2 stroke Rebuild 670 Rotax

How to do a complete top end 2 stroke rebuild

Category:

Howto & Style

Tags:

• two
• stroke
• 670
• rotax
• 1993
• mach
• formula
• ski
• doo
• skidoo
• ski-doo
• bombardier
• mx
• top
• end
• rebuild
• engine
• cylinders
• power
• valves
• bottom
• crank
• seals

[danceGIRLIES101]

Let's say a piston gets damaged in a 2-stroke and you want to rebuild it, do you have to hone the cylinder if it looks good? Or can you just replace the pisons as the cylinder is?

[1skiinIan]

@danceGIRLIES101 It's very rare that the piston get damaged without damaging the cylinder as they are in full contact but, if so, you still need to measure the bore of the cylinder in at least 3 different spots to make sure it hasn't worn in a taper or too much in an oval before you figure out the size of piston you will need to order. if your standard piston has become too small you will need to have the cylinders bored and honed for the larger sized pistons. always hone

[1skiinIan]

@1skiinIan when you replace pistons and/or rings

[117nathanmyers]

but on a 4 stroke you never want to line up the gaps in the rings... I guess you can do that on a 2 stroke because you don't have to trap the oil.

[1skiinIan]

@117nathanmyers The ring gaps should NEVER end in the same spot on the piston in any type of engine. This would result in a loss of compression. In most 2 strokes though, there is a tab where the ring gaps have to be so that they don't spin and catch a port.

[117nathanmyers]

@1skiinIan okay that helps. I figured they must be offset... I thought that it was weird that it looked like they ended in the same spot on the video. So they are are offset even on the 2 stroke that you are working on? watch 0:30. maybe I just need to go take one apart to really understand what you are talking about. I have obviously only worked on 4 stroke but I hope to expand to 2 stroke very soon.

[1skiinIan]

@117nathanmyers i don't know it seems pretty clear to me. you can see the pin in the center of the ring gaps where they have to be when you install the cylinder over the piston. That pin stops the ring gaps from moving to a place where when they are installed could potentially catch on one of the ports in the cylinder. It doesn't matter in a 4 stroke because there are no ports in the cylinders.

[echo41911709]

Actually...I'm going to put a cloth on here so that nothing falls. cause if we do that were pretty fucked

[steveo8776]

ROTAX =MONSTER POWER

[SkinnySkinch]

@danceGIRLIES101 A lot of the newer 2 stroke motors can't be honed and therefore you must send them off to a machine shop to be re-plated or resleeved.

[abobiso]

rotax austria power!

[gunshow2323]

I don't need new nuts lol

[loller25]

is this the engine used in lynx rave?

[classicoutboards]

Just did a fresh top end on my 787 SeaDoo Rotax, 0.040 over.

[plzb4nd0z]

nice vid :) i have the same engine in mine 670 :) moster power! but i was wondering, are thos hardchrome? and do you have to replace the cylinder while doing this, or only the piston?

[pualsharkfella]

@117nathanmyers 4 smokers are totally different ball game than 2 stroke engines. 4 stompers need more maintenance. long live the 2 strokes.