First ride and "rich" experience

[emdude]

REWIND, I messed up

Hi oldsalt:

After reading my last post I realized I was thinking about a few things incorrectly. So let me correct myself:

I wrote:

>Looking into the intake with the piston at TDC I did notice that the piston >skirt was still visible by over 1 mm. In other words the piston skirt does not >fully get out of the way of the intake at TDC. But what's really scary is that >with the piston at BDC and looking into the intake the UPPER piston ring is >clearly visible. This seems almost dangerously close to being able to get >leakage above the piston.

The above observations are correct, this is what I found. The conclusion below is wrong...and nobody noticed!?!?!?

>Also a small spacer under the cylinder would move the relative position of >the piston skirt up and closer to fully out of the way.

No, I was thinking about this backwards of course. The piston would now go LOWER into the cylinder. So the top of the piston would be even closer to being open to the cylinder. And the skirt would clear even less on the intake side. Not much can be done about this I guess. After thinking about it for while...now fully awake... a spacer may not be a good idea because the intake is in the wrong place anyways. I'd love to try for better more manageable top clearance but the location of the intake would be the miteing factor. Of course the piston skirt could be cut for longer intake timing and just to be full out of the way even now. It's hard to say if this would help anything on it's own.

I'm still concerned about top ring being visible at the intake with the piston in BDC. That seems real close and is the only thing possibly preventing the use of a spacer.

I'm under the impression the intake was cast "To High" in the cylinder relative to the other ports. I wonder if your engine is the same? Maybe your ports are cast differently/better.

Sadly I can't think of any reasonable way to "re-engineer" the intake port. It would be nice to be able to modify the intake port...adding some meat so to speak in this location...so that the upper part of the port is flush with the bottom of the piston skirt when the piston is at TDC.

In any case I'm very curious to read about what you find when you examine your engine.

BTW I have an "80cc" unit.

It just occurred to me that if the cylinders for all engines are the same casting but just bored out to a larger diameter the smaller engines would have the intake port in a better location because it would reach a bit farther "down". This of course assumes the smaller diameter pistons are the same length.

anybody know???

 

[oldsalt]

emdude

Interesting investigation. My engine is also an '80'.

Before I can tear down my engine it's necessary to do some work on a land speed car which has priority. Might be a few days before it's on the bench. Here's my thoughts:

I'm not worried about notching the piston skirt to open up the intake port at TDC if that turns out to be a problem with the barrel raised a tad. I'll be intrested to see what the head looks like to determine the best way to cut it down.

Why is it a problem haveing some top ring showing in the intake port at BDC? The piston is at its slowest at the end of the stroke...as far as negative and positive gas pressures, not much is happening in comparison to 40 or so degrees before then.

As above, that doesn't worry me. What is the worst that can happen? The engine loses an unacceptable amount of torque at the low end. Probably won't happen and a complete new engine is less than a hundred dollars.

I've been to two county fairs and three goat ropeings and have never encountered a modern two stroke that had its max torque at so low an RPM. Well, I do have a Wade drag saw, built before 1920 that runs even slower but that is an extreme example. I'm not interested in doing a study on the engine to determine the actual port timing as that would take the fun out of it. No academics, no high teching.

Your thought on the use of an unaltered 50cc casting to produce a '80cc' motor certinally sounds like something that can be expected from China. But the little motors work good as they are. It seems they're just too dilligent in their quest for low end torque.

 

[emdude]

Hi oldsalt:

>I'm not worried about notching the piston skirt to open up the intake port at >TDC if that turns out to be a problem with the barrel raised a tad. I'll be >interested to see what the head looks like to determine the best way to cut it >down.

Well, last night I was poking around in some MB related archives and found that several other people had noticed that on their engines, the piston skirt does not completely clear the intake when the piston is at TDC. One guy even posted pictures of how he had cut it. So I would imagine this is pretty much the way they all are made. Others had posted that they too had found this and had cut the skirt to clear the upper end of the intake. I'm not sure I recall this being being found to be a benefit for sure though. I'll poke around some or make a new post to see what people may have found.

>Why is it a problem having some top ring showing in the intake port at >BDC? The piston is at its slowest at the end of the stroke...as far as >negative and positive gas pressures, not much is happening in comparison >to 40 or so degrees before then.

All true. In its current configuration this is probably not a problem. But if a spacer is used to raise the cylinder it can't be all that "thick" otherwise it would raise the top of the piston too close for comfort to the top of the intake. Then there could be problems.

> and a complete new engine is less than a hundred dollars

Yeah I know....I've thought of buying one just to tear it down and do everything right before I even install it. I'd like to see if balancing the crank would do much. I've seen that some have done this.

Also a whole new carb is only $12. I might want to get one of those as well just to have around for spare parts and experimentation. Can't say this is a particularly expensive hobby.

 

[oldsalt]

There wasn't too much snow on the ground today so I took a ten mile ride to really check out the difference the modified muffler made. The temperature went up to almost 50 F., and sure enough, it exhibited more 4-stroking, at WOT, that when it was doing 38 F.. All in all, the low end of the power band is really healthy, mid range rich but rideable, and the high end far too rich even in cold weather. Talked to my engine builder today. He of course is not real familiar with two strokes, but he agreed, after some explanation, that it would be difficult to screw up the useable power band by a small change in the port timing [in this case]. He also said that in as much as the engine is able to digest 'regular' grade gas an increase in the compression would not hurt a thing. If there's a problem just use better fuel.