Engine Swaps - Replacement Displacement

The Question - Hello I am Adam, a 16 year old quad-o-holic from backwoods Indiana. I have a 94' Blaster mostly stock, except for Holeshots on ITP aluminum rims, anyway I recently found a mid 80's YZ 250 for very cheap. I have a few questions for you if they aren't too much trouble for you.

1. Would I have to make new motor mounts for it if I swapped?

2. I have heard that it would shake from lack of a counter balance, is this true?

3. What kind of accommodations would I have to make for the radiator?

4. Would I need to alter exhaust or the frame?

5. Would I need a new intake boot from the air box?

6. Would it even be worth the power increase, being only 50 cc bigger?

7. Do you think that it would be like a light 250r?

8. Would sprockets line up and could I keep the same rear sprocket?

Any other tips and/or advice would be extremely appreciated, I am not a master mechanic nor am I a mechanical idiot. Thank you for your time.

An inquiring writer, Adam

The Response - I'll do my best to answer the questions you ask but please know that I'm shooting from the hip here since I've not performed this specific modification. Consider the answers "general" and by no means the last word.

Most engine transplants will require completely new engine mounts. In most cases they must be welded to the frame. It is critical to align the sprockets as best as possible and to place the engine countershaft sprocket in as close to the original position. I doubt the YZ and Blaster share the same chain or sprocket size.

Engines that don't use balancing shafts can produce vibration levels far above what is tolerable to the hands and feet. In addition to that it is not uncommon for stress cracks to develop in the frame due to the added depth and frequency of vibration. It is not a good idea to use an engine without a counter balancer for anything but short distance racing. This is a fact that is related to the quad/three wheeler vehicle type category.

A radiator can be fitted any place a suitable piece will fit - it must gather enough air to cool itself. Aside from that almost any location will be OK.

A custom exhaust would have to be made. It is unlikely the Blaster engine pipe will fit properly or allow the YZ engine to achieve its full potential without a pipe engineered specifically for it. There is a chance that a pipe made for a similarly equipped motorcycle could be cut and fit and be made to work pretty well.

The intake and almost everything else will need to be custom fitted. It is very unlikely that any of the components will align well enough to bolt up.

In my opinion the YZ swap may not be the best choice for your project. There would be more power, but the down side of more power is that increases can lead to other associated problems such as over powering the frame. This would indicate the need for additional components like swing arms and A-arms etc. The list goes on and on. I can appreciate that you may want to stay with a Yamaha engine in your Blaster but the amount of time and money it will require will most likely break the bank. I always tell people to figure out what they think it will cost to convert the engine, then triple it. Figure out how much time it will take and multiply it by four.

I don't by any means want to discourage you from engineering a suitable engine transplant for your quad - in fact I encourage it. You'll be much better off if you can find someone who has done the conversion you're considering and ask them for detailed information. Then you can make a list of problems associated with the project and be sure to avoid them.

I want you to know that these kind of projects are built out of the passion of their owners with a vision towards what the final outcome will be. Costs, related to time or money can't really be accurately calculated. If a marriage of the YZ engine and Blaster frame should come of your passion, so be it. I'd love progress reports and pictures as you proceed. If you decide that a balanced engine would better suit your needs please know that all of the manufacturers have made engines which might work pretty well. If what you really want is a faster quad that's still very reliable, consider performing the engine modifications outlined in my 1989 Blaster Engine Rebuild series of articles. Dollar for dollar you'll be way ahead by modifying your engine this way.

I want to thank you for writing. We need more smart young people like yourself who have enough interest and enthusiasm to ask about putting together a combination like this. I have appreciation for your wisdom in asking for information before you proceed with this kind of project. You took a smart step and made what could be classified as an honest engineering inquiry. Proceed with your dreams but use reality as a boundary. You, are already ahead of the game.

Rick

Update - I ran across this hybrid YFSYZ. Click here to view the scanned article and pictures.

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