My son's 04 viper 90 needs a new top end. Ive never worked on a 2 stroke motor before. I have worked on my yfz 450 motor and am very mech inclined. How difficult is it to replace the top end on one of these bikes. While I was at it I was going to put the speed kit in it which consists of a 100cc top end, pipe, clutch springs and weights. Maybe a new carb and filter.

Is it worth it on this bike and how difficult is it? Can I do it from a shop manuel? How long should it take? Thanks for any help. Chris.

 

It's not bad and a lot of us have been there and are willing to give advice. Set aside a weekend and then plan to spend some time tuning the carb (get a new one) and clutch.

Is it worth it? HELL YEAH!!!!

 

Im going to order the kit and Ill be sure to ask questions if they come up. Thanks.

 

I would agree with Raptorlegs.

To change the top end of a 2 stroke using a kit (re: piston, rings, cylinder block, head), one performs the following:
- Perform PSI test of original engine.
- Remove the plastic cover off the engine.
- Disconnect the pipe. re: 2 x Manifold bolts.
- Remove the 4 nuts holding the head on.
- Remove the head
- Slip the head off by 4" (to expose the piston's C-Clip).
- Remove the C-Clips and horizontal pin.
- Slide the block off the rest of the way (with piston in the block).
- Remove all gasket residue & super clean the surfaces
- Install a new base gasket (comes with the new kit).
- Apply thin amount of pure 2 stroke oil on the cylinder walls (wipe on with clean fingers), then slide piston into the block.
- Assemble in reverse order.
- Ensure the C-Clips are properly installed and facing the same direction as their original position. This is critical
- Torque down the new block/head between 11-14 lbs. Follow the torque specs of the new kit.
- Re-install the plastic cover.
- Reconnect the pipe. re: 2 x Manifold bolts.
- Some folks install the block / piston "dry" and when fully installed on the mini, then turn the mini vertical and pour a small amount of pure 2 stroke oil into the spark plug hole. Turn engine over many times with its spark plug removed. Thus, ensuring lots of oil goes on the cylinder walls. Then, re-install the spark plug.
- Run for 15-30 minutes at low RPMs, then re-torque the head & manifold bolts again.
- Test PSI of upgraded engine.
* If possible, test for air leaks before running engine for 15-30 minutes. For details, surf: http://www.off-road.com/atv/ptester.htm

To change the block using a kit, its really only 4 head nuts, 2 manifold bolts and 1 piston C-Clip. The fear of doing something wrong is actually more stress then doing the work.

As a suggestion, upgrade the engine using the origional carb and pipe. Allow it to burn in for 2 hours, then install the new pipe, carb and air filter. Thus, ensuring too many changes aren't done at the same time. Little steps at a time.

Hope this helps....

.

 

One more thing. Call Billy Holt at Wrh racing and find out what he recomends. He can sell you what you need and it will work.

 

Do you have a phone # please.

 

251-675-0383

 

If you want a used bigbore or stocker let me know. I've got one from a mini dragbike I traded. Billy may have some too.