CRM250SMR (using CR250/YZ490/KTM250SX internals)

Jeram
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CRM250SMR (using CR250/YZ490/KTM250SX internals)

Post by Jeram » 08 Apr 2012, 12:45

Hi Guys,

Being that my original thread is full of complete and utter crap including trash talking, disputes, vast time lapses of zero progress etc I have decided to build a new thread which will be far more concise and with a bit of luck gain a 'sticky' status in this forum area.

This build started of as me trying to buy a reliable workhorse for a road bike, I purchased a CRM250AR that I got a friend of a friend to look at but had not sighted it myself untill it was delivered.
first signs looked good but after a few engine dramas I decided to do a rebuild and was presented with some pretty horrible engine internals including a rod which was close to separating from the crank, a cracked piston, lots of rust in chassis and bearings and a host of other little nightmares.

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I dont know why, but something clicked in my mind to build a bad arse SM.

my first concept with a little ill fated as I attempted to build a skinny tire motard using the stock rims and pirrelli scorpion tires.
The engine was to contain a TRX piston and a TRX rod.
After realising my errors: which were the fact that the AR had a larger bore than the TRX, I decided to abandon that idea all together and build an ever more 'stupidly mental' motard.

I decided to set my goal as "the worlds fastest CRM" and set off from there.

I started off by completely stripping down and rebuilding the bottom end while i contemplated the rest of the build.

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during my investigations into CRM250 performance we concluded that no amount of porting would ever yield more than 40hp from a CRM250 due to the size of the exhaust port and being unable to build boost ports into the cylinder due to water jack positioning.

so we starting thinking about what cylinders could be used when I stumbled across this when comparing a heap of base gaskets I purchased for comparisons. The 2005 CR250 base gasket is almost identical in shape to the CRM minus the rear studs which are 3.5 and 4mm offset respectively. So it was decided that we were going to build a CR/CRM hybrid motor.
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before any of this could proceed we needed to get the bottom end completed. but with MR honda wanting 899 dollars for a crank and rod, I decided to flip him the bird and build a better crank.
So I aquired the only decent rod that had a 25mm big end pin, while being light/strong and most importantly VERY LONG!
how long exactly? the rod we found was from a YZ490 which measures 137.5mm in length.
That is a wopping 12.5mm longer than a CR250 rod (125mm) and 5.5mm longer than a CRM rod (132mm). This will make for a very mid rangy engine that is also rev hungry. large rod/stroke ratios also have the benefit of putting less thrust on the piston skirts which results in longer piston and bore lives too.

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So the YZ rod was ordered and shipped to Graham at Crank Rebuilding Services in Alora, Queensland, Australia. His work is bloody brilliant. He was able to widen my crank webs via grinding to accept the wider rod and rebuild the crank for $80 (AUD)

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Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals) WITH PICS

Post by Jeram » 08 Apr 2012, 12:47

and I got it back within 2 weeks

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next on the list was rebuilding the bottom end which went fairly smoothly without any hickups.

I then decided to pick up some decent SM forks that a friend was selling cheap, So I went and picked myself up a set of Husky 45mm Marzocchi forks which as very nice and firm almost a firm as a sportbike.

Then it was frame stipping time to get the chassis powdercoated and every bearing/bush replaced.
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In the process of this, I managed to pickup a Husky factory racing 320mm disc adapter and a caliper from an RSV1000R which provide superb braking power. If 2 of them are good enough to slow down a 200kg race from 300kmh, 1 will be good enough to slow me down on this 100kg racebike from must more modest speeds.


I then ditched the whole CRM intake tract and replaced with a billet intake boot, a CR250 VF3 reed cage and a PWK39mm from a late model RM250.



after being sent of 3 weeks prior, my powdercoated frame turned up. even though the color wasnt what I asked for, I was pretty happy.
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needless to say, I was very keen to start putting it all back together.
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Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals) WITH PICS

Post by Jeram » 08 Apr 2012, 12:51

Hmmm, seems like this website doesnt like 21st century camera phone pixels, so unfortunately I cant post most of the pics, but the links are posted to them.

A 68.50mm ktm 250sx piston was selected as it had a shorted compression height which balanced out the long rod a little bit.
it is also a flat top, and is much lighter.

CR vs KTM piston comparison
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The powervalve was then machined down for the larger bore size (+2mm), this actully took alot of time, even 6 months later I was still trimming little bits off here and there.

then it was time to install the wheels, brakes and drive train
http://i70.photobucket.com/albums/i92/S ... 0148-1.jpg
http://i70.photobucket.com/albums/i92/S ... 0144-1.jpg

Once that was installed, The bike then immediately started looking more like... a bike
http://i70.photobucket.com/albums/i92/S ... 010264.jpg
http://i70.photobucket.com/albums/i92/S ... 010261.jpg

Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals) WITH PICS

Post by Jeram » 08 Apr 2012, 12:53

and the graphics kit
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the rear disc (mito) was machined down to fit the stock caliper

http://i70.photobucket.com/albums/i92/S ... 030509.jpg

and I build my own quickshifter which seems to work brilliantly

http://i70.photobucket.com/albums/i92/S ... 030512.jpg

oil holes were added to the KTM piston to lubricate the exhaust bridge.
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Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals) WITH PICS

Post by Jeram » 08 Apr 2012, 12:55

I than began the machining and porting of the cylinder with MR Two Stroke Institute while working on the KTMito380 project with him

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The shock was rebuilt by a friend and shipped back to me, this was rebuilt to match the marzocchi forks and seems to do a very good job.

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It was then time to install the cylinder onto the top end, It took a few hours with the dremel to correct a few mistakes but I got there in the end.
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http://i70.photobucket.com/albums/i92/S ... 138ebb.jpg

While there the braking system was also replaced with the 320mm wave disc, as the EBC disc I was using had radial movement in the bobbins which is a big NO-NO
http://i70.photobucket.com/albums/i92/S ... 25e71a.jpg

Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals) WITH PICS

Post by Jeram » 08 Apr 2012, 12:59

It all seems to be going together rather seamlessly, I found it interesting that the hardest part was the planning, the rest was just hurting my bank balance and bolting stuff on the bike.
http://i70.photobucket.com/albums/i92/S ... 6d853a.jpg
and the 5mm spacer plate needed.
http://i70.photobucket.com/albums/i92/S ... cc3666.jpg

My torroidal cylinder head turned up which was machined my two stroke institute to Superkart (CR250) specs,
As you can see, it is a much better shape than the 'Lampshade' combustion chamber on my expensive CNC head which is complete rubbish.
http://i70.photobucket.com/albums/i92/S ... d4cc06.jpg


The engine was finally put together and was looking like it was close to being started up for the first time
http://i70.photobucket.com/albums/i92/S ... e88286.jpg

It litterally on took 3 kicks to start the bike.
1. to release the ignition wasnt turned on
2. to prime the motor
3. to kick it to life

Video of first fire up:
http://youtu.be/S2k8rry1XWQ
http://youtu.be/S2k8rry1XWQ[/youtube]

Now since getting the jetting sorted it starts with only a quarter kick! which Iv honestly never heard of. But I need to be careful becuase if it doesnt fire it often kicks back like a rabbid bull.

The remaining gremlins to fix on the bike are the PV servo which is on the fritz, so a new servo from an R6 Yammy is on its way.
And then the bike will be 100% complete!

but for now the bike is good enough for some high speed testing as it still has a very respectable mid range even with the PV wide open giving it an exh duration similar to a superkart.

After I fix the PV servo issue, I might pop it on the dyno with an EGT and my O2 sensor and see how many ponnies she is putting out.


Enjoy!

A quick recap of the bikes spec:
rebuilt bottom end
137.5mm rod from a yz490
custom machined crank to accept the wider rod
KTM250SX piston with custom machined oiling holes
2005 CR250 cylinder, transfer ports reshaped, stud holes offsef, spigot machined down, 5mm cylinder spacer. bored to 68.5mm (265cc) and Nikasilled.
CR250 cylinder head, machined to Superkart specs, toroidal shape
stock 05 CR250 expansion chamber for the beast overall spread of power for now untill a custom pipe is made
Vforce 3 reed cage
custom made alloy intake boot
RM250 PWK39mm with TPS
modified flywheel
she drinks 100octane + a few secrete additives with 20:1 AGIP castor/synth

Electronics are taken care of by an ignitech programable ignition unit

chassis:
powdercoated frame
marzochi 45mm shiver forks
rebuilt and resprung CRM showa shock
320mm wave disc
Aprilia RSV caliper
braided lines
mito wheels
machined down rear disc
CRF rear master cylinder
new plastics and custom designed graphics
BT003 tires

Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals) WITH PICS

Post by Jeram » 08 Apr 2012, 13:01

testing from the weekend :)



went pretty well, and top end is very strong

however the mid range is lacking big time due to the PV servo not working and the needle clip being too low making it too rich.

but other than that it was very very fun!

http://www.youtube.com/watch?v=jgFWm9S_BDs
http://www.youtube.com/watch?v=jgFWm9S_BDs[/youtube]

http://www.youtube.com/watch?v=_Rk76UxT ... ure=relmfu
http://www.youtube.com/watch?v=_Rk76UxT ... ure=relmfu[/youtube]

Ill get the jetting a bit closer, get the PV working then head out for one more test like this.
then Ill dyno tune the bike, and then it'l be race ready :)

Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals) WITH PICS

Post by Jeram » 08 Apr 2012, 13:07

Just did a full top end teardown after todays ride.

few things to note, all looks good apart from some polished sections on the piston which will need cross hatching with a diamond file.
Now that Iv seen that there are high spots, I will need to continually monitor the piston. Top end teardowns will need to be done after each trackday.
But being a two stroke, It only takes me 30-45 mins to tear the bike down if Im taking my sweet arse time so Its no big deal to ensure reliability.
hopefully after being re-cross hatched a few times it will no longer be an issue, but by that time it will be almost time to buy a new piston haha

The bore seemed to be a little wet as well as oily,but that could have been from when I lifted the head a few drops may have fallen in. But I wont take any chances. Ill be buying new base gaskets and making a new head gasket.

Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals)

Post by Jeram » 20 Apr 2012, 10:02

While prepping the CRM for the track next friday I found time to start brainstorming the next project.
Somewhere along the way I forgot what brainstorming was and began buying parts including a complete donor motor.

The project will be an attempt to make a GP spec big bore (300-400cc) disc valve single.

But Im not going to reveal anything more.

Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals)

Post by Jeram » 28 Apr 2012, 04:29

Got 40 minutes of tracktime yesterday before I destroyed a piston ;(

good news is that the bike pulls like a freight train even without the PV operating, its pulls well on the corner exits and puts 600 sports bikes to shame untill the pass me half way down the straights.

but I stupidly got the powerjet solonoid set up wrong. i ticked the 12V supply to turn on the power jet at high RPM, but infact I was powering the solenoid which was turning off the power jet! FML.

So before I race the bike again I need to do the following

-order a new piston, a wosner this time.
-apply some pool acid to the bore to remove the aluminium deposits,
-hone the cylinder,
-just purchased an expensive denso racing plug that has a short porcelain plug which will make plug chops without removing the head possible and these plugs yeild 2% extra power on 125gp bikes so I should see 1 free hp haha.
-make a better head gasket design
-buy the next two larger pilot jets, the next 2 larger needles, and a few larger main jets
-buy a zeeltronic ignition so that I can get my PV working, and then save the ignitech ignition that im currently using for my next project.
-install my EGT probe

Im prett flat out with Uni exam study at the momment and thesis writing (final year), but hope to have all of this done over the winter so Ill be ready to rock and roll as soon as the weather starts warming up in a couple months.

Overall Im still very happy with how the bike ran and the performance was more than I had expected, i still think that there is more power to be found in the bike (at least another 5hp once I get it set up right).
other than that, the handling was great and the suspension did really well (5 inch suspension travel under brakes)


Image
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should have her up and running in no time... I learnt a mildly expensive lesson today, but shouldnt cost more than 200 bucks to fix...
my lesson was... dont be a tight ass, buy the expensive short porcelain racing spark plugs so I can do plug chops without fowling on frame.

Jeram
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals)

Post by Jeram » 29 Apr 2012, 09:28

cancel that optimism, the nikasil has flaked off the bored in one tiny section so It will need re-plating.

should have it up and running over winter.

Im thinking that due to the really good performance, I might even try and enter it in the 250 proddy racing class rather than supermoto.

back off road
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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals)

Post by back off road » 01 Jul 2012, 01:44

so after a f==k up is this a runner or a BIG BANG fail :?:
Im thinking about a bike with more valves than a powervalve

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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals)

Post by Jeram » 03 Jul 2012, 04:50

never a failure :)

cylinder is currently in the USA getting re-plated and a new Wosner piston.

just had the powerjet programmed wrong so it cut the fuel supply at high rpm instead of the other way around so it leaned out on me, everything else is a success on the bike.

should have her up and running again with the refreshed top end, better jetting, and EGT guage and an upgraded ECU that lets me control the Powervalve properly.

Im going to gear it down a bit too, I had it geared for 185kmh which is a bit unrealistic for short circuits on a naked bike.
so it should be much perkier with the PV working and shorter gearing...

looking forward to riding it again :)

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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals)

Post by Jeram » 03 Jul 2012, 09:45

should be back looking like this in a month

Image

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Re: CRM250SMR (using CR250/YZ490/KTM250SX internals)

Post by Jeram » 16 Aug 2012, 01:12

cylinder is back looks great!

just going to try some new porting techniques while I wait for the new power-valve controller to turn up. We got these techniques after studying an Aprilia RSA125 cylinder. allows you to boost top end RPM and HP without effecting bottom end. This technique can be applied to any two stroke.

It could actually work well on a stock CRM cylinder to make it a little more potent on top while keeping the characteristic bottom end.


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