Minarelli 2T rings

[duosport]

My engine is liquid cooled, so I have an outer O ring and an inner rubber seal too. the surface area adgacent to the O rings is small. There is some slight darkening on all of the surfaces facing in towards the water jacket. The surface outside of the outer O ring has some slight discoloration around a third of the circumference. When I drained the fluid from the cooling system this morning there was no evidence of any contamination.

[stepthrutuner]

In ScootDawg I noted that you were advised to check your reeds. Did you do that?

[duosport]

Of course not. I have low compression. Reeds do not have anything to do with low compression. After I solve this compression issue I will look into all the other aspects of the scooter.

[stepthrutuner]

Don't reeds trap the charge in the crankcase? And if the charge is not being trapped effectively by the reeds in the crankcase then there is less charge to be transferred to above the piston to be compressed in the combustion chamber by the piston and thus compression pressure suffers. Now, doesn't that make sense to you?

[duosport]

No because what I have read is that pre compression has very little effect on compression. I have 92 PSI. That is way way low. There is a big problem causing this. Pre compression is not the reason.

[90GTVert]

Even if the reeds are stuck open and you can't build primary compression, I would think the piston is still going to draw in a given volume of air. Once all of the ports close that air will be compressed. I would think reeds would have a minimal effect on compression if any, but I would check the reeds anyway just to be sure.

[duosport]

May 8, 2010 22:36:33 GMT -5 90GTVert said:

...I would think reeds would have a minimal effect on compression if any, but I would check the reeds anyway just to be sure.

Huh?? I am trying to fix the lack of compression.

[90GTVert]

You don't have to check them obviously. I'm just saying I would if I was still stuck. It's one of those things where I could have checked them and had an answer if they were bad in a few minutes. Done. Next suspect.

There have been a few occasions where I've thought, "this isn't gonna fix it, but it takes 2 minutes" and fixed the problem. You probably won't be that lucky here, because I also believe that reeds should have little to no bearing on secondary compression, but if you've got gaskets or gasket maker around and you were going to check the reeds later anyway, why not?

[stepthrutuner]

Ok. I'll admit that at engine cranking speeds reed petal function has little to do with engine cranking compression but at running speeds, especially in the upper ranges, reed function would have an effect on charge density and therefore power output.

[duosport]

May 9, 2010 0:23:08 GMT -5 stepthrutuner said:

Ok. I'll admit that at engine cranking speeds reed petal function has little to do with engine cranking compression but at running speeds, especially in the upper ranges, reed function would have an effect on charge density and therefore power output.

Reeds do not have much to do with compression at any RPM.

[duosport]

Stepthrough, You gave me a link to an excellent tutorial on top end rebuilds. Thanks for that. I have read in it that there is a secondary and less than perfect way of checking piston clearance of the piston in the bore. It is to use feeler gauges on the sides of a piston in the cylinder. I shall try this and see what results I get for clearance.

[2strokd]

Yea, we dont need no stinking reeds man !
, LMAO! Good luck with it duosport, hope ya fix it up nice and
tight

[duosport]

OK here is what I have:

I placed the piston in the bore. I proped it up from underneath so that it positioned just before the appex of its travel in the cylinder, near the top. This is where it says that the most wear is expected. I then inserted two equal thickness feeler gauges into the gap on either side, increasing till I received a slight tighness. at .002 on either side I had some friction. At .0025 I had considerable friction. Beyond that it was not possible to insert a thicker size. So I have between .002 and .005

The guide states that there should be about .001 inch of gap from piston to cylinder for ever inch of diameter of piston. my piston is about 5 inches in diameter so that would mean .005 of an inch was ideal. I am gathering that I am adding the two gauge thickness together for the proper gap. When I do that I get .005 of an inch. That was a tight .005 too. It may actually be slightly smaller of a gap. So that specs out pretty good. Now this is not the best method but it tells me that it is not wildly bad.

[duosport]

I did this test of both pistons, my original Minerlli and the aftermarket piston. They were close but not exactly the same. There was a very slight difference in the gap. They both would not accept two .003 feeler gauges. The new piston would accept a .003 and a .0025, the original piston would accept two .0025's only. So the replacement piston is ever so slightly smaller at the top. Both appear to be within spec.

[stepthrutuner]

May 9, 2010 8:32:49 GMT -5 duosport said:

OK here is what I have:

I placed the piston in the bore. I proped it up from underneath so that it positioned just before the appex of its travel in the cylinder, near the top. This is where it says that the most wear is expected. I then inserted two equal thickness feeler gauges into the gap on either side, increasing till I received a slight tighness. at .002 on either side I had some friction. At .0025 I had considerable friction. Beyond that it was not possible to insert a thicker size. So I have between .002 and .005

The guide states that there should be about .001 inch of gap from piston to cylinder for ever inch of diameter of piston. my piston is about 5 inches in diameter so that would mean .005 of an inch was ideal. I am gathering that I am adding the two gauge thickness together for the proper gap. When I do that I get .005 of an inch. That was a tight .005 too. It may actually be slightly smaller of a gap. So that specs out pretty good. Now this is not the best method but it tells me that it is not wildly bad.

If your cylinder is stock your piston should be 4 cm in diam. 0r 1.57 "