CR motor into a YZF frame ??

[rwhitlock]

Hello all..

I'm just trying to be a bit different....

I have a '97 CR500 motor that I am planning on dropping into an '03 YZ450F rolling chassis.

Has anyone else done this? Any advice would be appreciated.

Rod

 

[jmics19067]

I am in a somewhat similar situation, taking an old IT 465 engine and putting it in a 426 frame.

Physically the engine will fit in the frame, the IT is a long stroke aircooled with big fins and it sets inside so you should have no problem putting relatively shorter stroke water cooled engine in there.

The major problems you will come up with are the exhaust port will be pointed at the frame down tube and probably having to build a pipe that will set in the frame nice. Quite possibly the singarm/rear motor mount pivot /front sprocket relationship and the front sprocket /rear sprocket chain alignment will not be correct. Also the air box to carb rubber boot being able to hook up the two with out hitting the shock is an issue.

you will be exercising a lot of welding/fabricating and backyard engineering skills to get it to fit together nicely.

 

[nzfred]

you guys are nuts, why would you bother putting a 2-stroke in a 4-stroke frame?

 

[jmics19067]

why does a man climb mountains?

 

[fuzzy]

LOL! Different strokes for different folks! Good luck w/ your project. A cutting edge chassis/susp upgrade for a 500 can only be obtained this way!!

 

[SK 250]

whats wrong with the CR 500 from service Honda???? Cutting edge Chassie and a fresh 500 two smoke.

 

[jmics19067]

I think that would be the ultimate answer if a 10,000$ bike was in your plans.Fortunately for cheap skates like me the YZF chassis are relatively cheap from people buying them to get a motor for a quad. I wanting to keep to the Yamaha parts bin was unfortunately stuck with an ancient air cooled big bore.

 

[demographic]

Originally posted by SK 250
whats wrong with the CR 500 from service Honda???? Cutting edge Chassie and a fresh 500 two smoke.

Perhaps the bloke does not have enough houses to re-mortgage to pay for it?

Service honda might be good but jeez they should be for the price.

For that much cash I would want a bike plus hot and cold running pit girls.

 

[rwhitlock]

I have looked into the Service Honda bikes, but 2 main things stopped me..

1. To buy new, they are too pricey for me.
2. I already have a CR500 that I wanted to keep the motor (thanks to Eric Gorr).

Service Honda does not seem to sell a rolling chassis for me to drop my motor into, so I found a YZF that (so I'm told) will take a CR500 with minor modifications.

I have since sold my CR chassis, and will now begin the fun of 'custom fitting' the motor I like into the newer YZ chassis...

Plus, I should be one of the only people around that has a nice Blue CR... :-)

Rod

 

[Studboy]

That sounds like a cool project. I am interested to see how it turns out.

People are going to be giving you lots of blank looks when they see you on a blue 500cc machine... :debil:

Tell them you just overbored your 250, really REALLY overbored it!!! :)

 

[Racer#213]

unless you have the yzf frame baught, look for a crf or cr chassis. but with the yzf it will prolly take some personal modifications, but anythings possible, just have to put your mind to it.

 

[mtneufer]

You should be able to buy a crf rolling chassis off ebay for$1200-2000.Good luck.

 

[rwhitlock]

Well, I started this project a few days ago. I plan on taking my time and 'doing it right' rather than just slapping it together. Here are some quick things that I see need to be modified.

1. The spacers in the back of the motor (swingarm pivot point) are 17mm, the pivot point axel on the yz is an 18mm. So I need to bore out the spacers.

2. The swingarm pivot point fits perfectly! Sprockets line up and all is well.

3. None of the other motor mounts line up. Each one will have to be 'custom fit'.

4. The airboot for the back of the carb does not line up, nor is it big enough. I am looking at a YZ 250 2-stroke air boot to see if that will work out.

5. The radiators will require some work to get the hoses routed the right way.

All in all.. when I am done I will like what I have. But, it will take more than what I expected to get there...

Thanks for all your help.

Rod

 

[jmics19067]

Here is another option for the rear motor mount bushings. Just buy the ones for the YZ and put them in the CR engine.

Those bushings are very hard and difficult to machine,and relatively cheap to buy. If you heat up the back of the cases they should tap out nicely with a hammer and punch. If you want I can mail you my old bushings,swingarm pivot bolt hole too small, but you can use it to match up all the other dimensions to see if buying new bushings will work within the engine.

Yamaha air boots/air box bolt pattern are all similar and using the same air filter from like 92 on. I know 94 yz 250 will not clear the shock or frame. If you get say 96 on to fit please let me know.

I am pleasantly surprised for you that the exhaust spigot /pipe clears the frame downtube.

 

[rwhitlock]

Here is another option for the rear motor mount bushings. Just buy the ones for the YZ and put them in the CR engine.

Those bushings are very hard and difficult to machine,and relatively cheap to buy. If you heat up the back of the cases they should tap out nicely with a hammer and punch. If you want I can mail you my old bushings,swingarm pivot bolt hole too small, but you can use it to match up all the other dimensions to see if buying new bushings will work within the engine.

Yamaha air boots/air box bolt pattern are all similar and using the same air filter from like 92 on. I know 94 yz 250 will not clear the shock or frame. If you get say 96 on to fit please let me know.

Originally posted by jmics19067
I am pleasantly surprised for you that the exhaust spigot /pipe clears the frame downtube.

 

[rwhitlock]

Sorry for the mulitple posts.. trying to figure out the quote button...

Anyway, I will have to cut out a section of the downtube for the exhaust port to fit. It will all depend on how much I want to tip the motor forward.

The swingarm pivot point is higher on the YZ than it was on the CR, so I can tip the motor forward a bit, but not sure if I really want to do that.

I did get the bushings out, just a few taps with a hammer and punch.

Like I said, this will be a fun winter project for me. That is if I can keep money flowing to my wife at the same time.. :-)

-- Rod

 

[jmics19067]

let me clarify what I meant by the rear mount bushings.

I had the same problem with the old IT engine having a smaller swing arm pivot bolt than the YZF so I installed YZF collars in the back of the IT engine. the collars where the same except for inside diameter, I could send you the IT collars to make sure they will set in the CR engine nicely that way you know you won't be wasting money to see if the YZF collars will work in your engine. I hope I am clearing up my concern and offer.

I am not sure on the forces involved with the piston going up and down or flywheel effect on handling either,angle and height setting in the frame that is. I opted to get the front sprocket as close as I could to the stock location to try and minimize any wierd rear suspension bugs from chain torque angle.