Top Ends....check your ring end gap OR don't touch your motor

diamonddave · Nov 22, 2014

I was going through some of notes today and thought this wold be a good topic for those of us that are replacing pistons in the 800 CFI-2 Pro-RMK. I install MTNTK kits in theses sleds. But this topic is about ring end gap.

I have been noticing something through the evolution of the 800 CFI 's. Both the 4 injector (Dragon) and 2 injector (Pro).

Either the cylinders have been tightening up as they get newer in model year, or the rings in the MTNTK kit are just a tad longer. I am guessing the cylinders are tightening up just a tad since the stock pistons seem to be just a tad tighter in the bore as well.

The kit's I put together back in 2010-2011, the rings would have about 0.022" +/- 0.002". I Didn't have to file the rings.

The kit's I have installed since 2012, have been tighter, down to as tight as 0.016" and have required filing to bring up to a minimum of 0.022". I've been setting mine up to 0.024"

Out of all of the kit's I have installed, we have not had one comeback.

It doesn't matter whose kit you install, you must check this. If you don't, then you will likely have a problem.

BILTIT · Nov 22, 2014

Any recommendations for an old carls 910? .024 aswell?

89sandman · Nov 22, 2014

I'm touching my motor right now and will not be checking the ring gaps

Seriously this is what happens when everyone says "its no problem you can do it yourself" and they really have no idea of what they are doing. Rebuilding a 2 stroke top end is not all that complicated for a mechanically inclined person with experience but if the most wrench turning you've done is to tighten the chain on your kids bike you should leave it to a mechanic.

Ski-Dont89 · Nov 22, 2014

hmmm. i installed my rktek pistons today. all the rings were either .018 or .019 which is in the spec of what rktek reccomends? hope i did this right?

TRS · Nov 23, 2014

diamonddave said:
I was going through some of notes today and thought this wold be a good topic for those of us that are replacing pistons in the 800 CFI-2 Pro-RMK. I install MTNTK kits in theses sleds. But this topic is about ring end gap.

I have been noticing something through the evolution of the 800 CFI 's. Both the 4 injector (Dragon) and 2 injector (Pro).

Either the cylinders have been tightening up as they get newer in model year, or the rings in the MTNTK kit are just a tad longer. I am guessing the cylinders are tightening up just a tad since the stock pistons seem to be just a tad tighter in the bore as well.

The kit's I put together back in 2010-2011, the rings would have about 0.022" +/- 0.002". I Didn't have to file the rings.

The kit's I have installed since 2012, have been tighter, down to as tight as 0.016" and have required filing to bring up to a minimum of 0.022". I've been setting mine up to 0.024"

Out of all of the kit's I have installed, we have not had one comeback.

It doesn't matter whose kit you install, you must check this. If you don't, then you will likely have a problem.

And there is an art to filing rings

4Z · Nov 23, 2014

TRS said:
And there is an art to filing rings

Tongue in left cheek, PBR, and a clockwise swirl.... :face-icon-small-ton

TRS · Nov 23, 2014

4Z said:
Tongue in left cheek, PBR, and a clockwise swirl.... :face-icon-small-ton

:face-icon-small-win

granto · Nov 23, 2014

So exactly what is the correct way to file rings?

Gvrunyn · Nov 24, 2014

I have had my 2013 Motor apart many times since installing a big bore, first because the piston to cylinder clearance was too tight, Next because of ring end gap being too tight. I put mine together at .018 with Wossner pistons and it did not last. I am now at .024 at the beginning of this season and I am hoping for a little better ring seal and some longevity! Wider gap is definatley better than tight error on the side of more!

Ski-Dont89 · Nov 24, 2014

are you sure it didnt last because your ring gap wasnt enough when you set it up at .018? how do you know that was the cause?

j9845 · Dec 9, 2014

bikeman durability kit says to spec theres to 0.15-0.17. Is that too thight?

BILTIT · Dec 9, 2014

I would say yes. I just set my 910 up at (0.024 and 0.028). The rings were 0.024 out of the box. Manufacturers spec was 0.015/0.019 but many told me that is too tight.

j9845 · Dec 9, 2014

Thanks for the response. I'm just about to install the kit. Glad I asked first. At what height in the cylinder should you place the ring to check the ring gap?

Dirty Steve · Dec 9, 2014

Touch....

Sent from my SM-G900V using Tapatalk

BILTIT · Dec 9, 2014

I used the piston upside down to push the ring down flat to just above the port.

trey4x4 · Dec 9, 2014

What is stock? Also any of you guys use auto trans fluid to instantly seal the rings on first fire up? It's a old hot rod engine building trick. Just wipe the walls with ATF instead of 2 stroke oil.

Wood · Dec 9, 2014

trey4x4 said:
What is stock? Also any of you guys use auto trans fluid to instantly seal the rings on first fire up? It's a old hot rod engine building trick. Just wipe the walls with ATF instead of 2 stroke oil.

I always use reg mineral oil.

So what's the consensus on this? Seems like quite a variance on what the ideal gap should be....is there much difference in ring material from one supplier to the next (more expansion)? Are there different diameters of locating pins? :noidea:

roni87 · Dec 9, 2014

end gap

I helped some friends set up their bikeman kits, wosner pistons- instructions say to set gap at .015"

My rk tek kit, wosner pistons- .018-.020"

Rings look the exact same with both kits. And all of them were about .016" out of the package.

So we left the bikeman ones and I opened mine up a bit.:face-icon-small-dis

j9845 · Dec 10, 2014

Thanks for heads up I think I may shoot for .020 on mine this week

Snowbird11 · Dec 10, 2014

Wood said:
I always use reg mineral oil.

So what's the consensus on this? Seems like quite a variance on what the ideal gap should be....is there much difference in ring material from one supplier to the next (more expansion)? Are there different diameters of locating pins? :noidea:

i set my fix kit rings at .018 and had to open them up after i noticed scoring. i ended up about .022 if i recall correctly. i think i paid $80 for another set of rings. i only had 100 miles on the tight gap set but better safe than sorry.

Top Ends....check your ring end gap OR don't touch your motor

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