the case and boost ports via the wrist pin area. This is really bad... The engine will never run its best, if at all at certain speeds.

The 500 is a beast, there will be a power loss with the prox, no doubt there. how much, who knows unless they measure it etc. with all that engine grunt it may not be obvious. im sure there are lots of prox cr engines out there, most people would never notice during rebuild.

I was able to return the prox, and i got me an oem 0.25 piston kit on its way... For more $ unfortunately, but hey. when i go to 0.50 oversize i will use a vertex. Prox looked like a good option, sucks they have that port flaw.

Think the stones were 230 grit, would have to ask my buddy. they were the long ones, maybe 4 inches. he said not to ball hone it for that catching reason. it was done on a hone machine.
blackz34
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Joined: August 29th, 2009, 10:34 am

Post by blackz34 »

Powdercoat will hold no problem. I've done my 2 engines last winter, one satin black, and the other one silver metallic + clear. They both still looking good.

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sdnative
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new styling idea

Post by sdnative »

Was inspired flipping through some of my dads old classic moto books. Rather than just another generic cr rehash, gonna take this project a new direction. Got an oldschool husky tank on its way. time to get out the air tools and mig welder....

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