CR500 conversion to 250 Alloy Frame

[YZ-Red]

Hi all,

Im in a far away country and I want to build a trail bike/Supermotard weapon using a cr500 engine in a Alloy cr250 chassis.

My questions for any knowledgeable ones out their;

1) My understanding is that when you cut and weld alloys that have previously been heat treated you must use the same type of alloy to add bits/brackets and then you must heat treat the whole piece in a jig once finished to remove stresses and strengthen.

Where i'm leading is that the 1st generation frame doesnt have to be cut (which the 2nd & 3rd do) so therefore (as re-heat treating isnt an option) wouldnt this be the best choice for this project.

On the possible down side is vibration, would this be better or worse between generations 1,2 &3 ?

Will different types of head stays make a difference ie like a one sided verses two, and strong verses slight flex- thin brackets?

Thanks in advance for any input and help

cheers
Red

 

[Faded]

www.servicehonda.com

Talk to them, they do a CR500 in an alum. frame. You might explain to them where you're from and maybe they'll fill you in on how they make it fit. Worth a try.

 

[YZ-Red]

Thanks Faded,

I am comparing the cost of building a generation 1 framed version here in NZ to buying a second hand 01 cr500af off service honda and exporting it to New Zealand.

Our dollar is weak to the American so it would land owing more than a brand new 250 here.

If I build a gen 1 version here, I will have the budget for Ohlins front & rear, (in fact it would look very similar to the red one at larrys cr500 page reviews-1990-2001, under Aluminum reviews) As I am 6ft 6 tall and way over 220lbs means suspension is critical especially for muti-use such as road racing and trail riding.

If I ring service honda they will naturally be biased to there own product so that would not totally answer my questions.

cheers
Red

 

[kiwi_925]

Red have you seen or been to any of the NZ motox rounds?? Theres a guy out there that has a 500 in a 250 frame, dont know the guy or where hes from or anything, but just know hes in the 500 class. Im trying to get my old man into buying some road tyres for my YZ, get him on it and have a bash myself as we've both done buckets which is fine for him but im pretty much your size and in need of more power, but just to have a go at it and then maybe buy the rims and that later. Saw them at wanganui and would have loved to be out there trying it but comes back to $$ as usual.

 

[YZ-Red]

No I havent been to any NZ rounds.

I think they have a lights class this year which allows for stock up to 300 class. You run your dirt rims with road tyres, should be fun, my first road race was at wanganui on a 1988 CR500 with a trials front tyre, I had a ball.

thanks for the input.

cheers
Red

 

[SMMICK]

I'm in OZ and I started building one last night using a Gen 1 frame. I chose the Gen 1 because of the cost, the fact that you don't need to cut the frame and also because the Gen 1 are a lot stiffer which is good for what I'm using it for- supermoto.

I'm trying to find info on the engine mounts in particular where I should be positioning the engine and if anyone makes ready made mounts to weld on.

Tried Service Honda but they didn't respond to my emails and when I called them they weren't interested.

I have found a few issues already- coolant pipe sizes are mismatched and the bottom of the fuel tank fouls on the cyl head

 

[SMMICK]

Just read my post and realised I forgot to answer your q's !!

If heat treated Alloy is welded it should be re treated, hence my reluctance to use the late model frame and apparently there are issues heat treating a frame made out of a combination of extruded, billet and cast material.

As for the vibes.....its gonna vibe a lot! no matter which frame you use and from what I've been told by a guy thats built a couple, the vibes resonate in the frame spars and make a really funky sound.

Do not get the head stay wrong!!! I know this from experience which ended in a broken cylinder on a KX500...I'm making one as close to the original as possible and then a little stronger just in case.

 

[YZ-Red]

Thanks SMMICK.

My understanding is that you can solve the fuel tank problem by going to an NSR250 spark plug which is the same heat range but is half as long, or you can heat the standard tank up and bend it to make room, which will reduce fuel range.

if you go to larrys cr500 page and look at the review of the 1990-2001 models, under aluminum models the red one's review shows a picture of the top head-stay they made. This should get you started. I know service honda make a one sided head stay for there models and i wonder if this is to do with vibration????

My email is gillard@ihug.co.nz if you want to stay in touch and swap info, photos etc.

cheers
Red

 

[YZ-Red]

OK not much response from the 500 guys, what about you 250 guys who have owned a 97-99 cr250 and then a 2000-2003 cr was their alot of difference in the handling, vibration. I dont care about suspension , more chassis related feed back.

cheers
Red

 

[Faded]

Had a 98, now have an 02. Chassis is very solid on both models. The 98 seems a little slimmer than the 02, but that can be attributed to the larger shrouds on the 02. Vibration is about the same (before my motor work) but I never felt that it was an issue on either bike. I feel that I can turn better on the 02, but I think a lot of that is related to the suspension being better. Both bikes exhibited good manners at higher speeds as well. I prefer the 02 because it feels lighter and a little more forgiving. Either one is a solid platform IMO.

 

[YZ-Red]

Thanks heaps Faded,

just the sort of feed-back im after.

Have you ever ridden a 2nd generation as a comparison?

cheers
Red

 

[Faded]

Sat on the seat of a double-0, foam was noticable stiffer... :confused: J/K!

 

[YZ-Red]

I just secured a 97 cr250 which I pick up Thursday.
So im all go as well.

How are you going??

Did you try contacting a guy called DREDGE (I think) on Larrys CR500 site? He is talking about making the appropiate kits if enough interest. You will find him in the message board,

Got a digital camera, progress photos would be interesting.



cheers
Red

 

[bigcr]

My brother and I both have 2000 CR500AF's. They vibrate less than the steel framed 500's we had previously. If you use RG3 4-post clamps, pro-taper bars with a bar snake and balance the crank you'll vibe less than most 250's. They feel like they vibrate a lot when running on the stand, but when you're actually riding you won't notice it. You'll be more worried about keeping the front end on the ground :)

 

[James]

I can't tell any vibration difference between the 00 and 02

 

[SMMICK]

YZ-Red: Its all going good, Both bikes disassembled and I've got the 500 engine sitting in the 250 frame & it looks awesome!! I decided to pull my finger out and go ahead and make all the mounts and spacers myself. Once I've got the exact measurements I can let you know if you like.

The swingarm/bottom mount line up fine, just have to make new spacer for swingarm & bottom mount.
Had to cut off the front mounts from the 250 frame as they are not close at all!! New mounts getting machined atm.
There is a cross brace on the two front down tubes that i had to cut away a section so that it clears the exhaust collar.
I've ordered a NSR250 spark plug to try it out but the tank still hits on the cylinder head at the rear where the mounting lug is....just going to attack the tank with a heat gun.
Stock exhaust can be easily modded but I need a new pipe anyway so I'm getting a pipe from SPES in Belgium thats made for CR250/500 hybrids.
I'm also inthe middle of making the new head mount and lowering the forks & shock.
I haven't got a digicam yet but I'm about to buy one....I've got no idea which to buy, any Ideas anyone, I only want to spend about $400

 

[YZ-Red]

Thanks SMMICK

I just got back from picking up my 97 250 which is in good nick, and I bring home my 87 500 tomorrow.

If you could send me the measurements that would be awesome.

Were are you getting your spes pipe from? do they make a silencer? how much?

I can get a Bills Pipe & muffler here, anyone had experience with Bills??

We have a Fuji film camera at work and it is excellent.

Cheers
Red

 

[YZ-Red]

Hey, hows it going?

Some Questions for you and other knowledgle ones;

1) Can you use the CR250 Coil on the 500 motor & electrics/ignition?

This would mean a simple connector change. If you have to stick to 500 coil then welding probably required?

My motor is now in chassis. Looking good.

2) Does the airbox/carb line up? If not, how are you going to resolve?

3)Rear spacer sizes for swingarm pivot?

Cheers

Red

 

[keith500r]

hey bigCR, what was involved with balancing the crank? Was the amount of vibration it got rid of worth the cost to you?

 

[yzeater]

Best digital camera for $400 is, without a doubt, the Nikon Coolpix 4300. 4MP, 3x optical zoom. Amazing camera

 

[YZ-Red]

Hey SMMICK how your conversion going?

Have you got an email, i have a few questions and some answers.

How do you solve the carb being 25-30mm higher than the airbox boot.

Anybody know?

cheers
Red

 

[brake check]

consider making the headstays outta carbon fiber...check out the helmet cams at helmetcamera.com ...and i`d consider an 84 aircooled cr500 motor-less weight-more horsepower!-also no radiator and coolant weight-depending on what you`re doing with the machine-it may suit your purpose..if it`s supermotard,then who needs a stinkin airbox...i`ve raced many years of cr500`s...the 84 had the hardest hit by far...as for vibration-there are ways of dampening-a few were mentioned allready-sounds like a fun project!

 

[bigcr]

hey bigCR, what was involved with balancing the crank? Was the amount of vibration it got rid of worth the cost to you?

To balance the crank you'll have to split the cases and have someone do it for you. It is worth it on long rides. :aj:

 

[vic580]

I am getting rid of my 98 250 because the turning sucks and at 250lbs and 6'6" I need power,am going back to a CR500.

 

[rwhitlock]

Hello all..

I stumbled onto this thread and thought I would chime in..

This past winter I dropped a CR500 motor into an '03 YZ-F frame.

I feel your pain of 'customizing' everything! I never did find a way to match up the back of the carb to an air boot, so I just went with a straight Uni Filter. It works out fine, just makes me nervous when riding in muddy or rainy weather.

The bike is done and it is a blast to ride! It feels so slim and trim (read light). I have no problem bringing the front end up on command.

If anyone would like a pic of this bike, let me know (us free loaders can't post pics on this site) 'rodw_248@yahoo.com' is my email.

Thanks,

Rod