051 porting questions

[Sinij kot]

I usually find the answers here by doing a search but couldn't get this one.

So I started porting my 051, the squish measured at 0.031 without gasket, so I milled the cylinder base down by 10mils. I am not doing anything to the transfers and just wanted to widen the exhaust port. This is the case where the sides of the skirt is very far away so I have to go by the 65% of the cylinder bore diameter.
The first question is, when 65% rule is used how is the port width defined? Is it straight line from one side of the port to the other or do I need to measure the arc and have the arc length be 65% of the bore?

The second question I have has to do with piston at BDC. It does not completely clear the exhaust port (see picture 1). I don't think it is a big disadvantage because most of the flow happens at the top of the port, and it probably doesn't make sense taking off a section of the piston crown since that would significantly increase squish volume. I just wanted to get a confirmation on this.

Third question/concern. Someone has messed with this saw and when I took the cylinder off I noticed that the piston was on backwards and the rings were worn out at the ends to the point that I picked that out visually, the cylinder however is flawless. The rings ends were not showing in the intake or exhaust ports but I should check the transfers. Other than that the piston looks symmetrical to me and I don't know if there is any concern with having it on backwards. I will check the transfers thou.

 

[a_tittman]

I am in interested to see how it turns out for you. I have a 051 that I am considering porting as well. Keep us posted.

 

[tdi-rick]

Firstly, I wouldn't be too worried about the piston at BDC and the exh port.

As you said, that vast majority of flow happens in the first instances of the port opening, and your squish, compression and not trapping excessive end gases is far, far more important in terms of efficiency than a small step at BDC.

From what I've read (Bell and Jennings) and seen discussed, ports are measured as a chord (straight line) dimension, if you take a port map you could end up confusing yourself.
Also make sure you have sufficient piston skirt either side of the port.

 

[Evan]

i make it habit to not measure or do mathmatics in my porting.
i trace the ports on the piston then grind for awhile. then trace the ported ports on the piston grind alittle more. till i feel satisifed im close enough to the piston sqirt and have removed enough material to actualy do something.

im all about visual. put numbers in front of me and im likly to run away

 

[Brmorgan]

If you did take the edge off the piston crown to clear the port, you could mill the block down even further and have a "pop-up" piston to increase compression even further. Not sure what you're going after though, or even how well an 051 would respond to such treatment. I've never done it myself, just read a lot here about it.

 

[Sinij kot]

From what I've read (Bell and Jennings) and seen discussed, ports are measured as a chord (straight line) dimension, if you take a port map you could end up confusing yourself.
Also make sure you have sufficient piston skirt either side of the port.

Thank you for clarifying this for me. No problem with skirt clearance on this one. There are the rings gap pins on the side of the port which do limit how wide the port can be. I went for 65% which put the port at roughly 34mm (52mm bore). The exhaust port ended up being a bit wider than the intake. I measured 0.125" and 0.175" from the side of the port to the side of the gap pin, I hope that is enough.

If you did take the edge off the piston crown to clear the port, you could mill the block down even further and have a "pop-up" piston to increase compression even further. Not sure what you're going after though, or even how well an 051 would respond to such treatment. I've never done it myself, just read a lot here about it.

I think it would be pretty involved to make a pop out of this piston because the top is domed and the cylinder has a off center combustion chamber, so you can't just push the piston more into the chamber by cutting squish band.

My palns for this saw is to turn it into a milling saw so I am not looking to go all out, it still needs to be reliable. I just like to make "free" upgrades to get more power.

Here are few pictures of the porting:

Stock cylinder, notice the intake vs exhaust port width.

Ported

Some piston shots. The piston had quite a bit of material removed, I didn't alter the windows and just cleaned up right behind them and the underside. I have to clean this thing up before I put it back.

Next the intake extension was port matched. It was overlapping the port, some some material was removed and the molding lines were smoothed out, also I had to work the round to rectangular transition area to make it more gradual.
Stock part

Modified

The intake port has this round area where I took off some material to make it a larger radius, it seemed very tight to me.

Please post your thoughts and suggestions.

 

[buck futter]

I would think it would be better to leave the intake block on the saw then port it. you will guarantee the stream lined flow.



David

 

[luke051]

This is great to see. Also doing my old 051. I'm aiming to clean the intake gasket/heat shield overlap more then major porting.
The squish definitely needs reducing but that means hooking up timing wheel and other adjustments to make it all bang once more...